Sex And Fertilization Flashcards
Only a small percentage of semen is sperm, the rest is secretions from the accessory gland. (Seminal Plasma)
What are 3 functions of this Seminal Plasma?
- Nutrition source for spermatozoa
- Acts as a transport medium
- Neutralises acidic environment of vagina
What causes semen to clot initially?
What stops this?
- Initially, semen clots due to clotting factors provided by Seminal Vesicles
- Secretion from Prostate contains enzymes that break down the coagulation
Describe Phases of the Human Sexual Response in Men and Women
- Excitement phase- Psychogenic/ somatic stimuli
- Plateau phase- Stimuli is maintained
- Orgasm phase- If stimulus is maintained, and a threshold is reached
- Resolution phase- Return to haemodynamic norm, followed by a refractory period in males (NOT IN FEMALES)
Describe the Excitment Phase in Men
- Occurs due to psychogenic stimuli/ sensory afferents
Erection comes about due to;
- Parasympathetic efferents via Pelvic nerve
- Somatic efferents via Pudendal nerve
What 3 haemodynamic changes occur in the penis to bring about an erection?
- Relaxation of sinusoids within Corpus Cavernosa
- Arterial dilation
- Venous compression within Tunica Albuginea
What happens to the Corpus Spongiosum in an erection
Partially compressed, as semen would not pass through urethra if fully compressed
To get an erection, sympathetic tone needs to be inhibited while parasympathetic innervation is stimulated by what 2 nerves?
What neurotransmitter does this?
Pelvic
Cavernous
Nitric Oxide (NO)
Outline how NO is released and how it acts to help cause an erection?
- Postganglionic fibres release ACh, which binds to M3 receptors on endothelial cells-> Increased [Ca]i
- Rise in [Ca]i causes NOS activation-> NO formation
- NO diffuses into vascular smooth muscle and causes relaxation (Vasodilation, A key mediator is cGMP)
List 4 causes of ED
What are 2 methods of improving erection/ correcting underlying disorders?
- Psychological factors
- Vascular disorders
- Drugs (Anti-hypertensives)
- Trauma to Corpus Cavernosa tissue
- Increasing amounts of NO and cGMP
How does Viagra help ED?
- Viagra slows the rate of cGMP degradation
- cGMP drives PKG which causes vasodilation which causes erection
Describe Emission
- Under sympathetic control
- Semen moved into Prostatic Urethra via
- SM contraction in Prostate, Vas deferens and Seminal Vesicles
Describe Ejaculation
- Under sympathetic control
- Expulsion of semen via
- SM contraction in Glands and Ducts
- Ryhytmic contraction of pelvic floor muscles and perineum
- Internal sphincter also contracts to prevent Retrograde ejaculation
How does cervical mucus appear when;
- Oestrogen is present
- Oestrogen and progesterone are present
Oestrogen mainly;
- Thin, stretchy
Oestrogen + progesterone;
- Thick, sticky, forms a plug
Describe how the sperm cell changes, in Capacitation when deposited in the female reproductive tract
- Cell membrane changes to allow fertilisation
- Tail movement changes from beat-> Whip-like
- Now capable of undergoing Acrosome reaction
What is the fertile window?
A period of time where sperm can be deposited up to 3 days before ovulation fro fertilisation to be successful
(Sperm can survive for 48-72 hours, Ovum can survive 6-24)
