Gametes - Fertilisation Flashcards
Overview of sperm penetration of the egg
MOA of erection
PS reflex - Arterioles dilate & SM relaxes via NO
Penis is engorged with blood
Expansion compresses the veins, slowing blood leaving the penis
Reflex is intitiated by a sensory stimuli
What sort of drugs may cause erectile dysfunction
Anti-cholinergic drugs
Erectile dysfunction and T2D
Hyperglycaemia - damages autonomic nerves
MOA of ejaculation
Spinal reflex is initiated (lack of muscle in penis shaft)
Sympathetic discharge to genital organs
Reproductive ducts/accessory glands contract peristaltically, discharging their contents into the urethra
Bulbocavernous muscle at the base of the penis experiences a rapid series of contractions, propelling semen from the urethra
How does viagra cause penile erection
ACh increases NO, increasing conc of cGMP
cGMP causes SM relaxation
Relaxation of arterioles leads to increased blood flow to penis
normally cGMP is degraded by phosphodiesterase 5, terminating its action
Viagra hence inhibits the PDE5 => decreased cGMP breakdown
Prolonged arteriolar dilation
Prolonged erection
How to know th effectiveness of a vasectomy
2 -ve samples, 1 month apart
Content of semen
Prostatic fluid - 30%
Epididymal fluid - 50%
Seminal vesicle fluid
CELLS
spermatozoa
Leukocytes
bacteria
epithelial cells
Reference ranges for semen
Function of fructose in seminal vesicle
Marker for seminal vesicle function - energy source
Function of prostaglandins in semen (from seminal vesicle)
Sperm motility
Function of proteins in semen (from seminal vesicle)
Coagulate semen
Function of alpha glucosidase (from epididymis)
Marker for epididymal function
Function of CD52 (from epididymis)
Seminal glycoprotein that is incorporated into sperm membrane
Substances present in semen that are produced by the seminal vesicles
Fructose
Prostaglandins
Proteins
(Also makes semen alkaline)
Substances present in semen that are produced by the epididymis
alpha glucosidase
CD52
Glycogen
Name the prostate secretions and their functions
Calcium - contractility of sperm & fertility
Zinc - anti-bacterial (marker for prostate function)
Citric acid - present in high conc, hence reduced levels are a biomarker in prostate cancer
Acid phosphatase - marker for prostatic function
Albumin
Prostatic Specific Antigen (PSA) - a protein produced by the epithelial cells of the prostate that is a biomarker for porstate cancer (> 4ng/ml)
Name 2 markers for prostatic function
Zinc
Acid phosphatase
Biomarkers for prostate cancer
Citric acid
PSA
At what pH do sperm die
6.9
Normal range is 7.2-8.4
Variation in speed of motility of sperm
Rapid progressive - >25 um/s
Slow progressive - 5-25 um/s
Non progressive - <5um/s
IMMOTILE - no flagellar movement
Aspermia
No semen ejaculated
Haematospermia
Blood present in semen
Leucocytospermia
WBCs present in semen
Azospermia
No spermatozoa found in semen
Normospermia
Normal semen parameters
Oligospermia
Low sperm conc
Asthenospermia
Poor motility and/or forward progression
Teratospermia
Reduced % of morphologically normal sperm
Necrospermia
No live sperm in semen
How would you describe sperm produced in the ST
Morphologically mature, functionally immature
Non-motile and not capable of fertilisation
Define capacitation of sperm
The biochemical changes that happen within sperm allowing for full functional maturity
Takes place as the sperm travels within the uterine and oviductal fluid
Removal of glycoprotein covering the head of sperm
What are the sperm cell membrane changes with capacitation
- Removal of cholesterol - increased fluidity of membrane
- Loss of glycoproteins - expose egg binding protein
- Fluctuations in Ca2+ - protein phosphorylation via cAMP (ABSOLUTE REQUIREMENT)
Cellular processes that lead to capacitation
Consequences of changes in sperm due to capacitation (due to increase in Ca2+)
Increased metabolism = fructose for energy
Flagellum increases rate of beating - increased sperm motility
Activation of acrosomal enzymes - pro-acrosin → acrosin
Site of fertilisation
Tubal ampulla
Sperm are deposited in vagina and travel to tubal ampulla by flagellar movement
What factors increase uterine contractility
Ovarian steroids influence sperm transport
- High oestrogen of late follicular phase makes the cervical mucus alkaline and less viscous
- PGs in seminal fluid
- Oxytocin - localised
Transport of sperm and egg in female reproductive tract
Structure of ovulated oocyte
Where is the zona pellucida first detected
Composition
When is the ZP no longer present
- First detected in primary follicle
- Matrix composed of sulfated glycoproteins
- CHO residues (sperm receptors?)
- Increase in width with development of oocyte
- ZP stays until blastocyst is formed @ day 7 - embryo hatches out of ZP and implants on main body of uterine wall
Function of zona pellucida
Species specific barrier
Removal of ZP allows cross fertilisation to occur with relative ease
What does ZP3 do
Mediates sperm specific egg binding
Function of ZP2
Mediates subsequent sperm binding
Function of ZP1
Cross links ZP2 and ZP3
Protein meshwork formed
Not essential for fertilisation
NB -structural integrity of ZP
What happens in the absence of ZP1
Premature hatching of embryos
Overview of ZP1, ZP2 and ZP3 functions
Sperm egg binding overview
What is the sperm receptor of the egg
Galactosyl Transferase (Galtase)
What are th egg receptors
O-linked oligosaccharide residues of ZP3
What rxns does egg sperm binding intitiate
Acrosomal rxn
Sperm & cortical rxn
ZP3 and the acrosome rxn
What is the mediator of the acrosomal rxn
Galtase
Overview of acrosomal rxn
Describe the cortical rxn
- Cortical granules are membrane bound vesicles just beneath the egg cell membrane
- Exocytosis at fertilisation - granule enzymes released - digest proteins of ZP
- Prevents poly spermy
Overview of cortical rxn
Cortical granules = enzymes that digest ZP and prevent entry of 2 male pronuclei
When is there decreased effective block to polyspermy
Age of ova
- Time of insemination relative to ovulation
- Aged oocyte increases chance of polyspermy
Heating of ova
- Increased metabolism and lifespan of egg
- Fever or environmental effect on body temp
Excessive sperm numbers
- at site of fertilisation
- Sperm barriers reduce numbers - cervix, uterus, utero-tubular junction
What is the window of viability of an egg
24 hours
Consequences of triploidy
3 pronuclei within one zygote
In vivo, such embryos almost always abort spontaneously
Overview of egg activation
Describe pronuclei fusion
- Haploid sperm enters the egg
- Becomes the sperm pronucleus
- Sperm pronucleus swells and migrates towards the egg pronucleus
- The pronuclear envelopes vesiculate (nuclear membranes break up to form a circle of small vesicles) and surround the chromatin of each nucleus
- Chromatin from each pronucleus intermixes, forming the diploid zygote nucleus
- Nuclear envelope reforms around the zygote nucleus & embryonic development begins
Fusion of nuclei
Early embryonic development
