Flashcards in 7.1 Coitus and Fertilisation Deck (36):
Where are sperm produced?
Seminiferous tubules of testes
What are the main constituents of sperm?
60% from seminal vesicles:
- Alkaline fluid (neutralise urethra acid)
- Fructose (ATP)
- Prostaglandins (Increased motility)
- Clotting factors (coagulation agent)
- Proteolytic enzymes
- Citric acid (ATP)
5% bulbourethral (Cowper's) glands
- Mucous for lubrication
Alkali - netralise acid in distal urethra
What is assessed in semen analysis?
Sperm count (200-500 million)
What is emission? Nervous system involved?
Movement of ejaculate in prostatic urrethra before ejaculation.
Due to vas deferens perstalsis and sminal vesicle secretion.
Describe what occurs in emission.
Stimulation of thoracolumbar sympathetic reflex
Contracitno fo smooth muscle in ductus deferens ampulla, seminal vesicles and prostate.
Internal and external urethras contract.
Semen is pooled in urethral bulb.
What are the phases of coitus?
Stimulation of what nerves cause erection? NS?
Somatic an autonomic efferents
Pelvic nerve (parasympathetic)
Pudendal nerve (somatic)
Describe the physiological process in erection of penis.
Inhibition of sympathetic arterial vasoconstrictor nerves.
Activation of parasympathetic NS - pelvic nerve
Increase in parasympathetic stimulation
ACh --> M3 receptors on endothelium
Rise in Ca2+
Activation of Nitric Oxide Synthase
Formation of NO
NO diffuses into and causes relaxation of vascular smooth muscle - vasodialtion
Increased formation of cGMP
Ca2+ taken up into intracellular stores
Reduced Ca2+ leads to less actin-myosin cross bridges -> SM relaxes
Blood fills copra cavernosa helicine arteries when they straighten.
Blood --> cavernous spaces in the corpora of the penis
Corpus spongiosum dilates but not as much.
Bulbospongiosus and sichiocavernosus muscles compress veins egressing from corpora cavernosa, impeding venous return.
Corpa cavernosa becoem engorged causing erectile bodies to become turgid and erection occurs.
What factors cause erectile dysfunction?
Descending inhibition of spinal reflexes
Tears in fibrous tissue of corpora cavernosa
Arterial and venous
Factors blocking NO
How does viagra work??
Inhibits breakdown of cGMP, increasing penile blood flow and maintaining erection.
What happens in the male plateau phase?
Activation of sacrospinous reflex
Contraction of ischiocavernosus (compression of crus penis impedes venous flow0
Rise in intracavernosus pressure --> Decreased arterial inflow.
Stimulation of secretion from accessory glands.
What NS and roots cause ejaculation?
What occurs in ejaculation?
1. Contraction of glands and duct smooth muscle
2. Bladder internal urethral sphincter contracts to prevent semen entering bladder.
3. Rhythmic contractions of striatal muscles:
Filling of the internal urethra stimulates pudendal nerve --> contrition of genitals and pelvic floor, ischiocavernosus, bulbospongiosus, hip, anal muscles.
4. Explsion of semen.
What occurs in male resolution?
Activation of thoracolumbar sympathetic pathway.
Contraction of smooth arteriolar muscle in corpora cavernosa.
Increased venous return
Detumescence and falccidity
Followed by refractory period.
What is the physiological process in the female excitement phase?
Inhibition of sympathetic stimulation.
Parasympathetic stimulation via pelvic nerve leading to vasocongestion and vaginal lubrication.
Clitoris engorges with blood
Swelling and engorgement of external genitalia.
Internal enlargement of vagina
Increase muscle tone, heart rate and BP
What is the function of cervical mucous? How does this change with hormones?
Facilitates sperm survival and transport:
Alkalinity and low viscosity.
Oestrogen - abundant, clear, non-viscous
O&P - thick, sticky mucous plug. Prevent sperm entry
What is the most common form of sexual dysfunction?
