Lecture 16: sperm + fertility Flashcards
Where does spermatogenesis take place and when during the lifetime of males does it take place
In seminiferous tubules of the 2 testes. It takes place at the onset of puberty where 300/600 sperm per gram per second.
What are the three stages of spermatogenesis
- mitotic division
- Meiotic division
- Cytodifferentiation
Describe the first step of spermatogenesis stage of mitotic division + where it occurs
At puberty the spermatogonial stem cells (primordial germ cell) that sit on the basement membrane of the seminiferous tubule are reactivated. They undergo the 1st assymetric mitotic division where 1 daughter cell remains undifferentiated to maintain the stem cell population and the other daughter cell continues to divide by mitosis, forming a number of spermatogonia. This happens in the basal compartment of the seminiferous tubule.
where do the spermatogonia migrate before first meiotic division
They migrate from basement membrane between the adjacent sertoli cells held together by tight junctions into the Adluminal compartment of the seminiferous tubules
Describe the 2nd step of spermatogenesis stage 1 of meiotic division + where it occurs
Spermatogonia now are called primary spermatocytes in the adluminal compartment. They undergo meiosis I. this leads to DNA content doubled so each spermatocyte has 46 chromosomes. The primary spermatocytes then divide to produce secondary spermatocytes with only 23 chromosomes but with each chromosome having two chromatids.
Describe the 3rd step of spermatogenesis stage 2 of meiotic division + where it occurs
Secondary spermatocytes undergo meiosis 2 to give 4 daughter spermatids each with 23 chromosomes
Describe the 4th step of spermatogenesis (spermiogenesis) + where it occurs
Round spermatids differentiate their shape and become elongated spermatozoa. The excess cytoplasm of the spermatid is also lost into a structure called the residual body which is phagocytosed by the sertoli cells after the sperm leaves to the lumen of the seminiferous tubules.
Describe the structure of the spermatozoa
The head contains DNA and is covered by acrosome which is a compartment filled with enzymes for egg penetration.
The midpiece is packed with mitochondria to produce energy to drive the tail
In the absence of testosterone in the seminiferous tubules what will happen to spermatogenesis
Without testosterone spermatogenesis commences but it doesn’t finish. We need a high level of testosterone in the testes to produce mature sperm
Compare Sertoli and Leydig cells: Location, what acts on it, what does it produce
Sertoli cells are inside the seminiferous tubules, closer to the basement membrane. Whereas Leydig cells are interstitial cells outside the seminiferous tubules. Sertoli cells are acted on by FSH and produce Androgen binding protein as well as inhibin whereas Leydig cells are acted on by LH and they produce testosterone
What are the hormones involved in the negative feedback system of sertoli and leydig cells
Testosterone by leydig cells inhibits the hypothalamus and anterior pituitary whereas inhibin produce by sertoli cells acts on only FSH production
What are the 3 types of male fertility
Oligospermia: Reduced sperm count (below 20 million/mL)
Azoospermia: No sperm
Immotile sperm: Plenty of sperm but sperm can’t swim
Describe IVF (in vitro fertilisation)
The oocytes are harvested, kept in a petri dish with some embryo culture medium and fertilised ex vivo, with the 50 000 motile sperm injected into the droplets. Embryo is then reimplanted to the mother
Describe ICSI (intracytoplasmic sperm injection)
A single sperm (This technique works for sperm harvested from biopsy of epididymus, motile or not) is injected directly into the oocyte using a micropipette. While this is happening there is a holding pipette holding the oocyte still
