Repro11 - Sex & Fertilisation

Question 1

3 features of epididymal maturation of sperm

Entering Epididymis
Maturation
Leaving Epididymis

Answer 1

1.) Entering Epididymis - spermatoza is incapble of movement

2.) Maturation - dependent on support of the epididymis by androgens
- changes in concentration, sperm modelling, mobility metabolism, and membrane

3.) Leaving Epididymis - spermatoza become capable of movement and have the potential to fertilise
- addition of secretory products to semen

Question 2

6 Normal values for semen analysis

Volume of Ejaculate
Count
pH
Viscosity
Motility
Morphology

Answer 2

1.) Volume of Ejaculate - 2-6 mL
2.) Count - >20 million/ml
3.) pH - 7-8
4.) Viscosity - liquefaction in 1 hour
5.) Motility - >50%
6.) Morphology - 60% normal

Question 3

4 features of an erection

Excitement Phase
Parasympathetic Innervation
Haemodynamic Changes x3
Neurophysiology

Answer 3

1.) Excitement Phase - due to psychogenic stimuli and tactile sensory afferents as part of the spinal reflex
- parasympathetic efferents dominate via pelvic nerve
- somatic efferents also involved via pudendal nerve

2.) Parasympathetic Innervation - pelvic nerve and pelvic plexus are the pregang parasympa fibres (S2-S4)
- cavernous nerves are the postgang parasympa nerves innervating corpus cavernosum and vasculature to facilitate penile erection

3.) Haemodynamic Changes
- sinusoidal relaxation and arterial dilation in the corpus cavernosum due to neuronal input
- increased blood flow against tough tunica albuginea compresses venous drainage within tunica albuginea
- corpus spongiosum not completely compressed to allow passage of semen via the urethra

4.) Neurophysiology - inhibition of sympathetic tone and activation of parasympathetic innervation
- activation of NANC, to release NO

Question 4

Role of nitrous oxide (NO) in an erection

4 steps

Answer 4

1.) Activation of M3 Receptors - postgang fibres release ACh which binds to M3 receptors on endothelial cells
- this leads to a rise in intracellular Ca2+ ions

2.) Activation of NOS - due to rise in intracellular Ca2+ leads to formation of nitrous oxide (NO) in endothelium

3.) Activation of Guanylyl Cyclase - NO diffuses into vascular smooth muscle where it causes GTP –> cGMP, which breaks down into protein kinase G (PKG)
- viagra slows rate cGMP is degraded
- cavernous nerves also releases NO directly into vascular smooth muscle

4.) Penile Erection - PKG triggers vasodilation which leads to an erection

ACh —> M3 —> Ca2+ —> NO —> GTP —> cGMP —> PKG

Question 5

5 features of erectile dysfunction

4 Groups of Causes
Management

Answer 5

1.) Psychological - descending inhibition of spinal reflexes

2.) Physical - tears in fibrous tissue of corpus cavernosum means less blood retained in the penis

3.) Vascular Disorders

4.) Drugs - e.g. anti-depressants

5.) Management - treat underlying condition
- can also increase amounts of NO and cGMP

Question 6

3 features of emission and ejaculation

Answer 6

1.) Under only Sympathetic Control

2.) Emission - movement of semen into prostatic urethra
- due to contraction of smooth muscle in prostate, vas deferens, and seminal vesicles

3.) Ejaculation - expulsion of semen
- caused by rhythmic skeletal muscle contractions of the pelvic floor and perineal muscles
- contraction of the internal urethral sphincter prevents retrograde ejaculation

Question 7

Cervical mucus changes over the course of the menstrual cycle

Oestrogen
Oestrogen + Progesterone

Answer 7

1.) Follicular/Proliferative Phase - only oestrogen present
- cervical mucus is thin and stretchy, aiding sperm

2.) Luteal/Secretory Phase - oestrogen and progesterone
- cervical mucus becomes thick and sticky, forming a plug to prevent access to female tract

Question 8

5 features of sperm capacitation

What is it?
Function
Sperm Membrane
Sperm Tail
IVF

Answer 8

1.) What is it? - final maturation step, that occurs in the female reproductive tract
- activates sperm signalling pathways

2.) Function - allows sperm to bind to zona pellucida of oocyte and initiate acrosome reaction

3.) Sperm Membrane - removal of glycoproteins and cholesterol to allow fusion with zona pellucida

4.) Sperm Tail - tail movement: wave-like –> whip-like
- allows penetration of the zona pellucida

5.) IVF - human sperm in IVF must first be incubated in capacitation media

Question 9

What is the fertile period?

Answer 9

Spermatoza Lifespan - 48-72 hours
Oocyte Lifespan - 6-24 hours

Fertile Period - sperm deposition 0 to 3 days prior to ovulation

Question 10

3 features of the acrosome (reaction)/fertilisation

The Acrosome
Acrosome Reaction
Fertilisation

Answer 10

1.) The Acrosome - derived from golgi region of developing spermatids
- contains enzymes needed for fertilisation

2.) Acrosome Reaction
- sperm pushes through corona radiata (granulosa cells surrounding oocyte) to reach the zona pellucida
- sperm surafce receptor bind to ZP3 glycoprotein of zona pellucida to trigger the acrosome reaction
- leads to digestion of the zona pellucida

3.) Fertilisation - one sperm penetrates leading to fusion of the ova and sperm membrane
- cortical reaction is triggered which blocks polyspermy
- series of calcium waves are activated to allow completion of meiosis II (arrested in metaphase)

Question 11

4 phases of the human sexual response

Answer 11

1.) Excitement Phase - psychogenic or somatic stimuli

2.) Plateau Phase - maintains the stimuli

3.) Orgasm Phase - if a stimulus threshold is reached

4.) Resolution Phase - return to haemodynamic norm
- there is a refractory period in men but no refractory period in women