The Reproductive System

The Reproductive System
Chapter 24

Reproductive System Unlike other body systems which functions almost continuously the reproductive system is inactive until puberty The primary sex organs or gonads are the testes in the male and the ovaries in the female

Reproductive System The gonads produce sex cells, or gamates as well as secreting hormones The remaining diversion organs of the reproductive system (ducts, glands and external genitalia) are referred to as accessory reproductive organs Although male and female reproductive organs are quite different they have a common origin and a common purpose to produce offspring

Reproductive System The male’s reproductive role is to manufacture males gametes called sperm and to deliver them to the female reproductive tract, where fertilization can occur The mutually complimentary role of the female is to produce female gametes, called ova or eggs.

Reproductive System When these events are properly timed, a sperm and an egg fuse to form a fertilized egg, the first cell of the new individual, from which all body cells will arise The male and female reproductive systems are equal partners in events leading up to fertilization Once fertilization has occurred, the female uterus provides a protective environment for the embryo until birth

Reproductive System The sex hormones - androgens in males and estrogens and progesterone in females play vital roles in both the development and function of the reproductive organs and in sexual behavior and drives These hormones also influence the growth and development of many other organs and tissues of the body

Male Reproductive System
The image which follows represents an overview of the male reproductive system

Male Reproductive system
The sperm-producing testes, or male gonads, lie within the scrotum From the testes the sperm are delivered to the body exterior through a system of ducts in the following order; Epididymis Ductus deferens Urethra

The accessory sex glands, which empty their secretions into the ducts during ejaculation are Seminal vesicles Prostrate gland Bulbourethral glands

The Scrotum The scrotum is a sac of skin and superficial fascia that hangs outside of the abdominopelvic cavity at the root of the penis

The Scrotum

The Scrotum Covered with sparse hairs, the scrotal skin is more heavily pigmented than that elsewhere on the body

The Scrotum The paired testes, or testicles, lie suspended in the scrotum A midline septum divides the scrotum into right and left halves, one compartment for each testis

The Scrotum The location of a man’s testes appears to make them vulnerable to injury However, viable sperm cannot be produced at core body temperature (36.2 C) The superficial location of the scrotum provides a temperature which is about 3 degrees cooler

Scrotum The scrotum also responds to temperature changes
When it is cold, the testes are draw closer to the warmth of the body and the scrotum becomes shorter and heavily wrinkled to reduce heat loss When it is warm, the scrotal skin is flaccid and loose to increase cooling, and the testes hang lower

The Scrotum These changes maintain a fairly constant temperature and reflect the activity of the two sets of muscles Dartos Cremaster

The Testes Each testes is approximately 4 cm long and 2.5 cm in diameter It is surrounded by two tunics Tunica vaginalis Tunica albuginea

The Testes The outer tunic is the two layered tunica vaginalis which is derived from the peritoneum Deep to this is the tunica albuginea, the fibrous capsule of the testis

The Testes Septa extending from the tunica albuginia divide the testis into wedge shaped compartments or lobules Each lobule contains 1-4 semiinferous tubules

The Testes The seminiferous tubules produce the sperm
The seminiferous tubules of each lobule converge to form a tubulus rectus

The Testes The tubulus rectus is a straight tubule that conveys sperm into the rete testis The rete testis is a tubular network from which the sperm leave via the efferent ductules

The Testes Sperm leaving the efferent ductules enter the epididymis which is located on the external surface of the testis

The Testes Lying in the soft connective tissue surrounding the seminiferous tubules are the interstitual cells or Leydig cells

The Testes Interstitial cells produce androgens (most importantly testosterone), which is secreted into the surrounding interstitual fluid It is significant that the sperm producing and hormone producing functions of the testis are carried out by completely different cell populations

The Testes The long testicular arteries, which branch from the abdominal aorta, supply the testes

The Scrotum The testicular veins draining the testes arise from a vinelike network called the pampiniform plexus that surrounds the testicular artery

The Scrotum The plexus absorbs heat from the arterial blood, cooling it before it enters the testes Thus, it provides an additional avenue for maintaining the testes at their cool homeostatic temperature

The Testes The testes are served by both divisions of the autonomic nervous system Associate sensory nerves transmit impulses Nerve fibers are enclosed in the spermatic cord

Homeostatic Imbalance
Although testicular cancer is relatively rare (1 in 20,000) it is the most common cancer in young men (15-35) A history of mumps or orchitis (inflammation) increases the risk The most important risk factor is cryptochidism (non-descent of the testes) The most common sign is a painless solid mass in the testes (self-exam)

The Penis The penis is a copulatory organ designed to deliver sperm into the female reproductive tract

The Penis The penis and the scrotum which hang from the peritoneum make up the external reproductive structures or genitalia

The Penis The male perineum is a diamond shaped region located between the public symphysis anteriorly, the coccyx posteriorly, and the ishial tuberosities laterally

The Penis The floor of the perineum is formed by muscles;
Ishiocavernous Bulbosponginous Superficial transverse perineus

The Penis The penis consists of an attached root and a free shaft or body that ends in an enlarged tip, the glans penis The skin of the penis is loose, and it slides distally to form a cuff of skin called the prepuce or foreskin around the glans

The Penis Internally, the penis contains the spongy urethra and three long cylindrical bodies (corpora) of erectile tissue Erectile tissue is a spongy network of connective tissue and smooth muscle riddled with vascular spaces

The Penis During sexual excitement, vasular spaces fill with blood causing the penis to enlarge an become rigid This event, called an erection, enables the penis to serve as a penetrating organ

The Penis The midventral erectile body, the corpus spongiosum, surrounds the urethra It expands distally to form the glans and proximally to form the part of the root called the bulb of the penis

The Penis The bulb is covered externally by the sheetlike bulbospingiosus muscle and is secured to the urogential diaphragm

The Penis The paired dorsal erectile bodies called the corpora cavernosa make up most of the penis and are bound by fibrous tunica albuginea Their proximal ends from the crura of the penis and each is surrounded by the ischiocavernosus

The Penis Each crus is surrounded by an ischiocavernosus muscle and anchors to the pubic arch of the bony pelvis

The Male Duct System Sperm travel from the testes to the outside of the body through a system of ducts The accessory ducts are… Epididymis The ductus deferens Urethra

The Male Duct System The comma-shaped epididymis is about 3.8 cm long
Its head, which joins the efferent ductiles, caps the superior aspect of the testis Its body and tail regions lie on the posteriolateral aspects of the testis

The Male Duct System The bulk of the epididymis consists of the highly coiled duct of the epididymis with an uncoiled length of about 6 meters

The Male Duct System Within the duct of the epididymis some of the cells of pseudostratified epithelium mucosa exhibit long, nonmotile microvilli which absorb excess testicular fluid and pass nutrients to the sperm in the lumen

The Epididymis The immature, nearly nonmotile sperm that leave the testis are moved slowly through the duct of the epidymis As the sperm move along the twisting course, a trip of 20 days, the sperm gain the ability to swim

The Epididymis When a male is sexually stimulated and ejaculates, the smooth muscle in the walls of the epididymis contracts, expelling sperm from its tail section into the next segment of the duct system the ductus deferens Sperm can stay in the epididymis for several months If held longer, they are eventually phago-cytized by epithelial cells of the epididymis

The Ductus Deferens The ductus deferens or vas deferens is about 45 cm (18 in) long It runs upward as part of the spermatic cord from the epididymis through the inguinal canal into the pelvic

The Ductus Deferens It is easily palpated as it passes anterior to the pubic bone It then loops medially over the ureter and descends along the posterior wall of the bladder

The Ductus Deferens Its terminus expands to form the ampulla and then joins with the duct of the seminal vesicle (a gland) to form the short ejaculatory duct Seminal vesicle Ejaculatory duct

The Ductus Deferens Each ejaculatory duct passes into the prostate gland where it empties into the urethra Prostate Gland Ejaculatory duct

