Spermatogenesis Flashcards
1
Q
Give a brief overview of the male reproductive anatomy
A
- Sperm is made in the testes and stored short-term in the epididymis
- Moves up the vas deferens, the two VD join at the seminal vesicles, then join the urethra where the prostate gland is
- From there it is a single common outlet to the outside world - the urethra
- The penis itself is made up of 3 tissues, two corpora cavernosa and and corpus spongiosum
- They are designed to fill with blood to give an erection
2
Q
What is the purpose of the testes?
A
- Produce sperm and store it
- Produce hormones which regulate spermatogenesis
- Lie in scrotum outisde the body cavity, their optimum temperature for production is 1.5-2.5C below body temp. Overheating can reduce sperm count
- Well vascularised, well innervated
- Normal volume of testis approx 15-25ml
3
Q
What is the structure of the testicles?
A
- Series of lobules in the testes, each contains seminiferous tubules, which make up 90% of the testis
- Tubules lead to an area on one side called rete testis
- Rete leads to epideidymis and vas deferens
- Sperm are made in semiferous tubules, then all arrive in the epididymis where they are stored short-term, and at ejaculation they go up the vas deferens
4
Q
What is the strucure of a seminferous tubule?
A
- Walls of the tubule are made up of tall columnar endothelial cells - Sertoli cells
- Between these, lying on the basement membrane are primary germ cells - Spermatogonia
- Spaces between the tubules are filled with blood and lymphatic vessels, Leydig cells and interstitial fluid
5
Q
What are the tight junctions?
A
- Open to allow passage of spermatogonia prior to completion of meiosis
- Divides into luminal and adluminal compartments
- Protects the spermatogonia from immune attack
- Allows specific enclosed environment for spermatogenesis which is filled with secretion from sertoli cells
- Vasectomy - cut tube, immune system see sperm for the first time. Make antibodies for its own sperm, can get agglutination of the sperm.
6
Q
Whereabouts in the seminiferous tubule are sperm produced?
A
- On the outside of he tubule we have A and B spermatogonia - primordial germ cells
- A turn into B, then some of the B start to commit to meiosis
- These turn towards the lumen
- When they complete meiosis they lose their cytoplasm and grow a tail
- By the time they fet to the lumen, they are sperm
- Sertoli cells surround the developing sperm
- They have tight junctions between them creating a separated compartment that is filled with secretions from sertoli cells, separated from the immune system and outside world - creates a blood-testis barrier
- called the adluminal compartment
7
Q
What are the male vs female analogues of sertoli and leydig cells?
A
- Sertoli = Granulosa
- Leydig = Theca cells
8
Q
Oogonia vs Spermatogonia
A
- Oogonia all laid down in foetus - Spermatogonia laid down in foetus
- Begin meiosis to make oocye (cannot make more by mitosis)- Begin meiosis to make spermatocyte (OR divide mitotically to make more)
- Limited supply of eggs - Lifetime supply of sperm, retain ability to undergo mitosis and replenish themselves
9
Q
What is the cycle of spermatogenesis?
A
- New cycle every 16 days, entire process take approx 74 days
- 1) Mitotic proliferation of spermatogonia
- 2) Meiosis and development of spermatocytes
- 3) Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents
- ## Movement into lumen controlled by Sertoli secretions. Factors produced by sertoli cells are required for development
10
Q
What are the different cells called at different stages?
A
- A dark and A pale are diploid spermatogonia, capable of mitosis
- Once they commit they become spermatocytes and then undergo meiosis
- When meiosis is complete we have haploid cells - need to turn into sperm (spermiogenesis)
- Creates spermatids - lose their cytoplasm, has a compacted haploid nucleus and grows a tail
11
Q
How does the HPG axis differ in males to females?
A
- In females, oestrogen is produced in first half of the cycle and then progesterone in the second
- Males don’t have a cycle, they have a steady state negative feedback system. Leydig produce testosterone, which has an effect on the testis and then feeds back
12
Q
How is spermatogenesis controlled?
A
- Leydig cells contain LH receptors and primarily convert cholesterol into androgens - intratesticular testosterone levels are 100x times plasma levels
- Androgens cross over to stimulate Sertoli cell function and thereby control spermatogenesis
- Sertoli cells contain FSH receptors and converts androgens to oestrogen
- FSH establishes a quantitatively normal Sertoli cell population, whereas androgen initiaes and maintains sperm production.
13
Q
How are the steroids produced in the testis?
A
- GnRH acts on hypothalamus to produce LH and FSH
- LH acts on Leydig cells to produce Testosterone. This acts on receptors inside Sertoli cells, stimulating them to control spermatogenesis via its secretions
- FSH acts on Sertoli cell surface receptors to maintain Sertoli cell population
- So testosterone controls activity of Sertoli, and FSH maintains their population
14
Q
What can interfere with the negative feedback?
A
- Anabolic steroids
- They aromatise androgens to oestrogens
- They also reduce FSH/LH from the pituitary, which leads to testicular atrophy
- This reduces sperm count as LH is suppressed, and reduces Sertoli cell count due to lack of FSH
15
Q
How does erection and ejaculation work?
A
- Vasodilation of the corpus cavernosum and partial constriction of the venous return allows lots of blood flowing in, that cannot get out
- ANS (unconscious control) gives coordinated contractions of VD and glands
- Erection and evacuation of urethra is under parasympathetic control
- Movement of sperm into epididymis, VD, penile urethra and the expulsion of glandular secretions, are under sympathetic control
