General physiology

Question 1

Regulation of body temperature

Answer 1

Anterior hypothalamus

Activation of heat sensitive neurons –>

• Skin vasodilation
• Sweating

Activation of cold-sensitive neurons –>

• Inhibition of heat-sensitive neurons
• Vasoconstriction
• Shivering

Question 2

Reflex vasoconstriction

Answer 2

Contact with cold stimulus of a limb –> vasoconstricton of ipsilateral and contralateral cutaenous area

Afferent: cutaneous nerve

Centre: hypothalamus and spinal cord

Efferent: Sympathetic nerves

Question 3

Reflex vasodilatation

Answer 3

Reflex vasodilatation occurs when radiant heat is applied to part or the whole of a body.

Afferent neuron: cutaneous nerve.

Centre: above C5 of the spinal cord

Efferent pathway: sympathetic nerves (reduced activity).

Question 4

Variation in core temperature

Answer 4

Higher in the evening vs morning

Higher in luteal / latter half by 0.5 C

Question 5

Heatstroke

Answer 5

Occurs when core body temperature reaches 41 C

Hypothalamus moves set-point inappropriately so lose ability to lower temperature

Question 6

Anaesthetic effects on thermoregulation

Answer 6

Depresses hypothalamic function

Vasodilatation with increased heat loss

Lack of shivering

–> Hypothermia

Question 7

Body water composition

Answer 7

70 kg bloke

25L intracellular 60-65%

19L extracellular 35-40%

• -> 3L is blood plasma 5%
• -> 15L interstitial fluid 24%
• -> 1L transcellular fluid e.g. CSF, peritoneal, intraocular

Question 8

Obligatory urine volume

Answer 8

600 mosmol of solutes must be excreted each day in the urine

Maximal achievable urinary osmolality is about 1200
mosmol/L and therefore the obligatory volume of urine
is about 500 mL per day.

Question 9

Re-absorbtion of Na in kindey

Answer 9

99% filtered Na is reasbsorbed

65% on PCT
25% in the loop of Henle,
10% in the distal tubules and collecting ducts

Question 10

Renal Na control

Answer 10

Renal
-eGFR
-prostaglandins
AT II –> constriction of renal glomerular arterioles –> reducing eGFR
AT II –> increased Na reabsorption nephron segments

Question 11

Extra-renal Na control

Answer 11

Extra-renal

• Renn-Angiontensin – > Aldosterone
• Atrial natriuretic peptide

Aldosterone promotes sodium reabsorption in the
distal tubule and collecting ducts as well as in colonic
epithelium and the ducts of salivary and sweat
glands

ANP is released from the cardiac atria in response
to stretch.
–> ANP increases the excretion of Na+:
■ by increasing GFR
■ inhibiting Na+ reabsorption in the collecting ducts
■ reducing the secretion of renin and aldosterone