Flashcards in L03: Testicular Function Deck (41):
When does spermatogenesis begin? Where does it occur?
At puberty in seminiferous tubules
What forms Sertolli cells?
Mesodermal cord cells
Describe testes development until week 7
Primordial germ cells arise during gastrulation (wk 3/4) in epithelium of yolk sac
They then migrate to genital ridges on dorsal embryo wall in AGM region
Describe testes development from week 7-8
Depends on SRY gene on Y chromosome - Produces TDF that activates other genes (architectural TF)
Influx of 3 cell population to gonads:
- columns of coelomic epithelium proliferate + penetrate deep into medullary mesenchyme forming primitive sex cords
- PGCs arrive & cord cells surround forming seminiferous tubules - PGCs become prospermatogonia
- migratory cells from mesonephric primordia form Leydig cells, myoid cells + vasculature
Describe testes development following week 8
SRY no longer needed - testes direct further growth
- Formation of Sertolli cells from mesodermal cord cells
- Inhibition of meiosis until puberty, prospermatogonia become dormant
- Clusters of Leydig cells form between tubules + vascularisation occurs
- Production of androgens & AMH
Where is AMH produced? What is its role?
Sertolli cells - they’re then activated by SOX 9
Prevents formation of female reproductive system
What are the functions of Leydig & Sertolli cells?
Leydig - produce testosterone
Sertolli - produce AMH, inhibin, ABP, site of spermatogenesis
When does puberty begin?
When hypothalamus starts to release GnRH —> LH & FSH release
Where is the blood testes barrier found?
Within seminiferous tubules, between basal + adluminal compartments
Formed by adherens, gap + tight junctions between Sertolli cells
When does the BTB form?
Prior to onset of spermatogenesis
FUNCTION of BTB
- separates sperm from immune system to prevent immune response
- selective transport of molecules to create right environment for spermatogenesis
How many sperm are made per day?
100,000 x 100 million
Describe the proliferation phase of spermatogenesis (16 days)
OCCURS IN BASAL COMPARTMENT
- prospermatogonia reactivated + undergo mitosis compartment —> As spermatogonia
- As spermatogonia —> A spermatogonia by mitosis (start of spermatogenesis)
- A —> B spermatogonia (first mitotic division of spermatogenesis)
- B —> primary spermatocytes (2nd division)
What are As spermatogonia?
Stem cells - hence they can undergo mitosis or self renewal
Why can males produce sperm for whole life?
As spermatogonia can self renew hence there will be constant supply
Describe the division phase of spermatogenesis
OCCURS IN ADLUMINAL COMPARTMENT - MEOSIS PHASE
- primary spermatocytes —> 2 secondary spermatocytes (meiosis!)
- recombination occurs for genetic variation (takes 24 days)
- secondary —> 2 haploid round spermatids (few hrs)
Describe the differentiation phase of spermatogenesis
- round spermatids elongate to form elongated spermatids + finally mature spermatozoa
- formation of specialised structures e.g. acrosome, flagellum occurs
How does the acrosome form?
From Golgi apparatus
Contains hydrolytic enzymes for acrosome reaction
Inner acrosomal membrane contains receptor for egg fusion (hence fertilisation cant occur w/o acrosome reactiom
How does the flagellum form?
From distal centriole - elongates to from axoneme (microtubules)
Proximal centriole remains to act as spindles for 1st mitotic division of zygote (as egg has to centriole)
What changes occur to the nucleus of sperm during differntiation phase?
DNA becomes condensed to fit inside head + his tones replaced w protamines for compact coiling
DNA no longer accessible for transcription (dependent on environment for further changes)
What changes occur to the cytoplasm of sperm during differentiation phase?
Cytoplasm buds off as residual body - phagocytosed by Sertolli cells
Allows cell to be streamlined but translation can no longer occur
What is spermiation?
Occurs after spermatogenesis
Release of mature spermatozoa from Sertolli cells to lumen of tubule
Washed down into epididymis via rete testes
How long does spermatogenesis take in humans?
What is the spermatogenic wave?
Cells enter spermatogenesis at diff days hence there are always cells at diff stages
Allows constant production
What are the main products of the testes?
Androgens - for embryonic development, reproductive + sexual function
Oestrogen (small amount)
Cytokines e.g. inhibin, AMH
What is the role of oestrogen in males?
Modulates libido, erectile function, spermatogenesis
Fate of testosterone after production?
- travel in blood to rest of body (can suppress HPG axis)
- travel in lymph to accessory sex glands
- bind to ABP for storage + carriage in testicular fluid
- Stimulate spermatogenesis
How is testosterone carried out of testes?
In testicular fluid bound to ABP
Where does LH & FSH act?
LH binds to LHCG on Leydig cells for testosterone production
FSH binds to Sertolli cells & activates many genes
Why does sperm need further maturation after leaving testes?
At this point they’re on morphological mature - they’re immobile + can’t recognise egg
Describe sperm maturation - where & how does it occur?
- oestrogen regulates absorption of fluid for concentration of spermatogenesis within semen
- cells lining epididymis act on sperm, dependent on androgens
- sperm acquires motility (in head of epididymis) + fertilising ability (body)
How long does maturation within epididymis take?
Function of vas deferens
Storage reservoir of sperm before ejaculation, densely packed
Vasectomy = cut/seal ends of vas deferens
What is contained within the ejaculate?
Semen = sperm & seminal plasma (approx 3ml in humans w 100 million sperm)
What is seminal plasma.?
Fluid from prostate + seminal vesicles to facilitate transport, provide nutrition for sperm (fructose), buffer acidic urine, antioxidants to protect DNA
Also contains STI agents
Forms 60-70% of ejaculate volume
Is semen homogenous?
No - first part from prostate, middle from vas deferens containing spermatogenesis & last from seminal vesicles
Role of seminal vesicles
Sac like glands that empty seminal plasma into ejaculatory duct upon ejaculation
Secretes fibrinogen like substance to induce clotting of ejaculate
Role of prostate
Secrets prostate fluid during intercourse
Alkaline to neutralise acidic vagina, enzymes for ejaculate clotting + liquefaction, high in zinc
Role of Bulbourethral gland
Produces pre-ejaculate during arousal phase
For lubrication, neutralisation of acidic urethra, flushes it out
What is capacitation?
Final maturation of sperm within female tract
Sperm acted on by uterine flushings - causes sperm hyperactivation (increased motility for getting through ZP) + acrosome reaction