How long during gestation are the gonads indifferent?
the first 5 weeks
When do the testes begin to develop? the ovaries?
The testes begin to develop at gestational weeks 6-7 while the ovaries begin to develop at week 9
What are the cell types of the male gonads?
germ cells, Sertoli cells, and Leydig cells
What are the cell types of the ovaries?
the germ cells (produce oogonia), granulosa cells, and theca cells
What structure gives rise to the epididymis, vas deferens, seminal vesicles, and ejaculatory ducts?
What stimulates the growth and differentiation of the wolffian ducts?
testosterone. This testosterone from rach testis acts ipsilaterally (same side) on its own wolffian duct
T or F. Testosterone has to be converted to DHT to act on the wolffian ducts
What causes atrophy of the mullerian ducts?
AMH from the Sertoli cells (this mullerian ducts would have become the female genital tract if they had not been suppressed by AMH)
When do the external male genitalia, the penis and scrotum, differentiate during gestation?
Growth and development of the external male gentialia depend on what?
covnersion of testosterone to DHT
Why do the mullerian ducts develop into the interal female tract (fallopain tubes, uterus, and the upper one third of the vagina) in women?
Because women lack AMH so the mullerian ducts develop by default
What happens if a gonadal female is exposed to high levels of androgens in utero (e.g. from excessive production by the adrenal cortex) when the external genitalia are differenitating?
a male phenotype will develop. If such exposure occurs AFTER differentiation of the external genitalia, the female phenotype is retained, but possibly with enlargement of the clitoris
In both males and females, gonadal function is driven by what?
the hypothalamic-pituitary axis
When does secretion of GnRH begin during gestation?
gestational week 4, but its levels remain low until puberty
When does secretion of LH and FSH begin during gestation?
between gestational weeks 10-12 (these too remain low until puberty)
T or F. During childhood, FSH levels are relatively higher than LH levels
What happens to the secretion of GnRH, FSH, and LH after puberty?
it increases and becomes pulsatile, with the relative rates of LH becoming higher than FSH levels and the establishment of a 28-day cycle of gonadotropin secretion called the menstrual cycle
What happens to levels of GnRH, FSH, and LH in senescence?
gonadotropin levels increase further, with FSH levels becoming higher tahn LH levels again
What is one of the earliest events of puberty?
the appearance of large nocturnal pulses of LH during REM sleep and an increased sensitivity of the GnRH receptor in the anterior pituitary (thus, at puberty GnRH up-regulates its own receptor in the anterior pituitary and a given conc of GnRH produces a greater stimulation of FSH and LH secretion).
Pulsatile secretion of FSH and LH at puberty then stimulate what?
secretion of the gonadal steroid hormones, testosterone and estradiol, which then drive appearance of the secondary sex characteristics
T or F. The onset of maturational processes in men and women are genetic and programmed
T. For example, the age at menarche is similar between mothers and daughters (however, the mechanisms underlying the onset of pulsatile GnRH secretion remains a mystery)
What are the suggested thoughts on what causes the pulsatile increase of GnRH at puberty?
-Melatonin could inhibit GnRH (melatonin is high during childhood and decreases during adolescence, and removal of the pineal gland has been shown to precipitate early puberty)
Is the pulsatile nature of GnRH required to produce puberty and secondary growth or can the same effects be seen if you just give a long acting GnRH analogue?
It's required! Puberty will NOT be initiated using a long-acting GnRH analogue in a GnRH deficient person
What causes growth of the testes during puberty?
largely increases in the number of seminiferous tubules
What else occurs during male puberty?
-increased growth of sex accessory organs such as the prostate
-linear growth spurt and closure of the epiphyses
-appearance of facial, pubic, and axillary hair as testosterone increases
-growth of the penis
-initiation of spermatogenesis
What changes occur in pregnancy in females?
-first sign is budding of the breasts, which is following in approx. 2 yrs by menarche
-growth spurts and epiphysis closure occuring faster and earlier than in boys
The appearance of pubic and axillary hair precedes menarche in girls and is dependent on increased secretion of _____
adrenal androgens (called adrenarche)
Describe the temperature of the testes
They are maintained at 1-2C below body temp. which is essential for normal spermatogenesis and is maintained by a countercurrent arrangement of testicular arteries and veins, which facilitate heat exchange
80% of the adult testis is composed of what?
seminiferious tubules, oriented in lobules, which produce sperm
the remaining 20% is composed of CT interspersed with Leydig cells
The epithelium lining the seminiferous tubules consists of what three cell types?
spermatogonia, the stem cells
spermatocytes, which are cells in the process of becoming sperm
Sertoli cells, which support developing sperm
What are the roles of Sertoli cells?
