S5) Sexual Function and Fertilisation Flashcards
Describe the composition of semen
- Spermatozoa +
- Seminal plasma
Identify 3 functions of the semen
- Transport medium
- Nutrition
- Buffering capacity
Where is seminal plasma derived from?
Accessory glands of the male reproductive tract:
- Prostate gland
- Seminal vesicles
- Bulbourethral gland
What is the usual site for fertilisation?
Ampulla of uterine tube
Identify the 4 phases in the sexual response
- Excitement phase
- Plateau phase
- Orgasm phase
- Resolution phase
What sort of stimuli trigger the excitement phase?
Psychogenic and / or somatogenic stimuli
What happens after the resolution phase in the sexual response?
Return to haemodynamic norm followed by a refractory period (males), build up of blood in the penis goes back to normal
Identify the 2 stimulants of the male sexual response – erection
- Psychogenic
- Tactile (sensory afferents of penis and perineum)
Identify the 2 efferent nerves in the male sexual response – erection
in the first part of the sexual response its the parasympathetic part that causes change (erection)
Somatic and autonomic efferents:
- Pelvic nerve dominates the → PNS
- Pudendal nerve → Somatic
Which three processes are required for an erection to occur?
- Sinusoidal relaxation
- Arterial dilation
- Venous compression → muscles expand and compress the veins within the tunica alburgenia to stop blood flowing back
Identify the nerves involved in the parasympathetic innervation of the penis
- Pelvic nerve and pelvic plexus
- Cavernous nerve
Describe 3 neurophysiological events which produce an erection
- Inhibition of sympathetic arterial vasoconstrictor nerves
- Activation of non-adrenergic, non-cholinergic, autonomic nerves to arteries
- Release of Nitric Oxide (NO)
In five steps, describe the events leading to the release of NO in an erection
⇒ Post-ganglionic fibres release ACh
⇒ ACh bonds to M3 receptor on endothelial cells
⇒ Rise in [Ca2+]i activates NO synthase and formation of NO
⇒ NO diffuses into vascular smooth muscle and causes vasodilation
⇒ NO is also directly released from nerves
- nerves involved are pelvic and cavernous nerves
Identify 4 causes of erectile dysfunction
- Psychological (nervous)
- Tears in fibrous tissue of corpus cavernosa
- Vascular
- Drugs (anti-depressants)
Describe the psychological cause for erectile dysfunction
Psychological – descending inhibition of spinal reflexes
What sort of neural control governs emission and ejaculation?
Sympathetic Nervous System
Describe the origin, structure and function of the acrosome
- Origin: derived from golgi region of developing spermatid
- Structure: contains enzymes
- Function: necessary for fertilisation
What is the result of the acrosome reaction?
- sperm loses its outer membrane so the single head can penetrate and fuse with membrane
Which 2 processes lead to fertilisation?
- One sperm penetrates leading to fusion of plasma membranes
- Cortical reaction occurs (blocks polyspermy)
What is unique about the cells of the morula?
Each cell at this stage of development is totipotent
Describe the structure of a blastocyst
- It has an inner cell mass which eventually forms the embryo
- It has an outer cell layer called the trophoblast
What is the significance of the blastocyst hatching from the zona pellucida?
- Blastocyst can enlarge freely
- Blastocyts interact with uterine surface & implants
How does implantation occur?
- Outer cell mass (trophoblast) interacts with endometrium
- Endometrium controls degree of invasion
How is placenta praevia caused?
Implantation of blastocyst in lower uterine segment can cause placenta praevia
