201 reproduction
-
Upload
mrwestbury -
Category
Technology
-
view
551 -
download
4
description
Transcript of 201 reproduction
Endocrine System & Reproduction
20-18
Sexual Differentiation
• Early embryonic gonads can become testes or ovaries– Y chromosome induces formation of testes
• Testosterone (T) from testes induces formation of male sex organs
• In absence of T, female sex organs develop
20-4
Sexual Reproduction
• Gametes (sperm or eggs) are formed in gonads by meiosis– Each has haploid
number of chromosomes (23)
– Fusion of sperm & egg during fertilization results in diploid zygote with 43 chromosomes
20-5
Fig 20.1
Hypothalamus & Pituitary
• Hypothalamus controls release of LH & FSH from anterior pituitary (Ant Pit) with GnRH
• LH & FSH stimulate production of sperm & eggs, & gonadal sex steroids; & maintain size of gonads
• Sex steroids provide negative feedback on hypothalamus & Ant Pit
• Gonads also secrete hormone inhibin which negatively feeds back on FSH secretion
20-19
Fig 20.9
Male Reproductive System
20-25
Male Reproductive System• Testes contain
seminiferous tubules (STs) where spermatogenesis occurs; & interstitial tissue housing T-secreting Leydig cells
• Sertoli cells of STs contain receptors for FSH– FSH stimulates
spermatogenesis
• Leydig cells contain LH receptors– LH stimulates
secretion of TFig 20.12
20-26
Control of LH & FSH Secretion
• Is by negative feedback– T inhibits LH & GnRH
secretion but not FSH
– Inhibin from Sertolis provides negative feedback on FSH
Fig 20.1320-27
Spermatogenesis
• Germ cells that migrate from yolk sac during development become spermatogonia (stem cells)– Spermatogonia
replicate selves throughout life by mitosis
– Give rise to haploid sperm by meiosis
Fig 20.16
20-31
• Have oval-shaped head that contains DNA & the acrosome (a cap of digestive enzymes)
• Have a midpiece & flagellar tail– Tail will become motile in epididymus
Spermatozoa
20-36
Fig 20.19
Female Reproductive System
20-46
Female Reproductive System
• Ovaries contain large number of follicles that produce female gametes (eggs or ova) in ovarian cycle
• Extensions of fallopian tubes called fimbriae partially cover each ovary– The cilia of its lining
draw in ovulated eggs
20-47
Fig 20.24
Female Reproductive System continued
• Uterus has 3 layers:• Perimetrium is outer
layer of connective tissue
• Myometrium is middle layer of smooth muscle
• Endometrium is hormonally-responsive inner epithelial layer that is shed during menstruation
• Between uterus & vagina is cervix
Fig 20.24
20-48
Ovarian Cycle
• 1o oocytes are contained in 1o follicles– Consisting of oocyte + follicle cells
• In response to FSH some follicles enter ovarian cycle & grow, producing layers of granulosa cells
• Some 1o follicles continue, developing vesicles & becoming 2o follicles
20-51
Fig 20.29
Ovarian Cycle continued
• One follicle continues growth– Vesicles fuse, forming fluid-filled cavity called an antrum
• Is now called a Graafian follicle
20-52
Fig 20.29
Ovarian Cycle continued
• As Graafian follicle develops, 1o oocyte completes meiosis I
• This is an assymetric division because 1 daughter cell (the 2o oocyte) gets all cytoplasm– Other daughter becomes a
small polar body which will degenerate
– 2o oocyte arrests at metaphase II
• Only fertilized eggs complete meiosis II
20-53
Fig 20.31
Ovarian Cycle continued
• 2o oocyte is part of graafian follicle• Granulosa cells form layer around outside of follicle• Oocyte sits on mound in this layer called cumulus oophorus• 2o oocyte is enclosed by ring of granulosa cells called corona
radiata• Between oocyte & radiata is gelatinous layer called zona pellucida
– Which forms barrier to sperm penetration
20-54
Ovulation
