foetal adaptations of pregnancy and birth

intrauterine environment

• why do babies not need to generate their own heat

• how is their metabolic demand/energy kept low

• why do they not need to defecate

• why do they not need lungs or an active GIT

• Warm environment, dont need to generate own heat  

• Long nap times, no need to wake or move  

• Automatic waste filtration, no need to defecate  

• Ready oxygen supply, no need to use lungs  

• Ready food source, no need to eat  

respiration

• where is the site of gas exchange in foetus

• how do they ‘practice‘ breathing in the uterus, what pressure does this create

• why do they do this 2

• Placenta is the site for gas exchange in foetus  

• Foetal lungs undergo structural changes throughout pregnancy  

• Spend 1-4 hours each day making rapid respiratory movements  

• Creates negative pressure in chest  

• Diaphragmic  

• Moves amniotic fluid in and out of lungs  

• ‘practice’ 

• Promotion of lung growth  

why does the first breath need to happen

• what mechanisms can also encourage this

Upon birth, the neonate needs to clear its airways of fluid  

• Cold exposure  

• Environmental stimulation 

• Tactile  

• Gravitational  

• Auditory  

• Noxious  

what are the difficulties a neonate has to overcome on the first breath

• compliance

• fluids

• ST

• Low compliance of uninflated lungs  

• The viscosity of any remaining fluids in the airway  

• The surface tension created by the establishment of the air-water interface in the lungs  

• which cells secrete surfactant

• what does this help do

Type II pneumocytes  

• Secrete pulmonary surfactant 

• Helps reduce surface tension at newly formed air-water interface  

name a condition that is caused by a lack of surfactant (IRDS)

• why is this an issue

• symptoms

• treatment

• what does CPAP stand for

Infant respiratory distress syndrome  

• Risk increases with reduced gestational age   

• Failure to produce sufficient surfactant  

• Struggle to overcome increased surface tension  

• Main airways closed due to atelectasis  

Symptoms  

• Cyanosis, tachypnoea, tachycardia, nasal flaring, chest retractions and expiratory grunting  

Treatment  

• Injecting mother with glucocorticoids  

• Prior to pre-term birth  

• Provision of oxygen  

• CPAP – continuous positive airway pressure  

• Endotracheal tube  

• Introduction of exogenous surfactant  

• Breathing tube  

foetal circulation adaptations

• how do the ventricles pump

• what are the 3 vascular shunts

  • what is the purpose of these shunts

1. Two ventricles pump in parallel, rather than in series in the foetus  

2. Three vascular shunts (ductus venosus, foramen ovale, and ductus arteriosus), divert blood away from the lungs and liver towards the placenta  

explain the 3 vascular shunts

ductus venosus- bypasses the liver (U cord - ivc/heart)

foramen ovale - bypasses lungs (from r-l atrium to pump round the body)

ductus arteriosus - bypasses lungs (pulmonary artery - aorta)

haemodynamics: pre-birth

• why does the lungs have high vascular resistance

• what does a low systemic vascular resistance allow blood to travel to

• where does oxygenated blood travel to

• where does blood that travels into the RV travel to

High pulmonary vascular resistance

• needed to ensure that blood bypasses the fluid filled, non functioning lungs

• Collapsed, fluid filled lungs  

• Hypoxic pulmonary vasoconstriction  

Low systemic vascular resistance  

• Placenta  

• Highest O2  

• Umbilical vein -> ductus venosus -> IVC -> foramen ovale -> LV -> ascending aorta  

• Lower O2 

• SVC -> RV -> ductus arteriosus -> descending aorta  

haemodynamics: birth

• what does cord clamping increase 3

  • contributes to the closure of which shunt

• first breath decreases what pressure (pvp)

