Testicular Function

Question 1

What is a gamete?

Answer 1

mature haploid reproductive cell

spermatozoa and oocyte

Question 2

Describe the formation of the male reproductive system up to week 7

Answer 2

Male and female are indifferent until week 7
Primordial germ cells 
Diploid germ cell precursors 
Arise during gastrulation 
Epiblast-derived

Question 3

What is SRY?

Answer 3

Sex Determining Region Y gene
also called Testis Determining Factor
- discovery - conserved across mammals
- XY ‘females’ have mutations/deletions of these genes
- XX ‘males’ have translocation of these genes

Question 4

What is meant by SRY being an architectural transcription factor?

Answer 4

It does not act as a transcription factor directly but instead bends DNA in order for other TF’s do come in

Question 5

What are the 3 cell types present from week 7 in the testes?

Answer 5

1. Columns from cells from coelomic epithelium - proliferate and penetrate deep into the medullary mesenchyme - primitive sex cords - express SRY
2. Primordial germ cells, sex cords surround PGCs (seminiferous tubules)
3. migratory cells from mesonephric primordia - vasculature, Leydig, myoid cells

Question 6

What is present within the seminiferous tubules?

What is present between seminiferous tubules?

Answer 6

• prospermatogonia
• mesodermal cord cells from Sertoli cells
• inhibition of meiosis
• vascularisation and clusters of Leydig cells form

Question 7

Is SRY always expressed?

Answer 7

no longer expressed post testes development in utero

- testes direct further development of male reproductive system (via androgen and anti-Mullerian hormone)

Question 8

What are the two products of post-pubertal testes?

What are the two compartments within them?

Answer 8

products = spermatozoa, hormones
compartments =
- within seminiferous tubules - sperm develop, Sertoli cells
- between seminiferous tubules - Leydig cells

Question 9

Describe the structure of the blood-testis-barrier

Answer 9

• between basal and adluminal compartments of seminiferous tubule
• adherens, gap and tight junctional complexes link each Sertoli cell to its neighbour to form BTB
• develops during puberty prior to the onset of spermatogenesis

Question 10

What are the 2 functions of the blood-testis-barrier?

Answer 10

1. separates sperm from immune system preventing immune response (anti-sperm antibodies and autoimmune orchitis)
2. selective transport of ions and small molecules

Question 11

How many sperm are produced per day?

What are the 3 phases of spermatogenesis?

Answer 11

100 million per day

3 phases: proliferation, division, differentiation

Question 12

Describe the proliferation phase

Answer 12

• At puberty, prospermatogonia are reactivated and undergo mitosis in basal compartment of tubule
• A(s) spermatogonia –> start of spermatogenesis

Question 13

Describe the mitotic division

Answer 13

Each A spermatogonium undergoes mitosis to form type B spermatogonia which divide again to form primary spermatocytes
Number of mitotic divisions is species specific, in humans its two

Question 14

Describe the division phase

Answer 14

Primary spermatocytes move into adluminal compartment passing through BTB
Undergo 1st mitotic division (genetic recombination)
Form two secondary spermatocytes - 2nd division to form haploid round spermatids

Question 15

Describe differentiation (spermiogenesis)

Answer 15

• round spermatids elongate to form elongated spermatids and finally mature spermatozoa
• formation of specialised sperm structures: acrosome, flagellum, centrioles, mitochondria, nucleus, cytoplasm

Question 16

What is the acrosome formed from?

What does it do?

Answer 16

Formed from golgi apparatus
Contains hydrolytic enzymes - acrosome reaction
Receptors for fusion to zona pellucida

Question 17

What is the function of the flagellum?

How is it formed?

Answer 17

Sperm movement - female tract and penetration of the egg vestments
Centrioles migrated to opposite end of nucleus to acrosome
Distal centriole from axoneme
Proximal sperm centriole forms the spindle for the 1st mitotic division of the embryo

Question 18

What is the function of mitochondria in sperm?

Answer 18

Energy for motility - helically arranged around first part of flagellum (mid piece)

Question 19

What happens to the nucleus during differentiation?

What are the consequences of these changes?

