male tract, spermatogenesis and endocrine control (1) Flashcards
testis glands
exocrine glands
- secretory products = spermatozoa
endocrine gland
- secretory product = mainly testosterone
gonocytes
primitive germ cells that become spermatogonia
only present in early life - up to minipuberty
spermatogonia
germ cells - pre-sperm cells that replicate by mitosis
sertoli cells
epithelial cells - lumen of tubule help developing pre-sperm cells
- increase in number during minipuberty
leydig cells
interstitial cells
- main product is androgen
myoid cells
contractile
primordial germ cells
will become either sperm or oocytes
first seen around 3-4 weeks post-conception
first found in the yolk sac of the extraembryonic tissues and migrate to the gonadal ridges via the hindgut
germ cell tumours
thought to arise from PGCs
93% of germ cell tumours are found in the testis
leydig cells production
produce testosterone
adult leydig cells differentiate from stem cells at puberty
initial production by embryonic leydig cells not dependent on stimulation by testosterone 7-8 weeks
approx 14 weeks gestation production of testosterone becomes LH/hCG dependent
Leydig cells secrete testosterone from 8-10 weeks onwards
when do leydig cells produce the most testosterone
2 months postpartum
2-3ng/ml minipuberty
why is mini-puberty important
- masculinising the neonatal brain
- promoting sertoli cell proliferation
- promoting differentiation of gonocytes into dark AD-spermatogonia
- may have implication for the timing of orcidoplexy
role of steroli cells
nurse cells that promote post mitotis development of sperm precursors
line the inside of the seminiferous tubules (& produce ST fluid)
create the blood testis barrier
nourishing spermatogonia
reabsorb the excess cytoplasm - residual body
maintain the spermatogonial stem cell niche
steroli cell quantity
the number of cells is proportional to the sperm production capacity of the seminiferous tubule
the number does not increase after puberty
importance of blood-testis barrier
created by sertoli cells
important for fertility and prevention of anti-sperm antibody production
moving testes
descent of the testis occurs in 2 phases
1) transabdominal abdominal (10-15 weeks)
2) inguino-scrotal (25-35 weeks)
(androgen is important)
cryptorchidism
failure to descend (unilateral or bilateral)
- maldescent = goes to anterior abdominal wall, perineum or thigh -ectopic
- most self correct within 3 months
- can correct surgically - orchidopexy
failure of testes to descend leads to
- infertility - due to excess temperature
(spermatogenesis requires a lower temperature which is found in the scrotum but not abdomen) - is one of the few known risk factors for testicular cancer
changes at puberty
marked increase in proliferation of spermatogonia
cords develop a lumen - become seminiferous tubules
beginning of sperm production
spermatogenesis
- takes place in the seminiferous tubules of the testes
- only occurs after puberty
- huge no. of sperm produced constantly
- 3 phases
- mitotic division
- meiotic division
- cytodifferentiation
mitotic division
at puberty the primary germ cells are reactivated
spermatogonial stem cells
stermatogonia divide by mitosis
- 1 daughter cell remains undifferentiated to maintain the stem cell population
- the other daughter cell continues to divide by mitosis forming spermatogonia. the spermatogonia continue to divide by mitosis
where does mitotic division occur and what happens when its complete
occurs in the basal compartment of the seminiferous tubules
when the mitotic divisions are complete the spermatogonia move between adjacent sertoli to the adluminal compartment of the seminiferous tubules
(in the adluminal compartment the cells = primary stermatocytes which undergo meiosis)
meiosis
during meiosis 1 the DNA content doubles
- each of the spermatocytes stoll has 46 chromosomes
at the end of meiosis 1 the cells are called secondary spermatocytes (these have 23 chromosomes each with 2 chromatids)
secondary spermatocytes then divide very rapidly (meiosis 2) to give four spermatids each with 23 chromosomes
final process of spermatogenesis
spermiogenesis in which the round spermatids differentiate their shape and become spermatozoa (sperm)
residual body
unnecessary cytoplasm is shed as the residual body
what happens to spermiogenesis in the absence of androgen
is does not occur and spermatogenesis arrests after meiosis
the transition from round spermatids to elongated spermatids doesnt happen
describe the time of the spermatogenic wave
~16 days between successive waves of developing spermatozoa
thus at any one point on a tubule, the interval between the release of successive waves of sperm into the lumen is 16 days.
the cycle of the seminiferous epithelium is always the same length of time
epididymis shape and orientation
comma shaped organ running superior and posterior to the testes
efferent tubules of the rete testis drain into the head of the epididymis
7.5cm long with a single convoluted tubule of about 4-6m in length
epididymis function
sperm spend 1-14 days passing through the epididymis during which theyre concentrated 100 fold
fluid reabsoprtion is mediated by stereocilia
sperm gain the ability for motility and fertilisation
Vas deferens structure
45cm long
3 muscular layers surrounding the epithelial lining
- inner longitudinal - middle circular - outer longitudinal
at the epididymal end, lumen = simple tube
prior to prostate gland, lumen = enlarged and folded with many crypts (allows additional sperm storage)
- this region is called the ampulla
Vas deferens function
major site of sperm storage
seminal vesicles structure
highly folded tubular/pouch-like glands
surrounding the secretory tissue is extensive SM
excretory duct joins VD to become ejaculatory duct
unsusceptible to tumour growth
seminal vesicles secretion
secrete an alkaline fluid containing fructose which is the major energy source for sperm
semenogelin, a Zn2+ binding protein, is the major protein produced by the seminal vesicles
prostate gland
doughnut-shaped organ the size of a golf ball
surrounds the prostatic urethra
secretes a milky coloured slightly acidic fluid
secreted the protein = Prostate specific antigen
-PSA breaks down the seminal coagulum
prostate gland zones
central zone
- surrounds urethra 25% of glands (resistant to carcinoma
peripheral zone
- surrounds the central zone 70% of glands (main site of carcinoma)
transition zone
- 5% of glands surrounds the proximal prostatic urethra (major site of benign hyperplasia)
anterior zone
- fibromuscular tissue no glands
process of erection
- parasympathetic nerve activity induces ACh release
- ACh induces NO release by endothelial cells of the corpora
- NO induces cGMP production which in turn causes vasodilation
- corpora relax and engorge with blood
- venous outflow is reduced increasing erection
action of viagra
used to enhance erection
- blocks the action of type V phosphodiesterase
- phosphodiesterase breaks down cGMP
- inhibiting phosphodiesterase increases levels of cGMP
- = vasodilation
can viagra be used to treat erectile dysfunction
no
not useful if erectile dysfunction occurs because of parasympathetic nerve damage because there is no stimulation of NO and subsequent cGMP production
contents of semen
prostatic fluid = 30%
sperm = 10%
seminal vesicle fluid = 60%
normal ejaculates
2-5mls in volume
contain at least 20 million sperm/ml
