cardiovascular compensations Flashcards
what is the heart innervated by
autonomic nervous system
what does the sympathetic nervous system arise from
thoracolumbar spinal segments
where does the parasympathetic nervous system arise from
brainstem and sacral spinal segments
what does the sympathetic NS do in the cv system
acts to increase cardiac output - flight or fight response
what does the parasympathetic NS to do the cv system
lowers cardiac output when animals are resting = rest and digest system
what does the alpha adrenergic receptor cause
constriction of the arterioles of the non-essential organs and venoconstriction of the abdominal organs to maximise preload to the heart and hence increase cardiac output
what does the beta 1 receptor do to the heart
increase cardiac output leading to increased heart rate and conduction, reduced refractory period and stronger cardiac contractions.
what is increased during exercise
body’s requirement for oxygen delivery and removal of waste products
heat production by the tissues
what are the 5 systems that manage the CVS during exercise
metabolic autoregulation
psychogenic response
exercise reflex
baroreflex
skeletal muscle and respiratory pumps.
what happens during metabolic autoregulation
increased skeletal muscle causes vasodilation as metabolic waste products build up in the interstitial fluid.
reduced arterial pressure
what happens in psychogenic response
increases sympathetic activity to the heart and decreases parasympathetic activity
increased cardiac output
CO increased further by increased preload (increases SV) as venous return to heart increases due to vasoconstriction in non-essential organs.
vasoconstriction increases TPR
what does hypovolaemic mean
decreased volume of circulating blood
what causes hypovolaemic shock
haemorrhage
severe dehydration
sequestration of blood
what is the CV response to hypovolaemia
baroreflex provides the the first immediate compensations
increase in sympathetic stimulation to the heart causing increased contractility heart rate and conduction speed.
vasoconstriction to the non-essential organs.
venoconstriction of abdominal veins to increase TPR to increase blood available to perfuse essential organs (severe case)
splenic contraction to replace lost volume and cells.
why does pulse pressure remain low when CVS is responding to hypovolaemia
due to persistently low stroke volume
what activates if hypovolaemia persists
RAAS
what are the 2 types of heart failure
forward (systolic) or backward (congestive)
what is forward heart failure
failure of the systolic pumping action of the heart resulting in reduced cardiac output and reduced mean arterial pressure
signs of forward heart failure
reduced perfusion, slow capillary refill time, pale mucous membranes, weak pulse and cold extremities.
presentation of animals with forward heart failure
unable to exercise
weak and lethargic
exhibit vasovagal syncope when under distress. (faint)
what is dilated cardiomyopathy (initially presented as forward heart failure)
muscle wall of heart very thin and stretched so ventricles unable to contract properly so SV low.
what is backward heart failure
blood backs up in the venous circulation
=heart unable to cope with preload
what does backward heart failure cause
increased atrial pressure, increased venous pressure and leakage of fluid into the ISF due to increased hydrostatic pressure in the capillaries.
what is mitral valve disease (presented as left-sided CHF)
mitral valve becomes incompetent and allows blood to flow back into the left atrium during ventricular systole.
increases left atrial pressure and reduces pulmonary venous drainage into the atrium which increases pulmonary venous pressure
what does left sided CHF lead to
pulmonary oedema causing increased respiratory rate and respiratory difficulty
what does right sided CHF lead to
increased systemic venous pressure - distention of jugular veins and enlargement of liver and spleen
fluid leakage leads to effusion
what does the body use to compensate for forward heart failure
starlings mechanism, baroreflex and the RAAS
