Reproduction 13 Flashcards
What are the requirements for fertility?
Normal sperm normal eggs sperm can traverse the female tract to reach the egg- time restraint
Sperm can penetrate and fertilise the egg the embryo implants into the uterus normal pregnancy
Describe the male reproductive organs
Scrotum provides a cooler environment compared to the body 1-2C lower
Two products- spermatozoa and hormones
Two compartments- Within the seminiferous tubules (90%): sertoli cells and developing germ cells
Seroli cells maintian the spermatogonial stem cell niche, form a syncytium-like epithelial monolayer in which the germ cells are embedded, allow spermiogenesis and form the blood-testis barier
Between tubules- interstitial cells(10%): Leydig cells Leydig cells synthesis androgen (testosterone) from cholesterol
Briefly describe the blood testis barrier
Gap and tight junctions link each sertoli cell to its neighbour
Between basal and apical compartments of tubule develops during puberty prior to the onset of spermatogenesis
Function is to Separates the sperm from the immune system and controls the chemical microenvironment for spermatogenesis
Describe sperm development
Spermatogonia- diploid- base of the seminiferous
Spermatocytes- undergo meiosis
Spermatids- haploid- close to the lumen of the seminiferous tubule
Spermazoa- Sperm- lumen of the seminiferous tubule
Describe spermatogenesis
Takes 6-8 weeks in humans
Produce 100 million a day
3 phases-
Clonal expansion/Proliferation- mitosis
Maturation/Division- Meiosis
Differentiation: Differentiation- Spermiogenesis release- Spermeation
At pubery, prospermatogonia are reactivated and undergo mitosis in basal compartment of semerniferous tuble.
Describe the meiotic divisions that sperm undertake
Each A spermatogonium undergos mitosis to form type B spermatogonia which divide again t form primary spermocytes which under meiosis.
Spermatogonia –> Primary spermatocyte (Meiosis 1)–> secondary spermatocyte (meiosis 2)–> haploid round spermatid (spermiogenesis)–> elongated sperm 1 primary spermatocyte produces 4 round spermatids The round spermatids elongate to form elongated spermatids
Primary spermatocytes move towards lumen and through blood testis barrier, they enter a resting phase where chromosome duplicates ready for first meiotic division.
Describe the specialised structures of the sperm
Acrosome- formed by the golgi apparatus which migrates to one end of the nucleus. Contains hydrolytic enzymes (acrosome reaction) which are released upon binding to the zona pellucida of the egg and aids penetration
Flagellum- centrioles migrate to the opposite end to the acrosome and form axoneme, for sperm movement through the female tract and penetration of the egg vestments
Mitochondria- helically arranged around the first part of the flagellum , energy for motility
Nucleus- sex-determining, reshaped and elongated, DNA condenses and histones are replaced by protamines, transcriptionally and translationally inactive
Cytoplasm- superfluous cytoplasm forms residual body which is phagocytosed by sertoli cells, loss of organelles such as the ER
Describe spermiation
Last step of spermtogenesis
Sperm are released into the lumen of the testis after the synctium ruptures (cytoplasmic bridges that allows the sharing of essential proteins encoded on the X chromosome to the Y chromosome carrying sperm)
Movement of sperm into seminiferous tubles are due powerful contractions such as peristalsis
Describe the HPG axis in males
Hypothalamus- GnRH
Anterior Pituitary- Gonadotrophins:
LH–> Leydig cells Binds to LH receptors to induce the leydig cells to produce androgen
FSH–> sertoli cells–> Germ cell Maintains spermatogenesis, induce expression of androgen receptors, stimulates production of androgen binding protein (ABP) stimulates inhibin production by the sertoli cells (Sertoli) Inhibin–> Pituitary - (Leydig) Testosterone–> Pituitary and Hypothalamus
What is the role of testosterone in the testis?
in seminiferous tubule- promotes potential direct effects on the germ cells in sertoli cells- converted to dihydrotestosterone by 5alpha reductase also binds to receptors and affects sertoli function
Binds to ABP- carries testosterone in testicular fluid Negative feedback to the pituitary and hypothalamus
Tests for FSH/LH and Testosterone
Use blood tests for all 3
FSH = affects sperm production
LH= stimulates testes to secrete testosterone,
high FSH and LH indicates failure of testicular function
low FSH and LH indicate testes not recieving aqequate stimulatory message from hypothalamus abd pituitary
Testosterone measured with LH/FSH test
Low testosterone = damage to tesits/ hypothalamic and pituitary diease
High testosterone = testicular tumours
Describe sperm maturation
takes place in the male reproductive tract- epididymus (caput, corpus, cauda)
Gain motile potential in the Caput Corpus- fertile Cauda and vas deferens- sperm storage in non-human mammals
