The Reproductive System: Part A

The Reproductive System: Part A
27 The Reproductive System: Part A

Primary sex organs (gonads) - testes and ovaries
Reproductive System Primary sex organs (gonads) - testes and ovaries Produce gametes (sex cells ) – sperm & ova Secrete steroid sex hormones Androgens (males) Estrogens and progesterone (females) Accessory reproductive organs - ducts, glands, and external genitalia © 2013 Pearson Education, Inc.

Sex hormones play roles in
Reproductive System Sex hormones play roles in Development and function of reproductive organs Sexual behavior and drives Growth and development of many other organs and tissues © 2013 Pearson Education, Inc.

Male Reproductive System
Testes (within scrotum) produce sperm Sperm delivered to exterior through system of ducts Epididymis  ductus deferens  ejaculatory duct  urethra © 2013 Pearson Education, Inc.

Male Reproductive System
Accessory sex glands Seminal vesicles Prostate Bulbourethral glands Empty secretions into ducts during ejaculation © 2013 Pearson Education, Inc.

Figure 27.1 Reproductive organs of the male, sagittal view.
Peritoneum Seminal gland (vesicle) Ampulla of ductus deferens Ejaculatory duct Rectum Prostate Bulbo-urethral gland Anus Bulb of penis Ductus (vas) deferens Epididymis Testis Scrotum Ureter Urinary bladder Prostatic urethra Pubis Intermediate part of the Urogenital diaphragm Corpus cavernosum spongiosum Spongy Glans penis Prepuce (foreskin) External urethral orifice © 2013 Pearson Education, Inc.

Sac of skin and superficial fascia
The Scrotum Sac of skin and superficial fascia Hangs outside abdominopelvic cavity Contains paired testes 3C lower than core body temperature Lower temperature necessary for sperm production © 2013 Pearson Education, Inc.

Temperature kept constant by two sets of muscles
The Scrotum Temperature kept constant by two sets of muscles Dartos muscle - smooth muscle; wrinkles scrotal skin; pulls scrotum close to body Cremaster muscles - bands of skeletal muscle that elevate testes © 2013 Pearson Education, Inc.

Superficial inguinal ring (end of inguinal canal) Testicular artery
Figure Relationships of the testis to the scrotum and spermatic cord. Urinary bladder Superficial inguinal ring (end of inguinal canal) Testicular artery Spermatic cord Ductus (vas) deferens Penis Autonomic nerve fibers Septum of scrotum Pampiniform venous plexus Cremaster muscle Epididymis Tunica vaginalis (from peritoneum) External spermatic fascia Superficial fascia containing dartos muscle Tunica albuginea of testis Scrotum Internal spermatic fascia Skin © 2013 Pearson Education, Inc.

Each surrounded by two tunics
The Testes Each surrounded by two tunics Tunica vaginalis – outer layer derived from peritoneum Tunica albuginea – inner layer; fibrous capsule Septa divide testis into ~250 lobules, each containing 1–4 seminiferous tubules - site of sperm production © 2013 Pearson Education, Inc.

Seminiferous Tubules Thick, stratified epithelium surrounding central fluid-containing lumen Epithelium Spheroid spermatogenic cells embedded in sustentocytes Myoid cells surround each tubule May squeeze sperm, testicular fluids out of testes Tubules of each lobule form straight tubule © 2013 Pearson Education, Inc.

The Testes Sperm conveyed from Seminiferous tubules 
Straight tubule  Rete testis  Efferent ductules  Epididymis © 2013 Pearson Education, Inc.

Produce androgens, e.g., testosterone
Seminiferous Tubules Interstitial endocrine cells in soft tissue surrounding seminiferous tubules Produce androgens, e.g., testosterone Secrete it into interstitial fluid © 2013 Pearson Education, Inc.

The Testes Blood supply
Testicular arteries arise from abdominal aorta Testicular veins arise from pampiniform venous plexus surrounding each testicular artery Cooler; absorb heat from testicular arteries Keep testes cool Spermatic cord encloses nerve fibers, blood vessels, and lymphatics that supply testes © 2013 Pearson Education, Inc.

Figure 27.3a Structure of the testis.
Spermatic cord Blood vessels and nerves Ductus (vas) deferens Testis Head of epididymis Seminiferous tubule Efferent ductule Rete testis Lobule Straight tubule Septum Tunica albuginea Body of epididymis Tunica vaginalis Cavity of tunica vaginalis Duct of epididymis Tail of epididymis © 2013 Pearson Education, Inc.

