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
What are some renal system changes during pregnancy?
- Enalrgement in length and weight of kidneys
- Dilation of ureters and of the renal pelvis
- Urinary stasis, raised pyelonpephritis risk
- Renal blood flow increases (30-50%)
- GFR increases by ~ 40%
- Reduced serum creatinine, urea
- Increased tubular reabsorption of Na+(RAAS)
- Glycosuria due to increased filtered load
- Erythropoietin for increased erythrocyte number
What are the renal heamodynamic and metabolic changes during pregnancy?
- Anatomical :
- Increase in kidney size (1cm)
- Dilation of the collecting system R>L
Glomerular hemodynamics :
- Vasodilation
- increase in RPF and GFR
Tubular function :
- Altered tubular reabsorption of protein, glucose, amino acids and uric acid
Electrolyte balance :
- Increased total body Na up to 900-1,000 meq
- Increased total body potassium up to 320 meq
- Decrease in set point for thirst and ADH release
- Expansion of plasma volume
What are the GI changes during pregnancy?
- Reduced motility of GI tract
- Increased absorption of vital nutrients
- May lead to constipation
- Relaxed lower oesophageal sphicter ( heartburn)
What are the stages of labour and delivery?
**Show **:
- Mucus plug is dislodged and comes through the vagina
Waters breaking **
- Leak or flood of amniotic fluid
** Regular, strong uterine contractions
- period pains, tightenings
**Cervical effacement and dilation
Descent of the presenting part (fetal skull)**
What are the triggers for labour?
Pregnancy = Relaxation associated Proteins (RAPs) compared to Contraction associated Proteins (CAPs) in Parturition
Quiescence ( Progesterone , Nitric oxidase, K+ channels) compared to activation (oestrogen, corticotropin releasing hormone (CRH), Oxytocin, PGE2, PGF 2a, IL-1b can trigger labour , stretch)
LABOUR NOT TRIGGERED BY PROGESTERONE WITHDRAWL IN HUMANS!
What are features of the myometrium of the vagina?
- Myometrial synchrony and pacemaker activity
- Myogenic, smooth muscle
What is Myometrial excitability ?
Myometrial excitability
RMP of cells (myocytes) is hyperpolarised
As pregnancy progresses, depolarisation
* Reaches threshold for Ca2+ entry
- VGCC
* Release of Ca2+ from intracellular stores
* Action potential generation
— AP complex, required for contractions
Gap junctions, syncitium
Phasic contraction-relaxation cycle
What are the stages of labour?
- First stage :
- Time between onset of labour and full cervical dilation 10 cm (latent and active phase ; hours long) - Second stage :
- From dilation to delivery (<1hr) - Third stage
- Delivery to expulsion of the placeta
What is the oxytocin positive feedback loop?
- Nerve impusles from cervix transmitted to the brain
- Brain stimulates pituitary gland to secre oxytocin
- Oxytocin carried in bloodstream to uterus
- Oxytocin stimulates uterine contraction and pushes baby towards cervix
- Head of baby pushes against cervix
LOOP
What is the progress of labour?
- Myometrial contractions :
- prelabour 10-20 mmHg ; labour : 100mmHg
- Contractions initiated in fundus cause shortening of muscle fibres
- Fetus moves further into birth canal
- Rupture of fetal membranes
- Delivery of baby followed by placenta
- Initiation of lactation
What are the cervical changes that occur during labour>
A- Cervix not effaced.Length of cervical canal = 4cm
B- Cervix partly efffaced. Length of cervical canal = 2cm
C- Cervix fully effaced
D- Cervix dilated 3 cm
E- Cervix dilated 8 cm
What is the purpose of oxytocin?
- Maintaining contractions
- Positive feedback effect on pituitary to aid delivery
- Preventing postpartum haemorrhafe
- Stimulates milk ejection
- Bonding
- To deliver placenta (syntocinon injection in thigh)
- Used to induce labour (syntocinon drip)
What are the 4Ps of Birth?
- Power :
- strength of uterine contractions and maternal efforts to expel in 2nd stage of labour
- Involuntary contractions that dilates and efface the cervix
- Urge to ‘push’ by mother as fetus pushes through the maternal pelvis, Symphisis pubis softened to relaxin
- Passenger : size and position (lie, presenting part) of fetus and placenta
- Psyche Patients psychological state during labour, anxiety, birthing partner support etc
What are Braxton Hicks Contractions?
- False labour pains- preparing for labour but not as a sign that labour is imminent
- Do not result in cervical dilation/ efface,emt
- Start in early pregnancy but not felt until second half of pregnancy ; similar to menstrual cramps
- BH contractions have been linked to promoting blood flow to the placenta
- BH contraction often irregular, of less force ; change with activity
- Often felt in abdomen and not like labour pain
What is abnormal labour?
- Aprprox 20% of all labours are protracted or arrest-leading to CS
- Power: hypocontractile, incoordinate contractions
- Passenger : fetal malposition, macrosomia, cephalopelvic disproportion
- Passage : Uterine abnormalities, obesity (first stage)
- Psyche : increasing pain, anxiety can have inhibitory effect on uterne contractility
- Preterm labour
What happens to prolactin levels during pregnancy>
- Decreases
- Inhibited by Progesterone and Oestrogen
What happens to prolactin levels at term?
- Increase
- Decrease in Progesterone and Oestrogen
- Leads to ability to breastfeed
What is lactogenesis?
- Postpartum levels prolactin stimulated by suckling
- Strength and duration of suckling- raised PRL
- Colostrum (protein, fat-soluble vitamins, maternal igAs, leukocytes) produced initially
- Mature milk rich in alpha-lactalbumi, lipids, lactose and vitamins B,C
- Lactoferrin binds iron for fetus
What is the relationship between oxytocin and Lactation?
- Milk ejection reflex induced by OT
- Suckling activates OT neurones in the oaraventricular and supraoptic nuclei in hypothalamus
- Increased OT and secretion from posterior pituitary reaches mammary glands
- Contraction of myoepithelial cells causes milk to pass into the ducts
- There is increased intramammary pressure leading to milk ejection reflex
- Promotes expulsion of the placent a
- Helps control haemorrhage after birth
- Helps uterus return to normal size
What is puerperium?
- The gradual return to the non-pregnant state ~6 weeks
- Immediate 24 hrs =
- Uterus contracts to stop bleeding from placental site
- Seex steroid hormone levels dramatically reduced
- Uterus dimishes in size under influence of oxytocin and enzymes (collagenase, MMPs)
- Cardiac output/ plasma volume/ respiration return to normal
- Endometrial regeneration
- Oxytocin levels high if breastfeeding
