Learning to do what mum used to do Flashcards
What are the 4 principle routes of heat loss?
Radiation
Conduction
Convection
Evaporation
What is radiation?
transfer as infrared rays from warmer to cooler object
What is conduction?
transfer between materials in direct contact
What is convection?
transfer by movement of gas or liquid
What is evaporation?
heat consumption in association with conversion of liquid to vapour
What are the 3 methods of heat gain/conservation?
Metabolic activity
Shivering
Decrease in blood flow in dermis
What are the 2 mechanisms for heat loss?
Sweating
Increase in blood flow in dermis
What is the series of events that follows a decrease in body temperature?
Detection by thermoreceptors (skin & hypothalamus)
then
Transmission of signal to control centre in hypothalamus (via nerve impulses) & to anterior pituitary (via TRH)
then
Vasoconstriction in dermisActivation of shivering increased in metabolic activity
What is the series of events that follows a increase in body temperature?
Detection by thermoreceptors (skin & hypothalamus)
then
Transmission of signal via nerve impulses to control centre in hypothalamus
then
Vasodilation in dermis in sweating then an increase in heat loss by evaporation
What are the key differences in newborn infants?
Low body weight/surface ratio then capacity for heat production per unit surface area approx 50% adult capacity
Unable to shiver
Presence of brown adipose tissue
Substantial decrease in capacity to lose water by sweating per unit surface area
Limited ability to alter behaviour in response to heat/cold stress
What is Brown Adipose tissue and what is it used for?
Specialised heat-generation tissue
Fat store
High capacity for fatty acid catabolism - hydrogen atoms/electrons
Many mitochondria
Inner membrane contains special protein that allows reversible disruption of control of oxidative phosphorylation - heat generation
How is brown adipose tissue used as a control?
Cold exposure - catecholamine release
In brown adipose tissue - activation of:Breakdown of stored fat;Oxidation of fatty acids;Mitochondrial uncoupling
Latter involves reversible opening of proton channel in inner mitochondrial membrane
What are the 3 principles of waste disposal?
Major excretory routes = urine & bile
Both aqueous solutions - can only be used by relatively water soluble substances
Many foreign substances (xenobiotics) & metabolic waste products relatively insoluble - need to be metabolised prior to excretion
How does waste processing occur?
Major organ = liver
Overall aim: increase water solubility
Typically 2 phases
First phase = preparationInvolves insertion of reactive group into molecule, e.g. hydroxyl (-OH)
Second phase = conjugation Involves attachment of conjugating group to molecule, e.g. glucuronide
Is jaundice a disease?
Hyperbilirubinaemia, i.e. excess bilirubin in the circulation
Is jaundice always associated with pathological changes?
Some increase during first few days after birth “normal”
Is it only caused by liver/bile duct problems
Many different causes
What might high concentrations of bilirubin do?
Neurological damage
Describe the process of bilirubin metabolism
Red cell breakdown, haemoglobin catabolism & haem release - Haem catabolism - bilirubin - Transfer of bilirubin to liver - Uptake by liver cells (hepatocytes) & conjugation - Release of conjugate - bile
What are the factors that increase plasma unconjugated bilirubin?
Rate of supply > rate of conjugation due to: increase in red cell breakdown Problems with transfer to liver Limited uptake by hepatocytes Inadequate conjugation capacity increase in bilirubin recycling
Why are newborns susceptible?
High rate of haem catabolism due to faster red blood cell turnover & increase in relative red blood cell mass
decrease in bilirubin uptake by hepatocytes due to low level of carrier protein
Limited conjugation capacity
increase in recycling from gut due to lack of microbial metabolism of deconjugated bilirubin
Breast milk jaundice
Breastfeeding causes 3 x increase in moderate jaundice & 6 x increase in severe jaundice (plasma concentration > 200uM & 250uM, respectively)
Average plasma concentration higher in breast fed infants throughout first 5 days after birth
Whatis the aetiology?
No evidence for higher bilirubin production in breast fed infants
Breast milk may contain conjugation inhibitor, e.g. pregnanediol (steroid) &/or enzymes that catalyse deconjugation
May be increase in bilirubin recycling from gut due to slower clearance of meconium &/or differences in microbial colonisation
What other factors could there be?
PrematurityExpression of conjugating enzymes controlled by stage of development
Bruising, e.g. due to use of forceps
Delay in cord clamping increase in blood transfer to newborn
Use of oxytocin
Dehydration &/or under nutrition
Poorly controlled maternal diabetes mellitus
What are the interpretation problems
Pathological changes superimposed on physiological changes
Plasma bilirubin concentration changing rapidly
Individual variation in absolute levels & time-course of changes
Individual variation in sensitivity to toxic effects
Toxicity modified by other factors, e.g. condition of the baby
What is the treatment?
Exchange Transfusion
Used in otherwise healthy term infants if plasma concentration > 350mM
Phototherapy
Absorption of blue/green light by bilirubin - products which are more water soluble - excreted
Used in otherwise healthy term infants if plasma concentration > 250mM