• By 10-14 days after menstruation begins, only 1 follicle survives– Others become
atretic follicles (degenerate)
• Surviving graafian follicle forms bulge on surface of ovary– Secretes increasing
levels of E
20-55
Fig 20.29
Ovulation continued
• Graafian follicle releases egg into Fallopian tube at ovulation
20-56
Ovulation continued
• If fertilized, egg completes meiosis II with formation of another polar body
• Egg degenerates in 2 days if not fertilized
20-57
Fig 20.31
Ovulation
• LH causes empty follicle to become corpus luteum (CL)– Which secretes
progesterone (P) & estrogen
– If no fertilization, becomes corpus albicans (non- functional remnant)
20-58
Fig 20.32
Menstrual Cycle
20-59
Menstrual Cycle
• Is ≈ month-long cycle of ovarian activity seen in higher primates
• Characterized by shedding of endometrial lining & bleeding (menstruation)– & sexual receptivity throughout cycle
• Other animals have estrous cycles in which there is no shedding of endometrium & receptivity is limited– In estrous animals that bleed (dogs & cats), it is due to high
estrogen (E) that accompanies receptive period
20-60
Menstrual Cycle continued
• In humans is ≈28 days• Day 1 is taken to be first day of menstruation• Days 1 thru ovulation constitute the follicular
phase• Time from ovulation to menstruation is luteal
phase• Endometrial changes are called: menstrual,
proliferative, & secretory phases
20-61
Follicular Phase• Lasts from day 1 to
about 13• Is dominated by
growth & death of a cohort of 1o follicles into 2o follicles– With 1 survivor
becoming a graafian follicle
• Which will undergo ovulation
– As follicles grow, secrete larger amounts of E
• Reaching peak about day 12 Fig 20.33
20-62
Follicular Phase continued
• Follicular growth & E secretion are dependent on FSH from Ant Pit– FSH & E induce formation
of FSH receptors in granulosa cells
• Causing follicles to become increasingly sensitive to same level of FSH
• At same time, FSH & E recruit LH receptors in graafian follicle
Fig 20.3320-63
Follicular Phase continued
• Rapidly rising E secretion causes:– Hypothalamus to increase
pulses of GnRH – & Ant Pit sensitivity to
GnRH to increase, resulting in greater LH secretion
• A positive feedback between E & Ant Pit secretion develops– Resulting in LH surge that
peaks 16 hrs before ovulation
• & causes ovulation
Fig 20.3320-64
Luteal Phase
• After ovulation, LH causes empty follicle to become the corpus luteum (CL) which secretes E & P
20-65
Fig 20.34
Luteal Phase continued
• P levels rise & peak about a week after ovulation• Development of new follicles & another ovulation are inhibited
by:– High P & E exert strong negative feedback on LH & FSH – Inhibin from CL further suppresses FSH
Fig 20.34
20-66
• With no fertilization, CL regresses – Consequently E & P levels decline
• Causing menstruation & allowing new cycle of follicle development
Luteal Phase continued
20-67
Fig 20.34
Cyclic Changes in the Endometrium• Are driven by cyclic changes in E & P levels • Proliferative phase occurs during follicular phase; E levels
increase– E stimulates growth of endometrial lining
• Spiral arteries develop
– E causes cervical mucus to become thin & watery to allow sperm penetration
20-68
Fig 20.34
• Secretory phase occurs during luteal phase; endometrium becomes ready for implantation– P stimulates development of uterine glands – P & E cause endometrium to become thick, vascular, & spongy– P causes cervical mucus to thicken & become sticky
Cyclic Changes in the Endometrium continued
20-69
Fig 20.34
• Menstrual phase results from drop in P & E following CL degeneration– Low P causes constriction of spiral arteries– Blood flow stops, causing necrosis & sloughing of endometrium
Cyclic Changes in the Endometrium continued
20-70
Fig 20.34