Spermatogenesis

Question 1

What is the testes?

Answer 1

• produce sperm + store it
• produce hormones which regulate spermatogenesis
• lie in scrotum outside body cavity (optimum temp for sperm prod 1.5-2.5 deg below body)
• overheating of testes reduces sperm count
• well-vascularised, well-innervated
• normal volume of testis approx 15-25ml

Question 2

What is the structure of the testis like?

Answer 2

• testis is 90% seminiferous tubules - site of spermatogenesis
• 600m long in each testis, tubules are tightly coiled
• tubules lead to an area on one side called rete
• rete leads to epididymis and vas deferens

Question 3

What kind of cells are the walls of the tubule made up of?

Answer 3

• tall columnar endothelial cells = Sertoli cells

Question 4

What surrounds the sertoli cells?

Answer 4

• between sertoli cells, lying on basement membrane are primary germ cells or spermatogonia
• spaces between tubules are filled w/ blood + lymph vessels, Leydig cells + interstitial fluid

Question 5

The sertoli cells form tight junctions between each other. Why is this important?

Answer 5

• tight junctions open to allow passage of spermatogonia to completion of meiosis
• the junctions allow for divisions into luminal and adluminal compartments
• protects spermatogonia from immune attack
• allows specific enclosed enviroment for spermatogenesis which is filled w/ secretions from sertoli cells

Question 6

What are the comparisons and differences between oognia and spermatogonia?

Answer 6

Question 7

How long does spermatogenesis take?

Answer 7

• entire process = approx 74 days
• new cycle every 16 days

Question 8

What are the 3 main stages of spermatogenesis?

Answer 8

• mitotic proliferation of spermatogonia
• meiosis + development of spermatocytes
• spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents -> spermatids (haploid)

Movement into lumen controlled by sertoli cell secretions. Factors produced by sertoli cells are required for development

Question 9

What is the role of Leydig cells?

Answer 9

• contain LH receptors
• primarily convert cholesterol into androgens
• intra-testicular testosterone levels are 100x those in plasma

Question 10

What happens to the androgens following production by Leydig cells?

Answer 10

• androgens cross over to + stimulate Sertoli cell function
• thereby control spermatogenesis
• Sertoli cells contain FSH receptors
• convert androgen -> oestrogen
• FSH establishes a quantitavely normal Sertoli cell population
• whereas androgen initiates + maintains sperm production

so sertoli cells need FSH to maintain its population and need testosterone to undergo spermatogenesis

Question 11

How do anabolic steroids lead to testicular atrophy?

Answer 11

• negative feedback on hypothalamus/pituitary
• reduce FSH/LH secretion
• it’s FSH which maintains sertoli cell population
• so testicular atrophy results due to reduced FSH!

Question 12

How can anabolic steroids also lead to gynaecomastia in men?

Answer 12

• araomatase present in men (as well as women)
• lots of unbound anabolic steroids
• they are aromatised into oestrogens from androgens
• build up of oestrogen -> gynaecomastia

Question 13

What structural changes occur to cause and maintain erection?

Answer 13

• vasodilation of corpus cavernosum (+ its arteries)
• engorging corporal tissue with blood
• egorging causes corporal tissue to swell, erecting penis
• engorged corporal tissue compresses penile veins + venules, maintaining erection
• partial constriction of venous return

Question 14

What part of the nervous system are erection and ejaculation under control of?

Answer 14

• both under autonomic nervous system
• “point + shoot”

Question 15

What exactly is under each of parasympathetic and sympathetic control in terms of erection and ejaculation?

Answer 15

• parasympathetic: erection + evacuation of urethra
• sympathetic: movement of sperm into epididymis, vas def, penile urethra expulsion of glandular secretions

Question 16

How much sperm is produced per day on average?

Answer 16

• 300 million sperm produced per day
• 3,500 per second!

Question 17

What is normal ejaculate volume?

Answer 17

• 1.5ml - 6ml
• around one third to just over a teaspoon full

Question 18

The initial portion of the ejaculate is most sperm rich. How much sperm reaches the ampulla of the uterine tube?

Answer 18

• 99.9% lost before reaching ampulla of uterine tube
• around 120,000 sperm get near to egg
• only 1 enters

Question 19

Seminal fluid consists of secretions from where?

Answer 19

• seminal vesicles
• prostate
• bulbo-urethral gland combined w epididymal fluid

Question 20

What is the role of the bulbo-urethral gland in contributing to seminal fluid?

Answer 20

• secreted before ejaculation
• produces a clear viscous secretion high in salt
• known as pre-ejaculate
• this fluid helps to lubricate the urethra for spermatozoa to pass through
• neutralising traces of acidic urine

Question 21

What is the role of the seminal vesicles in contributing to seminal fluid?

Answer 21

• 50-70% of ejaculate
• contains proteins, enzymes, fructose, mucus, vit C, prostaglandins
• high fructose conc provide energy source
• high pH protects against acidic env in vagina

if you don’t find fructose in semen -> could be a seminal vesicle problem

Question 22

How does the prostate contribute to the seminal fluid?

Answer 22

• arrives here microsecond later following seminal secretions
• secretes milky white fluid
• 30% of seminal fluid
• protein content is less than 1%
• incldues proteolytic enzymes, prostatic acid phosphatase + prostate-specific antigen - all involved in liquefaction
• high zinc conc: 500-1,000 times that in the blood is antibacterial

Question 23

Describe semen analysis

Answer 23

• Volume: 1.5-6.0ml
• Sperm conc: >15million/ml
• Liquefaction: <30 mins
• Motility: >40%
• Prog motility: >32%
• Vitality (live): >58%
• Morphology: >4%
• pH: >7.2
• Leucocytes: >1million/ml

Question 24

What is the structure of a normal spermatozoon?

Answer 24