10-03-23 - Coitus, Fertilisation and Preimplantation Flashcards
Learning outcomes
- Describe the male and female sex response
- Explain the mechanisms responsible for penile tumescence and ejaculation
- Explain the events that occur to ensure that male and female gametes arrive at the site of fertilisation
- Describe the process of fertilisation and the changes that must occur in the gametes for fertilisation to be sucessfully completed
- Describe the preimplantation stages of embryonic development
- Explain the fate of trophoblast cells and the inner cell mass of the blastocyst
What are 4 parts of the male human sexual response (Masters & Johnson 1966)?
- 4 parts of the male human sexual response (Masters & Johnson 1966):
1) Excitement
* Psychological and physical stimulation of erogenous zones
* Tumescence and erection of penis
* Effect due to stimulation of parasympathetic NS
* Relaxation of smooth muscle of corpora cavernosa, corpus spongiosum allows inflow of blood resulting in increase in volume and rigidity
2) Plateau (Emission)
* Refers to movement of the ejaculate into the prostatic or proximal part of the urethra
* Primarily under sympathetic NS control
* Spinal reflex - forceful expulsion of semen from the urethra
* Reflex reaction triggered by the entry of semen from the prostatic urethra into the bulbous urethra
3) Orgasm (Ejaculation)
* Release of tension
* Generalized, rhythmic contraction of the pelvic floor, ischiocavernosus and bulbospongiosus muscles
* Spasmodic contractions of muscles of the hips and the anal sphincter
4) Resolution
* Return to pre-excitement state, Personal satisfaction and well-being
* Refractory period
How do erections occur?
- Erections occur when the corpus cavernosum receives sympathetic signalling, leading to blood flow to the penis
Innervation of Male and Female Reproductive Organs.
What are 3 ways arousal can be produced?
Where does sympathetic supply to the reproductive organs come from?
What nerves are they?
What 6 nerve plexuses does the sympathetic supply to the reproductive organs move through?
Where does parasympathetic supply to the reproductive organs come from?
Where does somatic supply to the reproductive organs come from?
- Innervation of Male and Female Reproductive Organs
- 3 ways arousal can be produced:
1) Erotic psychological stimuli (e.g. visual, olfactory)
2) Tactile stimuli at the level of the brain
3) Tactile stimuli can also mediate local spinal reflexes - Sympathetic (SN) to the reproductive organs:
- Lower thoracic and lumbar spinal segments – Hypogastric nerve, pelvic plexus, cavernous nerve
- Maintains flaccidity
- 6 nerve plexuses does the sympathetic supply to the reproductive organs move through:
1) Celiac
2) Superior mesenteric
3) Inferior (most nerves) mesenteric,
4) Superior hypogastric
5) Inferior hypogastric
6) Pelvic - Parasympathetic supply (PSN) to the reproductive organs:
- Control centre in sacral spinal segments – Pelvic nerve, pelvic plexus, cavernous nerve
- Parasympathetic stimulation leads to increased turgidity
- Somatic supply to the reproductive organs:
- Pudendal nerve
- Contraction of ischiocavernosus muscle
- Increases engorgement of corpus spongiosum
Tumescence (erection) of the Penis. Where is the erection centre?
What does the erection centre mediate?
What are the 4 parts of the erection reflex?
- Tumescence (erection) of the Penis
- The erection centre is in the sacral spinal cord (parasympathetic)
- The erection centre mediates the erection reflex
- 4 parts of the erection reflex:
1) Haemodynamic changes – involves corpus cavernosum (corpora cavernosa) – sinuses along most of the length of the penis
2) Dilatation (PS) of arterioles to – Corpus cavernosa and – Corpus Spongiosum
3) Closing of arteriovenous shunts that normally bypass the c. cavernosa
4) Probably also occlusion of veins draining the penis
What are 5 reasons for failure to obtain an erection?
- 5 reasons for failure to obtain an erection:
1) Mechanical damage to the c. cavernosa
2) Obstruction of the arteries to the penis
3) Drugs that block parasympathetic actions
4) Psychological factors
5) Stress associated with high sympathetic activity - NA causes vasoconstriction of penile arterioles and so inhibits erection
Parasympathetic Relaxation of Vascular Smooth Muscle.
What does parasympathetic action in the corpus carvernosum involve?
What effect does ACh have here?