Figure 27.3b Structure of the testis.
Spermatic cord Ductus deferens Epididymis Testis © 2013 Pearson Education, Inc.

Figure 27.3c Structure of the testis.
Seminiferous tubule Sustentocyte Areolar connective tissue Sperm Interstitial endocrine cells Myoid cells Spermatogenic cells in tubule epithelium © 2013 Pearson Education, Inc.

Homeostatic Imbalance
Testicular cancer Rare; most common cancer in men 15-35 Cryptorchidism is risk factor Sign – painless, solid mass in testis 90% cured by surgical removal of testis and often radiation or chemotherapy © 2013 Pearson Education, Inc.

Suspends scrotum; contains root of penis and anus
The Male Perineum Diamond-shaped region between pubic symphysis, coccyx, and ischial tuberosities Suspends scrotum; contains root of penis and anus © 2013 Pearson Education, Inc.

Figure 27.4 The male perineum, inferior view.
Penis Scrotum Pubic symphysis Ischial tuberosity Anus Coccyx © 2013 Pearson Education, Inc.

External genitalia - scrotum and penis Penis - male copulatory organ
The Penis External genitalia - scrotum and penis Penis - male copulatory organ © 2013 Pearson Education, Inc.

The Penis Penis consists of Root and shaft that ends in glans penis
Prepuce, or foreskin—cuff of loose skin covering glans Crura Proximal ends of corpora cavernosa surrounded by ischiocavernosus muscle; anchors penis to pubic arch © 2013 Pearson Education, Inc.

Surgical removal of foreskin 60% newborn boys in US circumcised
Circumcision Surgical removal of foreskin 60% newborn boys in US circumcised 15% in other parts of world Some claim medically unnecessary Studies show 60% reduction in HIV risk Reduced risk for other reproductive system infections © 2013 Pearson Education, Inc.

The Penis: Internally Spongy urethra and three cylindrical bodies of erectile tissue (spongy network of connective tissue and smooth muscle with vascular spaces) Corpus spongiosum - surrounds urethra and expands to form glans and bulb Corpora cavernosa - paired dorsal erectile bodies Erection - erectile tissue fills with blood, causing penis to enlarge and become rigid © 2013 Pearson Education, Inc.

Figure 27.5 Male reproductive structures.
Ureter Urinary bladder Ampulla of ductus deferens Seminal gland Prostate Prostatic urethra Ejaculatory duct Orifices of prostatic ducts Bulbo-urethral gland and duct Intermediate part of the urethra (membranous urethra) Urogenital diaphragm Bulb of penis Root of penis Crus of penis Bulbo-urethral duct opening Ductus deferens Corpora cavernosa Epididymis Corpus spongiosum Body (shaft) of penis Testis Section of (b) Spongy urethra Glans penis Prepuce (foreskin) External urethral orifice Dorsal vessels and nerves Corpora cavernosa Urethra Skin Tunica albuginea of erectile bodies Deep arteries Corpus spongiosum © 2013 Pearson Education, Inc.

Ducts carry sperm from testes to body exterior
The Male Duct System Ducts carry sperm from testes to body exterior Epididymis Ductus deferens Ejaculatory duct Urethra © 2013 Pearson Education, Inc.

Epididymis Head - contains efferent ductules; superior aspect of testis; body and tail on posterolateral area of testis Duct of the epididymis ~ 6 m in length Microvilli (stereocilia) absorb testicular fluid and pass nutrients to stored sperm Nonmotile sperm enter, pass slowly through (~ 20 days), become motile; can be stored several months During ejaculation epididymis contracts, expelling sperm into ductus deferens © 2013 Pearson Education, Inc.

Ductus Deferens and Ejaculatory Duct
Ductus deferens (vas deferens) ~ 45 cm Passes through inguinal canal to pelvic cavity Expands to form ampulla; joins duct of seminal vesicle to form ejaculatory duct Smooth muscle in walls propels sperm from epididymis to urethra Vasectomy - cutting and ligating ductus deferens; nearly 100% effective form of birth control © 2013 Pearson Education, Inc.

Conveys both urine and semen (at different times) Has three regions
Urethra Conveys both urine and semen (at different times) Has three regions Prostatic urethra – surrounded by prostate Intermediate part of the urethra (membranous urethra) – in urogenital diaphragm Spongy urethra – runs through penis; opens at external urethral orifice © 2013 Pearson Education, Inc.

