Mammalian reproduction control by Hormones Flashcards
wall of uterus (from external to internal)
perimetric, myometrium, endometrium
endometrium
Varies with the menstrual cycle
cervix
an extra-thick layer of muscle at the bottom of the uterus to hold the opening closed
uterine horns
present in mammals that have litters. They will have implantation all along the uterine horn.
corpus luteum
forms from the follicle cells that reorganize after the oocyte is ejected from the ovary. Corpus luteum secretes estrogen and progesterone. When the corpus luteum breaks down, estrogen and progesterone are not being secreted anymore. Progesterone maintains wall of uterus, so when the corpus luteum breaks down, the uterine wall begins to slough off –> period.
follicle cells
Grow around oocyte and secrete estrogen
corpus albicans
forms from the corpus luteum breaking down. Corpus albicans is scar tissue. When corpus luteum breaks down to corpus albicans, it stops producing estrogen and progesterone.
pituitary gland
secretes LH and FSH
LH
luteinizing hormone - secreted by pituitary. Spike in LH causes ovulation.
FSH
follicle stimulating hormone - secreted by pituitary. Tells primary follicles to grow. As follicle cells grow, they secrete more estrogen, which causes the thickening of the endometrium.
LH and FSH affects on menstrual cycle
FSH causes follicle cells to develop. LH causes ovulation.
follicular phase
the phase of the menstrual cycle when the follicle is developing. More estrogen is produced than progesterone during this phase.
ovulation
marks the end of follicular phase and beginning of luteal phase. Caused by spike in LH.
luteal phase
controlled by actions of corpus luteum. At the beginning of this phase, estrogen dips while follicle cells are reoraganizing. Then estrogen and progesterone are produced by corpus luteum.
estrogen
responsible for preparing wall of the uterus; cell division, vascularization
progesterone
maintains wall uterus. The fall of progesterone when corpus luteum becomes corpus albicans signals the uterine wall to start sloughing off - period ensues.
hormone feedback
corpus luteum releases estrogen and progesterone, which feed back to the hypothalamus to prevent the release of FSH and LH
HCG
Human chorionic gonadotropin.
If the egg has been fertilized by the sperm, HCG rescues the corpus luteum. (When corpus luteum degrades, progesterone stops being produced, which leads to the uterine wall sloughing off.) If progesterone and estrogen continue to be secreted, the wall of the uterus will continue to be maintained.
estrous cycle
The other type of cycle used by mammals (instead of menstrual cycle).
Key characteristics:
- -shorter luteal phase, so there is less endometrial buildup, so no menstruation
- -Period of heat
a. monestrous cycle - only one period of heat every year (e.g.. deer)
b. polyestrous cycle - multiple periods of heat every year (e.g. rabbits)
marsupial reproduction
- -shorter gestation
- -longer lactation
- -embryonic diapause
- -Marsupials are less developed at birth due to shorter gestation period.
- -Embryonic diapause –> kangaroos can carry 3 babies at 3 different stages of life at once
ways to have twins
- fertilization of 2 different oocytes–> 2 embryos in the uterus (fraternal twins)
- Single oocyte splits –> identical twins
a. can happen early in development so the embryos develop their own sac
b. can happen later in development so embryos share the same sac
c. can happen so late that the inner cell mass doesn’t completely split and then you get Siamese twins
placenta
forms from the outer chorion and syncytiotrophoblast cells.
chorion
the outermost membrane surrounding an embryo of a reptile, bird, or mammal. In mammals (including humans), it contributes to the formation of the placenta.
anencephaly
neural tube defect that results in the brain not forming. Typically results in death.
spina bifida
result of neural tube not closing at the bottom.
uncommitted internal reproductive structures
- gonads
- wolfian duct
- mullerian duct
male internal reproductive structure development
gonads–> testes
wolfian duct –> vas deferense
mullerian duct degenerates
female internal reproductive structure development
gonads –> ovaries
wolfian duct degenerates
mullerian duct –> fallopian tubes
Cleavage Stages
30 hours: 2-cell stage
60 hours: 4-cell stage –> 8-cell stage –> morula –> early blastocyst
4-5 days: Late blastocyst (inner cell mass, blastocyst cavity, trophoblast)
Implantation
- -Embryo arrives at wall of uterus about 6-7 days after fertilization. It’s a blastula at this point
- -Zona pellucida degenerates
- -Trophoblast cells of embryo need to interact with wall of uterus to implant - embryo breaks out of degenerating zone pellucida to latch onto uterine wall
Synctiotrophoblast cells
- -Degrade the wall of the uterus so embryo can attach
- -Reorganize themselves and form part of placenta
Early placental development
–The chorion and synctiotrophoblast cells form the placenta
Amniotic sac
–Composed of chorion and amnion
anencephaly
–When the top of the neural tube fails to close–>incomplete brain formation (anencephaly)
Spina bifida
–When the bottom of the neural tube doesn’t close
allantois
the fetal membrane lying below the chorion in many vertebrates, formed as an outgrowth of the embryo’s gut. In birds and reptiles it grows to surround the embryo; in eutherian mammals it forms part of the placenta.