What does NO then do?
How do medications such as Viagra affect this pathway?
What is alprostadil?
In what 2 forms is it available as?
- Parasympathetic Relaxation of Vascular Smooth Muscle
- Parasympathetic action in the corpus cavernosum involves ACh acting on vascular endothelial cells
- ACh binds to M3 muscarinic receptors via Gαq these receptors lead to stimulation of PLC, increased [Ca 2+ ]i and activation of NO synthase and local release of NO
- NO causes relaxation of vascular smooth muscle, resulting in vasodilation which allows for more blood to come in, leading to erection
- Medications such as Viagra (sildenafil) act as a phosphodiesterase inhibitor V, meaning cGMP won’t be converted to an inactive product in the pathway
- Alprostadil is a synthetic (man-made) hormone that helps to stimulate blood flow to the penis
- Alprostadil is available as:
1) An injection directly into your penis – this is called an intracavernosal injection
2) A small pellet placed inside your urethra (the tube that carries urine from your bladder to the tip of your penis) – this is called urethral application
What are 4 parts of the female human sexual response (Masters & Johnson 1966)?
- 4 parts of the female human sexual response (Masters & Johnson 1966):
1) Excitement (Seduction)
* Psychological and physical stimulation of erogenous zones
* Tumescence and erection of clitoris, engorgement of female tract
* Effects due to stimulation of parasympathetic NS
2) Plateau
* Marked vasocongestion
* “Sex flush” (maculopapular rash on breasts, chest, and epigastrium)
* Engorgement of the labia, Engorgement of lower third of the vagina, with narrowing of diameter, Dilation of upper two thirds of vagina
* Clitoral swelling and erection
3) Orgasm
* Release of tension
* Generalized, rhythmic myotonic contractions of perivaginal muscles, anal sphincter & Uterus
4) Resolution
* Return to pre-excitement state, Personal satisfaction and well-being
* New excitement cycles may be initiated
Which phases of menstrual cycle are fixed/varying?
How long is the luteal phase?
- Menstrual cycle phases:
- Length of luteal phase is fixed at approximately 14 days
- It is the follicular phase that varies
- Menstrual phase varies
How long are sperm viable?
How long are oocytes viable?
When must coitus occur for successful fertilisation?
- Sperm are viable for 24 - 72 hours
- Oocytes are viable for 12 - 24 hours
- For successful fertilisation, coitus must occur no more than 3 days before ovulation and no more than 1 day after ovulation
How long is the embryonic period?
What are the 3 stages in the embryonic period?
Why might this period be problematic for the mother?
How long is the foetal period?
What are 2 stages in the foetal period?
- 3 stages in the embryonic period (8 weeks):
1) Preimplantation embryo
2) Implantation
3) Differentiation & development of the organ systems - The mother may not know she is pregnant during this sensitive period, and so may not avoid harmful influences that may affect development of embryo (alcohol, tobacco, prescription drugs)
- Foetal period (8 - 40 weeks):
1) Differentiation continues
2) Growth
Describe the 5 steps in the transport of the ovum
- 5 steps in the transport of the ovum:
1) At ovulation - egg extruded onto surface of ovary
2) Fimbriae sweep over ovary surface and pick up ovum
3) Sticky cumulus cells cling to the ciliated surface of the fimbriae
4) Movement of cilia and smooth muscle of fallopian tube propel ovum to uterus
5) Ovum transported by ciliary current to ampulla of fallopian tube
When do most mammals mate?
How do many female mammals signal ovulation?
Why is this hidden in humans?
What is a suggestion for the development of sexual behaviour?
- Most mammals only mate when the female is ovulating.
- Many female mammals signal their ovulation by oestrous behaviour ‘heat’ (hence oestrous cycle).
- Human ovulation however is ‘hidden’ as females are receptive to males throughout their menstrual cycle.
- There is a suggestion that human sexual behaviour has developed as a way to strengthening pair bonding to support the long development of human children
What are 5 reasons for failure to obtain an erection?
- 5 reasons for failure to obtain an erection:
1) Mechanical damage to the c. cavernosa
2) Obstruction of the arteries to the penis
3) Drugs that block parasympathetic actions
4) Psychological factors
5) Stress associated with high sympathetic activity - NA causes vasoconstriction of penile arterioles and so inhibits erection