The Ductus Deferens The ductus deferens propels live sperm from their storage sites, the epididymis and distal part of the ductus deferens, into the urethra At the moment of ejaculation, the thick layers of smooth muscle in its walls create strong peristaltic waves that rapidly squeeze the sperm forward

The Ductus Deferens Part of the ductus deferens lies within the scrotal sac In a vasectomy the physician makes a small incision into the scrotom, cuts and then ties the ductus deferens

The Urethra The urethra is the terminal portion of the male duct system It conveys both urine and semen so it serves both the urinary and reproductive systems

The Urethra The three regions of urethra are Prostatic urethra
Menbranous urethra Spongy urethra

The Urethra The prostatic urethra is surrounded by the prostate gland
The membranous urethra is in the urogenital diaphragm The spongy urethra runs through the penis and opens outside at the external urethral oriface The spongy urethra is about 15 cm (6 in) long and accounts for 75% of the length of the urethra

Accessory Glands The accessory glands include;
Seminal vesicles (paired) Bulbourethral glands (paired) Prostrate gland (singular) These glands produce most of the volume the semen Sperm Accessory gland secretions

The Seminal Vesicles The seminal vesicles lie on the posterior wall of the bladder These glands are about 5-7 cm in length, roughly the size and shape of a little finger Seminal Vesicles

The Seminal Vesicles The secretion of the vesicles accounts for about 60% of the volumn of the semen It is a yellowish, viscous, alkaline fluid containing fructose sugar, ascorbic acid, a coagulating enzyme and prostaglandins

The Seminal Vesicles The duct of each seminal vesicle joins the ductus deferens on that side to form the ejaculatory duct Sperm and seminal fluid mix in the ejaculatory duct to enter the prostatic urethra together during ejaculation

The Prostate The prostate gland is a single dough- nut shaped gland about the size of a chestnut It encircles the part of the urethra just inferior to the bladder Prostate Gland

The Prostate Gland Enclosed by a thick connective tissue capsule, it is made up of 20 to 30 compound tubular-alveolar glands The glands are embedded in a mass of smooth muscle and dense connective tissue

The Prostate Gland The prostatic gland secretion accounts for one third of the semen volume is a milky, slightly acid fluid It contains Citrate (a nutrient source) Enzymes Fibrinolysin Hyaluronidase Acid prostrate specific antigen (activates sperm)

The Prostate Gland Prostrate gland secretions enter the prostatic urethra via several ducts when prostatic smooth muscle contract during ejaculation

The Prostate Gland Hypertrophy of the prostate gland affects nearly every elderly male, distorting the urethra The prostatic mass blocks the urethra making urination difficult This condition also enhances the risk of bladder infections and kidney damage There are a variety of treatments, and it is recommended to consult with your physician regarding the best course of action for you

Semen Semen is a milky white, mixture of sperm and accessory gland secretions The liquid provides a transport medium, nutrients, and contains chemicals that protect and activate the sperm and facilitate their movement

Sperm Mature sperm cells are streamlined cells containing very little cytoplasm or stored nutrients The fructose in seminal vesicle secretion provides nearly all their energy

Sperm The protoglandins in seman decrease the viscosity of mucus guarding the entry point of the uterus (cervix) and stimulate reverse peristalsis in the uterus and the medial parts of the uterine tubes These changes facilitate the movement of sperm through the female reproductive tract

Sperm The presence of the hormone relaxin and certain enzymes in semen enhance sperm motility The relative alkalinity of semen as a whole (pH ) due to bases (spermine and others) helps neutralize the acid environment of the male’s urethra and the female’s vagina This also helps protect the sperm and enhance their motility

Sperm Sperm also contains an antiboitic chemical called seminalplasmin, which destroys certain bacteria Clotting factors (fibrinogen and others) found in semen coagulate it just after it is ejaculated Upon ejaculation the fibrinogen liquefies the sticky mass, enabling the sperm to swim out and begin their journey through the female duct system

Sperm The amount of semen propelled out the the male duct system during ejaculation is relatively small (2-5 ml) but there are between 50 and 130 million sperm per milliliter

Physiology: Male System
The chief phases of the male sexual response are Erection of the penis; which allow entry into the female vagina Ejaculation; which expels semen into the vagina

Erection Erection, enlargement and stiffening of the penis results from engorgement of the erectile bodies with blood When a man is not aroused, the arterioles supplying the erectile tissue is constricted and the penis is flaccid

Erection However, during sexual excitement a parasympathetic reflex is triggered that promotes release of nitric oxide (NO) locally NO relaxes vascular smooth muscle, causing these arterioles to dilate, which allows the erectile bodies to fill with blood

Erection Expansion of the corpora cavernosa of the penis compresses their drainage veins, retarding blood outflow and maintaining engorgement The corpus spongiosum expands but not nearly as much as the cavernosa; its main job is to keep the urethra open during ejaculation

Erection Erection of the penis is one of the rare examples of parasympathetic control of arterioles Another parasympathetic effect is stimulation of the bulbourethral glands, which causes lubrication of the glans penis

Erection Erection is initiated by a variety of sexual stimuli, such as touching of the genital skin, mechanical stimulation of the pressure receptors in the penis and erotic sights, sounds, and smells The CNS responds to such stimuli by activating parasympathetic neurons that innervate the internal pudendal arteries serving the penis

Erection Sometimes erection is induced solely by emotional or higher mental activity (the thought of a sexual encounter Emotions and thoughts can also inhibit erection, causing vasoconstriction and resumption of the flaccid penile state Impotence, is the inability to attain and maintain erection

Ejaculation Ejaculation is the propulsion of semen from the male duct system While erection is under parasympathetic control, ejaculation is under sympathetic control When impulses provoking erection reach certain critical level, a spinal reflex is initiated, and a massive discharge of nerve impulses occurs over the sympathetic nerves serving the genital organs (L1& L2)

Ejaculation During ejaculation
The reproductive ducts and accessory organs contract, emptying their contents into the urethra The bladder sphincter muscle constricts, preventing the expulsion of urine or reflux of semen into the bladder The bulbospongiosus muscles of the penis undergo a rapid series of contractions, propelling semen at a speed of 200 inches/sec from the urethra

Ejaculation The rhythmic muscle contractions are accompanied by intense pleasure and many systemic changes such as generalized muscle contraction, rapid heartbeat, and elevated blood pressure The entire ejaculatory event is referred to as a climax or orgasm

Ejaculation Organism is quickly followed by muscular and psychological relaxation and vasoconstriction of the penile arterioles, which allow the penis to become flaccid again After ejaculation, there is a latent period, ranging in minutes to hours, during which a man is unable to achieve another organism The latent period length increases with age

Spermatogenesis Spermatogenesis is the sequence of events in the seminiferous tubules of the testes that produce male gametes or sperm or spermatozoa The process begins in puberty, around the age of 14 years in males, and continues throughout life Every day, a healthy adult male makes about 400 million sperm Ample supply of sperm for reproduction

Spermatogenesis Having two sets of chromosomes, one from each parent, is a key factor in the human life cycle

Spermatogenesis The normal chromosome number in most body cells is referred to as the diploid or 2n chromosomal number of the organism

Spermatogenesis In humans, the diploid number is 46, and such diploid cells contain 23 pairs of similar chromosomes called homologous or chromosomes or homologues

Spermatogenesis One member of each pair is from the male parent (paternal chromosome); the other is from the female parent (maternal chromosome)

Spermatogenesis Generally speaking, the two homologues of each chromosome pair look alike and carry genes that code the same traits However, the expression of those traits may differ in each parent

Spermatogenesis The number of chromosomes present in human gametes is 23, referred to as the haploid or n chromosomal number

Spermatogenesis Gametes contain only one member of each homologous pair When sperm and egg fuse, they form a fertilized egg that reestablishes the typical diploid chromosomal number of human cells

Spermatogenesis Gamete formation in both sexes involves meiosis, a unique kind of nuclear division, that for the most part, occurs only within the gonads Mitosis or cell division distributes replicated chromosomes equally between the two daughter cells Consequently, each daughter cell receives a set of chromosomes identical to that of the mother cell

