Fertilization And Implantation

Question 1

When does fertilization occur

Answer 1

Day 15-16 of menstrual cycle

Question 2

Where does fertilization happen

And what causes follicular rupture in ovary

Answer 2

Ampulla of oviduct

LH surge = ovum + corona radiate around it is ejected into peritoneum ——> oviduct moved by fimbriae—> ampulla

Question 3

How many sperm enter vagina and how many make it to ampulla and how many are infertile

Answer 3

300 million
200
<20 million

Question 4

Key thing that helps move sperm

Answer 4

Myometrium contractions as a result of increased estrogen near the ovulation period
+ increased progesterone to downregulate immune system (to help sperm survive)

Question 5

How are sperm in the 1epididymus and 2when ejaculated and then 3when entering vagina

Answer 5

1. Surface molecules surround the head
2. The surface proteins are coated with seminal plasma protein to mask sperm receptors
3. Capacitation

Question 6

Capacitated sperm is what

Answer 6

The spermatic enters the vagina and the seminal plasma coating and surface proteins are removed exposing surface receptors for 1. sperm to bind to Zona pellucida

2. Increase Ca+2 into cell during acrozomal reaction
   * this process is slow
3. Cause hyperactivation

Question 7

What signals capacitation

Answer 7

Ovulation signals

Question 8

Capacitation is low, what do incapacitated sperm do

Answer 8

They can bind to epithelial cells in ISTHMUS of oviduct
They unbind when they become capacitated
= to expend spree life and wait for ovulation

Question 9

What does hyper activation of sperm help with

Answer 9

This occurs when a sperm is capacitated and gets signals from oocyte
= whip-like, higher f movement of flagella
= help sperm unbind to epithelial cells, or to move through all the membranes of the oocyte, increase mobility

Question 10

How many barriers does the sperm need to go through in fertilization

Answer 10

Corona radiata (expanded cumulus)
Zona pellucida
Plasma membrane of oocyte

Question 11

What is the cumulus composed of and what does the sperm use to break this

Answer 11

Made of hyaluronic acid broken down by Hyaluronidase

Question 12

What comprises the zone pellucida and what does the sperm use to break it down

Answer 12

Made up of glycoproteins ZP1, ZP2, ZP3, ZP4

The sperm have ZP3 receptors that bind to the ZP3 = ACROSOMAL REACTION

Question 13

What 3 things happen during the acrosomal reaction

Answer 13

1. Inner sperm PM fuses with outer acrosomal membrane of sperm to release acrosomal vesicle contents
2. Acrosomal contents digest Zona pellucida
3. Sperm enters through hole made in Zona pellucida

Question 14

Cortical reaction -what triggers it

Answer 14

Happens with the fusion of the sperm and egg

Question 15

Cortical reaction steps

Answer 15

1. Ca+2 released
2. ZP proteins are altered = prevent other sperm to bind
3. Hyaluronic acid, proteoglycans, proteinases released and hydrated
4. Zona pellucida has now formed a physical barrier = X Polyspermy

Question 16

What does release of Ca+2 do

Answer 16

Stimulated completion of meiosis 2
-Breakdown MAPK proteins
-2nd polar body released
Alters ZP proteins

Question 17

When is the egg activated

Answer 17

When the sperm DNA condenses

Question 18

What happens after sperm DNA has condensed and the egg is activated

Answer 18

1. Pronucleus forms around the female egg chromosomes
2. The male and female chromosomes both replicate
3. The pronuclei move together
4. The pronuclei fuse = first embryonic cleavage *beginning of embryonic development

Question 19

What is cleavage

And what is the egg at day 3,4,6-8

Answer 19

Cell division without growth
Day 3 = 16 cell(blastomeres) morula
Day 4 = early blastocyst
Day 6-8 = implantation

Question 20

What happens in blastocyst compaction and blastocele development

Answer 20

Compaction of morula : increase adhesion cell-cell(desmosomes +TJ) =

1. trophoelctoderm forms, - cells move to outside sphere
2. Na+ transport forms the blastocele

Question 21

Inner cell mass

Answer 21

In the blastocele DAY 5

They form the embryo proper - pluripotent

Question 22

Steps in blastocyst hatching

Answer 22

*before implantation
Zona pellucida detaches and oocyte comes out
1. Trophoblasts secreation proteases that digest ZP
X hatching - infertility, premature hatching - abnormal implantation

Question 23

Blastocyst after hatching

Answer 23

Synthesis and secretion of molecules to promote pregnancy and implantation and placenta development
+ immunosuppressive factors (platelet-activating factor, hCG, prostaglandin E2, IL1,6

Question 24

How does the sperm enter the PM

Answer 24

Spree have a protein called Izumo binding to Izumo R on oocyte
Entire sperm enters
DNA in spree condenses and forms male pronucleus
Then the release of Ca+2

Question 25

Blastomeres are known as

Answer 25

Totipotent = can give rise to any cell, an entire offspring

Question 26

What secretes hCG and when can it be seen

Answer 26

Trophoblasts and syncytiotrophoblasts | Seen after day 8 post ovulation

Question 27

hCG function

Answer 27

1. Prevents involution of the corpus luteum - Prevent menstruation - increased secretion of progesterone and estrogen 2. Autocrine growth factor - stimulates trophoblast growth and development - stimulate placenta growth

Question 28

3 stages of implantation

Answer 28

Apposition Attachment Invasion

Question 29

Apposition

Answer 29

Contact between endometrium and trophoblast of oocyte in a crypt of the endometrium The inner cell mass rotates to face the endometrium attachment

Question 30

Attachment stage

Answer 30

Trophoblasts adhere to luminal endometrium and interact with surface proteins = initiates changes in endometrial stroma (DECIDUATION)

Question 31

DECIDUATION - part of attachment stage

Answer 31

Stroma of the endometrium changes due to invasion and progesterone 1. Increased vascular permeability 2. ICM made 3. stromal cells get more enlarged + glycogen filled

Question 32

Invasion stage

Answer 32

Degradation of endometrial cells Trophoblasts fuse with stroma layer, as syncytiotrophoblasts form and protrude through the BM to the stroma 1. Paracrine and autocrine factors degrade stroma and ECM 2. Finger like projections reach maternal BVs 3. Epithelium is restored eventually *most done by the syncytiotrophoblasts

Question 33

4 functions of the syncytiotrophoblasts

Answer 33

1. Express adhesive proteins, bind to ECM and when invading (Cadherins and integrity’s) 2. Breakdown of ECM (and stroma): secretion of matrix metal lop rotate and hydrolysis enzymes 3. hCG secretion : maintains corpus luteum = secrete progesterone + make progesterone independent of corpus luteum (WEEK10) 4. Phagocytosis + placental transfer of gas, nutrients, wastes

Question 34

what happens after DECIDUATION

Answer 34

When the stroma cells have changed and become decidual cells, the endometrium is ready for implantation = the decidual cells around the embryo prevents it from moving and prevents embryo from invading into myometrium - hemorrhage

Question 35

Ectopic Pregnancy

Answer 35

The egg is fertilized in the oviduct in most cases, (any place but the uterus) and there is no stroma = no decidualization = implantation causes rupture of tissues- hemorrhage

Question 36

When does Placentation occur

Answer 36

DAY 9

Question 37

What happens during placentation

Answer 37

Spaces occur in the syncytiotrophoblasts = lacunae that later fill with maternal blood and endometrial secretions ——> then primary, secondary (forming chorionic membrane), the tertiary villi form