LECTURE 7 (Male hormones) Flashcards
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
Where is testosterone formed?
Interstitial cells of Leydig
ADDITIONAL INFO: almost non-existent during childhood when testes secrete almost no testosterone but are numerous during the first few months of life and after puberty
Describe the metabolism of Testosterone
- Either loosely bound with plasma albumin or more tightly bound with sex hormone-binding globulin
- Circulates in blood for 30 mins to several hours
[then is either transferred to tissues or degraded into inactive products] - Converted by tissues into dihydrotestosterone
What is the function of Testosterone during foetal development?
The formation pf the prostate gland, seminal vesicles and male genital ducts while suppressing the formation of female genital organs
Explanation: SRY gene on the Y chromosome encodes a protein called the testis determining factor -> Initiation of cascade of gene activations that cause genital ridge cells to differentiate into cells that secrete testosterone and become testes -> formation of penis and scrotum
What are the effects of testosterone on males?
- Causes growth of hair
[pubic hair, libia alba above abdomen, face, chest and back] - Decreases the growth of hair on top of the head
- “cracking voice” [caused by hypertrophy of laryngeal mucosa and enlargement of the larynx]
- Increases the thickness of skin + excessive secretion of sebaceous glands
[can result in acne] - Increase protein formation and muscle development
- Bones grow thicker + deposit calcium salts in response to increased protein
- Increases metabolic rate
- Increase red blood cell number indirectly due to increase metabolic rate
- Increase reabsorption of sodium in distal tubules of kidneys
What happens when you give a still-growing child testosterone?
- Rate of bone growth increases markedly, causing a spurt in total body height
- Causes epiphyses of long bones to unite with shafts of bones at an early age
[child doesn’t grow to full potential]
What is the MOA of testosterone?
1) Testosterone is converted to dihydrotestosterone by 5α-reductase which binds with a cytoplasmic “receptor protein”
2) Combination migrates to cell nucleus where it binds with a nuclear protein + induces DNA-RNA transcription
3) Increase in production of proteins
Which hormones control the male sexual functions?
- GnRH from the hypothalamus
[secreted by neurons of the arcuate nuclei of the hypothalamus which terminate in the median eminence of the hypothalamus -> release GnRH into the hypothalamic-hypophysial portal vascular system to the anterior pituitary gland] - FSH and LH from the anterior pituitary
What is the difference between LH and FSH in relation to GnRH?
LH = cyclical + depends on the release of GnRH
[explains why GnRH is known as LH-releasing hormone]
FSH = increases and decreases only slightly when GnRH secretion changes + changes slowly in response to longer-term changes in GnRH
Which feedback mechanism does Testosterone secretion fall under?
Negative feedback
Explanation: Testosterone causes a decrease in secretion of GnRH from the hypothalamus -> little to no secretion of LH and FSH -> Leydig cells cannot be acted on which inhibits testosterone secretion
What MOA do LH and FSH follow?
They activate the cyclic adenosine monophosphate second messenger system which activates specific enzyme systems in respective target cells
What is the MOA of FSH on spermatogenesis?
1) FSH binds with specific FSH receptors attached to the Sertoli cells in the seminiferous tubules
2) Sertoli cells grow and secrete various spermatogenic substances
3) Testosterone diffuse into seminiferous tubules from Leydig cells + alongside FSH initiate spermatogenesis
What is the function of Inhibin?
Secreted by Sertoli cells, it affects the anterior pituitary gland to inhibit the secretion of FSH + slight effect on hypothalamus to inhibit secretion of GnRH
What is the effect of hCG during pregnancy?
It acts like LH and if the foetus is male it causes the testes of the foetus to secrete testosterone -> promotes formation of male sexual organs
Describe Prostate cancer
An abnormal overgrowth of prostate tissue that can cause urinary obstruction
METASTASIS:
- cancerous cells are stimulated to more rapid growth by testosterone
TREATMENT:
- removal of testes so testosterone cannot be formed
- administration of oestrogen’s
or BOTH to slow cancer
Describe Hypogonadism in males
When the testes of a male foetus are non-functional during foetal life, none of the male sexual characteristic develop in the foetus
Explanation: Female sexual organs develop in the foetus if there are no sex hormones -> but in the presence of testosterone, formation of female sex organs is suppressed and male organs are induced
What happens when a boy loses his testes before puberty?
- Infantile sex organs and characteristics throughout life
- Height is greater than a normal man
[bone epiphyses is slow to unite - but bones are thin and muscles are weaker] - Voice is childlike
- No loss of hair on the head
- No normal adult masculine hair distribution
What happens when a man loses his testes after puberty?
- Sexual organs slightly get smaller
- Voice slightly regresses
- Loss of masculine hair, loss of thick bones, loss of muscle
- Sexual desires are decreased + ejaculation is rare
[semen-forming organs degenerate]
What is Adiposogenital syndrome/Frohlich syndrome/Hypothalmic eunuchism?
Obesity occurring with eunuchism
CAUSE:
Hypogonadism caused by a genetic inability of the hypothalamus to secrete normal amounts of GnRH -> simultaneous abnormality of the feeding centre of the hypothalamus, causing person to greatly overeat
What is Erectile dysfunction?
Also called “Impotence” is an inability of a man to develop or maintain an erection of sufficient rigidity for satisfactory sexual intercourse
CAUSES:
- Neurological problems (e.g parasympathetic trauma)
- Deficient levels of testosterone
- Drugs
- Underlying vascular disease (caused by uncontrolled hypertension, diabetes and atherosclerosis) -> impaired vasodilation + decreased release of nitric oxide
TREATMENT:
Phosphodiesterase inhibitors (e.g viagra)
[inhibit degradation of cyclic GMP allowing for erection]
What are the functions of the Pineal gland?
- Enhancing sex
- Staving off infection
- Promoting sleep
- Enhancing mood
- Increasing longevity
What are the effects of the Pineal gland?
- Controlled by the amount of light or “time pattern” of light seen by the eyes each day
- Secretes melatonin
- Secretion of melatonin decreases gonadotropic hormone secretion