Spermatogenesis Meiosis consists of two consecutive nuclear divisions, and its product is four daughter cells instead of two, each with half as many chromosomes as typical body cells Meiosis provides the means for reducing the chromosome number by half in gametes Mitosis and meiosis are compared on the next slide…

Spermatogenesis

Meiosis The two nuclear divisions of meiosis, called meiosis I and meiosis II are divided into phases for convenience Although these phases are given the same names as those of mitosis (prophase, metaphase, anaphase and telophase) events of meiosis I are quire different from those of mitosis

Meiosis In meiosis, as in mitosis, the chromosomes replicate before meiosis begins (Interphase) But in the prophase of meiosis I the replicated chromosomes seek out their homologous partners and pair up with them along their entire length

Meiosis

Meiosis The alignment of the homologues takes place at discrete spots along the length of the homologues - like a buttoning As a result of this process, called synapsis, little groups of four chromatids called tetrads, or bivalents, are formed

Meiosis

Meiosis During synapsis, a second unique event called crossover occurs
Crossovers are formed within each tetrad as the free ends of one maternal and one paternal chromatid wrap around each other at one or more points Crossover allows an exchange of genetic material between the paired maternal and paternal chromosomes

Meiosis

Meiosis During metaphase I, the tetrads line up at the spindle equator
This alignment is random; that is, either the paternal or maternal chromosome can be on a given side of the equator

Meiosis

Meiosis During anaphase I, the sister chromatids representing each homologue behave as a unit - almost if replication had not occurred - and the homologous chromosomes (each still composed of two joined sister chromatids) are distributed to opposite ends of the cell

Meiosis

Meiosis Thus, when meiosis I is completed, the following conditions exist: Each daughter cell has Two copies of one member of each homologous pair (either the paternal or maternal) and none of the other, and A diploid amount of DNA but a haploid chromosome number because the still-united sister chromatids are considered to be a single chromosome

Meiosis

Meiosis II The second meiotic division, meiosis II, mirrors mitosis in every way, except that the chromosomes are not replicated before it begins Instead, the chromatids present in the two daughter cells of meiosis I are simply parceled out among four cells Because the chromatids are distributed to the daughter cells, meiosis II is sometimes referred to as equational division meiosis

Meiosis II Meiosis accomplishes two important tasks
It reduces the chromosomal number by half It introduces genetic variability

Meiosis II The random orientation of the homologous pairs during meiosis I produces tremendous variability in the resulting gametes by scrambling genetic characteristics derived from the two parents in different combinations Variability is further increased by crossover because during late prophase I, the homologues break at points of crossover and exchange chromosomal segments

Meiosis II The net result is that it likely that no two gametes are exactly alike, and all are different from the original mother cells

Spermatogenesis A histological section of an adult testes shows that most of the cells making up the epithelial walls of the seminiferous tubules are in various stages of cell division

Spermatogenesis

Spermatogenesis These cells, collectively called spermatogenic cells, give rise to sperm in a series of cellular divisions and transformations

Mitosis of Spermatogonia
The outermost and least differentiated tubule cells, which are in direct contact with the epithelial lamina, are stem cells called spermatogonia The spematogonia divide more or less continuously by mitosis and, until puberty, all their daughter cells become spermatogonia

Spermatogenesis begins during puberty, and from then on, each mitotic division of a spermatogonium results in two distinctive daughter cells - types A and B The type A daughter cell remains at the basement membrane to maintain the germ cell line The type B cell gets pushed toward the lumen, where it becomes a primary spermatocyte and becomes four sperm

Meiosis: Spermatocytes
Still early in spermatogenesis, each primary spermatocyte generated during the first phase undergoes meiosis I, forming two smaller haploid cells called secondary spermatocytes The secondary spermatocytes continue on rapidly into meiosis II, and their daughter cells, called spermatids, are small round cells with large spherical nuclei seen closer to the lumen of the tubule

Spermatogenesis

Spermiogenesis: Spermatids
As late spermatogenesis begin, each spermatid has the correct chromosomal number for fertilization (n), but it is non motile It must undergo a streamlining process called spermiogenesis, during which it sheds its excessive cytoplasmic baggage and forms a tail

Spermatogenesis 1. Activity of the Golgi apparatus to package
acrosmal enzymes

Spermatogenesis 2. Positioning of the acrosome at the anterior
end of the nucleus and the centrioles at the opposite end of the nucleus

Spermatogenesis 3. Elaboration of microtubules to form
the flagellum of the tail

Spermatogenesis 4. Mitochondrial multiplication and their positioning
around the proximal portion of the flagellum

Spermatogenesis Sloughing off excess cytoplasm

Spermatogenesis Structure of an immature sperm that
has just been released from a sustentacular cell

Spermatogenesis 7. Structure of a fully mature sperm

Spermatogenesis The resulting sperm, or spermatozoon, has three major regions Head Midpiece Tail

Spermatogenesis The three regions correspond to Genetic Metabolic
Locomotor

Spermatogenesis The head of the sperm consists almost entirely of its flattened nucleus, which contains compacted DNA Adhering to the top of the nucleus is a helmet like acrosome The lysosome like acrosome is produced by the Golgi apparatus and contains hydrolytic enzymes (hyaluronidase and others) that enable the sperm to penetrate and enter the egg

Spermatogenesis The sperm midpiece contains mitrochondria spiraled tightly around the contractile filaments of the tail The tail is a typical flagellum produced by a centriole The mitrochondria provide the metabolic energy (ATP) needed for the whiplike movements of the tail that propel the sperm along its way in the female reproductive tract

Role of Sustentacular Cells
Throughout spermatogenesis, descenants of the same spermatogonium remain closely attached to one another by cytoplasmic bridges

The cells are surrounded by and connected to supporting cells, called sustentacular cells or Sertoli cells, which extend from the basal lamina to the lumen of the tubule

The sustentacular cells, bound to each other by tight junctions, form an unbroken layer within the seminiferous tubule dividing it into two compartments

The basal compartment extends from the basal lamina to their tight junctions and contains spermatogonia and the earliest primary spermatocytes

The adluminal compartment lies internal to the tight junctions and includes the meitoically active cells and the tubule lumen

The tight junctions between the sustentacular cells from the blood-testis barrier This barrier prevents the membrane antigens of differentiating sperm from escaping through the basal lamina into the bloodstream

Because sperm are not formed until puberty, they were absent when the immune system is being programmed to recognize one’s own tissues early in life The spermatogonia, which are recognized as “self” are outside the barrier and can be influenced by bloodborne chemical messengers that prompt spermatogenesis

Following mitosis of the spermatogonia, the tight junctions of the sustentacular cells open to allow primary spermatocytes to pass into the adluminal compartment

In the adluminal compartment spermatocytes and spermatids are nearly enclosed in recesses in the sustentacular cells spermatocytes spermatids

Sustentacular cells deliver nutrients to the dividing cells, move them along to the lumen, and secrete testicular fluid that provides the transport medium for sperm in the lumen spermatocytes spermatids

In addition, sustentacular cells dispose of excess cytoplasm sloughed off the spermatids as they transform into sperm The sustentacular cells also produce mediators that help regulate spermatogenesis

During spermatogenesis the time from the formation of a primary spermatocyte to release of immature sperm into the lumen takes approximately 64 to 72 days Sperm in the lumen are unable to “swim” and are incapable of fertilizing an egg

Sperm are pushed by pressure of the testicular fluid through the tubular system of the testes into the epididymis Within the epididymis sperm mature further gaining increased motility and fertilizing power

Hormonal Regulation: Male
Hormonal regulation of spermatogenesis and testicular androgen production involves interactions between the hypothalamus, anterior pituitary gland, and testes This relationship is called the brain testicular axis

1) The hypothalamus releases gonadotropin releasing hormone (GrRH), which controls the release of anterior pituitary gonadotropins, follicle stimulating hormone (FSH) and luteinizing hormone (LH)

