Repro Physiology 2 Flashcards
1
Q
Describe the initial sperm and egg interaction
A
- nucleus of secondary oocyte that has been ovulated and is in uterine tube
- zona pellucida on outside of egg
- because it is secondary, there is a 1st polar body with half of the genetic material
- corona radiata which are leftover cells from granulosa
- sperm meet egg in ampulla of uterine tube (midsection)
- sperm are capacitated (swim more vigorously and acrosome degrades)
- sperm penetrate corona radiata
- many sperm contact the glycoprotein of the ZP and the acrosome reaction occurs which causes the ZP to be digested
- one sperm contacts the plasma membrane of the ooctye
- the cell membrane of the oocyte depolarizes and cannot bind further sperm (the fast block to polyspermy) and the cortical reaction occurs
- the ZP hardens so no other sperm can get through
- the 2nd polar body is formed and meiosis II is finally complete, haploid male and female pronuclei are formed
- the female and male pronuclei fuse resulting in the zygote (a fertilized egg)
2
Q
Describe the development of egg to blastocyst
A
- the fimbriae of the uterine tube are close to the ovary at ovulation
- egg moves into ampulla of uterine tube
- egg is fertilized to form zygote in ampulla
- morula is 16 cells together in the zona pellucida 4 days after fertilization
- morula goes into the lumen of the uterus and hatches out of zona pellucida; blastocyst
- inner view of blastocyst showing the inner cell mass and the trophoblast separated by the blastocyst cavity
- moves to find a well vascularized area to implant
3
Q
Describe what happens when the blastocyst implants and becomes an embryo
A
- trophoblast (acellular) begin invading the endometrium
- embryo pushes itself into endometrium
- moves towards maternal blood vessels
- amniotic cavity begins to form at 7.5 days and spreads around outside of embryo
- at 9 days of implantation, it is complete (about 14 days after ovulation)
- at 16 days, there is the extraembryonic mesoderm which becomes part of placenta along with trophoblast cells
- contents from the inner cell mass that were pushed out
4
Q
What is the chorion?
A
-trophoblast in extraembryonic mesoderm that makes up fetal contribution to placenta
5
Q
What occurs to the amniotic cavity in a 28 day embryo?
A
- amniotic cavity expands and encompasses embryo
- head fold which moves where head is, tail fold where lower body is
- yolk sac is starting to be excluded from development (come out of endoderm)
- neural tube is beginning to form
- future umbilical cord will have the stalk and rest of yolk sac
- foregut in front of endoderm, hindgut in far end of endoderm, midgut
- heart begins to form
6
Q
A
- ectoderm gives neural tube
- endoderm gives guts
- mesoderm gives bone and muscle
7
Q
At what point does the embryo become a fetus?
A
- 8 weeks after fertilization or 10 weeks after missed period
- at ten week fetal stage, it is only 3cm long
-
8
Q
Describe the pre-embryonic phase of embryonic and fetal development
A
- Pre-embryonic phase:
- less than 14 days after fertlization
- conceptus is about 1.5mm in length by the end of this phase and is very poorly differentiated (egg and sperm-zygote-morula-blastocyst-implantation)
- tiny trophoblast and extraembryonic mesoderm which is the beginning of the fetal placenta
- for much of the earlier parts of this phase the ZP is present and the embryo is isolated from the maternal environment
9
Q
Describe the embryo phase of embryonic and fetal development
A
- 2-8 weeks after fertilization
- all major organs are assembled in this time so it is called the period of organogenesis
- embryo grows to about 3cm
- the placenta is far larger than the embryo at this point and there is complete access to materials in maternal circulation
10
Q
Describe the fetal phase of embryonic and fetal development
A
- >8 weeks to term (8 from fertilization, 10 from missed period)
- the organs grow during this period so it is called the histogenesis phase
11
Q
Why is the fetus particularly vulnerable to toxins in the phase from 14 days to 8 weeks?
A
- damage during this phase damages the organ itself
- anything after will change the development of the organ but the organ is at least there
- earlier than 2 week phase where the blastocyst is implanting, the cells are totipotent so it is usually okay because you have enough cells around to convert to what you need
12
Q
What problem in embryonic development occurred as a result of thalidomide?
A
- phocomelia
- shortening of the limbs
13
Q
What problem in embryonic development occurred as a result of valproic acid?
A
- if you take too much or not at the right time, the neural tube will not close
- spina bifida
- closure of neural tube happens in first 4 weeks and if it doesn’t happen, it will not happen in the entire fetal development
14
Q
What is microtia?
A
- small ears
- problem in fetal development
- can be corrected with surgery
15
Q
What problem in fetal development can occur from mom getting rubella?
A
- cataracts (lens is cloudy)
- but eye is still there so we see a incomplete/abnormal development in organ systems (histogenesis problem)
19
Q
What are the maternal and fetal contributions to the placenta?
A
- decidua
- functionalis layer of endometrium
- stratum basalis left in tact (when placenta is delivered, basalis is in tact and when hormones return we will begin to form a new functionalis layer)
- fetal contribution is the chorion and amnion
- extraembryonic mesoderm makes up inside part with the blood vessels
- blood flows in from maternal arteries into intervillus space, oxygen moves from maternal supply through the villus into the fetal supply (blood doesn’t move but gases can)
20
Q
What is usually occurring if there is not a lot of amniotic fluid?
A
- fetus will swallow amniotic fluid and it will be processed by the kidneys
- essentially is urine
- if there is not a lot, there is probably something wrong with the kidneys (or swallowing)
21
Q
A
22
Q
Describe placental circulation
A
- blood comes through maternal spiral endometrial arteriole (from maternal artery)
- moves into intervillous space
- comes back out through maternal endometrial venule
- fetal (umbilical) arteries bring in deoxygenated blood
- fetal (umbilical) vein take out the oxygenated blood
- it takes 20-25% of maternal circulation to feed the placenta
23
Q
A
- Wharton’s jelly provides structure to the umbilical cord
- jelly is the source for cord derived mesenchymal stem cells
- they come from the extraembryonic mesoderm
- the blood-derived stem cells are from the cord blood
24
Q
What does the cytotrophoblast do to the maternal arteries?
A
- invades the smooth muscle and endothelium of the maternal arteries into the myometrium
- those vessels can no longer control their lumen size
- if that doesn’t happen, woman will often develop pregnancy hypertension
- important that we have uninterrupted flow into the intervillus space to keep the blood flowing and fetus growing
26
Q
A
- hCG is how we detect pregnancy (the beta subunit)
- hCG rescues corpus luteum to keep making progesterone
- corpus luteum keeps placenta alive
- progesterone increases through pregnancy; at first it’s made my corpus luteum, hCG stimulates corpus luteum to have more progesterone
- hCG drops because placenta begins taking over the progesterone production
- estrogen levels at the beginning are low but the relative amount goes up rapidly
*units on the graph aren’t the same, it is showing relative amounts of hCG, estrogen, and progesterone (progesterone is higher than estrogen but relative amount of estrogen increases more)
