Male reproductive physiology Flashcards
Male Reproductive System Functions:
urine elimination and reproduction
___ - spermatogenesis and secretion of testosterone (male sex
hormone)
Gonads (testes)
_____ - transports and stores sperm, and assists in their maturation
Ductal system (epididymides, vas deferens, and ejaculatory ducts)
_____ - produce the fluid constituents of semen
Accessory glands (seminal vesicles, prostate gland, and bulbourethral glands)
____ - urine elimination and sexual function
Penis
Testes lie within the scrotum which hangs
outside the abdominal cavity, Surrounded by two tunics:
○ Tunica vaginalis - outer layer derived from
the peritoneum
○ Tunica albuginea - deeper layer of dense
connective tissue
The tunica albuginea divides the testes into
_____
200-300 wedge-shaped lobules
Each lobule of the testes contains ____
1-4 tightly coiled seminiferous tubules where sperm is produced and a connective tissue stroma where Sertoli cells are located
Testicular Functions
● Steroidogenesis (synthesis of
androgens or male sex hormones)
● Spermatogenesis (sperm
production)
Spermatogenesis requirements
○ Sperm production requires
temperatures that are 2-3 degrees C
below body temperature
○ The position of the testes in the
scrotum and the unique blood flow
cooling mechanisms provide this
environment
The testes produce several male sex hormones, what are they?
● Testosterone (steroid)
● Androstenedione and
dehydroepiandrosterone (DHEA)
Dihydrotestosterone (DHT) active
metabolite _____
→ binds to same intracellular
receptors in target cells but more stable
than testosterone
In the male embryo, testosterone is essential for ____
appropriate differentiation of the internal and external genitalia (DHT primarily), and is
necessary for descent of testes in the fetus
Spermatogenesis begins ____
shortly before puberty and continues throughout the life of men.
Sertoli cells
secrete inhibin and androgen-binding protein (ABP)
○ Located in the seminiferous tubules and activated by FSH
○ Surround the spermatogenic cells and provide structural support,
physical and nutritional support for germ cells (sperm)
Spermatogenic cells (AKA spermatogonia)
These are the building blocks of spermatozoa
The formation of a mature sperm from a primitive germ cell by
spermatogenesis takes approx. ____
74 days
In the absence of testosterone or androgen receptors in the
Sertoli cells, spermatogenesis does not proceed beyond _____
the meiotic stage (exact mechanism unknown)
Each milliliter of semen contains _____
about 100 million sperm.
Reduction in sperm production is associated with _____
infertility
After the seminiferous tubules, the
spermatozoa move into the _____
rete testis
final site for sperm
maturation
the epididymis
When ejaculation occurs, the smooth
muscle in the wall of the epididymis
contracts vigorously. This moves sperm into
the _____
vas deferens (ductus deferens).
Accessory genital glands =
the paired seminal vesicles,
bulbourethral glands (AKA
Cowpers), and the prostate
gland
Seminal Vesicles
The seminal vesicles lie on the posterior wall of the bladder and consist of
highly tortuous tubes that secrete fluid for the semen.
Each of the seminal vesicles secretes:
● Fructose - provides energy for sperm motility
● Prostaglandins - cause reverse peristaltic contractions in the
uterus and fallopian tubes to move sperm toward ovaries
The seminal vesicles combine with the ampulla of the vas deferens to form
the _____
ejaculatory duct which travels through the prostate
Both the vaginal secretions and the fluid from the vas deferens are strongly
_____
Acidic
Sperm mobilization occurs at pH of 6-6.5 so the alkaline nature of the prostatic secretions is necessary for successful fertilization of the ovum
Bulbourethral Glands
The bulbourethral glands are pea-sized
glands located on either side of the
urethra.
The glands produce a clear, mucus-like
secretion
The hypothalamus secretes
_____ which acts directly on the anterior
pituitary gland
gonadotropin-releasing hormone (GnRH)
FSH binds selectively to the Sertoli cells
where it initiates ____
spermatogenesis
_____ suppress LH secretion through direct action on the pituitary and hypothalamus
High levels of testosterone
FSH is inhibited by a substance called
____ produced by the Sertoli cells
inhibin
The three masses of tissue in the penis:
○ Corpora cavernosa (2)- fills with 90% of
the blood during penile erection
○ Corpus spongiosum - prevents the
urethra from pinching closed during
erection. It remains pliable during erection
while the corpora cavernosa becomes
engorged with blood
Neural Control of Male Sexual Function
Erection - controlled by the
parasympathetic nervous system
Ejaculation and penile
relaxation - controlled by the
sympathetic nervous system
Erection process
● Initiated by dilation of the arterioles of the penis
● As the erectile tissue of the penis fills with blood, the veins are compressed which blocks outflow and adds to the turgor of the
organ
● The integrating centers in the lumbar segments of the spinal cord are activated by impulses in afferent (sensory) nerves from
the genitalia and descending tracts that mediate erection in response to stimuli
● The efferent (motor) parasympathetic fibers are in the pelvic splanchnic nerves. The fibers presumably release cotransmitters: acetylcholine and the vasodilator vasoactive intestinal polypeptide (VIP)
Ejaculation: two parts
A two-part spinal reflex involving emission
(movement of the semen into the urethra) and
ejaculation proper (propulsion of the semen
out of the urethra at the time of orgasm)
Ejaculation: emission
Emission is a sympathetic response, integrated in the upper lumbar
segments of the spinal cord and affected by contraction of the smooth
muscle of the vas deferens and seminal vesicles in response to stimuli in
the hypogastric nerves
Ejaculation: ejaculation proper
Ejaculation - the semen is propelled out of the urethra by contraction
of the bulbocavernosus muscle, a skeletal muscle. The spinal reflex
centers for this part of the reflex are in the upper sacral and lowest
lumbar segments of the spinal cord, and the motor pathways traverse
the first to third sacral roots and the internal pudendal nerves