Answer 19

sex determination (X or Y bearing)
Sperm DNA becomes highly condensed - histones replaced by protamines (more tightly packaged)
- no gene expression
- no transcription/translation

Question 20

What happens to the cytoplasm during differentiation?

Answer 20

superfluous cytoplasm forms residual body (cytoplasmic droplet) which is phagocytksed by Sertoli cells

Question 21

What is spermiation?

Answer 21

sperm cells are released into the lumen of seminiferous tubules

Question 22

In the human, how long does spermatogenesis take?

Answer 22

64 days

- different areas of tubule enter spermatogenesis at different times to give continuous not periodic release

Question 23

What is spermatogenesis controlled by?

How was this proved?

Answer 23

controlled be germ cells

• injected rat SSC carrying reporting gene into immunodeficient sterile mile
• spermatogenesis occurred in all the mice
• rat sperm in mouse epididymis with normal morphology

Question 24

What are the 3 major products of the testes?

Answer 24

androgens - mainly testosterone
oestrogens - all amount in human males
cytokines - inhibin, AMH/MIS

Question 25

What are androgens produced by? What are they converted to and where? What do they bind to? What is their function?

Answer 25

- produced by leydig cells - blood, lymph and seminiferous tubules - covered to dihydrotestosterone in sertoli cells (5alpha reductase) - some binds to androgen receptors in sertoli cells - somes binds to ABP - high conc of testosterone and carrier of testosterone in testicular fluid - regulation of HPG axis

Question 26

Where is inhibin produced? | What is its function?

Answer 26

produced by sertoli cells | repressed FSH production by a pituitary

Question 27

Where is AMH produced? | What does it do?

Answer 27

- produced by sertoli cells | - embryonic role in development of reproductive system

Question 28

What happens to the HPG axis at puberty?

Answer 28

At puberty, the hypothalamus begins to secrete GnRH GnRH induces the a. pituitary to produce LH and FSH - LH binds to LHCGR on leydig cells and indices them to produce testosterone which moves to the tubules and binds to the androgen receptor on sertoli cells - FSH binds to the FSHR on sertoli cells, induces expression of androgen receptor, also stimulates production of ABP and inhibin

Question 29

Draw the feedback loops involved in the male HPG axis

Answer 29

inhibin has negative feedback on FSH | testosterone has negative feedback on LH and GnRH

Question 30

Spermatozoa leave the testis immotile and unable to recognise or bind an egg. What are the 2 processes that sperm must undergo in order be able to fertilise an egg?

Answer 30

- Maturation | - Capacitation

Question 31

What occurs in the epididymis?

Answer 31

- sperm pass through rate testis to the epididymis - single tube through which all sperm pass - most of the fluid in reabsorbed - oestrogen - sperm passage takes 10-14 - sperm maturation - epididymis plays active role - provides molecules necessary for sperm to acquire fertilising ability and motility - androgen dependent

Question 32

What are the sections of the epididymis? | What is each responsible for?

Answer 32

``` Caput/head = motilty Corpus/body = fertilising ability Cauda/tail = storage ```

Question 33

What is the function of the vas deferens?

Answer 33

Densly packed with little fluid Storage reservoir Vasectomy cut

Question 34

What is semen made up of?

Answer 34

sperm | seminal plasma

Question 35

Where is seminal plasma secreted? | What are the fractions?

Answer 35

- accessory sex glands - nutrition, transport, buffering, antioxidants - Fractions: prostate, vas deferens, seminal vesicles

Question 36

What are the seminal vescicles?

Answer 36

- sac-like glands - empty upon ejaculation into ejaculatory duct - provides majority of ejaculate volume - fibrinogen like substrate - ejaculate clotting

Question 37

What is the role of the prostate?

Answer 37

solid tissue like mass - secrete during copulation alkaline secretion high in zinc enzymes for ejaculate clotting and liquification

Question 38

What is the bulbourethral gland (Cowper's gland)?

Answer 38

pre-ejaculate lubrication neutralisation (protect against acidic urine)

Question 39

What is capacitation?

Answer 39

Sperm must undergo some form of physiological change or capacitation before it is capable of penetrating the egg - hyperactivation (tail) - acrosome reaction (head), bona penetration, sperm egg fusion