BIOLOGY 2D03 Study Guide - Ovulation, Estrogen, Uterine Contraction

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30 Jan 2013
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(1) Changes in Thermal Balance
Respiration + high growth rate increase heat
Heat excess transferred to cooler maternal blood by heat gradient
Mother loses this excess heat from her body
(2) Changes in Cardiac Output and Blood Volume and their Significance
High growth rate of fetus, placenta, maternal tissues (not just breast and uterus)
This increases O2 consumption/respiration
As maternal muscles have to work harder to move her increased size
Increases CARDIAC OUTPUT (= STROKE VOLUME x HEART RATE)
o Heart beats faster
o Increase in stroke volume
o Increase in cardiac muscle / heart chambers enlarge / output increases by 40%
Increase in maternal blood volume
o Changes in volume of plasma > increase in number of red blood cells
Birth
Fetus lies with its head down against stretched cervix
Weak contraction of uterus every ≈30min / increase in strength and frequency
Caused by hormone oxytoccin secreted by posterior pituitary gland
When cervix is fully dilated
Expulsion of baby by contractions of mother's abdominal muscles
o Umbilical cord shuts down, isolating baby from mother
o Rises CO2 content of the blood / stimulates baby's first breath
Expulsion of placenta → ≈30min after birth
o Pregnancy lasts ≈38 weeks from implantation, 40 weeks from last period
Hormonal Changes During And After Pregnancy
Human Chorionic Gonadotrophin hCG Hormone
Secreted by trophoblast and developing placenta
Maintains corpus luteum past the time it normally disintegrates
o Endometrium is maintained and menstruation does not occur
o Female sex hormones still at high level
Basis for pregnancy test → hCG can be detected in urine
Peak in bloodstream after ≈2months followed by a slow decline
Progesterone and Oestrogen
Secreted by corpus luteum for first 3 months
Maintain endometrium, development of uterus, prevent menstruation
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