Gametogenesis Flashcards
Compare oogenesis and spermatogenesis
Oogenesis:
potential gametes all developed before birth (max 7million) and then atresia with age -> 0% menopause
Few gametes (400 lifetime) Intermittent production
Spermatogenesis:
Many (200 million/day)
Continuous production
How does genetic variation arise?
Crossing-over
Independent assortment
Random segregation
Compartments of Sertoli cells and function of each
Basal compartment- primordial germ cells ->spermatogonia
Blood testis barrier allows for 2 compartments and prevents auto-immune destruction of sperm
Adluminal compartment -> spermatids
Sertoli cells in seminiferous tubules in testis
Sequence of spermatogenesis
Spermatogonia (raw material) mitosis ->
Ad spermatogonium (resting/ reserve stock) (dark) + Ap spermatogonium (active/ maintain stock) (pale) and from puberty give rise to type B spermatogonium ->
Primary spermatocytes, meiosis 1 ->
Secondary spermatocytes, meiosis 2 ->
Spermatids, spermiogenesis ->
4 spermatozoa/ sperm
What is a spermatogenic cycle and wave?
Cells tend to appear in groups of some maturation stage on a seminiferous tubules cross-section
Spermatogonia cycle- time taken for reappearance off same stage within a given segment of tubule (16 days)
Each stage follows in an orderly sequence along length of tubule (time goes on goes inwards)
Distance between same stage is called spermatogenic wave
What is spermiation, spermiogenesis and spermatogenesis?
Spermatids released into lumen of seminiferous tubules = spermiation
Remodel as they pass down through seminiferous tubules, rete testis, ductuli efferentes and into epididymis. -> spermatozoa
Non-motile transport via Sertoli cell secretions assisted by peristaltic contraction
Whole process: spermiogenesis
Spermatigenesis: this whole process + stages before from primordial germ cells
Why do mitochondria of sperm use fructose as a fuel?
So don’t compete with bacteria of female urinary tract
Which glands contribute to semen, what is in the secretions and what percent do they make up?
Seminal vesicle secretions (70%) AA/ citrate/ fructose/ prostaglandins
Secretions of prostate (25%) proteolytic enzymes, zinc (controls motility, higher = more motility)
Sperm via vas deferens (2-5%)
Bulbourethral gland secretions (Cowper gland, <1%) mucoproteins lubricate and neutralise acidic urine distal urethra
What is sperm capacitation? where does it occur? What’s involved? What is the purpose of this?
final maturation setup before sperm fertile
Conditions in female genital tract stimulate:
Removal of glycoproteins and cholesterol from sperm membrane
Activation of sperm signalling pathways (atypical soluble adenylyl cyclase and PKA involved)
Allow spermiation to bind to soma pellucida of ochre and imitate across me reaction
Maturation of oocytes,What and when? Pre-puberty
Begins before both
Germ cells (from yolk sac) colonise gonadal cortex and differentiate -> oogonia
Mitosis
End 3rd month:
Oogonia in clusters surrounded by flat epithelium
Mitosis
or meiosis 1 -> prophase arrested ‘primary oocytes’
Mid gestation: max germ cells 7million
-> cell death oogonia and primary oocytes atresia
All surviving (2mill) primary oocytes surrounded by flat epithelium called follicular cells, now: primordial follicles until puberty
Maturation of oocytes puberty onwards
Most oocytes undergo atresia so 40000 remain
15-20 oocytes mature each month through 3 stages:
Preantral
Antral
Preovulatory
What is the preantral stage of oocyte maturation and when does it occur?
Puberty onwards - 1st stage maturation
Primordial follicles grow, surrounding follicular cells change flat-> cuboidal and proliferate -> stratified epithelium of granulosa cells secrete glycoprotein on oocyte -> zone pellucida
(Driven FSh from APG)
-> primary follicle
What is the antral stage of oocyte maturation and when does it occur?
Puberty onwards, after preantral stage
Fluid filled spaces appear between granulosa cells -> coalesce form antrum
Several primary follicles develop with each ovarian cycle, usually only one reaches maturity
Now have:
~theca externa - outer fibrous
~Theca interna- inner secretory
~Granulosa cells (surrounding oocyte called cumulus oophorus secrete growth factors and oestrogen)
~ zone pellucida surrounding secondary follicle
What happens in the preovulatory stage and when?
Meiosis 1 complete now 2 haploid daughter cells With 46 chromatids. One cell receives most cytoplasm and the other (first polar body) practically none
-> meiosis 2 arrest metaphase (3hrs pre ovulation) only completed (in oviduct) if oocyte is fertilised, if not degenerates (24hrs post ovulation)
Dior got puberty, after antral stage
Ovulation
FSh and LH stimulate rapid growth follicle several days before ovulation now 2.5 cm = Graafian follicle
LH surge increases collagenase activity
Prostaglandins increase response to LH and local muscular contractions in ovarian wall
Oocyte extrudes and breaks free from ovary
