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Y4 Obstetrics and Gynaecology > Physiology of pregnancy and lactation > Flashcards

Physiology of pregnancy and lactation Flashcards

1
Q

Where does fertilisation of the ovum occur ?

A

In the ampulla of the uterus

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2
Q

What does the fertilised ovum progressively divide and differentiate into ?

A

A blastocyst

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3
Q

What are the 2 layers of the blastocyst and their importance

A
  • It has a inner cell mass - this is destined to become the fetus
  • It has a trophoblast - accomplishes implantation & develops into fetal portions of placenta
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4
Q

List the main stages of fertilisation

A
  1. Day 1: fertilisation of ovum occurs in the ampulla
  2. Day 3-5: transport of blastocyst into the uterus
  3. Days 5-8: Blastocyst ataches to the lining of the uterus (also the 1st stage of implantation)
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5
Q

Describe the main stages of implantation

A
  1. 1st stage: Blastocyst ataches to the lining of the uterus (also the days 5-8 of fertilisation)
  2. 2nd stage: cords of trophoblastic cells begin to penetrate the endometrium
  3. Advancing cords of trophoblastic cells tunnel deeper into the endometrium, caving out a hole for the blastocyst
  4. By day 12 implantation is finished & the blastocyst is completely buried in the endometrium. The site where the blastocyst penetrated the endometrium is now covered with a non-cellular plug
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6
Q

Describe the stages of placental development (ngl dont learn this for finals)

A
  1. Trophoblast cells (chorion) differentiate into multinucleate cells (syncytiotrophoblasts) which invade decidua and break down maternal capillaries to form cavities filled with maternal blood
  2. Developing embryo sends capillaries into the syncytiotrophoblast projections to form “placental villi” -Each villus contains foetal capillaries separated from maternal blood by a thin layer of tissue – no direct contact between foetal & maternal blood
  3. 2 way exchange of respiratory gases, nutrients, metabolites etc between mother and foetus, largely down diffusion gradient
  4. Placenta (& foetal heart) functional by 5th week of pregnancy
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7
Q

Prior to the placenta becoming functional in the 5th week of pregnancy what is fetal nutrition provided by ?

A

Early nutrition of the embryo - invasion of trophoblastic cells (syncytiotrophoblasts) into the decidua

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8
Q

What is the function of the placenta ?

A
  • Gas exchange - supply O2 & clearance of CO2
  • Nutrients supplied to fetus - H2O, glucose, electrolytes (iron,Ca2+), free fatty acids
  • Waste product removal
  • Acid-base balance
  • Hormone production - oestrogen, progesterone, HCG, Human chorionic somatotropin, human placental lactogen, placental growth hormone, relaxin & kisseptin
  • Transport of IgG - mainly in 3rd trimester
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9
Q

What hormone plays a crucial role in early nutrition of the embryo and how ?

A

Human chorionic gonadotropin (HCG) becuase it signals the corpus luteum to continue secreting progesterone which stimulates decidual cells to concentrate glycogen, proteins and lipids (the site that the embryo gets its early nutrition from)

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10
Q

What is the function of placental growth hormone ?

A

It promotes growth & has a similar effect on the maternal metabolism to lactogen

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11
Q

What is the function of relaxin ?

A

It causes relaxation of the pelvic ligaments & softening of the cervix

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12
Q

Why is the placenta so effecient at exchange of nutrients & waste materials ?

A

As placenta develops, it extends hair-like projections (villi) into uterine wall. This increases contact area between uterus and placenta & more nutrients and waste materials can be exchanged.

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13
Q

How does the placenta work as an arteriovenous shunt ?

A
  • Blood vessels from embryo develop in the villi. A thin membrane separates the embryo’s blood in the villi from mother’s blood in the intervillous space (ie. no direct contact between foetal & maternal blood).
  • Circulation within the intervillous space acts partly as an arteriovenous shunt (passage of blood directly from arteries to veins without going through capillaries)
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14
Q

How does O2 transport occur across the placenta?

A
  • O2 is transferred from maternal blood to the umbilical cord. The opposite occurs with C02.
  • Diffusion occurs because materal P02 is > fetal P02 (i.e. maternal blood is oxygen rich) and maternal PC02 < fetal PC02
  • Fetal O2 saturated blood then returns to the fetus via the umbilical vein
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15
Q

What 3 factors help supply the fetus with 02?

A
  1. Fetal Hb (increased ability to carry O2 compared to maternal Hb)
  2. Higher Hb concentration in fetal blood (50% more than in adults).
  3. Bohr effect (Fetal Hb can carry more oxygen in low pCO2 than in high pCO2)
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16
Q

Describe the diffusion of nutrients and waste products across the placenta

A
  • Water diffuses into placenta along its osmotic gradient. Exchange increases during pregnancy up to the 35th week (3.5l/day).
  • Electrolytes follow H20 (iron and Ca2+ only go from mother to child).
  • Glucose, (fetus’ main source of energy), passes the placenta via simplified transport.
  • Free diffusion of fatty acids
  • Diffusion of waste products is based on concentration gradient
17
Q

List the teratogenic drugs which can cross the placenta

A
  • Thalidomide, Carbamazepine, Coumarins, Tetracycline
  • Alcohol, nicotine, heroin, cocaine, caffeine
  • Drugs (excluding alcohol) - 3% of all congenital malformations
18
Q

What is the role of human chorionic gonadotropin (HCG) hormone during pregnancy

A
  • It prevents involution of Corpus Luteum (CL: stimulates progesterone, estrogen)
  • Also has an effect on the testes of male fetus - development of sex organs
  • Its levels during pregnancy peak at week 10 & then decrease and plateau
19
Q

What is the role of human chorionic somatomammotropin (HCS)?

