Pregnancy Parturition And Late Fetal Development

Question 1

What nutrition is early embryo dependent on

Answer 1

reliant on uterine gland secretions and breakdown of endometrial tissues
Histiotrophic

Question 2

What type of support is embryo fetal growth dependent on at the second trimester

Answer 2

Haemotrophic

Achieved in humans through a haemochorial-type placenta where maternal blood directly contacts the fetal membranes.

Question 3

What is the connecting stalk/what does it do?

Answer 3

connects the embryo unit to the chorion

Question 4

What are trophoblastic lacunae

Answer 4

Large spaces filled with maternal blood formed by breakdown of maternal capillaries and uterine glands
Become intervillous spaces aka maternal blood spaces

Question 5

Amnion

Answer 5

The inner fetal membrane

Arises from the epiblast (but does not contribute to the fetal tissues)
Begins to secrete amniotic fluid from 5th week – forms a fluid filled sac

Question 6

Amniotic sac

Answer 6

Encapsulates and protects fetus

closed, avascular sac, with the developing embryo at one end

Question 7

Chorion

Answer 7

The outer fetal membrane

Formed from yolk sac derivatives and the trophoblast
Highly vascularized

Question 8

Gives rise to chorionic villi

Answer 8

outgrowths of cytotrophoblast from the chorion through syncitiotrophoblaststhat form the basis of the fetal side of the placenta

Question 9

What is the allantois/

Answer 9

Outgrowth of the yolk sac
Grows along the connecting stalk from embryo to chorion

Question 10

How does allantois form the umbilical cord

Answer 10

Becomes coated in mesoderm and vascularizes to form the umbilical cord.

Question 11

How does the amniotic sac form?

Answer 11

Expansion of the amnion by fluid accumulation forces the amnion into contact with the chorion, which fuse, forming the amniotic sac

2 layers amnion on inside chorion on outside

Question 12

• Why are chorionic villi important?

Answer 12

Provide a substantial surface area for exchange of gases & nutrients

Question 13

primary phase of chorionic fetal development

Answer 13

Cytotrophoblast forms finger-like projections through syncitiotrophoblast layer, Into maternal endometrium, and branching of these extensions

• outgrowth of cytotrophoblast cells from the chorion

Question 14

secondary phase of chorionic fetal development

Answer 14

growth of the fetal mesoderm into the primary villi

Question 15

tertiary phase of chorionic fetal development

Answer 15

growth of the umbilical artery and umbilical vein into the villus mesoderm, providing vasculature.

Question 16

Terminal villus microstructure; what does the convoluted knot of vessels and vessel dilation do?

Answer 16

Slows blood flow enabling exchange between maternal and fetal blood

Question 17

Maternal blood supply to endometrium

Answer 17

Uterine artery → arcuate arteries → radial arteries → basal arteries → spiral arteries

U AR BS

Question 18

What do spinal arteries do

Answer 18

provide the maternal blood supply to the endometrium

Question 19

What do Extra-villus trophoblast (EVT) cells do?

Answer 19

cells coating the villi invade down into the maternal spiral arteries,
Form endovascular EVT when this happens

Question 20

What is conversion

Answer 20

transition from spinal arteries to non-spinal arteries

turns the spiral artery into a low pressure, high capacity conduit for maternal blood flow.

Endothelium and smooth muscle is broken down – EVT coats inside of vessels

Question 21

How is calcium exchanged

Answer 21

actively transported against a concentration gradient by magnesium ATPase calcium pump.

Question 22

How are amino acids exchanged

Answer 22

active transport of amino acids to fetus

reduced maternal urea excretion

Question 23

Which 4 changes occur in the maternal circulatory system

Answer 23

• Maternal cardiac output increases 30% during first trimester (stroke vol & rate)
• Maternal peripheral resistance decreases up to 30%
• Maternal blood volume increases to 40% (near term (20-30% erythrocytes, 30-60% plasma)
• Pulmonary ventilation increases 40%

Question 24

Why is the O2 content and saturation of fetal blood similar to maternal blood, even though fetal O2 tension is low? (what major difference does fetal Hb have to maternal Hb)

Answer 24

Embryonic and fetal hemoglobins: greater affinity for O2 than maternal hemoglobin.

Placenta consumes 40-60% glucose and O2 supplied by the mother

Question 25

How does fetal circulation differ from neonatal circulation

Answer 25

Ventricles act in parallel rather than in series (series in neonatal) Achieved **by vascular shunts which bypass pulmonary & hepatic circulation**, **these shunts close at birth** to give rise to normal pulmonary & hepatic circulation -

Question 26

What occurs in the lungs around 20 weeks and 28 weeks

Answer 26

primitive air sacs form **surfactant** production Lung vascularises at 28

Question 27

At which point is the endocrine pancreas functional, and at which point does insulin secretion occur?

Answer 27

start of 2nd trimester from mid 2nd trimester

Question 28

Which carbohydrate is progressively deposited towards the time of delivery

Answer 28

Glycogen

Question 29

The early fetus swallows large amounts of amniotic fluid, debris from this fluid along with bile acids form the first stool of the fetus, delivered just after birth, what is the name of this stool?

Answer 29

Meconium

Question 30

At which point/week does the fetus start to determine movement, and at which point/week is movement detectable by the mother?

Answer 30

late 1st trimester 14 weeks

Question 31

At which point does the fetus start to respond to stress, and at which point do thalamus-cortex connections form?

