Lecture 9: Fertilization and implantation Flashcards
What are the two tissue types of the Cervix?
Endocervix:
Columnar epithelium (cont w endometrium)
Glands, crypts (storage sites for sperm),
Fibrous stroma, a few smooth muscle cells
- *Ectocervix**
- Stratified squamous (flattened) epithelium*
These join in the space on 1 cell!
How does the cervical mucous change every cycle?
You will see changes due to a change in hormonal profile of E2 and P4 in:
- Volume
- Viscosity
- Threadability (spinnbarkeit): in the fertile window (ovulation, this occurs
How does E2 and P4 change the cervical mucous each cycle?
E2: increases volume, decreases viscosity (clear, watery mucous), and inceases threadability. Makes mucous receptive to sperm, and contains channels for sperm access.
P4: Stimulates a highly viscous and cross-linked mucous that is a barrier to sperm penetration.
Test putting mucous in a capillary tube, and testing how far through sperm can get. Shows lots of movement only with high estrogen (ovulation!!)
Stage 1) Meiosis in a female
Following LH surge, meiosis is resumed (also causes oocyte released) and the first reductive division is complete. (2n → n + polar body)
Process stops again at second metaphase.
Thus at ovulation, the egg consists of the oocyte and a small polar body (not used by oocyte) surrounded by the Zona Pellucida.
(Polar body retained in the ZP)
Meiosis is resumed for the second divison, at ovulation
How does cervical mucous ‘pick the best sperm’?
The tails of normal sperm cause cervical mucous fibres the vibrate in rhythm, ‘in cadence’ allowing them to break through.
(think of movement on a bridge)
Failure of normal sperm to induce this vibration → stops progress.
Abnormal sperm can’t get through!
What happens to the sperm once ejaculated?
Leaves male reproductive tract bathed in seminal plasma
- As the prostatic and seminal vesicle fluids mix for the 1st time (in the vagina), a coagulum is formed that:
- Holds the ejaculate together
- Adheres the ejaculate to the female reproductive tract during/after coitus
- Within 2-15min after vaginal insemination; “liquefaction” occurs and the sperm can begin their quest for an egg
Where does fertilisation usually occur?
Near the isthmus/ampulla junction.
If only one sperm fertilises an egg, what happes to the rest of the sperm?
Sperm in the uterus induces an innate immune response.
You get an infilitration of leucocytes (leucocytosis), which phagocytose dead/dying sperm.
There’s an idea this could be an adaptation where mum can see what dad looks like?
What is sperm liqufaction?
Breakdown of coagulated ejaculate 2-15min post insemination, dispersing the coagulum and therefore allow sperm to find an egg
How does the pH of the vagina affect sperm?
Vaginal pH: ~4.7 (3.5-7.4)
This pH is inhibitory to sperm motility and survival
Seminal plasma buffers the vaginal pH to around 7.2, allowing sperm to be motile.
What’s the acrosome reaction?
Fusion of the sperm heads acrosomal and plasma membranes.
This allows release of the acrosomal contents (help breakdown of egg exterior) to the environment around the sperm.
Trigger: an influx of calcium into the cell.
- Ca2+ influx is triggered by several factors, eg; progesterone or ZP3
Location: the acrosomal reaction must occur ein close proximity to the oocyte for natural fertilisation. Usually around 10% spontaneously undergo reaction distally → infertile sperm
How long do sperm survive, and how does that effect transport?
Survival Times:
- Vagina: 2.5h (due to acidic environment)
- Cervix: 48h (stored/released from crypts)
- Uterus: 24h
- Oviduct: 48h
Overal: 48+ hours post coitus. After this, sperm will usually die
Note: clinical advice to people AVOIDING getting pregnant say ~5days (just in case), ask them to work back from menstruation, but as this hasn’t happened yet its very hard!
What happens if sperm get to the fallopian tubes prior to ovulation?
Their rate of tail beating slows and they wait in the narrow isthmus of the tube.
At ovulation sperm move up to the egg and stored sperm may be released from cervical crypts
What is capacitation?
A series of events, occuring in the female reproductive tract, to allow sperm to be mobile
Freshly ejaculated sperm are not capable of fertilising an ovum!
Only capacitated sperm can undergo the acrosome reaction
Involves:
- Removal of capacitation inhibitory substances from sperm
- Loss of cholesterol from sperm membrane.
- Induces hyperactivtion of sperm.
Capacitated sperm are said to be ‘hyperactive’. WHat does this mean and what can they now do?
- Tail movement changes with increased bending of tail and swinging of the head “ thrashing”
- Facilitates movement of sperm through tortuous folds of the fallopian tube!! (instead of get stuck
