Physiology of Pregnancy and Lactation

Question 1

What name is given to the zygote immediately prior to becoming a blastocyst?

Answer 1

Morula

Question 2

What are the two main parts of the blastocyst?

Answer 2

Inner cell mass - develops into foetus

Trophoblast - implants into uterine wall and becomes foetal portion of placenta

Question 3

During what days of gestation does the embryo implant into the uterus?

Answer 3

5-8 days: blastocyst attaches to lining of uterus.

Question 4

How do the trophoblastic cells penetrate the endometrium?

Answer 4

• cords of trophoblastic cells penetrate the endometrium
• These tunnel deeper and carve out a hole for the blastocyst
• implantation finishes when the blastocyst is completely buried in the endometrium - DAY 12

Question 5

Placenta is derived from both trophoblast and decidual tissue. TRUE/FALSE?

Answer 5

TRUE

=> both foetal and maternal tissue

Question 6

Describe how the placenta develops

Answer 6

• Trophoblasts differentiate into multinucleate cells
• invade decidua and break down capillaries
  => form cavities filled with maternal blood
• Embryo sends capillaries into trophoblast projections to form “placental villi”
• Each villus contains foetal capillaries separated from maternal blood by a thin layer of tissue – no direct contact of foetal and maternal blood

Question 7

What can be exchanged between foetal and maternal blood in the placenta?

Answer 7

respiratory gases
nutrients
metabolites
** largely down diffusion gradient **

Question 8

When does the placenta become functional during pregnancy, and what other structure becomes functional at this point?

Answer 8

Placenta (and foetal heart) functional by 5th week of pregnancy

Question 9

How is the early embryo delivered nutrients?

Answer 9

• HCG signals corpus luteum to continue secreting progesterone
• Progesterone stimulates maternal cells to concentrate glycogen, proteins and lipids for diffusion

Question 10

Describe how circulation in the placenta works as a physiological arterio-venous shunt?

Answer 10

• hair-like projections (villi) into uterine wall.
• increases contact area between uterus and placenta
  => more nutrients and waste materials can be exchanged
• Circulation within the intervillous space acts partly as an arteriovenous shunt.

Question 11

Explain how the placenta plays the role of the foetal lungs?

Answer 11

O2 diffuses from maternal -> foetal circulation down concentration gradient

CO2 follows reverse conc gradient (due to partial pressure being elevated in foetal blood)

O2 saturated blood returns to fetus via umbilical vein
Maternal O2-poor blood, flows back into uterine veins.

Question 12

Foetal haemoglobin is higher than that of adults. TRUE/FALSE?

Answer 12

TRUE

• Higher Hb conc. in fetal blood
• 50% more than adults
• it also has a higher affinity for O2

Question 13

How do water and electrolytes get into the placenta from the mother?

Answer 13

• Water diffuses along osmotic gradient

- electrolytes follow water (iron and Ca2+ can only go from MOTHER -> CHILD)

Question 14

How is glucose transported into the placenta and when is the most glucose required for the foetus during pregnancy?

Answer 14

• simplified transport into placenta
• glucose = main energy source for foetus
• high glucose need in 3rd trimester

Question 15

How do the majority of waste products exit the foetus back into the placenta?

Answer 15

• diffusion based on concentration gradient

Question 16

What prescription and non-prescription drugs can cross the placenta?

Answer 16

• Teratogens e.g. valproate, carbamazepine, tetracycline

- Alcohol, nicotine, heroin, cocaine, caffeine

Question 17

Why is HCG important in pregnancy?

Answer 17

• promotes Corpus Luteum to remain and produce hormones (Progesterone and Oestrogen)
• Has an effect on the testes of male fetus - development of sex organs

Question 18

Why is Human Placental Lactogen (or Human Chorionic Somatomammotropin) needed in pregnancy?

Answer 18

• produced from ~ week 5 of pregnancy
• growth hormone-like effects: protein tissue formation.
• decreases insulin sensitivity in mother => more glucose to foetus
• breast development.

Question 19

What is progesterone release responsible for during pregnancy?

Answer 19

• development of decidual cells
• decreases uterus contractility
• preparation for lactation

Question 20

What is the role of oestrogen in pregnancy?

Answer 20

• enlargement of uterus
• breast development
• relaxation of ligments

Question 21

What are estriol levels used to indicate in pregnancy?

Answer 21

estriol level - indicator of vitality of fetus

Question 22

What other hormonal changes can occur in pregnancy and what complications can these cause?

Answer 22

• increased Aldosterone
  => salt and water retention
  => increased BP
• Increased Cortisol
  =>oedema and insulin resistance
  => Gestational Diabetes

Question 23

The placenta and baby demand higher Ca2+ levels during pregnancy. What complication can this cause in the mother?

Answer 23

Hyperparathyroidism

Question 24

What cardiovascular adaptations may a pregnant woman experience?

Answer 24

• Increased cardiac output (30 -50% more)
• CO decreases in last 8 weeks
• CO increases 30% more during labour
• Heart rate increases (90bpm) => Increase CO.
• Blood pressure drops during 2nd trimester (uteroplacental circ. expands and peripheral resistance decreases)
• vasodilation occurs

Question 25

What haematological changes can be experienced by a mother in pregnancy?

Answer 25

- plasma volume increases with CO (50%) - RBC erythropoesis increases - Hb is decreased by dilution (large PV) - Iron requirements increases (baby needs a lot of iron => mother may require supplements)

Question 26

What respiratory changes occur in a mother when she is pregnant?