Answer 31

18 weeks and 24 weeks

Question 32

Does fetus show conscious wakefulness

Answer 32

No In slow wave or REM sleep

Question 33

- Which hormone sub-class is organ maturation coordinate

Answer 33

Fetal corticosteroids

Question 34

Main aims of labor

Answer 34

T - safe expulsion of fetus at the correct time - Expulsion of placenta and fetal membranes - Resolution/healing to permit future reproductive events -

Question 35

What reaction type does labour have the characteristics of?

Answer 35

Pro inflammatory For Immune cell infiltration Inflammatory cytokine secretion Prostaglandin secretion

Question 36

First stage of labor

Answer 36

Contraction start and cervix dilated Latent phase-slow dilation of cervix 2-3cm Active phase-rapid dilation of cervix 10cm

Question 37

Role of cervix in pregnancy

Answer 37

Retains fetus in uterus High connective tissue content, (Bundles of collagen fibres embedded in a proteoglycan matrix) provides rigidity and stretch resistance Softening caused by changes to collagen bundle structure

Question 38

4 stages if cervical remodeling

Answer 38

Softening-measurable changes in compliance but retains cervicak competence in first trimester Ripening is where monocytes infiltration IL6 and IL8 secretion and hylarunonan deposition occurs weeks and days before birth Dilation is where increased hyaluronidase expression occurs and matrix metalloproteinases decrease collagen content Post party repair recovers tissue integrity

Question 39

Second stage

Answer 39

Myometrial contractions and fetal expulsion

Question 40

What do myometrial muscle cells connect to form?

Answer 40

a syncytium (extensive gap junctions, allowing muscle contraction to be coordinated)

Question 41

When do contractions start from and where do they spread

Answer 41

start from the **fundus**, **spread** **down upper segment**  -

Question 42

What can myometrial muscle contractions be described as

Answer 42

Brachystatic Fibres don’t return to fully relaxed state Causes lower segment and cervix to be pulled up

Question 43

Third stage

Answer 43

Delivery of placenta Rapid shrinkage of uterus after delivery Clamping stops fetal, blood flow so chorionic villi collapse ongoing contraction is expel placenta

Question 44

Why does uterus remain in contracted state

Answer 44

to facilitate uterine vessel thrombosis

Question 45

The uterus undergoes uterine involution and the cervix undergoes repair to restore a non-pregnant state, why is this important

Answer 45

- **Shielding uterus from commensal bacteria** - **Restore endometrial cyclicity in response to hormones**

Question 46

Corticotrophin-releasing hormone (CRH) and the initiation of labor, describe this theory

Answer 46

- The fetus determines timing of parturition through **changes in fetal HPA axis** **Corticotrophin Releasing Hormone (CRH) levels rise** exponentially towards the end of pregnancy

Question 47

What does an increase in fetal CRH release cause

Answer 47

Promotes fetal ACTH and cortisol release increased fetal CRH production → increased fetal adrenal cortisol (this travels to the placenta)→ increases placental CRH production → Placental CRH stimulates more fetal CRH release stimulates DHEAS production by the fetal adrenal cortex, DHEAS is a substrate for oestrogen production

Question 48

Why are high progesterone levels important to have throughout pregnancy?

Answer 48

Maintains uterine relaxation

Question 49

How might the oestrogen : progesterone ratio shift during labour?

Answer 49

Increases

Question 50

The uterus becomes ‘blinded’ (non-responsive) to progesterone action and sensitized to estrogen action, describe two ways this occurs?

Answer 50

- **Functional progesterone withdrawal, explain it:** switch from PR-A isoforms (activating) to PR-B and PR-C (repressive) isoforms expressed in uterus PR=progesterone receptor - **Increased oestrogen receptor alpha expression**

Question 51

Explain the Ferguson reflex

Answer 51

Stretch receptors in vagina and cervix trigger oxytocin release from the posterior pituitary

Question 52

- **Oxytocin,** how does oxytocin production change at the onset of labour?

Answer 52

Uterine oxytocin production increases sharpl

Question 53

What is oxytocin secreted by

Answer 53

utero-placental tissues maternal pituitary

Question 54

What is increased oxytocin production driven by?

Answer 54

Increased placental oestrogen levels

Question 55

- What receptor does oxytocin signal through?

Answer 55

G coupled oxytocin receptors - During pre-labour, what effect does progesterone have on the OXTR expression? **Inhibits OXTR expression**, which allows the uterus to remain in a relaxed state (so no contractions) - What effect does increasing oestrogen have on OXTR expression? increases it

Question 56

3 main functions of oxytocin

Answer 56

- **Increases connectivity of myocytes** in **myometrium** - **destabilise membrane potentials** to **lower threshold for contraction** - **Enhances liberation of intracellular Ca2+ ion stores**

Question 57

What are the 3 primary prostaglandins (PGs) synthesized during labour?

Answer 57

- PGE2, what is its main role? - **cervix re-modelling,** how? **Promotes** leukocyte infiltration into the cervix, **IL-8 release** and **collagen bundle re-modelling**  - PGF2 alpha, what is it’s main role? **myometrial contractions** by destabilising membrane potentials and promotes connectivity of myocytes (with Oxytocin) - PGI2, what is its main role? Promotes myometrial smooth muscle relaxation and relaxation of lower uterine segment

Question 58

- How does an increase in oestrogen levels drive prostaglandin action (2 ways)?

Answer 58

1. Increasing oestrogen **activates phospholipase A2 enzyme**, which generates more arachidonic acid for PG synthesis 2. **increases oxytocin receptor expression which promotes PG release**