The Male Accessory Glands
Paired seminal glands (seminal vesicles) Paired bulbo-urethral glands Prostate gland Produce bulk of semen Remainder - sperm from testes © 2013 Pearson Education, Inc.

Accessory Glands: Seminal Glands
On posterior bladder surface; smooth muscle contracts during ejaculation Produces viscous alkaline seminal fluid Fructose, citric acid, coagulating enzyme (vesiculase), and prostaglandins Yellow pigment fluoresces with UV light 70% volume of semen Duct of seminal vesicle joins ductus deferens to form ejaculatory duct © 2013 Pearson Education, Inc.

Accessory Glands: Prostate
Encircles urethra inferior to bladder; size of peach pit; smooth muscle contracts during ejaculation Secretes milky, slightly acid fluid Contains citrate, enzymes, and prostate-specific antigen (PSA) Role in sperm activation Enters prostatic urethra during ejaculation 1/3 semen volume © 2013 Pearson Education, Inc.

Prostatitis – inflammatory disorders
Prostate Disorders Prostatitis – inflammatory disorders Bacterial infection; acute and chronic; treated with antibiotics Benign prostatic hyperplasia May be age-related; distorts urethra; treated with surgery, microwaves, drugs, balloon compression, radio-frequency radiation © 2013 Pearson Education, Inc.

Prostate Disorders Prostate cancer
Second most common cause of cancer death in males Digital exam screening, PSA levels Biopsy if abnormal Treated with surgery and sometimes radiation; castration; drugs In clinical trials - cryosurgery, chemotherapy, ultrasound, proton beam therapy © 2013 Pearson Education, Inc.

Accessory Glands: Bulbo-Urethral Glands (Cowper's Glands)
Pea-sized glands inferior to prostate Produce thick, clear mucus during sexual arousal Lubricates glans penis Neutralizes traces of acidic urine in urethra © 2013 Pearson Education, Inc.

Milky-white mixture of sperm and accessory gland secretions
Semen Milky-white mixture of sperm and accessory gland secretions 2–5 ml semen ejaculated, contains 20–150 million sperm/ml Contains fructose for ATP production; protects and activates sperm; facilitates sperm movement Alkaline  neutralizes acidity of male urethra and female vagina  enhanced motility © 2013 Pearson Education, Inc.

Semen Functions Prostaglandins decrease viscosity of mucus in cervix; stimulate reverse peristalsis in uterus Hormone relaxin, enzymes  sperm motility Contains ATP for energy Suppresses female immune response Antibacterial action Clotting factors coagulate semen initially to prevent draining out; then liquefied by fibrinolysin  sperm begin journey © 2013 Pearson Education, Inc.

Male Sexual Response Erection Arterioles normally constricted
Sexual excitement causes CNS activation of parasympathetic neurons  nitric oxide (NO) release  local vascular smooth muscle relaxation  arterioles dilate  corpora cavernosa expands, retards venous drainage  engorgement of erectile tissues with blood  enlargement and stiffening of penis © 2013 Pearson Education, Inc.

Initiated by sexual stimuli
Erection Initiated by sexual stimuli Touch; mechanical stimulation of penis; erotic sights, sounds, and smells Can be induced or inhibited by emotions or higher mental activity Longitudinal and circular collagen fibers around penis prevent kinking/buckling of erect penis Corpus spongiosum keeps urethra open © 2013 Pearson Education, Inc.

Male Sexual Response Ejaculation
Propulsion of semen from male duct system Sympathetic spinal reflex Bladder sphincter muscle constricts, preventing expulsion of urine Ducts and accessory glands contract and empty their contents Bulbospongiosus muscles undergo rapid series of contractions  expulsion of semen at ~ 500 cm/s (close to 11 mph) Ejaculatory event – climax (orgasm) © 2013 Pearson Education, Inc.

Erectile dysfunction Parasympathetic nerves of penis release too little NO Causes – alcohol, drugs, hormones, blood vessel or nervous system problems, incompetent venous valves fail to retain blood in penis New drugs (Viagra, Cialis) potentiate existing NO effects © 2013 Pearson Education, Inc.

Sperm (spermatozoa) production in seminiferous tubules
Spermatogenesis Sperm (spermatozoa) production in seminiferous tubules Most body cells have 46 chromosomes - diploid chromosomal number (2n) Two sets (23 pairs) of chromosomes One maternal, one paternal – homologous chromosomes Gametes have 23 chromosomes - haploid chromosomal number (n) Only one member of homologous pair © 2013 Pearson Education, Inc.

