Gametes - Fertilisation Flashcards by Michelle Doody

Overview of sperm penetration of the egg

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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

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What sort of drugs may cause erectile dysfunction

Anti-cholinergic drugs

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Erectile dysfunction and T2D

Hyperglycaemia - damages autonomic nerves

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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

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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

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How to know th effectiveness of a vasectomy

2 -ve samples, 1 month apart

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Content of semen

Prostatic fluid - 30%

Epididymal fluid - 50%

Seminal vesicle fluid

CELLS

spermatozoa

Leukocytes

bacteria

epithelial cells

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Reference ranges for semen

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Function of fructose in seminal vesicle

Marker for seminal vesicle function - energy source

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Function of prostaglandins in semen (from seminal vesicle)

Sperm motility

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Function of proteins in semen (from seminal vesicle)

Coagulate semen

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Function of alpha glucosidase (from epididymis)

Marker for epididymal function

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Function of CD52 (from epididymis)

Seminal glycoprotein that is incorporated into sperm membrane

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Substances present in semen that are produced by the seminal vesicles

Fructose

Prostaglandins

Proteins

(Also makes semen alkaline)

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Substances present in semen that are produced by the epididymis

alpha glucosidase

CD52

Glycogen

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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)

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Name 2 markers for prostatic function

Zinc

Acid phosphatase

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Biomarkers for prostate cancer

Citric acid

PSA

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At what pH do sperm die

6.9

Normal range is 7.2-8.4

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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

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Aspermia

No semen ejaculated

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Haematospermia

Blood present in semen

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Leucocytospermia

WBCs present in semen

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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

1. Removal of cholesterol - increased fluidity of membrane 2. Loss of glycoproteins - expose egg binding protein 3. 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