Human Reproductive System Objectives: Identify the major structures of male and female reproductive system Describe the function of each structure of the reproductive system Describe how sperm and eggs are produced. Summarize the stages of the ovarian cycle Describe the stages of pregnancy Summarize the development of an embryo during gestation

Types of Reproduction Asexual – does not involve the union of gametes; a single parent donates the entire genome to offspring Limits the amount of variation in phenotypes of offspring Makes organism vulnerable environmental changes Sexual – production of offspring from the combination of genetic material from two parent organisms Increases the variation of phenotypes in offspring Increases the rate of survival of a species when environmental factors change Parents must produce sex cells through meiosis Produces 4 haploid cells from a single germ cell

Sexual Reproduction: An Evolutionary Enigma Sexual females have half as many daughters as asexual females; this is the “twofold cost” of sexual reproduction Despite this, almost all eukaryotic species reproduce sexually © 2011 Pearson Education, Inc.

Asexual reproduction Sexual reproduction Female Generation 1 Female Figure 46.3-1 Asexual reproduction Sexual reproduction Female Generation 1 Female Figure 46.3 The “reproductive handicap” of sex.

Asexual reproduction Sexual reproduction Female Generation 1 Female Figure 46.3-2 Asexual reproduction Sexual reproduction Female Generation 1 Female Generation 2 Male Figure 46.3 The “reproductive handicap” of sex.

Asexual reproduction Sexual reproduction Female Generation 1 Female Figure 46.3-3 Asexual reproduction Sexual reproduction Female Generation 1 Female Generation 2 Male Generation 3 Figure 46.3 The “reproductive handicap” of sex.

Asexual reproduction Sexual reproduction Female Generation 1 Female Figure 46.3-4 Asexual reproduction Sexual reproduction Female Generation 1 Female Generation 2 Male Generation 3 Figure 46.3 The “reproductive handicap” of sex. Generation 4

Introduction Reproduction is not essential to the survival of the individual Reproduction is vital to the survival of a species In humans, the reproductive system produces, stores, nourishes, and releases sex cells known as gametes Gametes come together to form the zygote, or fertilized egg In males, gametes are formed in the testes and in females they are formed in the ovaries

Intro cont. During the 7th week of embryonic development, testes produce hormones called androgens and ovaries produce hormones called estrogens that lead to the development of the respective reproductive organs Neither testes nor ovaries are capable of producing Active Reproductive Cells until Puberty Period of rapid growth and sexual maturation when reproductive organs become fully functional Occurs between the ages of 9 & 15, usually 1 yr earlier in females Begins with a change in the hypothalamus that instructs the pituitary gland to increase the levels of two hormones Follicle Stimulating Hormone (FSH) Luteinizing Hormone (LH)

Male Reproductive Anatomy The male’s external reproductive organs are the scrotum and penis Internal organs are the gonads, which produce sperm and hormones, and accessory glands

Seminal vesicle (behind bladder) Figure 46.11 Seminal vesicle (behind bladder) (Urinary bladder) Prostate gland Bulbourethral gland Urethra Erectile tissue of penis Scrotum Vas deferens Epididymis Testis (Urinary bladder) Seminal vesicle (Urinary duct) Figure 46.11 Reproductive anatomy of the human male. (Rectum) (Pubic bone) Vas deferens Erectile tissue Ejaculatory duct Prostate gland Urethra Penis Bulbourethral gland Vas deferens Glans Epididymis Testis Prepuce Scrotum

Male Reproductive Organs 1. Bladder 2. Vas deferens 3. Corpus Cavernosum 4. Corpus Spongiosum 5. Urethra 6. Glans penis 7. Prepuce 8. Testes 9. Epididymis 10. Bulbourethral gland 11. Prostate 12. Seminal Vesicle 13. Rectum 14. Ejaculatory Duct

Testes The male gonads, or testes, consist of highly coiled tubes surrounded by connective tissue Sperm form in these seminiferous tubules Leydig cells produce hormones and are scattered between the tubules Production of normal sperm cannot occur at the body temperatures of most mammals What structure has nature developed to remedy this? © 2011 Pearson Education, Inc.

The testes of many mammals are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity © 2011 Pearson Education, Inc.

