1 Biology Of The Neonate - University Of Hertfordshire

Biology of the NeonateJulia Petty

The NeonateNewborn the first 24 hours of lifeNeonate the first 28 days after birthInfant The first year of lifeA period of transition for both baby and thefamily. Survival is now extrauterine whichposes a physiological challengeLife tasks at birth: independent breathing,change from fetal to neonatal circulation,establishment of early feeding, thermal andglucose control and changes to fluid balance(File adapted from Petty, 2011- a,b and c)

First week of lifeStabilisation of body temperatureFeedingBladder and bowel functionRed blood cell breakdown /homeostasis

First year of life & beyondImmune response develops furtherDigestive function maturesAdult haemoglobin (Hb) is produced by6 monthsNeuro-endocrine function maturesfurtherRespiratory – alveolar growth continuesup to 3-5 yearsKidney function matures up to 2 years

Physical FeaturesWeight average birth weight 3.5kg.Lose 5-10% birthweight in the 1st weekof life and regains by day 10. Steadygain at 180-210 g per week thereafter.Length 51 cm average (50th centile)Head circumference (occipito-frontal) 35-36 cm and grows 2cm in first monthappearing larger than the chest

Birth weight on 50th‘centile’

The Head & faceUnfused cranial (skull bone) sutures forfirst 12-18 monthsPosterior fontanelle closes at approx. 68 weeks and anterior fontanelle atapprox. 18 monthsSkin should be clear, soft and silky andmay be covered with vernix and lanugoJaundice may be evident at 3 - 10 daysin a significant proportion of neonates.

Normal skin–with milia (small white spots)

The Trunk & LimbsShould be well aligned with arelatively large abdomenUmbilical cord separates 7-10 daysLimbs equal in length with correctnumber of digitsGood movement & tone ‘physiological flexion’Hips checked for dislocation

Respiratory systemShorter, narrower airways –Large tongue and large floppyepiglottisHigh epiglottisAirway shape more like a coneNose breathersDiaphragm is the main respiratorymuscle

Cardiovascular systemCirculating blood volume 85ml/kgHigher Hb and haematocrit in earlydays75-84% of Hb is fetal until 6months when adult Hb is produced

MetabolicHigh metabolic rateHigh oxygen and energy needsLimited nutrient storageGlycogen stores easily depletedLess able to mount metabolicresponse to stressHigh energy need for growth

NeurologicalThe normal neonate is expected toreact to certain stimuli in a particularway which gives an indication ofnormalityReflexes - abnormal, absent ofdelayed OR prolonged ? May besignificant

The SensesSight Eyes open and attention to visualstimulus. Prefer faces and brightness. Fix &follow at 6 weeks with full 20- 20 vision atapprox. 4-6 months.Hearing head turns, prefers human voicesTouch responsive, rooting, hand-to-mouthSmell breast milk and mother’s skinTaste differentiates sweet / sourPain perception is present

Normal neonatal behavioural states 5 behaviours 1 asleep2 awake / fussy3 awake and quiet4 awake and focusing / alert5 – crying tes-of-alertness/

Behaviour 1Asleep

Behaviour 2 – awake & fussy

Behaviour 3awake andquiet

Behaviour 4- awake and alert /focusing

Behaviour ng newborn.jpg

The gut & feedingMeconium passage in 12 - 24 hours,changing stools from Day 3Sucking coordinated at 34 weeksgestationStomach capacity increases rapidly infirst few weeksEnzyme function matures in 1st yearLower oesophageal sphincter (muscle)is weak (reflux common)

Renal / FluidsTotal body water is 75 %High proportion of extra cellular fluidHigh surface area to volume ratioFunctionally immature kidneysFirst urine should be passed at birth orwithin the first 24 hoursBuild fluid intake up gradually - normallythe neonates guages this naturally

Immune SystemLow levels of specific immunoglobulinsReduced antigen recognitionLocal bacterial infections can easilyprogressPassive immunity for a given period

ThermoregulationImmature hypothalamus along with highsurface area predisposes to poortemperature controlSubcutaneous & brown fat reduced (inpreterm)- thermogenesis from brown fatoccurs instead of shiveringSweat mechanism is poor and ability tospontaneously generate heat.

Further ReadingPetty, J. (2011a). Fact Sheet; Neonatal Biology – An Overview Part 3.Journal of Neonatal Nursing, 17(4), 128-131.Petty, J. (2011b). Fact Sheet; Neonatal Biology – An Overview Part 2.Journal of Neonatal Nursing, 17(3), 89-91.Petty, J. D. (2011c). Fact Sheet; Neonatal Biology – An Overview Part1. Journal of Neonatal Nursing, 17(1), 8-10.For further detail and more resources, go to the onlineresource Units 2D and 2Ehttp://www.cetl.org.uk/learning/neonatal/unit atal/unit 2e/player.html

Fact Sheet; Neonatal Biology –An Overview Part 3. Journal of Neonatal Nursing, 17(4), 128-131. Petty, J. (2011b). Fact Sheet; Neonatal Biology –An Overview Part 2. Journal of Neonatal Nursing, 17(3), 89-91. Petty, J. D. (2011c). Fact Sheet; Neonatal Biology –An Overview Part 1. Journal of Neonatal Nursing, 17(1), 8-10. For further detail and more resources, go to the online resource .