LECTURE 7 (Male hormones) Flashcards
(45 cards)
Describe the anatomy of the male sexual organs
Testis is composed of 900 SEMINIFEROUS TUBULES where sperm are formed -> sperm empty into the EPIDIDYMIS which leads into the VAS DEFERENS which enlarges into the AMPULLA OF THE VANS DEFERENS before entering the body of the PROSTATE GLAND -> contents from the TWO SEMINAL VESICLES empty into an EJACULATORY DUCT into the INTERNAL URETHRA + PROSTATIC DUCTS contents empty into an EJACULATORY DUCT into the PROSTATIC URETHRA -> URETHRA is supplied with mucus from URETHRAL GLANDS (along its length) and BULBOURETHRAL GLANDS (COWPER GLANDS) near the origin of the urethra
How is sperm formed?
1) During the formation of the embryo, PRIMORDIAL GERM CELLS migrate into the testes and become SPERMATOGONIA (premature germ cells) lying in 2-3 layers of inner surfaces of seminiferous tubules
2) Spermatogonia begin to undergo mitotic division during puberty and continue to differentiate and proliferate into SPERM
How long does Spermatogenesis occur?
74 days
What are the steps of Spermatogenesis?
1) Spermatogonia migrate among Sertoli cells towards the central lumen of the seminiferous tubule
2) Spermatogonia enlarge to form PRIMARY SPERMATOCYTES that undergo meiotic division to form two SECONDARY SPERMATOCYTES
3) Spermatocytes divide to form SPERMATIDS that are modified to become SPERMATOZOA
Describe the anatomy of the sperm
- Head composed of condensed nucleus of cell + thin cytoplasmic and cell membrane layer
- Anterior 2/3 of head is ACROSOME has hyaluronidase and proteolytic enzymes (allows sperm to enter ovum + fertilise it)
- Tail consists of axoneme (central skeleton of 11 microtubules), thin membrane covering the axoneme and mitochondria in the body of tail
What are the hormones that stimulate spermatogenesis?
- Testosterone = secreted by Leydig cells + essential for growth and division of testicular germinal cells
- LH = secreted by anterior pituitary gland + stimulates Leydig cells to secrete testosterone
- FSH = secreted by anterior pituitary gland + stimulates Sertoli cells to convert spermatids to sperm
- Oestrogens = formed from testosterone by Sertoli cells when stimulated by FSH + essential for spermiogenesis
- Growth hormones = promote early division of spermatogonia
When do sperm become motile?
Sperm in the early portions of the epididymis are non-motile but become motile 18-24 hours being in the epididymis
ADDITIONAL INFO: several inhibitory proteins in the epididymal fluid prevent final motility until after ejaculation
Where is Sperm stored?
A small amount is stored in the epididymis but a large amount is stored in the vas deferens, for at least a month
ADDITIONAL INFO: After ejaculation, sperm become motile and can fertilise the ovum, a process called MATURATION
What increases the activity of sperm?
- Neutral + slightly alkaline medium (e.g semen)
- Increase temperature
What is the function of Seminal vesicles?
It secretes nutrient contents into the ejaculatory duct which provides the sperm of nutrients until it fertilises the ovum
Explanation: Seminal fluid contains fructose, citric acid, prostaglandins, fibrinogen and other nutrient substances
How do prostaglandins help aid fertilisation?
- React with female cervical mucus to make it more receptive to sperm movement
- Cause backward, reverse peristaltic contractions in the uterus + fallopian tubes to move ejaculated sperm towards the ovaries
What is the function of the prostate gland?
- It secretes a thin, milky fluid containing calcium, citrate ion, phosphate ion, a clotting enzyme and profibrinolysin
- Secretion is alkaline so can prevent sperm from dying in acidic conditions
How long can sperm last inside the female?
24-48 hours at body temperature
What happens during “Capacitation” of spermatozoa?