Male Reproductive System Testosterone FSH and LH stimulate the testes to make testosterone Testosterone is the principle male sex hormone It produces secondary sex characteristics that appear at puberty Voice deepens Facial hair Body hair Muscle development FSH and Testosterone stimulate the development of sperm When large numbers of sperm have been produced, the process of puberty is complete and the reproductive system is fully functional

Male Reproductive Cells Sperm Formed through meiosis – reduces the # of chromosomes to 23 Consists of 3 main parts Head – contains the nucleus and enzymes that help penetrate the egg Mid piece – contains mitochondria to provide energy to reach the egg Tail – consists of a single, powerful flagellum that propels the sperm

Accessory Glands Semen is composed of sperm plus secretions from three sets of accessory glands The two seminal vesicles contribute about 60% of the total volume of semen The prostate gland secretes its products directly into the urethra through several small ducts The bulbourethral glands secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra © 2011 Pearson Education, Inc.

Path of sperm Sperm travels from the testes to the epididymus Matures and develops tail Storage of sperm Some sperm leave and enter the vas deferens Duct that extends from the epididymus and wraps around the bladder and merges with the urethra In the urethra, sperm mix with fluids from the 3 glands: Seminal Vesicles, Bulbouretheral gland, and the Prostate gland – this mixture is called semen Semen contains fructose to provide energy and alkaline fluids to neutralize the acidity of the vagina Semen also contains prostaglandins which stimulate smooth muscle contractions in the female reproductive system

Path cont Sperm exits the body through the urethra – tube that leads out of the body through the penis Sperm are ejected from the body by smooth muscle contractions in the vas deferens – this process is called ejaculation Controlled by the autonomic nervous system 300-400 million sperm are released in a single ejaculation Most are killed by the acidity of the vagina

Female Reproductive Anatomy The female external reproductive structures include the clitoris and two sets of labia The internal organs are a pair of gonads and a system of ducts and chambers that carry gametes and house the embryo and fetus © 2011 Pearson Education, Inc.

Major vestibular (Bartholin’s) gland Labia minora Labia majora Figure 46.10 Oviduct Ovary Uterus (Urinary bladder) (Pubic bone) (Rectum) Urethra Cervix Body Vagina Glans Clitoris Prepuce Major vestibular (Bartholin’s) gland Labia minora Labia majora Vaginal opening Oviduct Ovaries Figure 46.10 Reproductive anatomy of the human female. Follicles Corpus luteum Uterus Uterine wall Endometrium Cervix Vagina

Female Reproductive System Ovaries Primary organ Located in the lower abdomen Usually produce one egg, or ovum, per month Produce the principle sex hormone of females – estrogen Estrogen FSH and LH stimulate the ovary at puberty to release this hormone Produces secondary sex characteristics Enlargement of breasts Widening of hips Growth of body hair

Female Reproductive Cells Ovum (egg) Each ovary contains about 400,000 primary follicles, which are immature eggs (oocyte) Some follicles will mature and become eggs Other follicles prepare an egg to be released into the reproductive system where it can be fertilized Fewer than 500 ova (eggs) are released in a lifetime Ovulation is when an ovum matures and is released into the reproductive system Begins at puberty and continues until a woman reaches her late 40’s – menopause Follicle development ceases Without follicles, ovaries cannot secrete enough estrogen and progesterone to continue menstrual cycle

Path of an Ovum Once the egg has matured in the ovary, it is ruptured into the fallopian tubes Provide a path from ovary to uterus Ovum is moved by cilia that line the walls Fertilization must occur in the fallopian tubes within 48 hours of being released – egg begins to breakdown after 48 hrs If the egg is fertilized, it attaches to the uterus and develops into an embryo If the egg is not fertilized, it signals the body to enter the 3rd stage of the menstrual cycle

Gametogenesis Gametogenesis, the production of gametes, differs in male and female, reflecting the distinct structure and function of their gametes Sperm are small and motile and must pass from male to female Eggs are larger and carry out their function within the female © 2011 Pearson Education, Inc.

Oogenesis, the development of a mature egg, is a prolonged process Spermatogenesis, the development of sperm, is continuous and prolific (millions of sperm are produced per day; each sperm takes about 7 weeks to develop Oogenesis, the development of a mature egg, is a prolonged process Immature eggs form in the female embryo but do not complete their development until years or decades later © 2011 Pearson Education, Inc.

