Physiological Adaptations to Pregnancy Flashcards
What are the key stages of pregnancy?
- First trimester : 1-12 (3-8) weeks/ preembryonic and embryonic stages
- Second trimester : Weeks 13-16 (9-40) (24) - stages = fetal development ( fetal period) (viability)
- Third trimester : week 27-40 (38-42) - Stages ( Maturation Delivery
- Delivery + 6weeks (Puerperium) due date from LMP (14 days to ovulation)
What are the first signs of pregnancy?
- Nausea (morning sickness)
- Hyperenesis gravidarum 0 extreme form of nausea - treated with antiemetics, injections
- Amenorrhoea - missed period
- Breast tenderness due to increased production of steroid hormones
- Fatigue
- Food cravings ‘PICA’- more sensitive sense of smell
Describe weight gain during pregnancy.
- MATERNAL :
- MYOMETRIUM 0.9 kg
- fat 4kg
- blood 1.2 kg
- FETAL :
- PLACENTA 0.7 kg
- Amniotic fluid 0.8 kg
- Fetus ~ 3.3 kg
Essential nutrients : Folic acid ( Pre-pregnancy), iron, Vitamin K, Vitamin B
What is spinal arter?y remodelling
- the vessel structure changes with loss of vascular cells, and this increases the size of the arteries to create a high-flow, low resistance vessel.
- These changes - brought about partially by maternal immune cells (dnK cells and macrophages) and completed by invading interstitial and endovascular EVT. The remodelled vessel consists of trophoblasts embedded in a fibrinoid material as a replacement for the VSMCs, with subsequent re-endothelialisation occuring later in pregnancy
What are structural/anatomical changes that occcur during pregnancy?
Structural/anatomical changes…
Invasion of endometrium and
uterine arteries by trophoblast
Formation of placenta
* Growing fetus displaces
diaphragm, heart, bladder
Myometrial cells undergo
hyperplasia and hypertrophy
Cervix firm and non-compliant
- Mucus plug formed thereby
maintaining closed uterine
environment - Measuring fundal height ( —1 cm per week)
What are some pigmentation/ skin changes during pregnancy?
- Melasma/ Chloasma, Linea nigra
- caused by production of melanocyte stimulating hormone by oestrogen
- Caused by thinning of collagen fibres and skin distension
- Stretch marks
- Line down the middle of belly
What is maternofetal transfer?
- no mixing of maternal and fetal blood
( haemochorial placentation) - Chorionic villi in close contact with maternal blood
- Hugely increased SA provided by chorionic villi
- Syncytiotrophoblast membranes provide a barrier to large proteins
- Permeable to alcohol ( fetal alcohol syndrome), heroin, nicotine , caffeine
- Teratogens - e.g. thalidomide
- Placenta ; chorionic villi, stem villi
- Umbillical cord : Wharton’s jelly (glycosaminoglycans - water soluble products)
- Two arteries : deoxygenated blood to placenta
- One vein : oxygenated blood to fetus
What is uteroplacental bloodflow?
- Maternal blood flow through the placenta
- 300ml/min @20 wks
- 600 ml/min @40 wks
How does the pocess of maternofetal transfer work?
3 shunts in fetus:
- Lungs bypassed via the ductus arteriosus
- Liver bypassed by the ductus venosus
- Foramen ovale shunt blood between the right and left atria
- Shunts are closed by the first breath of the baby as O2 levels rise and by increased blood pressure
- Prostaglandins from the placenta keeps shunts open
What is the function of the placenta?
- Nutrient and gas transfer
- Gaseous exchange by passive diffusion
- Glucose-main energy substrate for fetus : f. diffusion (GLUT-1 transporter) ; maternal insulin resistance
- Transfer of waste products
- Disposal of waste products (urea, creatinine, billirubin down conc.gradients)
- Immune protection IgG crosses the placenta as fetus has no developed immune system
- Steroid and peptide hormone production (steroids, hPL, hCG, relaxin, leptin)
- Support for the fetus
- Amnion : strong, expands to accomodate fetus
- Amniotic fluid : cushioning, movement
- Umbilical cord : attachment
- Active transport of a acids, water-soluble vits, Ca2+ Fe2+ (System A transporter)
- Pino/endocytosis- lipoproteins , viruses, IgG, Iron (Transferrin transporter)
- Bulk flow (Water, electrolytes)
What are the main function of sex steroids in pregnancy?
Main Function of Sex Steroids
Oestrogen
Stimulate uterine growth through endometrium/myometrium
— Initiates cardiovascular changes
Promote ductal development in breast
Effects on connective tissue
Oestrogens (oestriol -90%)
Progesterone
Implantation, maintenance, antagonists are abortifacients
Decidualization of endometrium
Progesterone (pro-gestation)
Uterine quiescence
Generalized relaxant effect on musculoskeletal system
Respiratory changes
Promotes alveolar development in breast
What are other hormones of pregnacy?
. Relaxin
- Corpus luteum, decidua, trophoblast, fetal membranes
- Uterine relaxation, softening
* Human chorionic gonadotrophin (bhCG)
- Syncytiotrophoblast
- Maintains corpus luteum, immune tolerance
* Human placental lactogen (hPL)
- Syncytiotrophoblast
Breast development, inhibits maternal glucose uptake
* Oxytocin
Posterior pituitary
* Uterotonic
* Prolactin
* Anterior pituitary, decidua
* Amniotic fluid genesis, osmolarity and volume, immunity
What are the haematological changes during pregnancy?
- 40-50% increase in plasma volume
- Increases nutrient delivery
- Erythrocyte number increases but less than plasma volume
- Total Hb decreases overall
- Haemodilution - (need for iron supplementation as demand increases)
- Pregnancy is a ‘hypercoagulable’ state
- Thrombin, fibrinogen, VII, VIII, IX, X
What are the changes in the respiratyory system during pregnancy?
Respiratory System Changes
Progesterone effects via respiratory
centre
Little change in respiratory rate
15-20% increase in 02 consumption
40% increase in minute ventilation due to
increased tidal volume.
pC02 lowered (respiratory alkalosis) but
increased renal compensation through
bicarbonate maintains mild alkalotic
blood pH
C02 gradient helps fetus
Hyperventilation
Dyspnoea - combination of acid-base
balance, metabolic adjustments,
increased perception of discomfort on
breathing
-egg
