Session 5 - Sex And Fertilisation Flashcards
What is the most common site of fertilisation?
Ampulla of uterine tube
What are the phases of the human sexual response?
Excitement phase
Plateau phase
Orgasm phase
Resolution phase (refractory period in men)
What are the stimulants for erection?
Psychogenic
Tactile (sensory afferent of penis and perineum)
Which nerves carry the efferent response in erection?
Pelvic nerve (parasympathetic) Pudendal nerve (somatic)
What must happen to the blood vessels of the corpus cavernosum on order for an erection to occur?
Sinusoidal relaxation (push against tunica albuginea) Arterial dilation (increase blood entering penis) Venous compression (reduce blood leaving the penis)
Which nerves carry parasympathetic innervation to the penis?
Pelvic nerve and pelvic plexus Cavernous nerve (to corpora and vasculature)
What is the role of NO in erection?
NO (released from parasympathetic nerves and endothelial cells) diffuses into vascular smooth muscle and causes relaxation (vasodilation).
What are some possible causes of erectile dysfunction?
Psychological (descending inhibition of spinal reflexes)
Tears in the fibrous tissue of the corpora cavernosa
Vascular problems (arterial and venous)
Drugs
What is emission?
Movement of sperm into the prostatic urethra.
Contraction of smooth muscle in prostate, vas deferens and seminal vesicles.
What is ejaculation?
Expulsion of semen
Are emission and ejaculation under sympathetic or parasympathetic control?
Sympathetic
During ejaculation, why does the bladder’s internal sphincter contract?
To stop retrograde ejaculation
How does the character of cervical mucus change over the course of the menstrual cycle?
At time of ovulation —> high oestrogen:
- mucus is thin, stretchy. Allows sperm to enter.
After ovulation —> high oestrogen and progesterone:
- mucus is thick, sticky, forms a plug. Limits access of sperm.
What is the site of sperm deposition?
Just outside the cervix
What is capacitation?
The further maturation of sperm that occurs in the female reproductive tract.
What happens to the sperm during capacitation?
Sperm cell membrane changes to allow fusion with oocyte.
Tail movement changes from beat-like to whip-like action.
Sperm is now capable of undergoing the acrosome reaction.
How long are oocytes and spermatozoa viable for, and therefore how long is the fertile window?
Spermatozoa: 48-72 hours
Oocytes: 6-24 hours
Fertile period: sperm deposition up to 3 days prior to ovulation or on day of ovulation
What is the acrosome reaction?
Release of enzymes from the acrosome of the sperm which digest the zona pelucida, allowing the two gametes to then fuse.
What is the function of the cortical reaction?
Blocks polyspermy (only allows one sperm to fertilise the oocyte)
What happens following fusion of the oocyte and sperm membranes?
Resumption of meiosis II
Pronuclei move together
Mitotic spindle forms leading to cleavage
Divides to form morula
What type of stem cells are found in the morula?
Totipotent stem cells
What happens in in vitro fertilisation?
Oocytes are fertilised in vitro and allowed to divide to the 4 or 8 cell stage (morula stage).
The morula is then transferred into the uterus.
What happens in Pre-implantation Genetic Diagnosis?
A single cell is taken from the morula and tested for serious hereditary conditions prior to transfer of the embryo into the mother.
Differentiation of inner and outer cell masses of the morula produces what?
Blastocyst
What happens in blastocyst hatching?
The blastocyst hatches from the zona pelucida.
This means it is no longer constrained and is free to enlarge.
The blastocyst can also now implant in the uterine wall.
What happens in implantation?
The outer cell mass (trophoblast) interacts with the endometrium. The endometrium controls the degree of invasion.
What is ectopic implantation?
Implantation of the blastocysts at sites other than the endometrium lined uterine cavity. Invasion at these sites is not controlled because there is no endometrium to control it.
Implantation in the lower uterine segment can cause what?
Placenta praevia
What is placenta praevia?
When the placenta is unusually low lying in the uterus, next to or covering the cervix.
