Reproductive System Flashcards
Active role of the scrotum
(1) Thermoregulation
Active Role of the Testes
(1) Spermatogenesis
(2) Androgen secretion
Origin of spermatogenesis in the testes
Seminiferous Tubules, the walls of which are formed by sustentacular cells (sertoli cells).
Sustentacular cells protect and nurture sperm.
Testicular interstitum
Tissue inbetween seminiferous tubules.
Contain Interstitial cells that are responsible for androgen production.
Testes structures from Epididymis to Urethra
Seminiferous tubules empty into the epididymis.
It is a long coiled tube at the back of the testes which empties into the DUCTUS DEFRENS (or vans deferens) that then leads, via the INGUINAL CANAL, to the pelvic cavity where it joins the duct of the SEMINAL VESICLES where it becomes the EJACULATORY DUCT. Both seminal vesicles become the ejaculatory duct, which lead to the urethra.
Inguinal canal
A tunnel that travels along the body wall toward the crest of the hip bone. (this means there are two)
Semen
Highly nourishing fluid for sperm.
Seminal vesicles secrete about 60% of semen into the ejaculatory duct.
Prostate (35% of ejaculatory volume) and the bulbourethral glands (3% of ejaculatory volume) produce the remaining semen.
2% additional consist of sperm.
Acessory glands
Seminal vessicles
Prostate
Bulbourethral
Testes
Seminal Vesicles
Secrete 60% of ejaculate, mainly fructose, nourishes sperm.
Prostate
Secrete about 35% of ejaculate, mainly fructos and a coagulent, helps to make the sperm coagulate after ejaculation.
Bulbourethral Glands
Secrete about 3% of ejaculate, thick alkaline mucus.
Lubricates urethra and neutralizes acids in male urethra and female vagina.
Erectile Tissue
Specialized tissue that allows for erection.
Composed of modified veins and capillaries surrounded by connective tissue.
Three compartments containing erectile tissue
Corpus cavernosa (two; plural is corpora)
Corpus spongiosum (one)
Male sexual act
Controlled by integrating centre in the spinal cord that responds to physical stimulation and brain input (can excite or inhibit).
Three components: Arousal, ejaculation, resolution.
Male Arousal
Relies on the parasympathetic nervous system.
Two stages: erection and lubrication
Erection - dilation of arteries supplying erectile tissue. Swelling obstructs venus outflow.
Lubrication - bulbourethral gland secretes alkaline lubricant
Male orgasm
Requires stimulation by the sympathetic nervous system.
Two stages: emission and ejaculation
Emission - propulsion of sperm from ductus deferens and semen from accessory glands (product of contracting smooth muscle around organs)
Ejaculation - rythmic contractions by muscles at the base of the penis propel semen out (actually a reflex reaction from semen in the urethra)
Male resolution
Controlled by sympathetic system.
Return to unstimulated state. Result of constriction of erectile arteries.
timeline 2 - 3 minutes.
Spermatogenesis
Produces spermatozoa (gametes)
Cells that give rise to sperm are GERM CELLS.
Immature sperm are found in the outer wall of the seminiferous tubule, and almost mature sperm are deposited into the lumen - form head and tail and neck region, that has mitochondria. Final maturation occurs in the epididymis.
Syngamy
Fusion of the sperm with ova.
Produces a zygote. Note that the only component of the zygote provided by the sperm is the haploid genome.
Formation of spermatozoa
Spermatogonium (mitosis occurs, diploid) > Primary spermatocyte (diploid) > Secondary spermatocyte (haploid, but with sister chormatids) > Spermatids (haploid after second meiotic division) > Spermatozoa
remember spermatoGOnium is GOing to become a sperm
Any term with “cyte” undergoes meiotic division
Spermatid is a kid, almost mature
Spermatozoa = mature.
Ductus Defrens
Secrete inhibitory material to stop motility of sperm. Allows for decreased metabolism and storage for up to a month.
How do spermatozoa get energy?
From fructose in semen and vaginal secretions.
Acrosome
Area of the sperm head that contains hydrolytic enzymes necessary to penetrate ovum protective layers.
Bindin
Protein at the surface of sperm heads that attaches to receptors of the zona pellucida.
Testosterone impact on spermatogenesis
Stimulates division of spermatogonia
Note that testosterone (along with estrogen, progesterone, and inhibin) all inhibit the antuitary pituitary and hypothalamus.
During development it results in Wolffian duct development.
Luteinizing Hormone (LH)
Secreted from antuitary pituitary.
Stimulates interstitial cells to stimulate testosterone secretion
Follicle Stimulating Hormone (FSH)
Secreted from antuitary pituitary.
Stimulates sustenacular cells
Inhibin
Secreted by sustenacular cells, inhibits FSH
Early weeks of development gonadal development
At this stage it is impossible to differentiate between male and female from gonad formation.
All embryos will have Wolffian ducts (ductus defrens, seminal vesicles, epididymis) and Mullerian ducts (Uterine tubes, uterus, vagina)
Default gonad formation
In the absence of Y chromosome, Mullerian duct development occurs.
Internal female genitalia result.
External female genitalia (labia, clitoris) are also the default but they do not result from mullerian ducts.
Y Chromosome impacts
Produces testosterone and Mullerian inhibiting factor (MIH) that drive the development of male genitalia and regression of the Mullerian duct, respectively.
Secretion of testosterone happens around week 7, and by week 9, testicles will have formed.
Note though that supposedly if an XY chromosome embryo does not secrete testerone that it will likely still develop testes.