Spermatogenesis differs from oogenesis in three ways All four products of meiosis develop into sperm while only one of the four becomes an egg Spermatogenesis occurs throughout adolescence and adulthood Sperm are produced continuously without the prolonged interruptions in oogenesis © 2011 Pearson Education, Inc.

Figure 46.12 Exploring: Human Gametogenesis Figure 46.12a Epididymis Seminiferous tubule Testis Primordial germ cell in embryo Cross section of seminiferous tubule Mitotic divisions Spermatogonial stem cell 2n Mitotic divisions Sertoli cell nucleus Spermatogonium 2n Mitotic divisions Primary spermatocyte 2n Meiosis I Secondary spermatocyte n n Figure 46.12 Exploring: Human Gametogenesis Meiosis II Lumen of seminiferous tubule Spermatids (two stages) Early spermatid Neck n n n n Tail Midpiece Head Differentiation (Sertoli cells provide nutrients) Plasma membrane Sperm cell n n Acrosome n n Nucleus Mitochondria

Cross section of seminiferous tubule Secondary spermatocyte Figure 46.12aa Epididymis Seminiferous tubule Sertoli cell nucleus Spermato- gonium Primary spermatocyte Testis Cross section of seminiferous tubule Secondary spermatocyte Spermatids (two stages) Figure 46.12 Exploring: Human Gametogenesis Sperm cell Lumen of seminiferous tubule

Primordial germ cell in embryo Mitotic divisions Figure 46.12ab Primordial germ cell in embryo Mitotic divisions Spermatogonial stem cell 2n Mitotic divisions Spermatogonium 2n Mitotic divisions Primary spermatocyte 2n Meiosis I Secondary spermatocyte n n Meiosis II Figure 46.12 Exploring: Human Gametogenesis Early spermatid n n n n Differentiation (Sertoli cells provide nutrients) Sperm cell n n n n

Neck Tail Midpiece Head Plasma membrane Acrosome Nucleus Mitochondria Figure 46.12ac Neck Tail Midpiece Head Plasma membrane Acrosome Nucleus Figure 46.12 Exploring: Human Gametogenesis Mitochondria

Menstrual Cycle Last About One Month Normal cycle every 28 days Called menstrual cycle because they are marked by 3-7 days of bleeding called menses. Menstrual cycle can be described a number of ways: Ovarian cycle- changes to follicles Uterine cycle- changes to uterus

Ovarian Cycle Aided by the endocrine system Includes the development of an egg and a series of changes to the uterus Consists of 4 stages (about 28 days total) Follicular Stage (about 12 to 14 days) Egg matures Uterus lining thickens in preparation for embryo Ovulation (about 2 days) Shortest phase Release of ovum Fertilization

Ovarian Cycle cont. Luteal phase (about 7 to 10 days) Cells of the ruptured follicle grow and form a new structure called the corpus luteum Corpus luteum secretes large amounts of progesterone and estrogen which causes the pituitary gland to stop producing FSH and LH Progesterone causes the uterus to thicken even more in preparation for embryo If no embryo arrives, corpus luteum produces less and less hormones – causes blood vessels in uterine lining to close and break Cells of the lining do not have adequate blood supply and break loose – mixture cells and blood is called menstrual fluid Menstruation (about 3 to 7 days) Passage of menstrual fluid through the vagina and out of the body

Figure 46.12 Exploring: Human Gametogenesis Figure 46.12b Primary oocyte within follicle Ovary Growing follicle Primordial germ cell In embryo Mitotic divisions 2n Oogonium Mitotic divisions Primary oocyte (present at birth), arrested in prophase of meiosis I Mature follicle 2n Ruptured follicle Completion of meiosis I and onset of meiosis II First polar body n n Secondary oocyte, arrested at metaphase of meiosis II Ovulated secondary oocyte Figure 46.12 Exploring: Human Gametogenesis Ovulation, sperm entry Completion of meiosis II Second polar body Corpus luteum n Fertilized egg n Degenerating corpus luteum

Primary oocyte within follicle Figure 46.12ba Ovary Ruptured follicle Primary oocyte within follicle Ovulated secondary oocyte Growing follicle Figure 46.12 Exploring: Human Gametogenesis Corpus luteum Mature follicle Degenerating corpus luteum