2) Binding of GnRH to pituitary cells (gonadotrophs) prompts them to secrete FSH and LH into the blood

3) FSH stimulates spermatogenesis indirectly by stimulating the sustentacular cells to release androgen binding protein (ABP)

3 (con’t) ABP prompts the spermatogenic cells to bind and concentrate testosterone which in turn stimulates spermatogenesis Thus, FSH makes the cells receptive to testosterone’s effects

4) LH binds to the interstitial cells and stimulates them to secrete testosterone and a small amount of estrogen LH is sometimes referred to as interstitial cell-stimulating hormone (ICSH) in males

4) (con’t) Locally testosterone serves as the final trigger for spermatogenesis Testosterone entering the bloodstream exerts a number of effects at other body sites

5) Both the hypothalamus and the anterior pituitary are subject to feedback inhibition by bloodborne hormones Testosterone inhibits hypothalamic release of GnRH and acts directly on the anterior pituitary to inhibit gonadotropin release

5) (con’t) Inhibin a protein hormone released by the sustentacular cells, serves as a barometer of the normalcy of spermatogenesis

5) (con’t) When the sperm court is high, inhibin release increases and it inhibits anterior pituitary release of FSH and GnRH release by the hypothalamus When sperm court falls below 20 million/ml, inhibin secretion declines steeply

The amount of testosterone and sperm produced by the testes reflects a balance among three sets of hormones GnRH, which indirectly stimulates the testes via its effect on FSH and LH (ICSH) release Gonadotropins, which directly stimulate the testes Testicular homones (Testosterone and inhibin), which exert negative feedback controls on the hypothalamus and anterior pituitary

Since the hypothalamus is also influenced by input from other brain areas, the whole axis is under CNS control In the absence of GnRH and gonadotropins, the testes atrophy, and for all practical purposes, sperm and testosterone production ceases

Development of male reproductive structures depends on prental secretion of male hormones, and for a few months after birth, a male infant has plasma gonadotropin and testosterone levels nearly equal to those of a midpubertal boy Soon thereafter, blood levels of these hormones recede and they remain low throughout childhood

As puberty nears, much higher levels of testosterone are required to suppress hypothalamic release of GnRH As more GnRH is released more testosterone is secreted by the testes, but the threshold for hypothalamic inhibition keeps rising until the adult pattern of hormone interaction is achieved

Maturation of the brain-testicular axis takes about three years, and once established, the balance between the interacting hormones remains relatively constant Consequently, an adult male’s sperm and testosterone production remain fairly stable as opposed to females where there are normal cyclic swings of gonadotropin and female sex hormones

Effects of Testosterone Activity
Testosterone, like all steroid hormones, is synthesized from cholesterol Its exerts its effects by activating specific genes to transcribe messenger RNA molecules, which results in enhanced synthesis of certain proteins in the target cells

In some target cells, testosterone must be transformed into another steroid to exert its effects In the prostrate gland, for example, testosterone must be converted to dihydrotestosterone (DHT) before it can bind with nucleus

In certain neurons of the brain, testosterone is converted to estrogen to bring about its stimulatory effects Thus, in this case, a “male” hormone is transformed into a “female” hormone to exert its masculinizing effects

As puberty ensues, testosterone not only prompts spermatogenesis but has multiple anabolic effects throughout the body It targets all accessory reproductive organs (ducts, glands, penis) causing them to grow and assume adult size and function

In adult males, normal plasma levels of testosterone maintain these organs When testosterone is deficient or absent, all accessory organs atrophy, semen volume declines markedly, and erections and ejaculation are impaired In this circumstance a male would become sterile and impotent This situation would be remedied by testosterone replacement therapy

Male secondary sex characteristics induced in nonreproductive organs by the male sex hormones (mainly testosterone) make their appearance at puberty These induced changes include the appearance of pubic, axillary, and facial hair, enhanced hair growth on the chest and other body areas, deepening of th voice as the larynx enlarges

The skin thickens and becomes oiler (which predisposes men to acne), bones grow and increase in density, and skeletal muscles increase in size and mass The last two effects are often referred to as the somatic effects of testosterone (some = body)

Testosterone also boosts basal metabolic rate and influences behavior It is the basis of the sex drive (libido) in both males and females Although testosterone is called a “male” hormone, it should be specifically tagged as a promoter of male sexual activity In embryos, the presence of testosterone masculinizes the brain

The testes are not the only source of androgens; the adrenal glands of both sexes also release androgens However, the relatively small amounts of adrenal androgens are unable to support normal testosterone-mediated functions when the testes fail to produce androgens We can assume that it is the testosterone production by the testes that supports male reproductive function

Female Reproductive System
The image which follows represents an overview of the female reproductive system

The reproductive role of the female is far more complex than that of a male She must produce gametes, but her body must prepare to nurture a developing embryo for a period of approximately nine months

Ovaries, the female gonads, are the primary reproductive organs of the female Like the testes of the male, ovaries serve a dual purpose Produce gametes Produce female sex hormones (estogen and progesterone) The accessory ducts (uterine tubes, uterus, and vagina) transport or otherwise serve the needs of the reproductive cells and fetus

The ovaries and duct system, collectively known as the internal genitalia are mostly located in the pelvic cavity The female’s accessory ducts, from the vicinity of the ovary to the body exterior, are the uterine tubes, uterus and vagina The external sex organs of the females are referred to as the external genitalia

The Ovaries The paired ovaries which flank the uterus on each side are shaped like almonds and are about twice as large

The Ovaries Each ovary is held in place within the peritoneal cavity by several ligaments

The Ovaries The ovarian ligament anchors the ovary medially to the uterus

The Ovaries The suspensory ligament anchors the ovaries laterally to the pelvic wall

The Ovaries The mesovarium ligaments suspends the ovaries between the fallopian tubes and the uterus

The Ovaries Both the suspensory ligament and the mesovarium are part of the broad ligament

The Ovaries The broad ligament is a peritoneal fold that “tents” over the uterus and supports the uterine tubes, uterus and vagina

The Ovaries The ovaries are served by the ovarian arteries which are branches of the abdominal aorta

The Ovaries The ovarian blood vessels reach the ovaries by traveling through the suspensory ligaments and mesovaria

The Ovaries The ovaries are surrounded externally by a fibrous tunica albuginea

The Ovaries The tunica albuginea is in turn covered by a layer of cuboidal epithelium called the germinal epithelium of the mesovarium

The Ovaries The term germinal epithelium is a misnomer because this layer does not give rise to ova

The Ovaries The ovary has an outer cortex, which houses the forming gametes, and an inner medullary region containing large blood vessels and nerves

The Ovaries Embedded in the highly vascular connective tissue of the ovary cortex are many tiny sac like structures called ovarian follicles

The Ovaries Each follicle consists of an immature egg, called an oocyte encased in one or more layers of very different cells

The Ovaries The surrounding cells are called follicle cells if a single layer is present

The Ovaries If more than one layer is present, the cells are called granulosa cells

The Ovaries Follicles at different stages of maturation are distinguished by their structure A primordinal follicle, has one layer of squamous like follicle cells surrounding the oocyte A primary follicle having two or more layers of cuboidal or columnar type granulosa cells enclosing the oocyte

The Ovaries In a secondary follicle the fluid filled spaces appearing between the granulosa cells coalesce to form a fluid filled cavity called an antrum

The Ovaries At its most mature stage, when it is called a vesicular or Graafian follicle, the follicle bulges from the surface of the ovary

The Ovaries The oocyte of the vesicular follicle sits on a stalk of granulosa cells at one side of the antrum

The Ovaries Each month in adult women, one of the ripening follicles ejects its oocyte from the ovary, an event ovulation

The Ovaries After ovulation, the ruptured follicle is transformed into a structure called the corpus luteum which eventually degenerates