Systemic Testosterone in development
Note that testosterone in development needs to be converted to dihydrotestosterone in target tissues to have its effect.
Clarification:
XY –> Teste development and three factors result
Local testerone - promotes wolffian duct development (Ductus defrens, seminal vesicles, epididymis)
Systemic testerone - converted to dihydrotestosterone, and results in development of male genitalia.
MIH - Mullerian duct regression
Lubrication glands in male and female reproductives systems
Bulbourethral glands (males)
Greater vestibular glands (females)
External Skin folds in male and females
Scrotum (male) forms from the labioscrotal swellings
Labia majora (female) also formed from the labioscrotal swellings
Androgens
Hormones involved in development and maintenance of male characteristics.
Estrogens
Hormones involved in development and maintenance of female characteristics.
Testerone peaks during development
Before birth and at puberty. It is largely at negligible levels otherwise.
Secondary Sexual Characteristics
Males: maturation of genitalia; facial hair and body hair, deepening of the voice, increased muscle mass
Females: maturation of genitalia; breast development; wider hips; pubic hair
Tumors in the interstitial cells causes
Precocious puberty as a result of excess testosterone secretion
Testerone v. Dihydrotestosterone concentrations in blood
Testosterone is much higher in blood.
Dihydrotestosterone is produced in target cells.
Regulation of sex steroid hormones
Gonadotropin Releasing Hormone, GnRH (hypothalamus) > Gonadotropins (Pituitary)
Gonadotropins
LH and FSH
In males: LH stimulates interstitial cells and therefore increases testosterone; FSH stimulates the sustentacular cells
In females: FSH stimulates granulosa cells to produce estrogen; LH stimulates the formation of the corpus luteum and progesterone secretion
Negative feedback regulation on the hypothalamus and the pituitary. Inhibin, produced by sustentacular and granulosa cells also inhibits.
Clitoris
Forms from the same structure as the penis in the males.
Urethral opening
Just under the clitoris. Where urine exits the body.
Surrounded by the labia minora.
Labia minora
Surrounds the urethral opening and the vaginal opening.
Female internal genitalia
Vagina, uterine tubes, uterus - derived from the Mullerian ducts, so no homologus structures in males.
Vagina
A tube that ends in the pelvic cavity - although the uterus (another tube) opens into the vagina
Cervix
Where the uterus opens into the vagina.
Endometrium
Inner most lining of the uterus.
Responsible for nourishing a baby. It is shed each month resulting in vaginal bleeding if not pregnant.
Myometrium
Thick layer of smooth muscle behind the endometrium that lines the uteran wall.
Uterus
Ends in two uteran tubes that end with finger-like structures called Fimbrae - which bruch against the ovary.
Oocytes come from the ovary and are swept int the uterine tube via cillia.
Female Sexual Act
Arousal, orgasm, and resolution
Arousal
Swelling - of the clitoris and labia minora (As a result of erectile tissue)
Lubrication - provided by secretions of the greater vestibular glands
Controlled by the parasympathetic system.
Orgasm
Controlled by the sympathetic nervous system.
Involves muscle contraction and a widening of the cervix
Resolution
The female does not ejaculate.
Resolution can take 20 - 30 minutes. Compare that to 2 - 3 minutes for men.
Oogenesis
Begins prenatally.
Germ cells in a the ovaries of a female fetus mitotically divide to produce many OOGONIA.
Also undergo the first phase of meiosis and arested in Prophase I as primary oocytes.
Oocyte numbers peak at about 7 million mid-festation, and decrease to about 2 million at birth. Only 400 000 at puberty. The average woman will ovulate only about 400.
First meiosis in women
Produces one large secondary Oocyte and one smaller (without organelles or cytoplasm) known as a polar body.
Second Meiotic division
Only occurs if the egg is fertilized.
Division is also unequal, results in a large OVUM and a second polar body.
This delays the merging of DNA as time is provided for the division to occur.
How many eggs result from meiotic divisions of a single oogonium?
One egg, and three cells (two polar bodies and the one egg)
Primary Oocyte
Is not a solitary cell, it is surrounded by granulosa cells (and the first polar body remains close). Granulosa cells assist in maturation and therefore are analogous to sustentacular cells.
Together this structure is known as a follicle.
When it is an immature primary oocyte it is considered a PRIMORDIAL FOLLICLE and surrounded by a single layer of granulosa cells.
Granulosa Cells
Surround a primary oocyte, assist in maturation and are therefore analogous to a sustentacular cell in males.
Together these structures are termed a Follicle
Primordial follicles
When a single layer of granulosa cells surrounds an immature primary oocyte.
During maturation, granulosa cells replicate and form a more substantive layer around the oocyte.
Zona Pellucida
Protective layer formed by a primary oocyte consisting of mucopolysaccharides.
Thecal cells
Seperate follicles, when there are multiples in the ovary. They respond to LH.
Analogous to Testicular interstitial cells. Also respond to LH.
Graafian follicle
Of all the follicles in the ovary, only one undergoes ovulation each month, all other degenerate.
Graffian follicle achieves ovulation.
During Ovulation - Follicles
The Graffian follicle will burst releasing the secondary oocyte with the zona pellucida and the layer of granulosa cells.
Corona radiata
The layer of granulosa cells that surround the oocyte after it bursts out of the graafian follicle.
Corpus Luteum
Follicular cells that remain in the ovary - eventually degenerate.
Corpus Luteum
Follicular cells that remain in the ovary - eventually degenerate.
Estrogen
Secreted by granulosa cells during the first half of menstruation
Estrogen and Progesterone
Secreted by the corpus luteum during the second half of the cycle
