4/20/08 Reproductive System Chapter 26 – Day 3

4/20/08 Gametogenesis  Production of gametes = haploid “sexual reproduction” cells  Testes = Spermatogenesis  Ovaries = Oogenesis

4/20/08 Spermatogenesis Fig. 26.6

4/20/08 Spermatogenesis  Takes place in the seminiferous tubules  Between the tubules there is areolar tissue ♦With interstitial cells = cells of Leydig ♦These cells produce adrogens including testosterone  Testosterone stimulates spermatogenesis  Seminiferous tubules have several layers of cells around a central lumen which is filled with fluid in the center

4/20/08 Spermatogenesis Fig. 26.5

4/20/08 Spermatogenesis  The outermost cells (away from the lumen) = spermatogonia go through cell division (mitosis)  Making more cells with identical chromosome numbers  These undergo further development to become primary spermatocytes  Second layer of cells (primary spermatocytes) begin meiosis ♦Making 2 cells with ½ the number of chromosomes = meiosis I ♦These are now secondary spermatocytes, = duplicated chrom. ♦Another division (meiosis II) occurs to yield 4 cells from the previous 2: these are the spermatids = immature haploid gametes  Cell division is complete, but sperm formation (spermiogenesis) needs to take place to produce actual sperm

4/20/08 Spermatogenesis Fig. 26.7

4/20/08 Spermatogenesis  Within the spermatocytes & spermatids are sustentacular cells ♦These cells help maintain the composition of the fluid = high levels of hormones There is actually a blood-testes barrier so that blood hormone level changes will not alter spermatogenesis ♦Respond to testosterone to stimulate spermatogenesis ♦Support spermiogenesis by providing proper nutrients ♦Secrete inhibin – inhibits spermatogenesis  Spermiogenesis: one spermatid becomes a spermatozoa  Spermiogenesis takes place near the lumen – sperm/spermatozoa are released into the lumen

4/20/08 Spermatozoon  Acrosomal cap contains enzymes for fertilization ♦These are released only upon contact with the egg  Head – nucleus with chromosomes (DNA)  Middle Piece – mitochondria for energy  Tail – flagellum for movement  Need energy for flagellar movement ♦Comes from mitochondria  Need sugars (glucose) to make energy ♦Comes from semen  Less content in sperm = better mobility (fast swimmers) Fig. 26.8

4/20/08 Spermatogenesis Fig. 26.5

4/20/08 Spermatogenesis Fig

4/20/08 Oogenesis  The ovaries are the site for oogenesis  Oogenesis begins before birth in females  Ovaries contain oogonia these go through mitosis to make primary oocytes  Development is suspended until puberty  Many get disintegrated – a fixed number remain  Every month after puberty - the development of one primary oocyte takes place

4/20/08 Oogenesis – Follicle Maturation  In the ovary the primary oocytes are clustered near the tunica albuginea  Each oocyte is surrounded by a layer of follicular cells = primordial follicle  At puberty the female body secretes FSH (follicle stimulating hormone) in cycles ♦FSH activates a group of primordial follicles ♦Follicular cells enlarge ♦oocyte enlarges ♦Cells around the follicle produce estrogens  Few proceed to the next step…  Become secondary follicle which, after further enlargement becomes a tertiary follicle

4/20/08 Follicle maturation Fig

4/20/08 Follicle maturation Fig

4/20/08 Oogenesis – Oocyte development  Now the follicle has expanded a central chamber (antrum) with follicular fluid  Primary oocyte is suspended in meiosis I ♦LH (leutenizing hormone) levels increase ♦The oocyte completes meiosis I ♦This yields a secondary oocyte & a polar body  These are suspended in meiosis II until fertilization

4/20/08 Oogenesis Fig

4/20/08 Oogenesis - Ovulation  The secondary oocyte is released from the tertiary follicle  The corona radiata stays attached to the ovary  Fluid currents push the secondary oocyte into the uterine tube  After the oocyte is released the follicle develops into the corpus luteum ♦These enlarged cells = endocrine cells ♦They make progestins (progesterone) and some level of estrogens (not nearly as much as during ovulation)  This stimulates the maturation of the uterine wall  Approximately 12 days later the corpus luteum is destroyed if the egg is not fertilized

4/20/08 Hormonal Changes in Female  Time of oocyte release depends on several hormones  Gonadotropin releasing hormone (GnRH) ♦Secreted by the hypothalamus ♦Triggers the adenohypophysis to secrete Follicle Stimulating Hormone (FSH) & Leutenizing Hormone (LH) ♦Frequency of GnRH pulses determines which hormones are secreted  The start of the ovarian cycle = follicular phase ♦GnRH is released slowly – triggers FSH ♦FSH stimulates the development of the primordial follicle into the primary follicle ♦The primary follicle begins secreting estrogen The primary follicle can also secrete inhibin, which would inhibit FSH production having the opposite effect

4/20/08 Hormonal Changes in Female  Increasing levels of estrogen and a higher frequency of GnRH pulses stimulates secretion of Leutenizing hormone (LH)  High LH levels promote the release of the secondary oocyte from the tertiary follicle = OVULATION  Promotes the production of the corpus luteum  Begins the Luteal Phase  The corpus luteum secretes progesterone & low levels of estrogen  LH & FSH levels are low  Completes buildup of endometrium  This is maintained for days (days of a womans cycle, she is most fertile

4/20/08 Hormonal Changes in Female  If there is no fertilization then the corpus luteum degenerates to the corpus albicans ♦Estrogen and progesterone production ends ♦The functional zone of the endometrium sloughs off – leading to menstruation (days 28-2 of cycle) ♦More GnRH is secreted & the pituitary gland secretes more FSH  If the egg IS fertilized it gets implanted in the endometrium & embryo development begins  Embryo and placenta release human chorionic gonadotropin (HCG) which keeps the corpus luteum from disintegrating – thus there is continuous secretion of estrogen & progesterone  If the levels of estrogen & progesterone decrease, this can lead to a miscarriage

4/20/08 Oogenesis Fig – 1 – also look at

4/20/08 Hormonal Changes in Male  GnRH released at a steady rate ♦Stimulates the release of FSH & LH from the pituitary  LH triggers testosterone production which affects ♦Spermatogenesis ♦Development of primary sex characteristics ♦Muscle growth  FSH triggers spermatogenesis  Inhibin, secreted by sustentacular (Sertoli) cells, slows down FSH production to control the rate of spermatogenesis

4/20/08 Hormonal Changes in Male  Testosterone is a very important hormone in males  Deficiency in testosterone production: ♦All male reproductive organs decrease in size ♦Sex drive ↓ ♦Penile erection ↓ ♦Volume of ejaculate ↓  Castration ♦There is no testosterone = loss of sex drive ♦Erection might still be possible ♦Gradual loss of facial hair & muscle tone  Prepubertal castration ♦Male will lack facial hair, will have fatty deposits in breasts & smooth skin

4/20/08 Sex & Sexual Dysfunction  Sexual intercourse is described by different terms: ♦Technical, colloquial, and clinical ♦Clinical = coitus ♦For legal purposes – intercourse = penetration of the penis into the vagina with or without ejaculation Events of Coitus:  There are 3 phases: 1.Excitement 2.Plateau 3.Orgasm/Ejaculation

4/20/08 Sex & Sexual Dysfunction  Excitement phase = “foreplay”

4/20/08 Oogenesis Fig