Neonatal physiology Flashcards
Explain newborn immunity
- Infant exposed to microoganisms at birth- transition from sterile to an antigen rich environment
- Passive immunity provided by maternal IgG crossing placenta
- IgA present in colostrum - passive immunity, protects stomach bt coating it
- IgM produced in blood as initial response to infection, commences at birth
- Little exposure to pathogens in utero
- Avoid activation of proinflammatory responses via Th2-cell activation
- Innate immunity initially activated
- Rapid colonisation of skin and gut (epithelia) by microorganisms
- Acute-phase immune response activated immediately
Facts about neonatal skin?
- Neonates covered with vernix
- Rash after birth
- Erythematous
- response to commensal organsisms (gram positive S.aureus)
- Maturation of immune system
What is the vernix caseeosa ?
- Vernix caseosa
Vernix (varnish) caseo (cheesy)
White, cheesy, lipi-rich, waxy biofilm covering infant in utero and at birth.
Produced at rv20 weeks by stratum corneum with corneocytes producing it
Facilitates adaptation of skin to external environment
Benefits
Easier passage through the birth canal
Waterproof, protective, temperature regulation
Anti-microbial properties against E. coli, Group B Streptococci, Candida etc, contains
antimicrobial peptides eyc defensins, antimicrobial free fatty acids
Aids swallowing reflex at birth, prepares for immunity and exposure to breastmilk.
Natural moisturiser
Wha are features of neonatal lungs?
- No Toll like receptor expression in lungs until late in gestation
- Environmental products/ amtigens link to allergy
- Overall, respiratory system prevents exaggerated inflammation
What is fetal oxygenation?
- Fetus has more RBCs and higher Hb than adult
- Fetal Hb has greater affinity for oxygen (Lower p50) than adult Hb hence better pick-up of O2 from mother’s blood
- Production of fetal Hb switched off at birth and replaced with adult Hb by 6 months
- Partial pressure of gas required to achieve 50% saturation of protein’s Hb binding sites
What are some fetal adaptations?
Fetal adaptations
Respiratory System
in utero, lungs are fluid-filled,
Surfactant, produced @24 weeks, prevents collapse of alveoli, ability of lungs to fill
during delivery, compression of fetal thorax draws air 02 into lungs and expansion of
alveoli, pushing out fluid
* first breath drawn (gaseous exchange established)
Decrease in pulmonary vascular resistance and an increase in pulmonary blood flow
after cord is cut, increased C02 levels in blood and low 02 *acidosis
* respiratory centre in the medulla is stimulated by acidic pH and breathing stimulated via
carotid chemoreceptors
* closure of shunts
— foramen ovale closes at moment of birth
— deoxygenated blood diverted to fetal lungs for the first time.
— ductus arteriosus & umbilical vein close down by muscle contractions & become
ligaments
What are the fetal shunts?
Foramen ovale : betwen right and left atria of fetal heart
- allows blood to bypass lungs
Ductus arteriosus : Lies between pulmonary artery and aorta
- Blood bypasses lungs
Ductus venosus : Found on underside of fetal liver
- Bypasses hepatic circulation to deliver oxygen to vital organs
What are the circulatory changes in neonates?
- Low PVR prevents blood flow through ductus arteriosus
- Increase in pulmonary blood flow as PVR decreases
- Shift from oxygen provision by placenta to lung
- May require more than one breath to inflate lung at delivery
- One third lung fluid removed by compression of fetal chest through nose/ mouth during delivery
- Remainder exits through alveoli into lymph surrounding fetal lung
What is the thernogenesis in neonates?
- Neonates lose heat rapidly
- Radiation and evaporation - non contact mediated heat loss to environment from body surface
- Infant : large surface area to volume, thinner layer of insulation
- Temp falls 2-3 degrees after birth and activates cold’induced metabollic response by receptors
- Moving from uterus to lower ambient temperatures with delivery (convection)
- Loss of heat by direct skin contact (conduction)
How do neonates generate heat?
- Limb movements, restlessness - increases BMR
- Non-shivering thermogenesis : brown adipose tissue (BAT) to generate heat but uses more oxygen and can lead to hypoxia
- Mediated by norepinephrine (synpathetic nervous system), binding to adrenoreceptors and lipolysis to generate FFFAs that activate uncoupling proteins (UCPs) located along the inner membrane of mitochondria leading to heat production
- BAT highest around adrenals and kidneys but also around trachea, oesophagus, heart, liver, neck muscles
Describe the intestinal tract in neonates?
- Fetal intestine bathed in sterile amniotic fluid
- 36 wks+ - Gl tract fully mature for simple digestion
- After delivery, rapid colonisation takes place
- Toll-like receptors (TLR4 activated by lipopolysaccharide) expressed on fetal enterocytes
- However endotoxin tolerance to prevent exaggerated responses
- Breastfeeding
What are other adaptations in neonatal physiology?
- Production of urine
- Newborn unable to concentrate urine, GFR low due to immaturity of glomeruli although full complement (1 million) present
- Hepatic function :
- Coagulation : Vit K required for coagulation products. At birth, levels low and given prophylactically to prevent diseases of bleeding (haemorrrhagic disease of the newborn).
- Uncojugated billirubin
- Billirubin produced from RBC breakdown, low liver capacity to convert billirubin to a water-soluble, conjugated form
- Jaundice, potentially toxuc
- Exposure to light at birth
- External sounds stimulate hearing
What is the neonatal assesment?
- APGAR score (Appearance, Pulse, Grimace, Activity, Respiration
- Measures how well newborn adapts to life and if ithey need immediate treatment
- Each scored out of 2/ overall 10
- Assess vital signs at 1 min, 5 min, 10 min
- Score 0,1,2 - critically low
- Score 4 to 6 - fairly low
- Score 7 to 10 - generally normal