Gamete formation involves meiosis
Differs from mitosis Two consecutive cell divisions (meiosis I and II); only one round of DNA replication Produces four daughter cells Functions of meiosis Number of chromosomes halved (from 2n to n) Introduces genetic diversity © 2013 Pearson Education, Inc.

Crossover  variability of gametes ~ No two gametes exactly alike
Meiosis Random alignment of homologous pairs in meiosis I  variability of gametes Crossover  variability of gametes ~ No two gametes exactly alike ~ All different from original mother cells © 2013 Pearson Education, Inc.

Figure 27.6 Comparison of mitosis and meiosis in a mother cell with a diploid number (2n) of 4.
(before chromosome replication) Chromosome replication Chromosome replication 2n = 4 MITOSIS MEIOSIS Replicated chromosome Tetrad formed by synapsis of replicated homologous chromosomes Prophase Prophase I Chromosomes align at the metaphase plate Tetrads align randomly at the metaphase plate Metaphase Metaphase I Sister chromatids separate during anaphase Homologous chromosomes separate but sister chromatids remain together during anaphase I Daughter cells of mitosis Daughter cells of Meiosis I 2n 2n No further chromosomal replication; sister chromatids separate during anaphase II Meiosis II n n n n Daughter cells of meiosis II (usually gametes) MITOSIS MEIOSIS Number of divisions One, consisting of prophase, metaphase, anaphase, and telophase. Two, each consisting of prophase, metaphase, anaphase, and telophase. DNA replication does not occur between the two nuclear divisions. Synapsis of homologous chromosomes Does not occur. Occurs during prophase I; tetrads form, allowing crossovers. Daughter cell number and genetic composition Two. Each diploid (2n) cell is identical to the mother cell. Four. Each haploid (n) cell contains half as many chromosomes as the mother cell and is genetically different from the mother cell. Roles in the body For development of multicellular adult from zygote. Produces cells for growth and tissue repair as multicellular adult develops. Ensures genetic makeup of all body cells is constant. Produces cells for reproduction (gametes). Introduces genetic variability in the gametes and reduces chromosomal number by half so that when fertilization occurs, the normal diploid chromosomal number is restored (in humans, 2n = 46). © 2013 Pearson Education, Inc.

Reduction division of meiosis – reduces chromosome number from 2n  n
Meiosis I Reduction division of meiosis – reduces chromosome number from 2n  n Prophase I events not in mitosis or meiosis II Synapsis - homologous chromosomes pair forming tetrads of four chromatids Crossover (chiasmata) – exchange of genetic material between male and female chromatid  unique chromosomes © 2013 Pearson Education, Inc.

End of meiosis I each daughter cell
Two copies of one member of each homologous pair (either maternal or paternal); none of the other Haploid chromosomal number; still-united sister chromatids one chromosome (twice amount DNA in each chromosome) © 2013 Pearson Education, Inc.

Equational division of meiosis
Meiosis II Equational division of meiosis Sister chromatids from meiosis I separated, one per cell Like mitosis except no chromosome replication before begins © 2013 Pearson Education, Inc.

Meiosis Animation: Interphase Animation: Prophase I
PLAY Animation: Interphase PLAY Animation: Prophase I PLAY Animation: Metaphase I PLAY Animation: Anaphase I PLAY Animation: Telophase I PLAY Animation: Meiosis II © 2013 Pearson Education, Inc.