Uterine Cycle Endometrial lining goes through various changes. Menses- beginning of follicular phases (bleeding) Proliferative phase- endometrium begins to thicken to prepare for possible implantation Secretory phase- after ovulation, corpus luteum converts thickened endometrium to secretory structure if pregnant. No pregnancy = sloughing of endometrium aka menses

Hormonal Control of the Female Reproductive Cycles Ovarian and uterian cycle are under primary control of various hormones: GnRH (Gonadotrophin Relasing Hormone) from the hypothalamus FSH (Follicle Stimulating Hormone) and LH (Luteinizing hormone) from anterior pituitary Esrogen, progesterone from ovary © 2011 Pearson Education, Inc.

The Ovarian Cycle The sequential release of GnRH then FSH and LH stimulates follicle growth Follicle growth and an increase in the hormone estradiol characterize the follicular phase of the ovarian cycle As the follicle matures, some follicles undergo atresia (hormonal cell death) to only allow 1 mature egg to survive) The follicular phase ends at ovulation, and the secondary oocyte is released © 2011 Pearson Education, Inc.

Following ovulation, the follicular tissue left behind transforms into the corpus luteum; this is the luteal phase The corpus luteum disintegrates, and ovarian steroid hormones (Estrogen and Progesterone) decrease if an embryo was not implanted. © 2011 Pearson Education, Inc.

Degenerating corpus luteum Figure 46.13 (a) Control by hypothalamus Inhibited by combination of estradiol and progesterone Hypothalamus  Stimulated by high levels of estradiol 1 GnRH  Anterior pituitary Inhibited by low levels of estradiol  2 FSH LH (b) Pituitary gonadotropins in blood 6 LH FSH 3 FSH and LH stimulate follicle to grow LH surge triggers ovulation (c) Ovarian cycle 7 8 Growing follicle Corpus luteum Degenerating corpus luteum Maturing follicle Follicular phase Ovulation Luteal phase Estradiol secreted by growing follicle in increasing amounts Progesterone and estradiol secreted by corpus luteum 4 (d) Ovarian hormones in blood Peak causes LH surge (see ) 5 6 Figure 46.13 The reproductive cycle of the human female. 10 Estradiol 9 Progesterone Estradiol level very low Progesterone and estra- diol promote thickening of endometrium (e) Uterine (menstrual) cycle Endometrium Menstrual flow phase Proliferative phase Secretory phase Days 5 10 14 15 20 25 28

Control by hypothalamus Figure 46.13a (a) Control by hypothalamus Inhibited by combination of estradiol and progesterone Hypothalamus  Stimulated by high levels of estradiol  1 GnRH Anterior pituitary Inhibited by low levels of estradiol  2 FSH LH Figure 46.13 The reproductive cycle of the human female.

Degenerating corpus luteum Figure 46.13b (b) Pituitary gonadotropins in blood 6 LH FSH 3 FSH and LH stimulate follicle to grow LH surge triggers ovulation (c) Ovarian cycle 7 8 Figure 46.13 The reproductive cycle of the human female. Corpus luteum Degenerating corpus luteum Growing follicle Maturing follicle Follicular phase Ovulation Luteal phase Days 5 10 14 15 20 25 28

Estradiol secreted by growing follicle in increasing amounts Figure 46.13c Estradiol secreted by growing follicle in increasing amounts Progesterone and estradiol secreted by corpus luteum 4 (d) Ovarian hormones in blood Peak causes LH surge (see ) 6 5 10 9 Estradiol Progesterone Estradiol level very low Progesterone and estra- diol promote thickening of endometrium (e) Uterine (menstrual) cycle Figure 46.13 The reproductive cycle of the human female. Endometrium (e) Menstrual flow phase Proliferative phase Secretory phase Days 5 10 14 15 20 25 28

