Sexual Differentiation
Genetic:
XX and XY
Gonadal:
For the first six weeks of gestation, male and female embryos are identical
- Sex determine region of y chromosome stimulate production of HY antigen which differentiates into testes
Phenotypic:
Penis or vagina
Sexual Differentiation of the Reproductive Tract
Wolffiam Ducts:
- The placenta secretes human chorionic gonadotropin
- If testes are present they produce testosterone and degrades mullerian ducts
- Male reproductive tract formed
- DHT forms external genitalia
Mullerian Ducts:
- Wolffian ducts degrade in absence of testosterone and mullerian ducts form female system
The Testes
- descend in early childhood
- if remain in body cavity the male has cryptorchidism and results in sterility
Temperature Regulation of Testes
Spermatogenesis is temperature sensitive
- When cold the cremaster and dartos muscle contract to bring testes closer to body
- When warm the muscles relax
Majority of testes consists of coiled seminiferous tubules where sperm is produced
Testosterone
Testosterone is secreted by leydig cells that connects seminiferous tubules
- Some testosterone is secreted into the blood while most is in the seminiferous tubules, aiding in sperm production
Functions of Testosterone
Effects Before Birth:
- masculinization of the reproductive tract and external genitalia
Effects on sex-specific tissues after birth:
- promotes spermatogenesis, and promotes maturation of the reproductive system at puberty.
Other reproductive effects:
- Develops sex drive at puberty and controls the secretion of gonadotropin hormone.
Effects on secondary sexual characteristics:
- Causes voice to deepen, body hair, and muscle growth
Non-reproductive actions:
- Promotes bone growth at puberty
- May also induce aggressive behaviour
Seminiferous Tubules
Highly coiled tubules
- Location of spermatogenesis
- Composed of germs cells and sertoli cells
Spermatogenesis
Mitotic Proliferation:
- Spermatogonia (ssDNA diploid) germ cells on outer layer of seminiferous tubule divide to produce primary spermatocytes ( diploid dsDNA)
Meiosis:
- Primary spermatocytes form haploid secondary spermatocytes (haploid dsDNA)
- in Meiosis 2 the spermatocytes form 2 spermatids (haploid ssDNA) (16 spermatids formed from 1 spermatogonia)
Packaging:
Spermatids into spermatozoa
Spermatozoa
Head:
- nucleus
Acrosome:
- enzyme packed vesicle at tip of head that penetrates ovum
Midpiece:
- Mitochondria to provide energy for locomotion
Tail (Flagellum):
- Movement
Sertoli Cells
Make up the walls of the seminiferous tubules
- connected by tight junctions
- Developing sperms cells migrate through the sertoli cells towards the lumen
Functions of Sertoli Cells
- The tight junctions prevent substance movement and allow Sertoli cells to control the intratubular environment.
- Nourish sperm cells.
- Absorb developing sperm cytoplasm and remove any defective germ cells.
- Secrete seminiferous tubule fluid into the lumen to flush released sperm into the epididymis for storage.
- Secrete androgen-binding protein that helps to concentrate testosterone in the lumen.
- The site of action for testosterone and FSH to regulate spermatogenesis
Hormonal Regulation of Testosterone and Speratogenesis
Gonadtropin release hormone (GnRH) from hypothalamus causes LH and FSH release from pituitary
- Luteinizing hormone (LH) stimulates leydig cells to secrete testosterone
- Follicle stimulating hormone (FSH) acts on sertoli cells to stimulate spermatogenesis and secrete inhibin
Testosterone is a neg fedback for GnRH, LH and FSH
Indibin is a neg feedback for FSH
Male Reproductive Tract
Epididymis and Ductus Deferens:
- Sperms stored in epididymis and is not motile due to low pH
- Epididymis converges into ductus deferens and empties into urethra
Male Accessory Sex Glands:
The Seminal Vesicles - empties bulk of semen (nutrients, prostaglandins and fibrinogen) into ductus deferens
Prostate Gland - Alkaline fluid to neutralize vagina pH and fibrin ogen to clot sperm in vagina
Bulbourethral Glands: Connects to urethra and secret pre-cum
Oogenesis
- Oogania divide to give 7 mill primary oocytes (surrounded by granulosa cella forimg primordial follicle)
- only 2 mill primordial follicles remain at birth - Primary follicle release to ova or undergo atresia and decay
- Prior to ovulation, primary oocytes undergo meiosis to produce secondary oocytes (retain entire cytoplasm)
- First polar body produced and degraded (no cytoplasm) - If fertilized the secondary oocyte undergoes second meiotic division (ssDNA haploid)
- Second polar body produced
The Ovarian Cycle
Two cycles:
Ovarian Cycle - prepares ova for release
Uterine cycle - prepares uterus for implanation
Mentration - Follicular phase - ovulation - luteal phase
Follicular Phase
First 14 days of the ovarian cycle
1. proliferation of granulosa cells in primary follicle to form layers around oocyte
2. Primary follicle (zona pellucida and thecal cell membranes) formed from influence of FSH and estrogen
3. Secondary Follicles produced from follicle enlargements. secretes estrogen
4. Antrum fluid formed in granulosa
5. Mature follicle. oocytes is now a secondary oocyte
6. During ovulations ovarian follicle ruptures to release ovum
Luteal Phase
Remaining 14 days in cycle
1. Follicular cells undergo luteinisation to form corpus luteum. Highly vascularized and secretes progesterone
2. If not fertilized the corpus lutem degenertaes to for corpus albican which is scar tissue
The LH Surge
Estrogen inhibits GnRH and FSH secretion
Estrogen has positive feedback on anterior pituitary to cause a LH surge
- It stops estrogen synthesis by follicular cells
- It reinitiates meiosis in the oocyte
- It triggers release of local factors that increase the swelling of the follicle and weaken the wall
- It differentiates the follicular cells into luteal cells
Hormonal Control of the Luteal Phase
LH continues to maintain the corpus luteum.
Corpus luteum begins
secreting progesterone to prepare the uterine line in case of a potential pregnancy.
- If no implantation occurs, the rapid degradation of the corpus luteum results in a rapid drop in progesterone
Uterus Layers
Myometrium:
- Outer layer comprised of smooth muscles
Endometrium:
Inner lining that is highly vascularized and slo has many glands
Three Phases of Uterine Cycle
Menstrual Phase:
- Decrease in estrogen and progesterone causes release of prostaglandins
- Constrict blood flow to endometrium and contracts myometrium
- Shedding of endometrial lining
Proliferative Phase:
- Estrogen release cause proliferation of endometrium cells and blood vessel growth in lining
- Ovulation occurs
Secretory Phase:
- Corpus luteum formed in luteal phase
- Progesterone converts endometrium into vascularized glycogen rich tissue
Endometriosis
Disorder in which endometrium grows outside of uterus
- Grows on ovaries, fallopian tubes and connective tissue
Menopause
End of reproductive capacity
- no more viable primary follicles in the ovaries
- Lower estrogen production so osteoclast activity increases resulting in osteoporsis
Erection
Penis is made up of three columns of sponge like vascular spaces
- Corpora cavernosa
- Arterioles that supply these vascular spaces dilate
