6. Sex And Fertilisation Flashcards
What is semen made up of?
Spermatozoa
Seminal plasma
What is the function of seminal plasma?
Transport medium
Nutrition
Buffering capacity
Role for prostaglandins in stimulating muscular activity in female tract
What is seminal plasma made up of?
Alkaline fluid, fructose, prostaglandins, clotting factors - seminal vesicles
Milky, slightly acidic fluid, proteolytic enzymes - prostate gland
Alkaline fluid, mucous - bulbourethral glands
Where is the fertilisation site usually?
Ampulla of uterine tube
What are the stimulants in male sexual response?
Psychogenic
Tactile - sensory afferent of penis and perineum
What are the efferent in male sexual response?
Somatic and autonomic efferent Pelvic nerve (PNS) Pudendal nerve (somatic)
What does erection require?
Sinusoidal relaxation
Arterial dilation
Venous compression
What is the parasympathetic innervation of the penis?
Fibres - lumbar and sacral spinal levels
Pelvic nerve and pelvic plexus
Cavernous nerve to corpora and vasculature
What is the neurophysiology of erection?
Inhibition of sympathetic arterial vasoconstrictor nerves
Activation of PNS
Activation of non-adrenergic, non-cholinergic, autonomic nerves to arteries, releasing nitric oxide
What is the role of nitric oxide in an erection?
Post-ganglionic fibres release ACh
ACh binds to M3 receptor on endothelial cells
A rise in [Ca2+], activation of NOS and formation of NO
NO diffuses into vascular smooth muscle and causes relaxation (vasodilation)
NO also released directly from nerves
What are the causes of erectile dysfunction?
Psychological (descending inhibition of spinal reflexes)
Tears in fibrous tissue of corpora cavernosa
Vascular (arterial and venous)
Drugs
How does viagra work?
Slows rate at which cGMP degrades
Describe the emission phase of male sexual response?
Under sympathetic control
Emission - movement of semen into prostatic urethra, contraction of SM in prostate, vas deferens and seminal vesicles
Ejaculation - expulsion of semen
Describe the ejaculation phase
Contraction of glands and ducts (smooth muscle)
Bladder internal sphincter contracts - preventing retrograde ejaculation
Rhythmic striatal muscle contractions
What muscles perform the rhythmic striatal muscle contractions?
Pelvic floor
Perineal muscles - ischiocavernosus, bulbospongiosus
How does oestrogen on its own affect cervical mucus?
Thin, stretchy
How does oestrogen and progesterone together change cervical mucus?
Thick, sticky, forms a plug
What is capacitation?
Further maturation of sperm in female reproductive tract (6-8 hrs)
Sperm cell membrane changes to allow fusion with oocyte cell surface
Tail movement changes from beat to whip-like action
Now capable of undergoing acrosome reaction
What is the acrosome?
Derived form Golgi region of developing spermatid
Contains enzymes
Cap like structure
What happens in the acrosome reaction?
Sperm pushes through corona radiata
Binding of sperm surface receptor to ZP3 glycoprotein of zona pellucida
Triggers acrosome reaction
Digestion of zona pellucida
What happens during the completion of meiosis II after fertilisation?
Series of calcium waves are activated following fusion of oocyte and sperm membranes
Resumption of meiosis II occurs
Pronuclei move together
Mitotic spindle forms leading to cleavage