Degenerating corpus luteum Figure 46.13 (a) Control by hypothalamus Inhibited by combination of estradiol and progesterone Hypothalamus  Stimulated by high levels of estradiol 1 GnRH  Anterior pituitary Inhibited by low levels of estradiol  2 FSH LH (b) Pituitary gonadotropins in blood 6 LH FSH 3 FSH and LH stimulate follicle to grow LH surge triggers ovulation (c) Ovarian cycle 7 8 Growing follicle Corpus luteum Degenerating corpus luteum Maturing follicle Follicular phase Ovulation Luteal phase Estradiol secreted by growing follicle in increasing amounts Progesterone and estradiol secreted by corpus luteum 4 (d) Ovarian hormones in blood Peak causes LH surge (see ) 5 6 Figure 46.13 The reproductive cycle of the human female. 10 Estradiol 9 Progesterone Estradiol level very low Progesterone and estra- diol promote thickening of endometrium (e) Uterine (menstrual) cycle Endometrium Menstrual flow phase Proliferative phase Secretory phase Days 5 10 14 15 20 25 28

Pregnancy The presence of a developing embryo as a result of fertilization Fertilization must occur in the upper 1/3 of the fallopian tube Enzymes in the head of sperm help the sperm to penetrate the egg When penetration occurs, the egg prevents the any further penetration Egg and sperm nuclei fuse to form a diploid zygote After fert. the cell undergoes a period of mitosis This is called cleavage The dividing mass of cells (morula) moves down the fallopian tube to the uterus The morula continues to divide and becomes a blastocyst which attaches to the uterine lining

Embryonic Development 1st eight weeks of development All major internal organs and external features appear During 2nd week, the inner cell mass transforms into the embryonic disk and layers form within it These layers become the 3 germ layers and give rise to all organ systems Ectoderm – nervous system, portions of sensory organs, the epidermis, and the linings of the mouth and anus Mesoderm – muscle and bone tissue, blood, blood and lymph vessels, internal reproductive organs, kidneys, and epithelial linings of body cavities Endoderm – epithelial linings of the digestive tract, respiratory tract, urinary bladder, and urethra

Embryonic Development cont. Also during the 2nd and 3rd weeks, the chorionic villi begins to develop from the trophoblast along with the yolk sac, amnion and allantois Chorionic villi will become the chorion, a portion of which becomes the placenta – receives nutrients, oxygen, antibodies, and hormones from the mother as well as filters out wastes Yolk sac is the first site of blood cell formation and stem cells for the immune system Amnion holds amniotic fluid and provides cushioning Allantois also forms blood cells and gives rise to umbilical arteries and veins.

Embryonic cont. Week 4 Weeks 5 – 8 Heart is beating, head and jaw appears and limb buds form Weeks 5 – 8 All major body systems form Embryo is now between 30 and 50 mm At the end of the 8th week the embryo is now referred to as a fetus

Fetal Development Begins at the end of the 8th week and lasts until birth Growth is rapid and body proportions change considerably Existing structures grow and mature and only a few new parts appear Limbs grow to relative size and bones begin to ossify During the 5th month (17 - 20 weeks) the mother can feel the fetus move In the final trimester, brain cells develop rapidly, organs mature, and the fetus greatly increases in size

Parturition Full term is between 30 and 40 weeks As the placenta ages, less progesterone is produced (usually inhibits uterine contractions) Decreasing levels of progesterone stimulate the synthesis of prostaglandins which initiate labor Stretching uterine tissues stimulate the production of oxytocin from the posterior pituitary which initiate uterine contractions As the fetal head stretches the cervix, a positive feedback mechanism results in greater uterine contractions and a greater release of oxytocin This causes the abdominal muscles to contract and force the fetus through the birth canal

Parturition cont. When the baby comes out (head first) it is still attached to the mother by the umbilical cord The umbilical is cut and clamped leaving a scar – naval or belly button Baby will begin to cough or cry to rid the fluid in the lungs – breathing begins almost immediately In the final contractions, the placenta, amniotic sac, and uterine lining are expelled – after birth

Postnatal Milk production and secretion Neonatal period After birth, prolactin stimulates the mammary glands in the breast to produce large quantities of milk First milk, or colostrum, is rich in proteins and antibodies Milk does not readily flow, but is triggered by the infant suckling at the breast Breast milk is the best possible food for the baby Neonatal period Lasts for about 4 weeks after birth Newborn must be able to live off fat reserves for 2-3 days until mother milk comes in Newborn is very susceptible to dehydration because the kidneys are not yet fully function Changes in circulation occur during the first few minutes but the foramen ovale may take up to year to close Allows blood to enter the left atrium from the right atrium in the fetal heart - lung bypass