Learning to do what mum used to do

Question 1

What are the 4 principle routes of heat loss?

Answer 1

Radiation
Conduction
Convection
Evaporation

Question 2

What is radiation?

Answer 2

transfer as infrared rays from warmer to cooler object

Question 3

What is conduction?

Answer 3

transfer between materials in direct contact

Question 4

What is convection?

Answer 4

transfer by movement of gas or liquid

Question 5

What is evaporation?

Answer 5

heat consumption in association with conversion of liquid to vapour

Question 6

What are the 3 methods of heat gain/conservation?

Answer 6

Metabolic activity
Shivering
Decrease in blood flow in dermis

Question 7

What are the 2 mechanisms for heat loss?

Answer 7

Sweating

Increase in blood flow in dermis

Question 8

What is the series of events that follows a decrease in body temperature?

Answer 8

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

Question 9

What is the series of events that follows a increase in body temperature?

Answer 9

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

Question 10

What are the key differences in newborn infants?

Answer 10

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

Question 11

What is Brown Adipose tissue and what is it used for?

Answer 11

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

Question 12

How is brown adipose tissue used as a control?

Answer 12

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

Question 13

What are the 3 principles of waste disposal?

Answer 13

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

Question 14

How does waste processing occur?

Answer 14

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

Question 15

Is jaundice a disease?

Answer 15

Hyperbilirubinaemia, i.e. excess bilirubin in the circulation

Question 16

Is jaundice always associated with pathological changes?

Answer 16

Some increase during first few days after birth “normal”

Question 17

Is it only caused by liver/bile duct problems

Answer 17

Many different causes

Question 18

What might high concentrations of bilirubin do?

Answer 18

Neurological damage

Question 19

Describe the process of bilirubin metabolism

Answer 19

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

Question 20

What are the factors that increase plasma unconjugated bilirubin?

Answer 20

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

Question 21

Why are newborns susceptible?

Answer 21

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

Question 22

Breast milk jaundice

Answer 22

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

Question 23

Whatis the aetiology?

Answer 23

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

Question 24

What other factors could there be?

Answer 24

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

Question 25

What are the interpretation problems

Answer 25

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

Question 26

What is the treatment?

Answer 26

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