Figure 27.7 Meiosis. © 2013 Pearson Education, Inc. Interphase cell
MEIOSIS I Prophase I Prophase events occur, as in mitosis. Additionally, synapsis occurs: Homologous chromosomes come together along their length to form tetrads. During synapsis, the “arms” of homologous chromatids wrap around each other, forming several crossovers. The nonsister chromatids trade segments at points of crossover. Crossover is followed through the diagrams below. Nuclear envelope Centromere Centriole pairs Crossover Spindle Sister chromatids Chromatin Nuclear envelope fragments late in prophase I 2n = 4 Interphase events As in mitosis, meiosis is preceded by DNA replication and other preparations for cell division. Metaphase I The tetrads align randomly on the spindle equator in preparation for anaphase. Tetrad Dyad Anaphase I Unlike anaphase of mitosis, the centromeres do not separate during anaphase I of meiosis, so the sister chromatids (dyads) remain firmly attached. However, the homologous chromosomes do separate from each other and the dyads move toward opposite poles of the cell. Chromosomes uncoil Telophase I The nuclear membranes re-form around the chromosomal masses, the spindle breaks down, and the chromatin reappears as telophase and cytokinesis end. The 2 daughter cells (now haploid) enter a second interphase-like period, called interkinesis, before meiosis II occurs. There is no second replication of DNA before meiosis II. Nuclear envelopes re-form Cleavage furrow MEIOSIS II Prophase II Meiosis II begins with the products of meiosis I (2 haploid daughter cells) and undergoes a mitosis-like nuclear division process referred to as the equational division of meiosis. Metaphase II Anaphase II After progressing through the phases of meiosis and cytokinesis, the product is 4 haploid cells, each genetically different from the original mother cell. (During human spermatogenesis, the daughter cells remain interconnected by cytoplasmic extensions during the meiotic phases.) Telophase II and cytokinesis Products of meiosis: haploid daughter cells © 2013 Pearson Education, Inc.

Spermatogenic cells give rise to sperm
Spermatogenesis Spermatogenic cells give rise to sperm Mitosis of spermatogonia (stem cell) forms two spermatocytes Meiosis Spermatocytes  secondary spermatocytes  spermatids Spermiogenesis Spermatids become sperm © 2013 Pearson Education, Inc.

Figure 27.8a Spermatogenesis.
Scanning electron micrograph of a cross-sectional view of a seminiferous tubule (165x) © 2013 Pearson Education, Inc.

Figure 27.8c Spermatogenesis.
Tight junction between sustentocytes Cytoplasm of adjacent sustentocytes Spermatogonium (stem cell) Sustentocyte cell nucleus Basal lamina Type A daughter cell remains at basal lamina as a precursor cell compartment Basal Type B daughter cell Primary spermatocyte Secondary spermatocytes Early spermatids Late spermatids Adluminal compartment Cytoplasmic bridge Lumen of seminiferous tubule Spermatozoa A portion of the seminiferous tublule wall, showing the spermatogenic cells surrounded by sustentocytes (colored gold) © 2013 Pearson Education, Inc.

Mitosis of Spermatogonia
Spermatogenesis begins at puberty Spermatogonia Stem cells in contact with epithelial basal lamina Each mitotic division  one type A daughter cell and one type B daughter cell © 2013 Pearson Education, Inc.

Mitosis of Spermatogonia
Type A cells maintain germ cell line at basal lamina Type B cells move toward lumen and develop into primary spermatocytes © 2013 Pearson Education, Inc.

Meiosis: Spermatocytes to Spermatids
Meiosis I Primary spermatocyte (2n)  two secondary spermatocytes (n) Meiosis II Each secondary spermatocyte (n)  two spermatids (n) Spermatid – small, nonmotile cells close to lumen of tubule © 2013 Pearson Education, Inc.

Figure 27.8b Spermatogenesis.
Basal lamina Spermatogonium (stem cell) 2n 2n Type A daughter cell remains at basal lamina as a precursor cell Mitosis 2n Type B daughter cell Growth Enters meiosis I and moves to adluminal compartment 2n Primary spermatocyte spermatogenesis) Meiosis (early Meiosis I completed n n Secondary spermatocytes Meiosis ll Spermatogenesis n n n n Early spermatids n n n n Late spermatids Spermiogenesis (late spermatogenesis) n n n n Spermatozoa Events of spermatogenesis, showing the relative position of various spermatogenic cells © 2013 Pearson Education, Inc.

Spermiogenesis: Spermatids to Sperm
Correct chromosome number (n) Nonmotile Spermiogenesis Spermatids elongate; lose excess cytoplasm; form a tail  spermatozoon (sperm) © 2013 Pearson Education, Inc.

Approximately 24 days Golgi apparatus Acrosomal vesicle Mitochondria
Figure Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 1 Approximately 24 days Golgi apparatus Acrosomal vesicle Mitochondria Acrosome Nucleus 1 2 Spermatid nucleus Centrioles Microtubules Midpiece Head 3 Flagellum Excess cytoplasm 4 Tail 5 6 7 © 2013 Pearson Education, Inc.

Approximately 24 days Golgi apparatus Acrosomal vesicle
Figure Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 2 Approximately 24 days Golgi apparatus Acrosomal vesicle 1 Spermatid nucleus © 2013 Pearson Education, Inc.