- Uterine and Fallopian tube fluids wash away the various inhibitory factors that suppress sperm activity in the male genital tracts
- Cholesterol in the seminiferous tubule cover the acrosome to toughen membrane + prevent release of enzymes -> after ejaculation, sperm swim away from cholesterol vesicle
- Membrane becomes more permeable to Ca2+ -> more movement + acrosome enzymes released more rapidly
What are the functions of Hyaluronidase and Proteolytic enzymes?
Hyaluronidase = depolymerises hyaluronic acid polymers in the intercellular cement that holds the ovarian granulosa cells together
Proteolytic enzymes = digest proteins in structural elements of tissue cells that adhere to the ovum
What happens in the “Acrosome reaction”?
Sperm go through the granulosa cell layers + penetrate through the zona pellucida -> Anterior membrane of sperm binds to receptor proteins in zona pellucida + entire acrosome dissolves + acrosomal enzymes are released -> Sperm head + oocyte fuse to form a single cell
Why does only one sperm enter the oocyte?
A few minutes after the first sperm penetrates the zona pellucida of the ovum, Ca2+ diffuse inward through oocyte membrane causing CORTICAL GRANULES to be released by oocyte into the PERIVITELLINE SPACE -> granules contain substances that prevent binding of additional sperm + cause any sperm that have already begun to bind to fall off
What is the effect of temperature on Spermatogenesis?
Increasing the temperature of the testes can prevent spermatogenesis by causing degeneration of cells of seminiferous tubules including spermatogonia
What is Cryptorchidism?
Failure of a testis to descend from the abdomen into the scrotum at or near the time of birth of a foetus
SIGNIFICANCE:
A testis that remains in the abdominal cavity/inguinal canal is incapable of forming sperm + tubular epithelium becomes degenerate, leaving only the interstitial structures of the testis [caused by the increase of temp since testis is close to the body]
TREATMENT:
- Testosterone
- Surgery
BOTH used to descend testes
Why is the “glans penis” the most important source of sensory nerve signals to initiate the male sexual act?
The slippery massaging action of intercourse on the “glans” stimulates the sensory end-organs -> signals pass through the pudendal nerve then through the sacral plexus -> then pass into the sacral portion of the spinal cord + up the undefined areas of the brain
ADDITIONAL INFO: surrounding areas can also stimulate sexual desire including inflammation + mild infection of sexual organs
How does “Erection” happen?
1) Parasympathetic impulses pass from the sacral portion of the spinal cord through the pelvic nerves to the penis + release NO, VASOACTIVE INTESTINAL PEPTIDE & ACETYLCHOLINE
2) NO activates guanylyl cyclase -> increase formation of GMP -> GMP relaxes arteries of penis and meshwork of smooth muscle fibers in the erectile tissue of the CORPORA CAVERNOSA and CORPUS SPONGIOSUM
3) As vascular smooth muscles relax, blood flow into penis increases -> release of NO causing further vasodilation
Is lubrication a parasympathetic function? (YES/NO)
YES
Explanation: Parasympathetic impulses cause urethral + bulbourethral glands to secrete mucous
What are the steps of “Emission” and “Ejaculation”?
1) Sexual stimulus becomes extremely intense -> reflex centers of the spinal cord emit sympathetic impulses that leave the cord at T12 to L2 + pass to the genital organs through the hypogastric and pelvic sympathetic nerve plexuses to initiate EMISSION
2) Vas deferens + ampulla contract to expel sperm into the internal urethra -> contractions of prostate gland + seminal vesicles expel prostatic and seminal fluid into the urethra, forcing the sperm forward [EMISSION]
3) Sensory signals excite rhythmical contraction of internal genital organs + rhythmical, wavelike increases in pressure in both the erectile tissue of the penis and the genital ducts and urethra causes “EJACULATION”
What is Resolution?
After ejaculation, male excitement disappears almost entirely within 1-2 mins and erection ceases
