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)
16
Q
Which of the following makes up the majority of the placenta?
a) the functionalis layer of the endometrium
b) the extraembryonic mesoderm
c) the yolk sac
d) the amnion
e) chorion laeve
A
b
17
Q
A
18
Q
Where is the majority of the placenta located?
A
- majority of important part of placenta is towards back (trophoblast, extraembryonic mesoderm is very thick)
- thin layer of trophoblast, extraembryonic mesoderm, and endometrium
- they don’t make anything except for some membranes
- underneath is the amniotic sac
- baby has to burst through amniotic sac and layers of placenta to get out
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
25
What are the maternal adaptations to pregnancy?
- cellular immunity decreases: the fetus is an allograft (ie. not the mom) but the mother has to remain tolerant of paternal antigens and yet maintain normal immune competence for defense against microorganisms
- the placental villi do not exhibit very many antigens and the activity of many types of helper T-cells decreases
- the placenta requires a lot of blood (blood volume increases 30-50%, cardiac output increases 20-30%)
- tidal volume increases 30-40% and airway resistance goes down to increase CO2 loss
- lower maternal CO2 levels create a stronger concentration gradient between mom and fetus
- myometrium mass increases from 60-80g to 900-1200g (about 15x increase) to accomodate the fetus
26
- 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)
27
What triggers parturition?
- the uterus at term is really irritable
- lots of oxytocin (OT) and prostaglandin (PG) receptors
- these cause a lot of uterine contractions
- stimulation/deinhibition of oxytocin and PG production
- so there are a lot of receptors and a lot of the ligand around
- cells in uterus stuck together in large syncitium so that the resting membrane potential decreases and gets closer to the threshold which makes them more likely to contract and the contraction will move down the uterus (more gap junctions between myocytes)
- the fetus appears to be in control around the initiation of labour:
- placental steroid hormones being produced from fetus
- more stretch on uterus, more stretch on smooth muscle, the more it wants to contract back down
- production of PG made by placenta and interacts with PG receptors becoming more abundant on myometrium
- secretion of oxytocin from posterior pituitary in baby and made by placenta
