Testicular Function Flashcards
What is a gamete?
mature haploid reproductive cell
spermatozoa and oocyte
Describe the formation of the male reproductive system up to week 7
Male and female are indifferent until week 7 Primordial germ cells Diploid germ cell precursors Arise during gastrulation Epiblast-derived
What is SRY?
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
What is meant by SRY being an architectural transcription factor?
It does not act as a transcription factor directly but instead bends DNA in order for other TF’s do come in
What are the 3 cell types present from week 7 in the testes?
- Columns from cells from coelomic epithelium - proliferate and penetrate deep into the medullary mesenchyme - primitive sex cords - express SRY
- Primordial germ cells, sex cords surround PGCs (seminiferous tubules)
- migratory cells from mesonephric primordia - vasculature, Leydig, myoid cells
What is present within the seminiferous tubules?
What is present between seminiferous tubules?
- prospermatogonia
- mesodermal cord cells from Sertoli cells
- inhibition of meiosis
- vascularisation and clusters of Leydig cells form
Is SRY always expressed?
no longer expressed post testes development in utero
- testes direct further development of male reproductive system (via androgen and anti-Mullerian hormone)
What are the two products of post-pubertal testes?
What are the two compartments within them?
products = spermatozoa, hormones
compartments =
- within seminiferous tubules - sperm develop, Sertoli cells
- between seminiferous tubules - Leydig cells
Describe the structure of the blood-testis-barrier
- 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
What are the 2 functions of the blood-testis-barrier?
- separates sperm from immune system preventing immune response (anti-sperm antibodies and autoimmune orchitis)
- selective transport of ions and small molecules
How many sperm are produced per day?
What are the 3 phases of spermatogenesis?
100 million per day
3 phases: proliferation, division, differentiation
Describe the proliferation phase
- At puberty, prospermatogonia are reactivated and undergo mitosis in basal compartment of tubule
- A(s) spermatogonia –> start of spermatogenesis
Describe the mitotic division
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
Describe the division phase
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
Describe differentiation (spermiogenesis)
- round spermatids elongate to form elongated spermatids and finally mature spermatozoa
- formation of specialised sperm structures: acrosome, flagellum, centrioles, mitochondria, nucleus, cytoplasm
What is the acrosome formed from?
What does it do?
Formed from golgi apparatus
Contains hydrolytic enzymes - acrosome reaction
Receptors for fusion to zona pellucida
What is the function of the flagellum?
How is it formed?
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
What is the function of mitochondria in sperm?
Energy for motility - helically arranged around first part of flagellum (mid piece)
What happens to the nucleus during differentiation?
What are the consequences of these changes?
sex determination (X or Y bearing)
Sperm DNA becomes highly condensed - histones replaced by protamines (more tightly packaged)
- no gene expression
- no transcription/translation
What happens to the cytoplasm during differentiation?
superfluous cytoplasm forms residual body (cytoplasmic droplet) which is phagocytksed by Sertoli cells
What is spermiation?
sperm cells are released into the lumen of seminiferous tubules
In the human, how long does spermatogenesis take?
64 days
- different areas of tubule enter spermatogenesis at different times to give continuous not periodic release
What is spermatogenesis controlled by?
How was this proved?
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
What are the 3 major products of the testes?
androgens - mainly testosterone
oestrogens - all amount in human males
cytokines - inhibin, AMH/MIS
What are androgens produced by?
What are they converted to and where?
What do they bind to?
What is their function?
- 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
Where is inhibin produced?
What is its function?
produced by sertoli cells
repressed FSH production by a pituitary
Where is AMH produced?
What does it do?
- produced by sertoli cells
- embryonic role in development of reproductive system
What happens to the HPG axis at puberty?
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
Draw the feedback loops involved in the male HPG axis
inhibin has negative feedback on FSH
testosterone has negative feedback on LH and GnRH
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?
- Maturation
- Capacitation
What occurs in the epididymis?
- 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
What are the sections of the epididymis?
What is each responsible for?
Caput/head = motilty Corpus/body = fertilising ability Cauda/tail = storage
What is the function of the vas deferens?
Densly packed with little fluid
Storage reservoir
Vasectomy cut
What is semen made up of?
sperm
seminal plasma
Where is seminal plasma secreted?
What are the fractions?
- accessory sex glands
- nutrition, transport, buffering, antioxidants
- Fractions: prostate, vas deferens, seminal vesicles
What are the seminal vescicles?
- sac-like glands
- empty upon ejaculation into ejaculatory duct
- provides majority of ejaculate volume
- fibrinogen like substrate - ejaculate clotting
What is the role of the prostate?
solid tissue like mass - secrete during copulation
alkaline secretion high in zinc
enzymes for ejaculate clotting and liquification
What is the bulbourethral gland (Cowper’s gland)?
pre-ejaculate
lubrication
neutralisation (protect against acidic urine)
What is capacitation?
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
