Coitus and conception Flashcards
What are the two stimulants of erection?
- Psychogenic
- Tactile
What is emission?
Movement of ejaculate into the prostatic urethra before ejaculation by peristalsis of vas deferens
What are the efferent so involved in erection?
- Pelvic nerve (PNS)
- Pudendal nerve (somatic)
What haemodynamic changes occur in erection?
- Inhibition of sympathetic arterial vasoconstrictor nerves
- Activation of PNS
- Activation of non-adrenergic, non-cholinergic nerves to arteries releasing NO
- Central arteries of corpus cavernosa straighten and dilate
- Bulbospongiosus and ischocavernosus compress veins
What does the PNS do to promote erection?
- Acts via pelvic nerve
- ACh binds to M3 receptors
- Rise in Ca concentration activates NOS
- NO increases
- NO diffuses into VSMC causing relaxation and thus vasodilation
How does NO cause vasodilation?
- Increases cGMP
- Ca moves into Intracellular stores, reducing its concentration
- Reduced actin-myosin cross bridges
- Relaxation of smooth muscle
What happens when central arteries of corpus cavernosa straighten and dilate?
Blood flows into and dilates the cavernous spaces
Why does corpus sponsiosum not dilate as much?
Do not want to compress urethra
How does the action of Bulbospongiosus and ischocavernosus help maintain erection?
- Compression of veins
- Corpra cavernosa become engorged with high blood pressure
- Erectile bodies become turgid
What are the causes of erectile dysfunction?
- Psychological
- Tears in fibrous tissue do corpus cavernosa
- Vascular pathology
- Factors blocking NO
What factors can block NO?
- Alcohol
- Anti-hypertensives
- Diabetes
How does Viagra work?
Inhibits the breakdown of cGMP
What nerve roots control ejaculation?
L1&2 SNS
What happens for ejaculation to occur?
- Contraction of glands and ducts
- Bladder and internal sphincter contract
- Rhythmic striated muscle contractions (pelvic floor, perineum, hip and anal muscles)
Why does the internal urethral sphincter contact in ejaculation?
To prevent retrograde ejaculation
What is the normal volume of ejaculate?
2-4 ml
What is the volume of sperm present in semen?
20-200 x10^6 per ml
How much do the seminal vesicles contribute to semen volume?
60%
What is present in secretion from the seminal vesicles?
- Alkaline fluid
- Fructose
- Prostaglandins
- Clotting factors
What is present in secretion from the prostate?
- Proteolytic enzymes
- Citric acid
How much does secretions from the prostate contribute to semen volume?
25%
What does the Bulbourethral gland do?
Secretes a small amount of alkaline fluid to lubricate the end of the penis and urethral lining prior to ejaculation
Why does semen coagulate immediately after ejaculation?
Prevents sperm being lost from the vagina
What causes semen to coagulate immediately after ejaculation?
Clotting factors
What causes semen to re-liquify?
Proteolytic enzymes
How long after ejaculation does semen re-liquify?
10-20 mins
What allows sperm to move?
- Own propulsive capacity
- Current caused by action of ciliated cells in uterine tract
Describe the process of capacitation.
- Further maturation of sperm
- Removal of glycoprotein coat allows fusion with oocytes
- Change in tail movement from beat to whip-like action
- Sperm become responsive to signals from oocyte
Describe the acrosomal reaction.
- Capacitated sperm makes contacts with oocyte zona pellucida
- Membranes fuse (this is the start of the reaction)
- Acrosome swells and liberates its contents by exocytosis
- Penetration of zona pellucida due to proteolytic enzymes and further binding
What physiological changes occur in the female?
- Vaginal lubrication
- Internal enlargement of vagina
- Swelling and engorgement of external genitalia
- Cervical mucus production
What type of mucus is secreted in the presence of oestrogen only?
Clear, non-viscous mucus
What type of mucus is secreted in presence of oestrogen and progesterone?
Thick, sticky mucus plug
When does meiosis I occur? (Primary oocyte)
At ovulation
What does meiosis I produce?
- Secondary oocyte
- First polar body
When does meiosis II occur? (Secondary oocyte)
At fertilisation
What does meiosis II produce?
- Second polar body
- Ootid ➡️ Ovum
Where does fertilisation usually occur?
Ampulla
What is an ectopic pregnancy?
Implantation of conceptus in any place other than uterine wall
Why does ectopic pregnancy occur?
Failure to transport egg
What are the sites of implantation in an ectopic pregnancy?
- Uterine tube
- Ovary
- Abdomen
What are the risks of an ectopic pregnancy?
Severe maternal haemorrhage
