NOTES – UNIT 11 part 3: Fertilization and Birth heck!” NOTES – UNIT 11 part 3: Fertilization and Birth

Recall that the corpus luteum is secreting progesterone & estrogen Recall that the corpus luteum is secreting progesterone & estrogen. High levels of progesterone & estrogen inhibit secretion of FSH while the egg is traveling through oviduct (no new follicles can develop).

IF embryo does NOT implant in uterine lining by the end of this phase, a new menstrual flow phase begins Disintegration of the Corpus Luteum reduces progesterone & estrogen which reduces blood flow to the endometrium  the endometrium breaks down & passes out of the uterus IF embryo is present, embryo secretes HCG (hormone) which maintains the Corpus Luteum. Therefore, estrogen & progesterone continue to be secreted and the endometrium is maintained And estrogen & progesterone inhibit any more follicles while fetus develops

PREGNANCY TEST: looking for HCG in urine Control: to make sure the test stick is working

FERTILIZATION & IMPLANTATION ● most fertilization occurs in the oviduct ● cell division (mitosis) begins approx. 24 hours after conception ● after 3 days, embryo contains approx. 16 cells ● embryo reaches uterus approx. 7 days after fertilization & contains approx. 100 cells (BLASTOCYST)

FERTILIZATION & IMPLANTATION ● implantation of blastocyst occurs within next 5 days ● for the first 2-4 weeks, embryo obtains nutrients directly from endometrium (glycogen) ● in 2nd trimester, fetus secretes its own progesterone to maintain pregnancy -HCG maintained pregnancy early on by causing estrogen & progesterone secretion by Corpus Luteum

HUMAN GESTATION: 3 trimesters ● 1st trimester: organogenesis At 8 weeks, embryo is called a fetus 5 cm long by the end of trimester ● 2nd trimester: hormone levels stabilize & placenta takes over prog. production Uterus & fetus growing! Can feel fetal movements ● 3rd trimester: as fetus grows, activity decreases Mother’s abdominal organs become displaced Complex interplay of local regulators (prostaglandins) & hormones (estrogen & oxytocin) induces labor

BIRTH ● High estrogen levels during the last weeks of pregnancy trigger formation of oxytocin receptors in uterus ● Oxytocin secreted by fetus & posterior pituitary of mother stimulate smooth muscles of uterus to contract

BIRTH ● Oxytocin stimulates prostaglandin secretion by placenta which enhances muscle contraction of uterus (positive feedback) ● Decreased levels of progesterone after birth remove inhibition from anterior pituitary which allows for prolactin secretion

birth bookmark!

BIRTH ● PROLACTIN stimulates milk production after 2-3 days ● Oxytocin controls release of milk from MAMMARY GLANDS (positive feedback)

Dangerous if fallopian tube ruptures! Symptoms of an Ectopic Pregnancy: Light vaginal bleeding Nausea and vomiting Lower abdominal pain Sharp abdominal cramps Pain on one side of your body Dizziness or weakness Pain in your shoulder, neck, or rectum Will have a positive pregnancy test Dangerous if fallopian tube ruptures!