Changes that occur at puberty in males?
Marked increase in proliferation of spermatogonia
Cords develop lumen - become seminiferous tubules
Beginning of sperm production
Spermatogenesis general feature?
Takes place in the seminiferous tubules of the testes and only occurs after puberty has begun
Produces huge numbers of sperm constantly
Three phases: Mitotic (asymetrical), meiotic and cytodifferentiation.
Mitotic division of spermatogonia (46ch) occurs in the basal compartment of the seminiferous tubules
Spermatogonia move between adjecent sertoli cells in a connected chain to the adluminal compartment of the seminiferous tubule
Here these primary spermatocytes undergo meiosis
At the end of meiosis I we have Secondary spermatocytes (23ch each with two chromatids) that quickly divide (meiosis II) to give four spermatids (23ch)
Spermiogenesis? necessary factors?
The final step of spermatogenesis
Round spermatids differentiate their shape and become spermatozoa (sperm)
- unnecessary cytoplasm is shed as the residual body
- sperm move into the lumen of the SNT
- in the absence of androgen this does not occur
Hormonal control of spermatogenesis?
GnRH from the hypothalamus to the anterior pituitary in the portal system to cause LH release.
Leydig cells are receptive to LH and release testosterone
Testosterone forms DHT -dihydrotestosterone (2x as potent) and together these cause the secondary sexual characteristics
FSH acts on sertoli cells inside SNT in direct contact with spermatognia. Stimulataion of Androgen binding protein (ABP)
Some ABP goes into SNT and maintains androgen conc inside SNT but most goes into blood to help transport DHT.
Secondary sexual characteristics from DHT?
Male pattern baldness
Control/Regulation of androgens?
- Testosterone bound to ABP heads back to the hypothalamus and anterior pituitary where it negatively inhibits FSH and LH
- Inhibin produced by the sertoli cells causes downregulation of FSH production by the Anterior pituitary.
The cycle of the seminiferous epithelium?
This enables continuous production of sperm
A new round of division/cycle starts every 16 days with a transit time from the first spermatogonal division to sperm release into the lumen of the tubule being approx 74 days
(adjecent cross sections through the SNT will never look the same)
What is the epididymis? Function?
A comma shaped organ running superior and posterior to the testes supplied by the rete testes from the SNTs into the head of the epididymis.
About 7.5cm long with a single convoluted tubule of about 4-6m
- Sperm spend 10-14 days here being concentrated 100fold from 5 x 107 to 5 x 109/ml, through fluid resorption mediated by stereocilia.
- Here they also gain the ability for motility and fertilisation.
Features of the Vas Deferens?
- Major site of storage of sperm
- At 45cm long it runs from the epididymis up the ingunal canal over the bladder and down to connect to the ejaculatory duct and urethra at the prostate gland
- consists of an inner longitudinal, middle circular and outer longitudinal muscle layer = peristalsis
- just prior to the prostate the tube widens with many folds and crypts to allow additional sperm storage = Ampulla
The accessory glands are the?
- Seminal vesicles
- prostate gland
What are the seminal vesicles? Secretions?
- Highly folded glands -surrouding the secretory tissue is SMC
- Connect to the VD via the excretory duct to form the Ejactulatory duct
- Secrete alkaline fluid containing fructose, semenogelin - a Zn2+ binding protein that causes clotting after ejaculation
- relatively unsusceptable to tumour growth
Prostate glad features? secretions?
- Doughnut-shaped organ the size of a gold ball
- surrounds the prostatic urethra
- secretes a milky colours slightly acidic fluid (overall is alkaline so not an important detail)
- a major protein is PSA - prostatic specific antigen. Used for cancer screening in some countries (NOT NZ)
- PSA breaks down the coagulation allowing sperm to swim
Prostate gland zones?
Central zone - Surrounds the urethra and is 25% of glands - resistant to carcinoma
Peripheral zone - surrounds th central zone and is 75% of glands - main site of carcinoma
Transition zone - is 5% glands and surrounds the proximal prostatic urethra - major site of benign hyperplasia
Anterior Zone - Fibromuscular tissue, no glands
3 major functional structures of the pen15? Erections?
There are two Corpora Cavernosa and one Corpus Spogiosum
- PSNS activity induces ACh release
- ACh induces NO release from endothelial cells of corpora
- NO induces cGMP production causing vasodilation
- Corpora BV relax causing engorgement with blood
- Venous outflow is reduced increasing engorgement/erection
Erectile dysfunction and Viagra?
- Viagra is sildenafil citrate and blocks the action of type V phosphodiesterase that would normally cause cGMP breakdown this increased these levels = vasodlation
- Only useful if there is still some PSNS stimulation
Semen consists of?
30% Prostatic fluid
60% seminal vesicle fluid
other minor secretions
= Normally are about 2-5ml containing 20million sperm/ml