Coitus and Conception Flashcards
Define sexual reproduction.
Formation of a unique individual from the gametes (spermatozoon and oocyte) of two other individuals
How long does it take spermatogonia to mature into spermatozoa?
Up to 74 days
50 in seminiferous, 12-26 in epididymis
What are the rates of sperm production?
1000 spermatozoa per second
20 yo - 6.5m/g/day
over 50 yo - 3.8m/g/day
What are the phases of coitus?
Excitement phase
Plateau phase
Orgasmic phase
Resolution phase (+/- refractory period)
What is the female sexual response?
Blood engorgement and erection: - Clitoris, vaginal mucosa, breast and nipples Glandular activity Sexual excitement (as in male) \+/- orgasm (not needed for reproduction) No physiological refractory period
What are the mechanisms of penile erection? ( The start)
Stimulants
- Psychogenic
- Tactile (sensory afferents of penis and perineum)
Which leads to (a spinal reflex for tactile)
Efferents
- Somatic and autonomic efferents
- Pelvic nerve (PNS)
- Pudendal nerve (somatic)
And this leads to haemodynamic changes
What are the haemodynamic changes that occur as part of a penile erection?
The arteries of the corpora cavernosa needs to vasodilate
Intracellular calcium in the smooth muscle of these arteries must reduce
Inhibition of sympathetic arterial vasoconstrictor nerves
Activation of PNS
Activation of non-adrenergic, non-cholinergic, autonomic nerves to arteries, releasing NO (Nitric Oxide)
These haemodynamic changes cause tumescence
How does nitric oxide work in relation to haemodynamic changes in penile tissue to cause tumescence?
Post-ganglionic PNS release ACh
ACh bonds to M3 receptor on endothelial cells
A rise in [Ca2+]intracellular, activation of NOS and formation of NO
NO diffuses into vascular smooth muscle and causes relaxation (vasodilation)
NO also directly released from nerves
What are the main categories of causes of erectile dysfunction?
Psychological (descending inhibition of spinal reflexes)
Tears in fibrous tissue of corpora cavernosa
Vascular (arterial and venous)
Drugs
Factors blocking NO:
- Alcohol, ant-hypertensives, diabetes
Describe emission in reference to male sexual response.
Movement of ejaculate into prostatic urethra (leakage)
Vas deferens peristalsis
Accessory gland secretion; e.g., bulbourethral
Describe the mechanism of ejaculation.
Spinal (& cerebral) reflex
Sympathetic nervous system control (L1, L2)
- Contraction of glands and ducts (smooth muscle)
- Bladder internal sphincter contracts
- Rhythmic striatal muscle contraction (pelvic floor, Ischiocavernosus, Bulbospongiosus, hip and anal muscles)
Describe the normal contents of ejaculate.
2-4ml 20-200 x 10/\6 sperm per ml Total sperm/ejaculate >40 x 10/\6 >60% sperm swimming forward vigorously ,30% abnormal morphology
What is classed as low sperm count, and what is it called?
Abnormal oligozoospermia
What are the glandular components of semen?
Seminal vesicles:
- 60% of volume
- Alkaline fluid (neutralizes the acid: male urethra, female
reproductive)
- Fructose, prostaglandins, clotting factors
Prostate
- 25% volume
- Milky, slightly acidic fluid
- Proteolytic enzymes (break down clotting proteins, re-
liquefying semen in 10-20 minutes)
- Citric acid, acid phosphatase
Bulbourethral glands (Cowper's gland) - Very small volume - Alkaline fluid - A mucous that lubricates the end of the penis and urethral lining
Where is semen deposited?
Just before the cervix
How does the oestrogen and progesterone levels affect the mucosa of the cervix?
When just oestrogen, no progesterone:
- Abundant clear, non viscous mucus
When both progesterone and oestrogen:
- Thick, sticky mucous plug.
Where is the site of fertilization?
The ampulla of the fallopian tube.
How does sperm change once deposited in the vagina?
Capacitation of sperm
Further maturation of sperm in female reproductive tract (6-8 hours)
Sperm cell membrane changes to allow fusion with oocyte cell surface
Tail movement changes from beat to whip-like action (3mm/hour)
Tell me a little about the amount of sperm involved in coitus.
200-300 million per ejaculation.
300 reach fertilisation site
1 sperm required for fertilization but
299+ needed to disperse the zona pellucida
What is the survival time of fertile gametes in female reproductive tract.
Spermatozoa - 48-72 hr (?)
Oocytes - 6-24 hr (max)
Fertile period:
- Sperm deposition up to 3 days prior to ovulation or day
of ovulation
How is an oocyte transported?
Beating cilia
Peristalsis of fallopian tube
Give an overview of fertilization.
Occurs at ampulla of Fallopian tubes
Requires loss of sperm outer shell (acrosome)
Penetration of ovum membrane, fusion of ova and sperm membrane
Eventual formation and fusion of pronuclei
Describe fertilization in some detail.
Sperm pushes through granulosa cells
Protein on sperm binds to ZP3 proteins of zona pellucida
Binding triggers acrosome reaction:
- Acrosome enzymes exposed to zona pellucida
- Hydrolysing enzymes digest through ZP
- One sperm penetrates: fusion of plasma membranes
(egg and sperm)
- Sperm moves into cytoplasm: zygote
- Polyspermy blocked (cortical reaction) (stops zona
pellucida from allowing any more sperm in)
Egg completes meiosis II
Pronuclei (2 sets of chromosomes)
Pronuclei fusion (diploid zygote)
Mitosis
What is cleavage in reference to fertilization?
Series of metabolic changes and rapid mitotic division (cleavage)
Increased number of cells 16 - 32 without growth
Totipotency
Describe conceptus in the uterine tube.
3 days, awaiting rise in progesterone (smooth muscle relaxation)
period of cell division to blastocyst stage
Blastocyst
- Loss of Totipotency
- Outer layer (trophobast surrounds embryo)
- Inner cell mass (becomes surrounds embryo)
- Fluid filled cavity
When and where does the blastocyst implant?
6 days
Endometrium of uterus
What is an ectopic pregnancy?
When there is a failure to transport the egg
Embeds in uterine tube, ovary or abdomen
Embryo dies
Severe risk of maternal haemorrhage
Describe what happens to the conceptus in the uterus
Zygote to blastocyst: days 14 to 21 of uterine cycle Progesterone priming of endometrium Conceptus nourished in intrauterine fluid, 3 days floating Sticky trophoblasts over inner cell mass, adheres to endometrium (hCG) Implantation commences (6 days after ovulation)