The Ovaries As a rule, most of these structures can be seen within the same ovary In older women, the surfaces of the ovaries are scarred and pitted, revealing that many oocytes have been released

Female Duct System The uterine tubes or fallopian tubes and oviducts form the initial part of the female duct system

Female Duct System They receive the ovulated oocyte and provide a safe site where fertilization can occur

Female Duct System Each uterine tube is about 10 cm (4 in) long and extends medially from the ovary to a constricted region called the isthmus

Female Duct System The distal end of each uterine tube extends as it curves around the ovary, forming the ampulla, which is where fertilization occurs

Female Duct System The ampulla ends in the infundibulum, an open, structure bearing ciliated projections called fimbriae that drape over the ovary

Female Duct System Unlike the male duct system, which is continuous with the tubules of the testes, the uterine tubules have little or no actual contact with the ovaries

Female Duct System An ovulated oocyte is cast into the peritoneal cavity, and many oocytes are lost there

Female Duct System The uterine tube performs a complex sequence of movements to capture oocytes

Female Duct System The infundibulum bends to drape of the ovary while the fimbriae stiffen and sweep the ovarian surface

Female Duct System The beating cilia on the fimbriae then create currents in the peritoneal fluid that act to carry the oocyte into the uterine tube

Female Duct System The ampulla ends in the infundibulum, an open, structure bearing ciliated projections called fimbriae that drape over the ovary

Female Duct System The uterine tube aids the process of an oocyte
Its wall contains sheets of smooth muscle, and its thick, highly folded mucosa contain both ciliated and nonciliated cells The oocyte is carried toward the uterus by a combination of muscular peristalsis and the beating of the cilia

Female Duct System Nonciliated cells of the mucosa have dense microvilli and produce a secretion that keeps the oocyte (and sperm, if present) moist and nourished

Female Duct System Externally, the uterine tubes are covered by visceral peritoneum and supported along their length by a short mesentary

Female Duct System The mesentary is called the mesosalpinx, a reference to the trumpet shaped uterine tube it supports

Female Uterus The uterus is located in the pelvis, anterior to the rectum and postero- superior to the bladder

The Uterus The uterus is a hollow, thick walled organ that functions to receive, retain, and nourish the ovum

The Uterus In a pre-menopausal woman who has never been pregnant, the uterus is about the size and shape of an inverted pear It is usually somewhat larger in woman who have borne children

The Uterus Normally, the uterus is fixed anteriorly where it joins the vagina, causing the uterus as a whole to be inclined forward or anteverted

The Uterus However, the uterus is often turned backward, or retroverted in older woman

The Uterus The main portion of the uterus is referred to as the body

The Uterus The rounded region superior to the entrance of the uterine tubes is the fundus, and the slightly narrowed region is the isthmus

The Uterus The cervix of the uterus is its narrow neck, or outlet, which projects into the vagina inferiorly

The Uterus The cavity of the cervix, called the cervical canal, communicates with the vagina via the external os

The Uterus The internal os opens into uterine body

The Uterus The mucosa of the cervical canal contains cervical glands that secrete a mucus that fills the cervical canal and covers the external os, presumably to block the spread of bacteria from the vagina into the uterus Cervical mucus also blocks the entry of sperm, except at midcycle, when it becomes less viscous and allows sperm to pass through

Uterus: Homeostatic Imbalance
Cancer of the cervix is common among woman between ages of 30 and 50 Risk factors include frequent cervical inflammations, sexually transmitted diseases including genital warts, and multiple pregnancies The cancer cells arise from the epithelium covering the cervical tip

In a Papanicolaou (Pap) smear, or cervical smear test, some of these epithelial cells are scraped away and then examined for abnormalities A Pap smear is the most effective way to detect this slow-growing cancer Woman are advised to have a Pap smear every year

Supports of the Uterus The uterus is supported laterally by the mesometrium portion of the broad ligament

Supports of the Uterus Inferiorly, the lateral cervical (cardinal) ligaments extend from the cervix and superior part of the vagina to the lateral walls of the pelvis

Supports of the Uterus The paired uterosacral ligaments secure the uterus to the sacrum posteriorly

Supports of the Uterus The uterus is bound to the anterior wall by the fibrous round ligament, which runs through the inquinal canals to anchor in subcutaneous tissue

Supports of the Uterus These various ligaments allow the uterus a good deal of mobility, and its position changes as the rectum and bladder fill and empty

Despite the many anchoring ligaments, the principle support of the uterus is provided by muscles of the pelvic floor, namely the muscles of the urogenital and pelvic diaphragms

These muscles are sometimes torn during childbirth Subsequently, the unsupported uterus may sink inferiorly, until the tip of the cervix protrudes through the vaginal opening

When the tip of the uterus extends trhough the external vaginal opening the condition is called a prolapse of the uterus

The Uterus The undulating course of the peritoneum around and over the various pelvic structures produces several blind ended peritoneal pouches

The Uterus The most important of these pouches are the vesicouterine pouch between the bladder and the uterus

The Uterus The rectouterine pouch lies between the rectum and the uterus

The Uterine Wall The wall of the uterus is composed of three layers; the perimetrium, myometrium and endometrium

The Uterine Wall The wall of the uterus
The perimetrium is the outermost serous layer composed of visceral peritoneum The myometrium is the bulky middle layer, composed of interlacing bundles of smooth muscle. It is the myometrium that contracts during childbirth to expel the baby The endometrium is a simple columnar epithelium underlain by a thick lamina propria of highly cellular connective tissue

The Uterine Wall If fertilization occurs, the young embryo burrows (implants) into the endometrium and resides there for the rest of development

The Uterine Wall The endometrium has two chief strata
The stratum functionalis (functional layer) undergoes cyclic changes in response to blood levels of ovarian hormones and is shed during menstruation (approx. 28 day cycle) The stratum basale is the thinner deeper layer which forms a new functionalis layer after menstruation ends It is unresponsive to ovarian hormones The endometrium has numerous uterine glands that changes with the endometrium

The Uterine Wall To understand the cyclic changes of the uterine endometrium it is essential to understand the vascular supply of the uterus The uterine arteries arise from the internal iliacs in the pelvis, ascend along the sides of the uterus and send branches into the uterine walls

The Uterine Wall The uterine arteries break up into several arcuate arteries within the myometrium

The Uterine Wall The arcuate arteries send radial branches into the endometrium, where they in turn give off straight arteries to the stratum basalis and spiral arteries to the stratum functionalis

The Uterine Wall The spiral arteries undergo repeated degeneration and regeneration, and it is their spasms that actually cause the functionalis layer to be shed during menstruation Veins in the endometrium are thin-walled and form an extensive network with occasional sinusoidal enlargements

The Vagina The vagina is a thin-walled tube 8-10 cm / 3-4 in. long
It lies between the bladder and the rectum and extends from the cervix to the exterior of the body

The Vagina The urethra is embedded in its anterior wall
Often called the birth canal, the vagina provides a passageway for delivery of an infant or for menstrual flow urethra

The Vagina The vagina receives the penis (and semen) during sexual intercourse It is the female organ of copulation The highly distensible walls of the vagina consists of three tunics Adventitia Muscularis Mucosa

The Vagina The adventitia is made of fibrous and elastic connective tissue The muscularis is smooth muscle The mucosa is epithelium The mucosa is marked by transverse ridges or rugae, which stimulate the penis during intercourse The mucosa is stratified squamous epithelium which is resistent to friction

The Vagina Certain mucosal cells (dendritic cells) act as antigen-presenting cells and are thought to provide the route of HIV transmission from an infected male to the female during sexual intercourse

The Vagina The vaginal mucosa has no glands; it is lubricated by the cervical mucus glands Its epithelial cells release large amounts of glycogen, which is anaerobically metabolized to lactic acid by resident bacteria Consequently, the pH of a woman’s vagina is normally quite acidic

The Vagina Acidity in the vagina helps to keep it healthy and free of infection, but it is also hostile to sperm Although vaginal fluid of adult females is acidic, it tends to be alkaline in adolescents, predisposing sexually active teenagers to sexually transmitted diseases

