Conception and contraception Flashcards
List the main constituents of semen and their origins
around 2-4ml of ejaculate on average
TESTES: 20-200 x10^6 sperm per ml. 60% must be swimming forward vigorously, no more than 30% abnormal.
SEMINAL VESICLES: makes up 60% of ejaculate. Alkaline solution to neutralise vaginal and urethral acidity. Contains fructose, prostaglandins and clotting factors.
PROSTATE: 25% volume, contains proteolytic enzymes, citrate and phosphatase to liquefy semen.
BULBOURETHRAL GLAND: Alkaline mucous secretions to lubricate male urethra
Describe the physiological processes involved in emission
Emission is the movement of ejaculate into the prostatic urethra before ejaculation. This mixes all elements of the semen and occurs through peristalsis of the vas def and secretions from the seminal vesicles.
Describe the physiological processes involved in the erection of the penis
- Psychogenic stimuli
- Tactile stimuli (through spinal reflexes)
both communicated through somatic and autonomic, pelvic nerve and pudendal nerve efferents. This causes haemodynamic changes, i.e. increased BP.
- inhibition of sympathetic vasoconstrictor nerves
- stimulation of parasympathetic nervous system through pelvic nerve
- Release of ACh binds to M3 epithelial receptors
- Increases intracellular calcium
- this activates Nitric Oxide Synthase ergo NO
- induces vasodilation and lessactin-myosin cross bridges formed due to NO increasing Ca uptake.
- CORPA CAVERNOSA dilates and fills
- CORPUS SPONGIOSUM dilates a little, protects urethra
- BULBOSPONGIOUSUS AND ISCHICAVERNOSUS muscles contract to stop the return of venous blood.
List the main causes of erectile dysfunction and the mechanism of action for viagra
- psychological - descending spinal reflex inhibition
- tears in fibrous corpa cavernosa
- vascular (most common)
- NO blockers (ETOH, antihypertensives, DM)
- Viagra inhibits the breakdown of cGMP. This keeps calcium levels low and smooth muscle relaxed, maintaining erections.
Describe the physiological changes in the female which facilitate coitus
- vaginal lubrication
- swelling and engorgement of external genitalia
- internal enlargement of vagina
- cervical mucus (oestrogen - clear, non-viscous)
Describe the mechanism of ejaculation
- Spinal reflex under sympathetic control (L1 and L2)
1. Contraction of glands and ducts (smooth muscle)
2. Bladder internal sphincter contracts
3. Rhythmic striated muscle contraction (S2-S4). This includes ischicavernosus, bulbospongiosus, hip and anal muscles.
Describe the process involved in sperm transport through the cervix and uterus
- immediately after ejaculation semen clots due to fibrinogen. This minimises loss of semen from vagina.
- 10-20 mins later, it reliquifies due to prostatic secretions
- most sperm lost from vagina, some make the 15-20cm journey to fallopian tubes and ampulla
- transport is through sperm propulsion and ciliated epithelia fluid currents.
Describe the capacitation of sperm and the acrosomal reaction
- both induced by influx of Ca into spermatozoa and subsequently an increase in cAMP
- capacitation: removal of glycoprotein coat and tail starts to whip instead of beat. Stronger oocyte signal
- acrosome reaction: sperm fuses with zona pellucida, membranes fuse, exocytoses contents, penetrates zona pellucida.
Describe the processes involved in fertilisation of the ovum
- secondary oocyte (completed meiosis 1) released from ovum in gelatinous matrix
- picked up by fimbrae of fallopian tubes
- fertilisation in ampulla
- cilia move zygote/ morula/ blastocyst to uterus
- implants into endometrium around day 5-6
Describe the main methods of contraception, their advantages and disadvantages
- Natural; either abstinence or coitus interruptus. However, there can still be sperm in the preejaculate
- Vasectomy; prevents sperm in ejaculate. Must wait a few months for vas defs to empty of sperm
- Barrier methods; prevents sperm reaching cervix and protects against STIs. Condoms, diaphragm, cap. Only condom is complete barrier.
- Hormonal; progesterone. Decreases GnRH pulses preventing follicular development and forms a thick mucus plug. Prevents sperm entering cervix.
- Oestrogen: increase negative feedback, no LH surge, no ovulation.
What are the general types of hormonal contraceptive pills?
- combined; progesterone and oestrogen
- progesterone only pill (POP)
- depot progesterone
- progesterone implants
- intrauterine contraceptive; inert copper, prevents implantation and endometrial enzymes; progesterone impregnation
- Post coitus: combined or high dose progesterone.