Answer 26

- progesterone signals to brain to lower CO2 levels | - O2 levels are increased (RR and Tidal vol increase) to meet demands of both mother and baby (20% more than normal)

Question 27

Explain how the urinary system of a pregnant mother is affected?

Answer 27

- GFR and renal plasma flow increase - Increased re-absorption of ions and water (oedema) - Slight increase of urine formation - Postural changes affect renal functions - upright position DOWN - supine position UP - lateral position during sleep VERY UP

Question 28

What is pre-eclampsia?

Answer 28

pregnancy induced hypertension + proteinuria

Question 29

What signs other than increased blood pressure and proteinuria may be seen in pre-eclampsia?

Answer 29

Kidney function decline => salt and water retention => oedema formation (esp hands and face) => Renal blood flow and GFR decreases

Question 30

Pre-eclampsia is more common in what groups of women?

Answer 30

- pre-existing hypertension - diabetes - autoimmune diseases (eg lupus) - renal disease - FHx of pre-eclampsia - obesity - multiple gestation (twins or multiple birth).

Question 31

What is the most significant risk factor for pre-eclampsia?

Answer 31

having had pre-eclampsia previously.

Question 32

What is Eclampsia?

Answer 32

- EXTREME pre-eclampsia (lethal without Tx) Symptoms: - vascular spasms - extreme hypertension - chronic seizures - coma

Question 33

How is eclampsia normally treated?

Answer 33

- vasodilators | - cesarean section (best Tx is to get the baby OUT)

Question 34

How many kilograms does the average mother put on during pregnancy?

Answer 34

11kg (5kg foetus and 6kg mother)

Question 35

How are the average 11kg split up into different components of maternal weight gain during pregnancy?

Answer 35

``` Foetus - 3.5kg Extra-embryonic fluid/tissue - 2kg Uterus - 1kg Breasts - 1kg Body Fluid - 2.5kg Fat accumulation - 1kg ```

Question 36

what should a pregnant mother be eating more of during pregnancy in relation to metabolism and nutrition for the foetus?

Answer 36

- 250 - 300 extra kcal/day for mother - Extra protein intake - 30g/day - At end of pregnancy - fetal glucose requirements higher => need to account for this

Question 37

What are the two different stages of metabolism that a mother experiences during pregnancy?

Answer 37

1st - 20th week - mother´s ANABOLIC phase: - small nutritional demands of the foetus 21 - 40 week (esp. last trimester): - high metabolic demands of the fetus - accelerated starvation of the mother

Question 38

What usually happens during the mother's anabolic metabolism phase of pregnancy?

Answer 38

- normal/increased sensitivity to insulin - lower plasma glucose - lipogenesis, glycogen stores increases - growth of breasts/ uterus /weight gain

Question 39

What occurs during the mothers catabolic metabolism phase of pregnancy?

Answer 39

- maternal insulin resistance - increased transport of nutrients through placental membrane - lipolysis

Question 40

What specific nutritional needs are important in pregnancy?

Answer 40

- Folic acid (folate) - reduces risk of neural tube defects - Vitamin D supplements - High protein diet, higher energy uptake - Iron supplements may be required - B - vitamins - erythropoesis

Question 41

Why should folic acid ideally be taken BEFORE pregnancy begins?

Answer 41

- it is taken to prevent neural tube defects | BUT often neural tube has formed BEFORE patient knows they are pregnant

Question 42

Describe how the uterus becomes more "excitable" towards the end of pregnancy?

Answer 42

- Oestrogen:Progesterone ratio INCREASES => oestrogen increases contractility and oxytocin receptors on uterus - Oxytocin (posterior pituitary) => increases contractions and excitability => stimulates placenta to make prostaglandins - Foetal hormones: oxytocin, adrenal gland, prostaglandin (control timing of labour) - Mechanical stretch of uterine muscles increases contractility - Stretch of the cervix also stimulate uterine contractions

Question 43

What are Braxton Hicks contractions?

Answer 43

Small contractions that do NOT indicate labour | - these increase toward the end of pregnancy

Question 44

Describe how stretching of the cervix causes positive feedback?

Answer 44

stretch of the cervix by fetal head => increases contractility => causes further oxytocin release

Question 45

How may a woman engage abdominal muscle contractions during labour?

Answer 45

- Strong uterine contraction / pain from birth canal cause neurogenic reflexes from spinal cord => Induce intense abdominal muscle contractions

Question 46

What are the 3 stages of Labour?

Answer 46

1st stage: cervical dilation (8-24 hours). 2nd stage: passage through birth canal (few min to 120 mins). 3rd stage: expulsion of placenta.

Question 47

How are the means to lactate developed in the mother during pregnancy?

Answer 47

Oestrogen = stimulates growth of ductile system Progesterone: development of lobule-alveolar system Prolactin stimulates milk production (steady rise in levels wk 5 – birth).

Question 48

Why can milk only normally be produced AFTER women give birth?

Answer 48

Oestrogen and Progesterone inhibit milk production | => At birth sudden drop in both

Question 49

How soon after birth does prolactin stimulate milk production and what are the contents of the first milk produced?

Answer 49

- 1-7 days after birth, prolactin induces high milk production. - Stimulates colostrum (low volume, no fat)

Question 50

What does the baby do to allow milk ejection from the mother's breast?

Answer 50

- suckling on mechanoreceptors in nipple - this sends signal to higher brain centres to allow production of oxytocin (for smooth muscle contraction) and prolactin (for milk production)

Question 51

Why may a post-partum haemorrhage occur after the delivery of the placenta?

Answer 51

If the womb doesn't contract down after placenta is delivered (to condense surface area and vasculature) then haemorrhage is likely to occur