The Vagina The vaginal orifice forms an incomplete partition called the hymen The hymen is quite vascular and tends to bleed during first coitus

The Vagina The durability of the hymen varies
In some females it is ruptured during sports, tampon insertion or pelvic exam Some individuals may need to be breached surgically

The Vagina The upper end of the vaginal canal loosely surrounds the cervix of the uterus, producing a vaginal recess called the vaginal fornix

The Vagina The posterior part of this recess, the posterior fornix, is much deeper than the lateral and anterior fornices

The Vagina Generally, the lumen of the vagina is quite small and, except where it is held open by the cervix, its posterior and anterior wall are in contact with one another

The Vagina The vagina stretches considerably during copulation and childbirth Its lateral distension is limited by ishial spines and ligaments

The External Genitalia
The external genitalia also called the vulva include Mons pubis Labia Clitoris Vestibule structures

The mons pubis is a fatty, rounded area overlying the pubic symphysis After puberty this area is covered with pubic hair

Running posteriorly from the mons pubis are two elongated, hair covered, fatty skin folds the labia majora These are the female counterpart of the male scrotum

The labia majora enclose the labia minora two thin, hair free skin folds, homologous to the ventral penis

The labia minora enclose a recess called the vestibule, which contains the external opening of the urethra more anteriorly followed by that of the vagina

Flanking the vaginal opening are the pea sized greater vestibular glands which are homologous to the bulbourethral glands of males

These glands release mucus into the vestibule to keep it moist and lubricated, facilitating intercourse

Just anterior to the vestibule is the clitoris This small protruding structure, composed of erectile tissue that is homologous to the penis of the male

It is hooded by a skin fold called the prepuce of the clitoris, formed by the junction of the labia minora folds

The clitoris is richly innervated with sensory nerve endings sensitive to touch, and it becomes swollen with blood and erect during tactile stimulation, contributing to a female’s sexual arousal Like the penis, the clitoris has dorsal erectile columns (corpora cavernosa) but it lacks corpus spongiosum

In males, the urethra carries both urine and semen and runs through the penis In females, the urinary and reproductive tracts are completely separate, and neither runs through the clitoris

The female perineum is a diamond shaped region located between the pubic arch anteriorly, coccyx posteriorly, and the ishial tuberosities laterally

The soft tissues of the perineum overlie the muscles of the pelvic outlet and the posterior ends of the labia majora overlie the central tendon, into which most floor muscles insert

The Mammary Glands The mammary glands are present in both sexes, but they normally only function in females

The Mammary Glands Since the biological role of the mammary glands is to produce milk to nourish a newborn baby, they are actually important only when reproduction has already been accomplished Developmentally, mammary glands are modified sweat glands that are really part of the skin, or integumentary system

The Mammary Glands Each mammary gland is contained within a rounded skin- covered breast anterior to the pectoral muscles of the thorax

The Mammary Glands Slightly below the center of each breast is a ring of pigmented skin, the areola, which surrounds the central protruding nipple

The Mammary Glands Large sebaceous glands in the areola make it bumpy and produce sebum that reduces chapping and cracking of the skin of the nipple

The Mammary Glands Autonomic nervous system controls of smooth muscle fibers in the areolar and nipple cause the nipple to become erect when stimulated by contact or sexual stimuli and when exposed to the cold

The Mammary Glands Internally, each mammary gland consists of 15 to 25 lobes that radiate around and open at the nipple The lobes are separated by fat and fibrous connective tissue

The Mammary Glands The interlobar connective tissue forms suspensory ligaments that attach the breast to the underlying muscle fascia and to the overlying dermis

The Mammary Glands The suspensory ligaments provide natural support for the breasts Within the lobes are smaller units called lobules which contain glandular alveoli that produce milk when lactating

The Mammary Glands These compound alveolar glands pass milk into the lactiferous ducts, which open to the outside at the nipple

The Mammary Glands Just deep to the areola, each lactiferous duct has a dilated region called a lactiferous sinus Milk accumulates in these sinuses during nursing

The Mammary Glands The discussion of the mammary glands given here applies only to nursing women or women in the last trimester of pregnancy In nonpregnant woman, the glandular structure of the breast is largely undeveloped and the duct system is rudimentary Breast size is largely due to the amount of fat deposits

Breast Cancer Invasive breast cancer, the most common malignancy of U.S. women, strikes nearly 200,000 American women each year One woman in eight develop this condition Breast cancer usually arises from the epithelial cells of the ducts, not from the alveoli A small cluster of cancer cells grows into a lump in the breast from which cells eventually metastasize

Breast Cancer Known risk factors for developing breast cancer include
Early onset menses and late menopause No pregnancies or first pregnancy late in life Previous history of breast cancer Family history of breast cancer (especially in a sister or mother) Other risk factors are also proposed

Breast Cancer Breast cancer is often signaled by a change in skin texture, puckering, or leakage from the nipple Early detection by breast self-examination and mammography is the best way to increase one’s chances of surviving breast cancer Since most breast lumps are discovered by women themselves in routine monthly breast exams this should be a priority

Breast Cancer Once diagnosed, breast cancer is treated in various ways on specific characteristics of the lesion Current therapies include Radiation therapy Chemotherapy Surgery, often followed by radiation or chemotherapy Radial mastectomy Lumpectomy Simple mastectomy

Breast Cancer Many mastectomy patients opt for breast reconstruction to replace excised tissue

Physiology: Female System
Gamete production in males begins at puberty and continues throughout life, but the situation is quite different in females A female’s total supply of eggs is already determined by the time she is born, and the time span during which she releases them extends from puberty to menopause (about age 50)

Meiosis, the specialized nuclear division that occurs in the testes to produce sperm, also occurs in the ovaries In this case, female sex cells are produced, and the process is called oogenesis The process of oogenesis takes years to complete

Flowchart of Events of Oogenesis

In the fetal period the oogonia, the diploid stem cells of the ovaries, multiply rapidly by mitosis and then enter a growth phase and lay in nutrient reserves

Gradually, primordial follicles begin to appear as the oogonia are transformed into primary oocytes and become surrounded by a single layer of follicle cells

The primary oocytes begin the first meiotic division, but become “stalled” late in prophase I and do not complete it

By birth, a female’s lifetime supply of primary oocytes, approximately 2 million of them, is already in place in the cortical region of the immature ovary Since they remain in their state of suspended animation all through childhood, the wait is a long one - 10 to 14 years at the very least

At puberty, perhaps 400,000 oocytes remain and beginning at this time a small number of primary oocytes are selected and activated each month

However, only one oocytes is selected each month to continue meiosis I ultimately producing two haploid cells (23 replicated chromosomes) that are quite dissimilar in size

The smaller cell is called the first polar body The larger cell, which contains nearly all the cytoplasm of the primary oocyte is the secondary oocyte

A spindle forms at the very edge of the oocyte and a little “nipple” into which the polar chromosomes will be cast appears at the edge

This sets up the polarity of the oocyte and ensures that the polar body receives almost no cytoplasm or organelles

The first polar body may continue its development and undergo meiosis II producing two even smaller polar bodies

In humans, the secondary oocyte arrests in metaphase II and it is this cell (not a functional ovum) that is ovulated

If an ovulated secondary oocyte is not penetrated by a sperm, it simply deteriorates

If an ovulated secondary oocyte is penetrated by sperm, it quickly completes meiosis II, yielding one large ovum and a tiny second polar body

The potential end products of oogenesis are three tiny polar bodies nearly devoid of cytoplasm, and one large ovum All of these cells are haploid, but only the ovum is a functional gamete This is quite different from spermatogenisis, where the product is four viable gametes - spermatozoa

The unequal cytoplasmic divisions that occur during oogenesis ensure that a fertilized egg has ample nutrients for its seven day journey to the uterus Without nutrient containing cytoplasm the polar bodies degenerate and die Since the reproductive life of a female is at best 40 years (11 to 51) and typically only one ovulation occurs each month, fewer than 500 oocytes are ever released