-providing nutrients to the differentiating sperm (which are isolated from the bloodstream)
-forming tight junctions with each other, creating the blood-testes barrier (which still allows testosterone to pass)
-secreting an aqueous fluid into the lumen of the seminiferous tubules, which helps to transport sperm through the tubules into the epididymis
What are the roles of Leydig cells?
-synthesis and secretion of testosterone, which has both local (paracrine) effects that support spermatogenesis in the testicular Sertoli cells and endocrine effects on skeletal muscle and the prostate
T or F. Spermatogeneis occurs continuously throughout the reproductive life of the male, from puberty to senescence
T. Occurring along the length of the seminiferous tubules
1) Mitotic divisions of spermatogonia to produce spermatocytes
2) Meiotic divisions to produce haploid spermatids
3) Spermiogenesis, in which spermatides lose cytoplasma and develop flagella to transform into mature sperm
What occurs in the epididymis?
This is the primary location for the maturation and storage of sperm once it leaves the seminiferous ducts. They remain viable in the epididymis for several months
What causes movement of sperm through the epididymis?
During sexual arousal, contractions of the smooth muscle around the ducts advance sperm and at ejaculation, sperm are excelled into the vas deferens and then into the urethra
What do the seminal vesicles secrete?
a fluid rich in fructose, citrate, prostaglandins, and fibrinogen. As the vas deferens empties its sperm into the ejaculatory duct, each seminal vesicle contributes its secretions, which also will be nutritive for the ejaculated sperm
What do the prostaglandins in sperm aid in?
1) They react with cervical mucus to make it more pentrable by sperm
2) Prostaglandins induce perstaltic contractions in the female tract to propel sperm forward
What does the prostate gland add to sperm?
a milky, slightly alkaline aqeuous solution rich in citrate, calcium, and enzymes
What is the advantage of the alkaline fluid from the prostate gland in sperm?
it increases sperm motility and aids in fertilization by neutralizing acidic secretions from the vas deferens and the vagina
Collectively, the combined secretions of the male sex accessory glands compose 90% of the volume of semen, and sperm compose the remaining 10%
T or F. Ejaculated sperm can immediately fertilize an ovum
F. It must reside in the female reproductive tract for 4-6 hrs for capacitation to occur
What is capacitation?
Capacitation is a process in which inhibitory factors in the seminal fluid are washed free, cholesterol is withdrawm from the sperm membrane, and surface proteins are redistributed. Calcium influx into the sperm increases their motility, and the motion of the sperm becomes whiplike.It also results in the acrosomal rxn in which the acrosomal membrane fuses with the outer sperm membrane, creating pores through which hydrolytic and proteolytic enzymes can escape from the acrosome, creating a path for sperm to penetrate the ovum
Where is testosterone made?
Note that testosterone is the main hormonal product of the testes, but testosterone is not active in all adrogenic target tissues. How is T converted to DHT?
Where is GnRH made?
neurons in the arcuate nuclei
Describe the secretion patterns of GnRH, FSH, and LH
They are all pulsatile. (Note that if GnRH is administered continuously, it inhibits FSH and LH secretion)
What does FSH stimulate in males?
spermatogenesis and Sertoli cell function
What does LH stimulate in males?
Stimulates Leydig cells to synthesize testosterone by increasing cholesterol desmolase
How does testosterone act in the testes (paracrine)?
It diffuses from the Leydig cells to the nearby Sertoli cells, where it reinforces the spermatogenic action of FSH
Describe the feedback of testosterone
Testosterone inhibits both GnRH and LH and Sertoli cells secrete inhibin, a glycoprotein which inhibits FSH production when sperm production is adequate
What would happen to GnRH, FSH, and LH pulses if the testes were removed?
No testosterone leads to increased pulses
DHT is involved in what processes?
-differentiation of external male genitalia (penis, scrotum)
-stimulation of hair follicles, male pattern baldness
-sebaceous gland activity
What processes are mediated by testosterone?
-differentiation of internal male genital tract (epididymis, vas deferens, etc.)
-development of muscle mass
-pubertal growth spurt and epiphyseal closure
-penis growth and seminal vesicles
-deepening of the voice
What determines if a person has testes?
Y chromosome (SRY region)
What hormones do the testes secrete?
AMH and testosterone
What does AMH do?
suppresses development of the mullerian ducts into the interal female genital tract, so no fallopian tubes, uterus, or upper third of the vagina will develop
What does testosterone cause in the developing fetus?
differentiation of the wolffian ducts into the internal male genital tract (epididymis, vas deferens, and seminal vesicles). Thus, this will occur even in a 5a-reductase deficiency