The story so far...

1
The story so far...

• http//pcwww.liv.ac.uk/dcmt/cvs10.ppt
• intrinsic (Starlings Law)
• extrinsic (principally autonomic)

Stroke volume
Cardiac output
Heart rate
2
Postulated mechanism

• Increased sympathetic activity
• Leads to increased cardiac output
• And peripheral vasoconstriction (to protect the
  capillary beds)
• Drop in blood flow
• Triggers renin-angiotensin system

3
Evidence

• Cross transplantation studies show that essential
  hypertension has its origins in the kidneys.
• Human and animal studies
• So does renal denervation
• Little evidence that stress is involved
• But, of course, drugs that decrease sympathetic
  activity lower blood pressure.

4
Control
Autonomic N.S.
Volume
ADH
Pressure
Chemicals
Angiotensin
Local Blood Flow
5
Pressure

• Sensed by baroreceptors
• in carotid arteries and aortic arch
• an increase in pressure causes a decrease in
  sympathetic activity
• a decrease in pressure causes an increase in
  sympathetic activity

6
Volume

• Sensed by atrial volume receptors
• A decrease in volume
• causes an increase in ADH secretion
• and a decrease in ANF secretion

7
Chemicals

• A decrease in O2, or more usually an increase in
  CO2 or H2 causes an increase in chemoreceptor
  activity which
• increases sympathetic activity

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Local Blood Flow (kidney)
Vasoconstriction
9
Hormones

• Angiotensin II is a vasoconstrictor
• Aldosterone increases vascular sensitivity to
  Angiotensin II
• ADH (anti-diuretic hormone) increases water
  reabsorption
• ANF decreases sodium reabsorption

10
Overview
ADH
vol
baro
veins
capillary pressure
chemo
renin/angiotensin
aldosterone
kidney
11
Shock

• David Taylor
• School of Medicine

12
Shock

• Stage 1 Compensated/Nonprogressive
• mechanisms work as planned
• Stage 2 Decompensation/Progressive
• if blood volume drops more than 15 - 25
• Stage 3 Irreversible

13
Progressive shock

• depression of cardiac activity
• bp lt60 mmHg poor flow through coronary arteries
  leads to ischemia
• depression of vasoconstriction
• bp 40 - 50 mmHg
• increased capillary permeability
• caused by hypoxia
• clotting, cell destruction, acidosis