The Ovarian Cycle The monthly series of events associated with the maturation of an egg is called the ovarian cycle The ovarian cycle is best described in terms of two consecutive phases The follicular phase is the period of follicle growth, typically indicated as lasting from the first to the fourteenth day of the cycle The luteal phase is the period of corpus luteum activity, days 14-28

The Ovarian Cycle The typical ovarian cycle repeats at intervals of 28 days, with ovulation occurring midcycle However, cycles as long as 40 days or as short as 21 days are fairly common In such cases, the length of follicular phase and timing of ovulation vary, but the luteal phase remains constant: It is 14 days between the time of ovulation and the end of the cycle

The Ovarian Cycle Hormonal controls of these events will be described later The next section will focus upon what happens each month within the ovary

The Follicular Phase Maturation of a primordial follicle to the mature state occupies the first half of the cycle and involves several events

The Ovarian Cycle 1) Primordial follicles surrounded by squamous like cells

The Ovarian Cycle 21) The squamous like cells surrounding the primary oocyte grow becoming cuboidal cells, and the oocyte enlarges

The Ovarian Cycle 3) Next the follicular cells proliferate until they form a stratified epithelium around the oocyte As soon as more than one cell layer is present, the follicle is called a granulosa cell

The Ovarian Cycle The granulosa cells are connected to the developing oocyte by gap junctions, through which ions, metabolites, and signaling molecules can pass One of the signals passing from the granulosa cells to the oocytes initiates cell growth

The Ovarian Cycle 4) A layer of connective tissue begins to condense around the follicle, forming the theca folliculi

The Ovarian Cycle As the granulosa cells continue to divide and the follicle grows, the thecal and granulosa cells cooperate to produce estrogens (the inner thecal cells produce androgens, which the granulosa cells convert to estrogens) At the same time, the granulosa cells secrete a glycoprotein-rich substance that forms a thick transparent membrane, called the zona pellucida around the oocyte

The Ovarian Cycle 5) Clear liquid accumulates between the granulosa cells and eventually coalesces to form a fluid filled cavity, the antrum The presence of an atrium distinguishes the new secondary follicle from the primary

The Ovarian Cycle The antrum continues to expand with fluid until it isolates the oocyte, along with its surrounding capsule of granulosa cells called a corona radiata on a stalk on one side of the follicle When a follicle attains full size (2.5 cm) it becomes a vesticular follicle

The Ovarian Cycle 6) The vesticular follicle bulges from the external ovarian surface This usually occurs by day 14

The Ovarian Cycle As one of the final events of follicle maturation, the primary oocyte completes meiosis I to form the secondary oocyte and first polar body Once this has occurred, the stage is set for ovulation At this point, the granulosa cells send another important signal to the oocyte, in effect holding the meiosis of the oocyte

The Ovarian Cycle 7) Ovulation occurs when the ballooning ovary wall ruptures and expels the secondary oocyte into the peritoneal cavity

The Ovarian Cycle Some women experience a twinge of pain in the lower abdomen when ovulation occurs This episode is caused by the intense stretching of the ovarian wall during ovulation

The Ovarian Cycle In the ovaries of adult females, there are always several follicles at different stages of maturation As a rule, one follicle outstrips the others to become the dominant follicle and is at the peak stage of maturation when the hormonal (LH) stimulus is given for ovulation

The Ovarian Cycle How this follicle is selected, or selects itself, is still uncertain, but it is probably the one that attains the greatest FSH sensitivity the quickest The others degenerate

The Ovarian Cycle In 1-2% of all ovulations, more than one oocyte is ovulated This phenomenon, which increases with age, can result in multiple births Since different oocytes are fertilized by different sperm, the siblings are fraternal or nonidentical twins Identical twins result from the fertilization of a single oocyte by a single sperm, followed by separation of daughter cells

The Ovarian Cycle 8) After ovulation, the ruptured follicle collapses, and the antrum fills with clotted blood

The Ovarian Cycle This corpus hemorrhagicum is eventually absorbed
The remaining granulosa cells increase in size and along with the internal thecal cells they form a new, quite different endocrine gland, the corpus luteum Once formed, the corpus luteum begins to secrete progesterone and some estrogen

The Ovarian Cycle If pregnancy does not occur, the corpus luteum starts degenerating in about 10 days and its hormonal output ends In this case all that ultimately remains is a scar called the corpus albicans (white body)

The Ovarian Cycle 9) If the oocyte is fertilized and pregnancy ensures, the corpus luteum persists until the placenta is ready to take over hormone production The placenta is ready to assume these duties at about three months

Hormones and the Ovarian Cycle
Ovarian events are much more complicated than those occurring in the testes, but the hormonal controls set into motion at puberty are similar in the two sexes Gonadotropin-releasing hormone (GnRH), the pituitary gonadotropins, and, in this case ovarian estrogen and progesterone interact to produce the cyclic events occurring in the ovaries

Establishing the Ovarian Cycle
During childhood, the ovaries grow and continuously secrete small amounts of estrogens which inhibit hypothalmic release of GnRH But as puberty nears, the hypothalamus becomes less sensitive to estrogen and begins to release GnRH in a rhythmic pulselike manner GnRH, in turn, stimulates the anterior pituitary to release FSH and LH which act on the ovaries

Gonadotropin levels continue to increase for about four years and, during this time, pubertal girls are still not ovulating and thus are incapable of getting pregnant Eventually, the adult cyclic pattern is achieved, and hormonal interactions stabilize

These events are heralded by the young woman’s first menstrual period, referred to as menarche Usually, it is not until the third year postmenarche that the cycles become regular and all are ovulatory

Hormones: Ovarian Cycle
Described at the right is the cycle of anterior pituitary gonadatropins (FSH & LH) and ovarian hormones, and their negative and positive feedback mechanisms

1) On day 1 of the cycle, rising levels of GnRH from the hypothalamus stimulate increased production and release of FSH and LH by the anterior pituitary

2) FSH and LH stimulate follicle growth and maturation and estrogen secretion FSH exerts its main effects on the follicle cells, Whereas LH targets the thecal cells

Why only some follicles respond to these hormonal stimuli is still a mystery However, there is little doubt that enhanced responsiveness is due to formation of more gonadotropin receptors As the follicles enlarge, estrogen secretion begins

LH prods the thecal cells to produce androgens These diffuse through the basement membrane, where they are converted to estrogens by the FSH-primed granulosa cells Only tiny amounts of ovarian andogens enter the blood, because they are almost completely converted to estrogens within the ovaries

3) The rising estrogen levels in the plasma exert negative feed-back on the pituitary, inhibiting its release of FSH and LH while prodding it to synthesize and accumulate gonadotropins

Within the ovary, estrogen increases output by intensifying the effect of FSH on follicle maturation Inhibin, released by the granulosa cells, also exerts negative feedback controls on FSH release during this period

4) The initial small rise in estrogen blood levels inhibits the hypothalamic- pituitary axis as just described, but high estrogen levels have the opposite effect

Once estrogen reaches a critical concentration in the blood, it exerts positive feedback on the brain and anterior pituitary

5) High estrogen levels set a cascade of events into motion There is a sudden burstlike release of accumulated LH (FSH to a lesser extent) by the anterior pituitary Occurs midcycle

6) The sudden flush of LH stimulates the primary oocyte of the dominant follicle to complete the first meiotic division The secondary oocyte continues on to metaphase II

LH also triggers ovulation at or around the day 14 Perhaps LH induces the synthesis of proteolytic enzymes too, but whatever the mechanism, the blood stops flowing through the protruding part of the follicle wall Within 5 minutes, that region of the follicle wall bulges out, thins, and then abruptly ruptures

The role (if any) of FSH in this process is unknown Shortly after ovulation, estrogen levels decline This probably reflects the damage to the dominant estrogen secreting follicle during ovulation

