Repro: Origin Of The Gametes Flashcards
Where do male and female germ cells enter the gonad?
Female germ cells enter the cortex of the gonad and become oogeonia, whereas male germ cells enter the medulla and become spermatogonia
How many gametes are produced from meiosis?
Males: produces 4 daughter cells
Females: only 1 develops into a mature oocyte, the their 3 form disposable polar bodies
1 gets all the cytoplasm
What are the ways that genetic variation arises from meiosis?
- crossing over occurs in prophase 1, formation of chiasmata to exchange DNA
- random segregation of chromosomes among 4 gametes
- independent assortment, 2 homologous chromosomes must go int separate gametes
Outline the process of spermiogenesis?
Spermatids are released into the seminiferous tubules (spermiation)
As they pass through the rate testis, ductility efferentes and epididymis they remodel (grow a tail)
They are non motile at first so transported via sertoli cell secretions an peristaltic contraction
What is the role of the sertoli cell barrier? (Or blood testis barrier)
Allows control of the environment the germ cells develop in - only androgens can penetrate the barrier
Also prevents antigenic products enter the blood stream and causing an autoimmune reaction (have different genes in the sperm)
What does the mitotic division of spermatogonia produce?
- Ad spermatogonia which maintain the stock
2. Ap spermatogonia which give rise to primary spermatocytes
What does each primary spermatocyte give rise to?
Each primary spermatocyte divides by meiosis to form 4 haploid spermatids which differentiate into spermatozoa
( NB spermatogenesis = the whole process, spermiogenesis = just the cytodifferentiation into spermatozoa)
What’s the difference between the spermatogenic cycle and wave?
Not all stages of spermatogenesis are visible in a cross section of seminiferous tubule at one time
- the spermatogenic cycle is the time take for reappearance of the same stage in a given segment (16 days)
- the spermatogenic wave is the distance between the same stage
What is the composition of ejaculate?
~2ml of semen per ejaculate
- 70% is seminal vesicle secretions eg AA, citrate, fructose, prostaglandins
- 25% is prostate secretions eg proteolytic enzymes, zinc
- 5% is sperm, 200-500million
- 1% is bulbourethral gland secretions eg mucoproteins to lubricate and neutralise urine in distal urethra
What is sperm capacitation?
Why is this important clinically?
Conditions in the female genital tract stimulate removal of glycoproteins and cholesterol from the sperm membrane and activation of sperm signalling pathways. This allows sperm to bind to the zona pellucida
Therefore in IVF the sperm has to be incubated in capacitation media before fertilisation
What is the primordial follicle?
A group of primary oocytes which are arrested in meiosis 1 and surrounded by flat epithelial cells called follicle cells.
The primordial follicle now waits until puberty
What are the 3 stages of maturation of oocytes that occurs from puberty onwards?
- Pre-antral
- Antral
- Preovulatory
Describe the pre-antral stage of oocyte maturation
The primordial follicles begin to grow and the follicular cells change to produce a stratified epithelium of granulosa cells. The granulosa cells secrete glycoprotein to form the zona pellucida
Describe the antral stage of oocyte maturation
A fluid filled space forms called the Antrum
The secondary follicle is now comprised of the oocyte surrounded by the zona pellucida, then the antrum surrounded by granulosa cells then the theca interna (secretory) and then external (fibrous)
Describe the preovulatory phase of oocyte maturation
An LH surge causes a growth phase and meiosis 1 is completed resulting in 2 haploid daughter cells (or is a polar body).
The cell then enters meiosis 2 but arrests in metaphase - meiosis 2 only completes if oocyte is fertilised
