testicular function Flashcards
up until which week are PGCs indifferent?
- week 6/7
what occurs during male puberty?
- complex process involving secondary sexual characteristic development and accelerated growth
- initiation of gametogenesis
- all caused by pulsatile release of GnRH from HT
why are the scrotum positioned outside the body?
- provides a cooler environment to aid spermatogenesis
what 2 products are produced by the testis?
- spermatozoa
- hormones
what are the 2 compartments within the testicles?
- within seminiferous tubules (90%)–> Sertoli cells
- nurture developing germ cells during spermatogenesis and spermiogenesis
- between tubules (10%)–> leydig cells –> androgen producing cells (T)
what are the 2 functions of the blood-testis barrier ?
Separates developing germ cells from immune system preventing immune response (anti-sperm antibodies and autoimmune orchitis – subfertility)
Controlled chemical microenvironment for spermatogenesis (selective transport of ions and small molecules)
what are the key phases of spermatogenesis?
- starts at puberty
- takes 74 days
1) proliferation
2) division meiosis 1/2
3) differentiation –> spermiogenesis
what occurs during mitosis 1?
- happens with pro-spermatogonia
- occurs within the basal compartment of seminiferous tubule
- starts at puberty
- -> form As spermatogonia
what are As spermatogonia ?
- reservoir of self renewal stem cells that maintain the germ line
- they remain within the outer edge of the seminiferous tubule as unD spermatogonia
what do As spermatogonia form?
- they form A type spermatogonia–> starts process of spermatogenesis
- A type undergo mitosis to form B type
what happens to type B spermatogonia?
- divide again to form primary spermatocytes of which undergo meiosis
all primary spermatocytes genetically identical to spermatogonia
what occurs during the resting phase ?
- chromosomes within primary spermatocytes duplicate ready for 1st meiotic division
what happens during meiosis 1 and meiosis 2?
1–> primary spermatocyte divides–> secondary spermatocyte
2–> secondary spermatocyte divides –> haploid round spermatid
what occurs during spermiogenesis?
- these round spermatids elongate to form spermatozoa
- highly specialised but very simplistic
- here we have the formation of specialised structures such as the acrosome, centriole, flagellum, mitochondria and the nucleus
what is the acrosome formed from?
- formed by the Golgi apparatus of which migrates to the one end of the nucleus
how is the flagellum formed?
- centrioles migrate to the opposite end of the nucleus to form axoneme
why is the flagellum important?
it is for sperm movement through the female tract and the penetration through egg vestments
where are the mitochondria found?
- helically arranged around first part of flagellum (midplace) providing the energy for motility
what happens to the spermatid cytoplasm?
- forms a residual body (droplet)
- phagocytksed by Sertoli cells with loss of ER organelles
- mature sperm have very little cyt
what occurs during spermination?
- developing spermatids from a syncytium
- persists until the final stages of spermatogenesis (last step)
- facilitated by Sertoli cell cytoskeleton
- formation of intercellular bridges
what is the purpose of spermination?
- allows the sharing of cytoplasmic components between spermatid and sertoli cells
- spermatids only carry a Y chromosome, but can be supplied with essential proteins encoded on the X chromosome from Sertoli cells (such as the acrosome and axoneme)
post testis sperm need to undergo which processes?
- epididymis in male tract
- capacitation in female tract
-both important for acquisition of motility and fertility potential
what is the epididymis ?
- is a highly segmented organs divided into 3 main anatomic regions
1) caput-> motility
2) corpus-> fertilising ability
3) cauda/vas deferens-> storage of spermatids
each segments display differential expression of genes that maintain luminal ion concentration
are essential for regulation of steps and sperm maturation
how are sperm pushed through the 3 regions of the epididymis ?
via peristalsis contraction of smooth muscle of the epididymal duct
what changes occur during migration through the epididymis ?
Sperm interact with epididymal epithelial cells – movement of cytoplasmic droplet Retention of cytoplasmic droplet associate with reduce fertility
Change sperm proteome – protein, lipid and sugar content Incorporated into the sperm cells
Change in sperm surface
Removal and/or modification of external proteins, sugars and lipid sperm membrane
Intracellular signalling pathways activation during transit
Addition or removal of protein phosphate groups - phosphorylation
sperm division is ?
even
