L03 - Testicular Function Flashcards
At which point in development is the male reproductive system distinguishable from the female reproductive system?
Week 7
Which cells are the precursors to the reproductive systems?
What ploidy are these cells?
- Primordial germ cells
- Diploid cells
What is the role of the Y chromosome in the determination of male sex?
- The Y chromosome has the sex-determining region Y (SRY) gene (testis determining factor) that codes for an architectural transcription factor that binds DNA and allows other TFs to upregulate other male determining genes
- SRY doesn’t contain the genes for testis, but switches on other genes essential for their development
What is the cause of females with XY chromosomes and males with XX chromosomes?
- SRY gene mutation/deletion ➡ XY ‘females’
- SRY gene translocation onto the X or a somatic chromosome ➡ XX ‘males’
What processes occur from week 7 in male reproductive development?
1 - Columns of cells from the coelomic epithelium proliferate and penetrate deep into medullary mesenchyme
2 - These are the cells that express SRY and they form the primitive sex cords
3 - Primordial germ cells (PGCs) become surrounded by these sex cord cells
4 - This forms the seminiferous tubules
From which cells are Sertoli cells derived?
Mesodermal sex cord cells
From which cells are prospermatogonoia derived?
Primordial germ cells (PGCs)
What is the fate of migratory cells from the mesonephric primordia?
They form the vasculature, Leydig cells and myoid cells
What cellular event is inhibited within seminiferous tubules?
Meiosis is inhibited and cells become dormant
When does SRY stop being expressed?
What directs further development of the male reproductive system?
- Once seminiferous tubules have formed
- The testes direct further development via androgens from Leydig cells and anti-Mullerian hormone (AMH) from Sertoli cells
List the two compartments of post-pubertal testis.
Which cells are present in these compartments?
- Within the seminiferous tubules – sperm develop, under the influence of Sertoli cells
- Between the seminiferous tubules – Leydig cells
What is the function of the Sertoli cells in the seminiferous tubules of the post-pubertal testis?
To produce sperm
What is the function of the Leydig cells in the seminiferous tubules of the post-pubertal testis?
To produce androgens
Where is the blood-testis barrier?
Between the adluminal and basal compartments of the seminiferous tubules
List the junctions that form the blood-testis barrier.
Which cells are being linked together by these junctions?
1 - Adherens junctions
2 - Gap junctions
3 - Tight junctions
- These junctions are linking adjacent Sertoli cells
When does the blood-testis barrier develop?
During puberty prior to the onset of spermatogenesis
What are the functions of the blood-testis barrier?
- To separate sperm from the immune system preventing an immune response (anti-sperm abs & autoimmune orchitis)
- Selective transport of ions & small molecules to control the chemical environment for spermatogenesis
What happens in the proliferation phase of spermatogenesis?
1 - At puberty, prospermatogonia are reactivated and are then known as ‘As spermatogonia’
2 - As spermatogonia undergo mitosis in the basal compartment of the seminiferous tubule to produce another As spermatogonium (renewal) and an ‘A spermatogonium’
3 -The A spermatogonia undergo mitosis to produce B spermatogonia
4 - B spermatogonia undergo mitosis to produce primary spermatocytes
What happens in the division phase of spermatogenesis?
1 - The primary spermatocytes move from the basal compartment of the seminiferous tubule through the blood-testis barrier into the adluminal compartment
2 - Here, they undergo the first meiotic division over the course of 24 days to form diploid secondary spermatocytes
3 - They then undergo the second meiotic division over the course of 24 hours to form haploid round spermatids
What happens in the differentiation phase of spermatogenesis?
1 - Round spermatids elongate to form elongated spermatids & finally mature spermatozoa
2 - There is also the formation of specialised sperm structures: the acrosome, flagellum, mitochondria, nuclear and cytoplasm
Describe the structure of the specialised sperm acrosome.
- Formed from Golgi apparatus, which migrates & sits atop nucleus at the sperm head
- Contains hydrolytic enzymes for the acrosome reaction
- Receptor for fusion located on the inner acrosomal membrane
Describe the structure of the specialised sperm flagellum.
- Function is to facilitate sperm movement through the female tract & penetration of the egg vestments
- Forms from centrioles that migrate to the opposite end of the nucleus to the acrosome
- The distal centriole elongates to form the axoneme & the proximal centriole remains inside the sperm to form the spindle for the 1st mitotic division of the embryo (as eggs have no spindle fibres)
Describe the structure of the specialised sperm mitochondria.
The mitochondria in the sperm lie in a helical arrangement around the first part of the flagellum (the midpiece). These provide energy for motility
Describe the structure of the specialised sperm nucleus.
- The nucleus of the sperm is either X or Y bearing, and determines the sex of the embryo
- The DNA of the sperm is highly condensed as histone proteins are replaced with protamines