Decidua
Area of some layers of cells that have been dropped in order to make blood islands that are in between the fingers of chorionic villi. The point: allows maternal blood to be as close as possible to embryonic blood
blood islands
Pools of the mother’s blood that sit around the chorionic villi so there’s a lot of surface area contact b/w mother’s blood and baby’s blood.
chorionic villi
part of fetal circulatory system that interacts with mother’s blood to exchange nutrients and gases.
Placenta
formed from chorion and synctiotrophoblast cells.
Synctiotrohpoblast cells do not express typical surface markers, meaning that the mother’s immune system does not attack the embryo when it implants in the uterine wall.
foramen ovale
The hole in a fetal heart that allows oxygenated blood to go from the right side of the heart to the left. In the fetus, oxygenated blood enters the right side of the heart, passes through the foramen ovale and goes to the left side of heart and out to rest of the body. The foramen ovale is present so that blood doesn’t get pumped from the right side of the heart to the lungs of the fetus, which aren’t working yet and don’t need blood in them.
In newborns, the foramen ovale closes as a result of the pressure change of being born. Babies begin to receive unoxygenated blood in the right side of the heart, which then gets pumped to the lungs to receive oxygen.
Ductus arteriosis
In a newborn, blood comes into right side of heart and gets pumped out to lungs.
In a fetus, blood comes into the right side of the heart and there’s a bypass that sends it straight to the pulmonary artery. This fetal bypass is the ductus arteriosis. That way, blood doesn’t get pumped to the lungs.
Ductus venosus
Shunts a portion of the left umbilical vein blood flow directly to the inferior vena cava, thus allowing oxygenated blood from placenta to bypass the liver.
Major pregnancy hormones
Placenta takes over from corpus luteum the production of estrogen and progesterone.
HCG was secreted early on from the chorion to rescue corpus luteum, but it fades away as placenta develops.
Placental progesterone
Inhibits production of prolactin, which signals production of milk. (It’s too early to produce milk during gestation.)
Lactogen
Made by placenta.
- -Signals breasts to construct milk ducts
- -Supports bone growth of fetus
- -Alters mother’s metabolism so she uses fats for energy more, which has the effect of leaving carbs for the baby
- -Inhibits ADH (antidiuretic hormone) so the mother can eliminate waste for the baby and herself
lanugo
fine hair covering fetus around the 5th month. disappears by birth
3rd trimester
–Most of the 3rd trimester is devoted to brain growth, which requires lots of nutrition. This is why babies in developing countries are frequently so affected by mother’s poor nutrition, causing developmental delays.
Placenta previa
Placenta comes out before the baby, which means the baby won’t be getting enough oxygen. Surgery can be necessary.
Pre-eclampsia
Malformed placenta which isn’t getting enough blood through it; signals mother’s blood pressure to go up; so that in turn the placenta is getting more blood. If it’s not dealt with, can cause stroke in the mother.
CRH
corticotropine releasing hormone. Produced by the hypothalamus. We think too much CRH –> early delivery. Too little –> late delivery.
Hypothesis:
- Maternal CRH stimulates fetal pituitary gland to secrete ACTH (adrenal corticotropin hormone), stimulating adrenal gland of fetus.
- Adrenal gland of fetus signals prostaglandin formation and secretion –> causes smooth muscle contractions and inhibits progesterone (progesterone relaxes smooth muscle of uterus, preventing it from contracting)
Birth process
- Initial contractions signaled by prostaglandin –> force baby up against cervix
- Cervix signals up to hypothalamus –> signals pituitary –> releases oxytocin
- Oxytocin travels through blood stream, causing stronger smooth muscle contractions –> baby’s head pushed out even more.
- Positive feedback loop - baby’s head gets pushed further down, contractions get stronger
When is the baby ready to come out?
The cervix must dilate and efface (get thin).
Lactation
- placental lactose causes formation of milk ducts
- placental progesterone was inhibiting prolactin, but once birth happens, placenta is gone and so is progesterone. So prolactin is produced, which produces milk.
- Colostrum is present at first, but milk comes in after a few days.
- Milk is released by baby suckling –> release of oxytocin –> smooth muscle contractions
relaxin
the hormone that loosens fibrocartilage in junction between pubic bones.
Relaxin is secreted by corpus luteum, which relaxes pubic bones during birth to widen birth canal.