A
  • Growth hormone-like effects: protein tissue formation.
  • Decreases insulin sensitivity in mother: more glucose for the fetus (as insulin isnt as good at converting glucose to glycogen ==> increaed free glucose in blood for fetus)
  • Involved in breast development.
  • It is produced from week 5 and levels increased until completion
20
Q

What is the role of progesterone throught pregnancy ?

A
  • |Development of decidual cells
  • Decreases uterus contractility
  • Preparation for lactation - development of lobule-alveolar system
  • Levels increase until completion
21
Q

What is the role of estrogens in pregnancy ?

A
  • Enlargement of uterus and increases contractility
  • Breast development - growth of ductile system (mammary glands)
  • Relaxation of ligments
  • Levels increase until completion
22
Q

What esotrgoen hormone is an indicator for the viability of a fetus ?

A

estriol

23
Q

Go over the hormone changes in pregnancy which can lead to problems

A
24
Q

What are the CV changes which occur during pregnancy ?

A
  • CO increases by 30-50% between weeks 6 to 24 due to the extra demands of the uteroplacental circulation (babies adding to mothers)
  • CO decreases during last 8 weeks (becomes sensitive to body position: uterus compresses vena cava)
  • Heart rate (HR) increases up to 90/min
  • BP decreases during 2nd trimester - nadir at 24 weeks
25
Q

What are the haematological changes which occur during pregnancy ?

A
  • PV increases by 50% ==> overall blood volume increases resulting in a decrease in Hb (due to dilution)
  • Erythropoesis (RBC) increases (25%)
  • Iron requirements increases significantly ==> supplements needed
26
Q

What are the respiratory changes which occur during pregnancy and why do they occur?

A

Occur because of increasing progesterone levels which tell the brain to decrease CO2 levels & the enlarging uterus interferring with lung function

Changes include:

  • Increased RR (to blow off CO2) and to meet increased O2 demand (increased by 20%)
  • Tidal & minute volume increase by 50%
  • pCO2 decreases
  • residual volume and expiratory reserve decrease
  • Vitcal capacity & PO2 dont change
  • FEV1 & PEFR unchanged
27
Q

What are the urinary changes which occur during pregnancy ?

A
  • GFR and renal plasma flow increases (up to 30 - 50 %: peaks at 16-24 weeks)
  • Increased re-absorption of ions and water due to Placental steroids and Aldosterone
  • Slight increase of urine formation
28
Q

Why does odema form in pre-eclampsia ?

A

Pre-eclampsia causing a decline in kidney function resulting in salt & H2O retention ==> causing oedema

29
Q

What is the average weight gain during pregnancy ?

A

Average weight gain – 24lbs, can be as much as 75lbs

30
Q

What are the extra nutritional needs of the mother during pregnancy ?

A
  • 250 - 300 extra kcal/day
  • Extra protein intake - 30g/day
  • Iron supplements - 300mg ferrous sulfate
  • B - vitamins - due to increased erythropoesis
  • Folic acid (folate) - reduces risk of neural tube defects
  • Vitamin D3 + Ca2+ supplements
  • Before parturition - K vitamin (prevention of intracranial bleeding during labour)
31
Q

Toward the end of pregnancy, uterus becomes progressively more excitable, why is this ?

A
  • The Estrogen:Progesterone ratio alters contributing to the increasing uterus excitability, because progesterone inhibits contractility while estrogen increases contractility.
  • Oxytocin (from maternal & fetal posterior pituitary gland): increases contractions and excitability
  • Oxytocin also stimulates the placenta to make prostagladins which stimulates more vigorous contractions of the uterus (these 2 hormones control onset of labour)
32
Q

Describe the way mechanical stretch and pain affect uterine contractility

A
  • Mechanical stretch of uterine muscles increases contractility
  • Stretch of the cervix also stimulate uterine contractions via positive feedback (as the contractility causes more stretch and so on) and also cause further oxytocin release
  • Strong uterine contraction and pain from the birth canal cause neurogenic reflexes from spinal cord that induce intense abdominal muscle contractions
33
Q

What are the hormones involved in the production and release of milk?

A
  • Both E & P play a role in breast development/ prep for lactation
  • Both E and P inhibit milk production. At birth sudden drop in E and P to allow milk production
  • Prolactin stimulates milk production (steady rise in levels wk 5 – birth). 1-7 days after birth, prolactin induces high milk production & also stimulates colostrum (low volume, no fat)
  • Oxytocin plays a role in the milk-let down reflex
34
Q

Describe the milk let down reflex

A
  • With sucking of the baby on the nippl or when babies cry, the hypothalamus is stimulated to release oxytocin and stop releasing prolactin inhibiting hormone
  • Prolactin then is not inhibted and causes milk secretion
  • Oxytocin causes smooth muscle contraction to aid milk ejection

Y4 Obstetrics and Gynaecology (63 decks)

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