PHGY 210 Lecture Notes - Lecture 9: Menstrual Cycle, Osteoporosis, Growth Hormone

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20 Jul 2016
o!Egg starts dividing to the stage of blastocyst during its transport
down the oviduct into the uterine lumen. %
!After Implantation%
o!Blastocyst differentiates into trophoblast (becomes the placenta) and
the inner cell mass (which will form the embryo). Trophoblast
invades uterine mucosa -> embedding of developing embryo in endometrium.%
o!Around time of implantation, trophoblast starts to synthesize human chorionic gonadotropin
(HCG) which has LH-like properties and stimulates the corpus luteum to continue secreting
gonadal steroids. After about 12th week of pregnancy endocrine function of corpus luteum taken
over entirely by placenta, which together with developing fetus forms the fetoplacental unit.%
o!Close functional interdependence between the fetal and maternal compartments, and fetal liver
acquires an important function in the synthesis of estriol (an estrogen).%
o!Placenta also produces human chorionic somatotropin, progesterone, and relaxin. %
!HCG quickly appears in blood and urine where it forms the basis for the biological or immunological
pregnancy test%
o!The secretion of milk by the breast (mammary glands) is termed lactation. Normal mammary
development required for lactation - under endocrine control.%
!Mature non-pregnant mammary glands (Ductal)%
o!With onset of puberty under the action of increasing levels of estrogens, marked enhancement of
duct growth and duct branching but relatively little development of the alveoli.%
o!Progesterone stimulates growth of alveoli.%
o!However, most breast enlargement due to fat deposition under the glandular tissue. %
!pregnant mammary glands (lobulo alveolar)%
o!Under influence of several hormones, including estrogen,
progesterone, prolactin, human placental lactogen, both ductal
and alveoli structures fully develop. Milk production during
pregnancy controlled by prolactin, however high estrogen levels
inhibit secretion. %
!Lactating mammary glands- After parturition, levels of estrogen
decrease, while levels of prolactin remain high. Prolactin induces milk
synthesis and the alveoli secrete milk, filling the ducts. %
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