Module 5 Physiology of the 1st trimester Flashcards
Pregnancy is dated how?
By weeks from first day of the last menstrual period or LMP
How long is gestation in weeks?
40 weeks
How long is gestation in days?
280 days
How many trimesters are there for gestation?
Three trimesters
What is the first trimester?
Week 0-12
6/7 weeks long
What is the second trimester?
Week 13-27
6/7 weeks long
What is the third trimester?
Week 28-40
The conceptus is called what?
Embryo
When can we call the embryo a embryo?
from 10 weeks from LMP
What dates do sonography uses?
LMP
What dates does Embryologists use?
Conception dates
After 10 weeks LMP the embryo is called what?
Fetus
In the first trimester what can we do? 5
- Confirm pregnancy
- Confirm location of pregnancy
- Confirm that the size of the embryo agrees with the LMP dating
- Confirm the number of embryos
- Confirm viability
How do we define location of pregnancy?
Intrauterine pregnancy vs uterine pregnancy
What measurement do we use to size the embryo with LMP dating?
CRL- crown rump length
When does ovulation occur?
Day 14 of the ideal cycel
What must happen for ovulation to occur?
LH must surge
Ovum lives for how long?
12 to 24 hours
During ovulation what happens to the ovum?
It is ejected from the follicle and is propelled towards the fallopian tube
Approximately how many sperm cells are deposited near the cervix?
Around 200-500 million
How many sperm reach the ovum?
300-500 sperm
What is the normal sperm count?
100 million sperm/ml
What amount of sperm is considered as sterile males?
20 million or less
How long does sperm live for?
24 hours (some have been known for living up to 72 hours)
How many autosomes are given from each sperm/egg?
22 autosomes
How many sex chromosomes are given from each sperm/egg?
One
What happens during fertilization of the sperm head?
The sperm head becomes enlarged to become the male pronucleus
During fertilization the ovum completes what? and this does what?
It completes it second meiotic division at this time to become the female pronucleus
Both pronuclei fuse and what happens to the chromosomes?
They intermingle
What does fertilization start with?
The sperm passes through the zona pellucida
What happens during cleavage? What are the daughter cells called?
The chromosomes of the zygote arrange in the preparation for the 1st cleavage division. The two daughter cells are called blastomeres
What is cleavage?
Rapid cell division without a change in the size of the original zygote
12- 16 blastomeres are called what?
Morula
What is a zygote? What is it also called?
- Union of the sperm and ovum
- Also called conceptus
What is the morula? What happens to the morula with each division?
- Cluster of cells
- The morula remains the same size but the cells become smaller and smaller with each division
How is the blastocyst formed?
Secretions cross the zona pellucida and enter the morula forming a fluid cavity
What is the journey of the ovum?
The ovum travels about 24-36 hours to reach the ampullar portion of the fallopian tube where fertilization occurs
What day does the blastocyst enter the uterus?
It enters the uterus 6-7 days after fertilization
What is the dating that Implantation is complete when?
By 11-12 days post ovulation or 9-10 days post fertilizations
Fluid enters the zygote and separates into how many parts? What are they called?
Two parts
1. Trophoblast
2. Embryoblast
What is a trophoblast?
Outer cell to be placenta and chorion
What is a embryoblast? What are the sections?
Inner cell mass forms
1. Embryo
2. Yolk sac
3. amnion
Once the zona pellucida disappears what happens?
The blastocyst implants in the uterus
During implantation, the blastocyst does what?
Attaches to endometrial epithelium
What does the trophoblast do during implantation? (What does it differentiate into?)
Differentiates into two layers
1. syncytiotrophoblast
2. Cytotrophoblast
What does the syncytiotrophoblast produce? What does the Syncytiotrophoblast do?
- Produces hCG
- Invasively erodes the endometrial stroma, which allows the blastocyst to sinks into the endometrium
What are lacunae?
The eroded spaces from the formation of the syncytiotrophoblast
The lacunae becomes what?
The intervillous spaces of the placenta
What does the cytotrophoblast do?
Produces fingerlike projections that extend into the forming lacunar network
What are the fingerlike projections of the cytotrophoblasts called?
Primary chorionic villi
What is the chorion frondosum? 2
- the villi directly at the implantation site
- Early placenta
What is the smooth chorion or chorion laeve?
All the remaining villi around the gestational sac
The decidua cells of the endometrium does what during implantation?
It increases in size and content
When the endometrium undergoes a decidual reaction what happens? what does this result in?
It results in a ectopic pregnancy as well as resulting in what we call a pseudo sac within the uterus