Menstrual Cycle and Fertilization

MC - FOLLICULAR PHASE Low levels of hormones as lining of uterus (endometrium) is shed Increase in FSH stimulates primary follicle to develop Growing follicle releases increasing estrogen, inhibits FSH release Estrogen develops the endometrium and, at its peak (critical level), releases LH from the pituitary LH releases egg from follicle (ovulation), follicle becomes corpus luteum

Ovulation This is the point when the egg can be fertilized by sperm. If the egg is NOT fertilized, the menstrual cycle will continue through the luteal phase (next slide) If the egg IS fertilized and implants in the uterus, a pregnancy will begin.

MC - LUTEAL STAGE Due to LH, corpus luteum releases more progesterone and some estrogen Progesterone maintains endometrium and thickens it for embryo Progesterone inhibits FSH and LH IF no embryo, corpus luteum breaks down, decreasing estrogen and progesterone  Endometrium is shed, low progesterone allows FSH release, follicle develops, cycle repeats

Menstrual cycle: continues until pregnancy or menopause Fertilization occurs in the fallopian tube (oviduct). Only a small percentage of sperm will reach the egg.

Menstrual cycle review What is happening in the ovary and the uterus at each stage? 3 2 1 4 5

Menstrual Cycle review Which hormones cause these changes? How are their levels changing? 4 1 3 2

In vitro fertilization 3 weeks of hormone injections stop the menstrual cycle High levels of FSH injected for 1.5 weeks to stimulate MANY follicles HCG (similar in structure to LH) is injected to cause ovulation The next day eggs are collected with a special tool and the father-to-be provides sperm The eggs are collected and combined with the sperm in a dish The eggs are incubated overnight and checked for fertilization Embryos are selected for health and implanted into the uterus

For IVF Against Allows childless couples to have (genetic) children, prevents suffering and sadness Allows genetic screening to prevent genetic disease Women who can’t be pregnant (organs removed due to disease / accident) can have genetic children through a surrogate Usually more embryos are created than can be used, these “potential people” will never develop (stored, used in research, or allowed to die) Embryos are selected, which some consider wrong on any grounds High risk of multiple births; health risks for fetuses Inherited fertility problems are passed on Expensive, not available to all