Cardiovascular related physiological adaptation to disease
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What are the clinical signs of haemorrhage?
- Rapid and feeble pulse
- Pale mucous membranes, longer capillary refill time
- Respiration is rapid
CO drops as a result of haemorrhage, what effect does this have on blood pressure?
It causes a sudden drop in blood pressure
List the six ways the body tries to recover from haemorrhage
Baroreceptor reflex, vasoconstriction, chemoreceptor reflex, cerebral ischaemia, atrial volume receptor reflex, reabsorption of tissue fluids
Describe the baroreceptor reflex
Decreased blood pressure leads to decreased baroreceptor stimulation. This results in increased sympathetic/decreased parasympathetic stimulation.
What are the affects of increased sympathetic/decreased parasympathetic stimulation?
- Tachycardia (to increase HR and therefore CO)
- Increased contractility (to increase SV and therefore CO)
- Increased vasoconstriction (to increase TPR and redirect blood back up to the heart)
In dogs, which organ contracts to increase blood volume?
In which organs is there a) no vasoconstriction b) only vasoconstriction in severe haemorrhage?
- a) brain and heart
- b) kidneys
Describe the chemoreceptor reflex
If BP drops very low the baroreceptor reflex is no longer sensitive and the chemoreceptors which respond to metabolites produced will aid
What does cerebral ischaemia result in?
Sympathetic discharge as a reflex response
Describe the atrial volume receptor reflex
These receptors detect a decrease in the volume of blood in the atria and add to the increased sympathetic activity
Increased sympathetic activity results in the secretion of which hormone that helps conserve fluid?
Angiotensin II and aldosterone decrease the secretion of which ion and therefore water?
There is also a reflex to increase the release of which other hormone that reduces water loss?
The baroreceptor reflex also acts through the hypothalamus to induce the sensation of ___ to increase blood volume?
List the 5 decompensatory mechanisms that occur in haemorrhage
Cardiac failure, acidosis, CNS depression, changes in clotting, inhibition of the immune system
Describe what happens in cardiac failure
Hypotension reduces coronary blood flow --> depresses ventricular function --> reduces CO --> reduces pressure --> reduces Q
Describe what happens in acidosis
Reduced Q leads to anoxia --> increases lactic acid production --> reduced H+ secretion by the kidney --> acidosis reduces CV response to catecholamines
Describe what happens in CNS depression
Reduced Q to CNS leads to increased sympathetic output --> if Q falls further however the cardiac and vasomotor centres become depressed --> this leads to loss of sympathetic tone --> reduces CO and further decreases cerebral Q
Initially is there an increased/decrease in clotting?
What happens to clotting eventually?
Eventually clotting time is prolonged (as all the clotting factors have been lost through haemorrhage) which aggravates haemorrhage
Inhibition of the immune system can leads to invasion of ____ into the circulation? What can this invasion induce?
- A form of shock
Define heart failure
A condition of depressed contractility and an inability of the heart to provide the metabolic requirements of the body
What are the two compensatory responses to heart failure?
- Starling mechanism - if the LV fails and SV decreases the is an accumulation of blood in the LA and pulmonary veins which leads to an increased preload and greater SV
- Baroreceptor reflex - drop in blood pressure initiates reflex, increases sympathetic activity and increases HR and contractility.
List the 4 complications in heart failure
Oedema, exercise intolerance, inadequate perfusion of 'non-critical organs', cardiac decompensation
Where would there be oedema in a) right sided heart failure b) left sided heart failure?
- a) systemic oedema
- b) pulmonary oedema
Why is renal failure often a terminal event in chronic heart failure?
As in severe heart failure the baroreceptor reflex causes vasoconstriction of non-critical organs e.g. kidney. This eventually causes permanent damage to the kidney.
What can ischemic damage to the intestinal mucosa lead to?
Bacteria and toxins from the gut getting into the blood stream and leading to septic shock.
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