Cord clamping increases SVR  

• Aortic pressure increases  

• Left ventricle afterload increases  

• Left atrium pressure increases  

  • Contributes to foramen ovale closure  

First breaths decreases PVP  

• Lung fluid absorbed and alveoli expand  

• Increased alveolar O2 reverses hypoxic pulmonary vasoconstriction  

• Pulmonary blood flow increases  

• Right atrial and ventricular pressure falls  

rise in PaO2

• inhibits what channel

• polarisation effect on sm

• what type of Ca2+ channels open

• causing what shunt to constrict

• Inhibition of voltage-gated K+ channels  

• Smooth muscle depolarisation  

• Opening of L-type Ca2+ channels  

• Increased intracellular Ca2+  

• Ductal constriction (ductus arteriosus)

thermoregulation

• name 3 ways to increase bosy temperature

• 4 ways of decreasing it

• basal metabolic rate, shivering/muscle contraction, non shivering thermogenesis

• conduction, convection, radiation, evaporation

what is BAT

• where is it significantly distributed round and why

Brown adipose tissue and non-shivering thermogenesis  

• Significant distribution of BAT  

• Interscapular region  

• Clavicles  

• Heart and aorta  

• Trachea  

• Kidney  

• Pancreas  

• Central blood vessels to ensure core body temperature stays high  

non shivering thermogenesis

• what 2 things does it have an increased consumption of

• what is the result of cold stress

• this can lead to a risk of

Non shivering thermogenesis  

• Increase O2 consumption by 2-3x  

• Increased glucose utilisation  

Consequences of cold stress  

• Increased metabolic rate -> increased O2 consumption -> increased O2 production  

Risk of: 

• Hypoxaemia  

• Anaerobic metabolism  

• Lactic acidosis  

• Pulmonary vasoconstriction ->^ PVR  

• Risk of persistent pulmonary hypertension of the newborn  

WHO warm chain examples

• warm delivery room

• immediate drying

• skin to skin

• breast feeding

• clothing

• warm transportation

energy stores

• what is usual gestation duration

• why does the placenta have a high amount of glycogen storage

• 36-40 week gestation  

• Insulin and high placental glucose delivery drive hepatic glycogen storage  - Glycogenesis  

• Preparation for a rapid release glucose reserve for the first hours after birth  

GI maturation

• what digestive enzyme is very high at birth

• what DE is low, why

• what 2 will increase after birth

• what proteins can GIT absorb

• why are bile and pancreatic lipase low 2

• Lactase relatively high at birth – cortisol  

• Amylase low (pancreatic and salivary) 

• Limited starch digestion  

• Pepsin and trypsin activity increases postnatally  

• Neonatal gut can absorb intact proteins (important for IgA, growth factors) 

• Bile acids and pancreatic lipase low  

• Human milk lipase compensates  

• Efficient fat absorption  

pre-term babies - GIT

• what is an issue with the GIT

  • symptoms

Underdeveloped GIT  

• Poorly coordinated motility > gastric reflux  

• Slowed gastric emptying  

• Slowed transit through the GIT  

• Feeding intolerance  

• Necrotising enterocolitis (GIT dies and leaves hole, bacteria can enter abdomen)

renal system - foetus

• what concentration of urine do babies produce

• GFR rate

• Foetal kidneys mainly produce hypotonic urine – amniotic fluid  

• Low GFR, low concentrating ability, limited sodium reabsorption  

• Renal blood flow is due to high pulmonary vascular resistance  

• Foetal aldosterone rises in late pregnancy  

at birth: renal

• what can low GFR and immature tubules lead to

• what 3 substances are released (adrenal G, liver, kidney) for homeostasis of BP, and salt conc

Low GFR and immature tubules  

• Vulnerability to dehydration, overload, hyponatraemia, acidosis  

The neonate most maintain blood pressure, circulating volume and electrolyte balance alone  

• This triggers: 

• ^^ renin release  

• > ^ angiotensin II  

• > ^ aldosterone secretion  

• Aldosterone becomes a primary stabiliser of neonatal homeostasis  

how does kidney function mature (DCT)

• Distal tubules become more responsive to aldosterone