Describe the types of arousal dysfunction.
Hypoactive - little interest in sex
Aversion - revulsion or fear of sex
Persistent recurrent inability to attain or maintain lubrication.
Describe what occurs in the female plateau phase.
Further increase in muscle tone, heart rate and BP.
Clitoris withdraw under hood
Bartholin's gland secretion lubricates vestibule
Outer 1/3 vagina forms orgasmic platform.
Describe the female orgasm
Orgasmic platfor (lower 1/3 of vagina) contracts rhythmically 3-15 times.
Uterus contracts, anal sphincter contracts
Clitoris udner hood
No refractory period.
Describe the female resolution phase.
Labia return to unaroused size and colour
Vagina shortens and narrows back to unaroused state.
Breasts reduce in size, reduced size of areola
What are the changes in coitus with age in females?
Reduced vasocongestion response
Vaginal and urethral tissue lose elasticity.
REduced expansion of vagina
More rapid resolution.
What happens following deposition of sperm in vagina?
Seme coagulates due to clotting factors from seminal vesicles.
This prevents sperm being physically lost.
10-20 minutes later it reliquaries by the action of proteolytic enzymes from prostate.
Most sperm do not enter the cervix and are lost by leakage.
Ones that do travel 15-20cm tot he uterine tube.
What leads to transport of sperm
Their own propulsive capacity
Fluid currents caused by action of ciliated cells in uterine tract.
What must sperm penetrate to get to the ovum?
Corona radiate (follicular cells)
Zona pellucida (glycoprotein shell)
What causes capacitation and acrosomal reaction?
Influx of Ca2+ and rise in cAMP in spermatozoa.
What is capacitation? How do sperm change?
• Further maturation of sperm in female reproductive tract (6 – 8 hours)
• Newly ejaculated spermatozoa cannot fertilise an oocyte until this has occurred – usually in the female genital tract but can be in vitro.
• Takes several hours
• Sperm cell membrane changes to allow fusion with oocyte cell surface
o Removal of glycoprotein coat
• Tail movement changes
o Beat → Whip-like action
• Sperm become responsive to signals from the oocyte
Describe the acrosome reaction.
• Capacitated sperm comes into contact with the oocyte zona pellucida
• Membranes fuse = Start of reaction
o Proteins on sperm head bind to ZP3 proteins on zona pellucida
• Acrosome swells and liberates its contents by exocytosis
• Proteolytic enzymes and further binding facilitate penetration of the zona pellucida by the sperm (takes about 15 minutes)
• Once sperm penetrates: fusion of plasma membrane of spermand egg
• Sperm moves in to cytoplasm: sperm and oocyte → zygote
• Polyspermy blocked (cortical reaction)
Site of fertilisation?
Ampulla of uterine tube
What happens following the penetration of a sperm into the cytoplasm of an ovum?
Nuclei fuse forming zygote.
Prevention of other sperm entering to ensure that the zygote contains diploid chromosomes.
What are the blocks to polyspermy?
Describe fast block to polyspermy
Electrical change in oocyte membrane
Na channels open
Wave of depolarisation at site of sperm entry, propagating along cytoplasm.
Describe slow block to polyspermy
Ca released from ER induces local exocytosis of cortical granules.
granules release enzymes to stimulate adjacent cortical granules to undergo exocytosis.
Wave of exocytosis occurs around oocyte in 2 dimensions front he origin site of sperm entry.
What is polyploidy?
EMbryo containing three or more pronuclei.
Entry of more than one sperm of failure of extrusion of second polar body.
What happens following fertilisation?
Zygote divides by mitosis in cleavage to form morula, which hollows to form blastocyst (trophoblast and epiblast).
Cleavage generates a large number of cells that can undergo differentiation and gastrulation.
Increase in nuclear:cytoplasmic ration,
It is gradually transported along the uterine tube.
Blastocyst is imbedded in endometrium in implatation.
Dependent in invasive property of trophoblast, which now has syncytiotrophoblast.