7) The LH surge also transforms the ruptured follicle into a corpus luteum (hence the name luteinizing hormone)

Almost immediately after the corpus luteum is formed, this newly formed endocrine gland begins to produce progesterone and estrogen

8) As progesterone and estrogen levels rise in the blood, the combination exerts a powerful negative feedback effect on anterior pituitary release of LH and FSH

Corpus luteum release of inhibin enhances this inhibitory effect With gonadotropin decline, the development of new follicles is inhibited, and additional LH surges that might cause additional oocytes to be ovulated are prevented

9) As LH blood levels decline, the stimulus for luteal activity ends, and the corpus luteum begins degenerating

As the corpus luteum, so go the level of ovarian hormones, and blood estrogen and progesterone levels drop sharply However, if implantation of an embryo has occurred, the activity of the corpus luteum is maintained by an LH-like hormone released by the developing embyro

10) A marked decline in ovarian hormones at the end of the cycle (26-28) ends their blockade of FSH and LH secretion, and the cylce starts anew

The Uterine (Menstrual) Cycle
Although the uterus is where the young embryo implants and develops, it is receptive to implantation only for a very short period each month Not surprisingly, this brief interval is exactly the time when a developing embryo would normally begin implanting, about seven days after ovulation

The uterine or menstrual cycle is a series of cyclic changes that the uterine endometrium goes through each month as it responds to changing levels of ovarian hormones in the blood These endometrial changes are coordinated with the phases of the ovarian cycle, which in turn are dictated by gonadotropins released by the anterior pituitary

Days Mentrrual phase In this phase, the uterus sheds all but the deepest part of its endometrium At the beginning of this stage, gonadotropins are beginning to rise a bit and ovarian hormones are at their lowest normal levels. Then FSH levels begin to rise The thick functional layer of the endometrium detaches from the uterine wall, a process that is accompanied by bleeding for 3-5 days

The detached tissue and blood pass out through the vagina as the menstrual flow By day 5, the growing ovarian follicles are starting to produce more estrogen Notice day 5 on the chart at right

Days 6-14: Proliferative phase In this phase the endometrium rebuilds itself Under the influence of rising blood levels of estrogen, the basal layer of the endometrium generates a new functional layer

As the new functional layer thickens, its glands enlarge and its spiral arteries increase in number

Consequently, the endometrium once again becomes velvety, thick, and well vascularized During this phase, estrogens also induce synthesis of progesterone receptors in the endometrial cells readying them for interaction with progesterone

Normally, the cervical mucus is thick and sticky, but rising estrogen levels cause it to thin and become crystalline, forming channels that facilitate the passage of sperm into the uterus Ovulation occurs in the ovary at the end of this stage (day 14) in response to the sudden release of LH from the anterior pituitary LH converts the follicle to a corpus luteum

Days 15-28: Secretory Phase In this phase, the endometrium prepares for implantation of the embryo Rising levels of progesterone from the corpus luteum act on the estrogen-primed endometrium causing the spiral arteries to elaborate and coil more tightly and converting the functional layer to a secretory mucus

The uterine glands enlarge, coil, and begin secreting nutritious glycoproteins into the uterine cavity These nutrients sustain the embryo until it has implanted in the blood-rich endometrial lining All events of the secretory phase are promoted by progesterone

Increasing progesterone levels also cause the cervical mucus to become viscous again, forming the cervical plug, which blocks sperm entry and plays an important role in keeping the uterus “private” in the event an embryo has begun to implant Rising progesterone (and estrogen) levels inhibit LH release by the anterior pituitary

If fertilization has not occurred, the corpus luteum begins to degenerate toward the end of the secretory phase as LH blood levels decline Progesterone levels fall, depriving the endometrium of hormonal support, and the spiral arteries kink and go into spasms

Denied oxygen and nutrients, the endometrial cells begin to die, and as their lysosomes rupture, the functional layer begins to self-digest, setting the stage for menstruation to begin on day 28 The spiral arteries arteries constrict one final time and then suddenly relax and open wide As blood gushes into the weakened capillary beds, they fragment

Fragmentation continues causing the functional layer to slough off The mentrual cycle starts again on this first day of menstrual flow

Notice that the menstrual and proliferative phases overlap the follicular stage and ovulation in the ovarian cycle

The uterine secretory phase corresponds to the ovarian luteal phase

Extremely strenuous activity can delay menarche in girls and can disrupt the normal mentrual cycle in adult women, even causing amenorrhea or cessation of menses Part of the problem appears to be that female athletes have little body fat, and fat deposits help convert adrenal androgens to estrogens

In addition, hypothalamic controls are blocked in some way by severe physical regimens These effects are usually totally reversible when the athletic training is discontinued, but a worrisome consequence of amenorrhea in young healthy adult women is that they suffer dramatic losses in bone mass normally seen only in old age

Once estrogen levels drop and the menstrual cycle stops (regardless of cause), bone loss begins Currently, female athletes are encouraged to increase their daily calcium intake to 1.5 g, roughly the amount in a quart of milk

Effects: Estrogen Progesterone
Estrogen is analogous to testosterone, the male steroid As estrogen levels rise in puberty they… Promote oogenesis and follicle growth in the ovary Exert anabolic effects on the female reproductive tract Consequently, the uterine tubes, uterus, and vagina grow larger and become functional - ready to support pregnancy

The uterine tubes and uterus exhibit enhanced motility The vaginal mucosa thickens The external genitalia mature

Estrogen supports the growth spurt at puberty that makes girls grow much more quickly than boys during ages of 12 and 13 This growth is short lived because rising estrogen levels also cause earlier closure of the epiphysis on long bones, and females reach their full height between the ages of 15 and 17 years of age while males continue to grow until 19 to 21

The estrogen-induced secondary sex characteristics of females include: Growth of the breasts Increased deposits of subcutaneous fat, especially in the hips and breasts Widening and lightening of the pelvis Growth of axillary and pubic hair Several metabolic effects including

The estrogen-induced secondary sex characteristics of females include: Several metabolic effects including: Maintaining low total blood cholesterol levels and (and high HDL levels) Facilitating calcium uptake to help maintain bone density

Progesterone works with estrogen to establish and then help regulate the uterine cycle and progesterone promotes changes in cervical mucus Its other effects are exhibed largely during pregnancy, when it inhibits the motility of the uterus and takes up where estrogen leaves off in preparing the breasts for lactation

It should be noted that the source of most estrogen and progesterone during pregnancy is from the placenta and not from the ovaries

Female Sexual Response
The female sexual response is similar to that of the males in most respects During sexual excitement The clitoris, vaginal mucosa, and breasts engorge with blood The nipples erect Increased activity of the vestibular glands lubricates the vestibule and facilitates the entry of the penis

These events, though more widespread, are analogous to the erection phase in men Sexual excitement is promoted by touch and psychological stimuli and is mediated along the same autonomic pathways as in males

The final phase of the female sexual response, orgasm, results in Muscle tension increases throughout the body Pulse rate and blood pressure rise The uterus begins to contract rhythmically As in males, orgasm is accompanied by a sensation of intense pleasure followed by relaxation

Orgasm in females is not followed by a refractory period Consequently females may experience multiple orgasms during a single sexual experience Female orgasm is not required for conception Some women may never experience orgasm, yet are able to conceive and bear children

Sexually Transmitted Diseases
Sexually transmitted diseases (STD’s) or venereal disease are infectious diseases spread through sexual contact The United States has the highest rates of infection among developed countries Over 12 million people in the U.S., a quarter of them adolescents, get STD’s each year

STD’s are the single most important cause of reproductive disorders STD’s that cause reproductive disorders are typically of a bacterial origin Gonorrhea Syphillis Chlamydia In addition, genital herpes can pose a risk to a developing fetus

Finally, the long term health risks posed by unrecognized or untreated STD’s can cripple and kill both host parent and offspring AIDS cripples the immune system also threatening life itself The risks are real

Yahoo!! We’re outta here!!

The Reproductive System

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