Lecture 5: Male tract and endocrine 2

Question 1

Changes that occur at puberty in males?

Answer 1

Marked increase in proliferation of spermatogonia

Cords develop lumen - become seminiferous tubules

Beginning of sperm production

Question 2

Spermatogenesis general feature?

Answer 2

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.

Question 3

Spermatogenesis sequence?

Answer 3

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)

Question 4

Spermiogenesis? necessary factors?

Answer 4

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

Question 5

Answer 5

Question 6

Hormonal control of spermatogenesis?

Answer 6

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.

Question 7

Secondary sexual characteristics from DHT?

Answer 7

Agressiveness

Libedo

Hair Growth

Male pattern baldness

Question 8

Control/Regulation of androgens?

Answer 8

1. Testosterone bound to ABP heads back to the hypothalamus and anterior pituitary where it negatively inhibits FSH and LH
2. Inhibin produced by the sertoli cells causes downregulation of FSH production by the Anterior pituitary.

Question 9

The cycle of the seminiferous epithelium?

Answer 9

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)

Question 10

What is the epididymis? Function?

Answer 10

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.

Question 11

Features of the Vas Deferens?

Answer 11

• 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

Question 12

The accessory glands are the?

Answer 12

1. Seminal vesicles
2. prostate gland

Question 13

What are the seminal vesicles? Secretions?

Answer 13

• 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

Question 14

Prostate glad features? secretions?

Answer 14

• 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

Question 15

Prostate gland zones?

Answer 15

1. Central zone - Surrounds the urethra and is 25% of glands - resistant to carcinoma
2. Peripheral zone - surrounds th central zone and is 75% of glands - main site of carcinoma
3. Transition zone - is 5% glands and surrounds the proximal prostatic urethra - major site of benign hyperplasia
4. Anterior Zone - Fibromuscular tissue, no glands

Question 16

3 major functional structures of the pen15? Erections?

Answer 16

There are two Corpora Cavernosa and one Corpus Spogiosum

Erections:

• 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

Question 17

Erectile dysfunction and Viagra?

Answer 17

• 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

Question 18

Semen consists of?

Answer 18

30% Prostatic fluid

10% Sperm

60% seminal vesicle fluid

other minor secretions

= Normally are about 2-5ml containing 20million sperm/ml