Approximately 24 days Golgi apparatus Acrosomal vesicle Centrioles
Figure Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 3 Approximately 24 days Golgi apparatus Acrosomal vesicle 1 2 Spermatid nucleus Centrioles © 2013 Pearson Education, Inc.

Approximately 24 days Golgi apparatus Acrosomal vesicle 1 2 Spermatid
Figure Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 4 Approximately 24 days Golgi apparatus Acrosomal vesicle 1 2 Spermatid nucleus Centrioles Microtubules 3 Flagellum © 2013 Pearson Education, Inc.

Approximately 24 days Golgi apparatus Acrosomal vesicle Mitochondria 1
Figure Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 5 Approximately 24 days Golgi apparatus Acrosomal vesicle Mitochondria 1 2 Spermatid nucleus Centrioles Microtubules 3 Flagellum 4 © 2013 Pearson Education, Inc.

Figure Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 6 Approximately 24 days Golgi apparatus Acrosomal vesicle Mitochondria Acrosome Nucleus 1 2 Spermatid nucleus Centrioles Microtubules 3 Flagellum Excess cytoplasm 4 5 © 2013 Pearson Education, Inc.

Figure Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 7 Approximately 24 days Golgi apparatus Acrosomal vesicle Mitochondria Acrosome Nucleus 1 2 Spermatid nucleus Centrioles Microtubules 3 Flagellum Excess cytoplasm 4 5 6 © 2013 Pearson Education, Inc.

Figure Spermiogenesis: transformation of a spermatid into a functional sperm. Slide 8 Approximately 24 days Golgi apparatus Acrosomal vesicle Mitochondria Acrosome Nucleus 1 2 Spermatid nucleus Centrioles Microtubules Midpiece Head 3 Flagellum Excess cytoplasm 4 Tail 5 6 7 © 2013 Pearson Education, Inc.

Sperm Major regions Head - genetic region; nucleus and helmetlike acrosome containing hydrolytic enzymes that enable sperm to penetrate egg Midpiece - metabolic region; mitochondria  ATP to move tail Tail - locomotor region; flagellum © 2013 Pearson Education, Inc.

Large supporting cells (Sertoli cells)
Role of Sustentocytes Large supporting cells (Sertoli cells) Extend through wall of tubule and surround developing cells Provide nutrients and signals to dividing cells Move cells along to lumen Secrete testicular fluid into lumen for sperm transport Phagocytize faulty germ cells and excess cytoplasm Produce chemical mediators to regulate spermatogenesis © 2013 Pearson Education, Inc.

Role of Sustentacular Cells
Tight junctions divide tubule into two compartments Basal compartment—spermatogonia and primary spermatocytes Adluminal compartment—meiotically active cells and tubule lumen © 2013 Pearson Education, Inc.

Figure 27.8c Spermatogenesis.
Tight junction between sustentocytes Cytoplasm of adjacent sustentocytes Spermatogonium (stem cell) Sustentocyte cell nucleus Basal lamina Type A daughter cell remains at basal lamina as a precursor cell compartment Basal Type B daughter cell Primary spermatocyte Secondary spermatocytes Early spermatids Late spermatids Adluminal compartment Cytoplasmic bridge Lumen of seminiferous tubule Spermatozoa A portion of the seminiferous tublule wall, showing the spermatogenic cells surrounded by sustentocytes (colored gold) © 2013 Pearson Education, Inc.

Role of Sustentacular Cells
Tight junctions form blood-testis barrier Prevents sperm antigens from escaping into blood  activation of immune system Important - sperm not formed until puberty, absent during immune system development, would not be recognized as "self" © 2013 Pearson Education, Inc.

Takes 64 – 72 days if conditions hospitable
Spermatogenesis Takes 64 – 72 days if conditions hospitable Pressure of testicular fluid pushes immotile sperm into epididymis  motility and fertilizing power © 2013 Pearson Education, Inc.

Infertility Gradual decline in male fertility past 50 years Xenobiotics (alien molecules) may be cause Environmental toxins, PVCs, phthalates, pesticides, herbicides, compounds with estrogenic effects, antibiotics, radiation, lead, marijuana Also, lack of selenium, excessive alcohol, lack of specific Ca2+ channel, anatomical obstructions, hormonal imbalances, oxidative stress, fevers, hot tubs © 2013 Pearson Education, Inc.

The Reproductive System: Part A

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