Download Neurohumoral Activation

• The signs and symptoms of Heart Failure are
due in part to compensatory or protective
mechanisms utilised by the body in an
attempt to adjust for a primary deficit in
cardiac output
• These compensatory mechanisms aim to
maintain perfusion to vital organs
Neurohumoral Activation
• Increased activity of the Sympathetic Nervous
System
• Activation of Renin-Angiotensin-Aldosterone
System
• Vasopressin
• Atrial Natriuretic Peptide
Increased Sympathetic Nervous
System Activity
• Forward pressure into the aorta begins to fallthe body responds by trying to preserve
perfusion pressure
• Changes in pressure are detected by
baroreceptors in the carotid sinus and the aortic
arch
• This increases levels of circulating
catecholamines, specifically noradrenaline.
• These produce a rise in heart rate and
contractility; and also impact upon
vasoconstriction
Activation of the RAA system
• The kidneys detect the drop in pressure
• Cells in the kidney juxtaglomerular apparatus
release Renin
• Renin catalyses a reaction which converts
Angiotensinogen to Angiotensin 1
• An Angiotensin Converting Enzyme( ACE)
produced in the lungs converts Angiotensin 1
into an active hormone-Angiotensin 11
• Angiotensin 11 is a vasoconstrictive hormoneincreases systemic BP, renal perfusion pressure
and Glomerular Filtration rate
• It constricts blood vessels all over the body and
the kidneys in order to maintain blood pressure
in the glomerulus to ensure the GFR stays normal
• It stimulates the production of Aldosterone
which increases the absorption of sodium in the
renal tubules
• Water follows sodium thereby increasing fluid in
the blood vessels and subsequently increasing BP
Vasopressin (ADH)
• Anti Diuretic Hormone is secreted by the
posterior pituitary gland in response to
activity of atrial baroreceptors and the action
of angiotensin 2.
• Acts on kidneys and blood vessels
• Helps prevent loss of water from body by
reducing urine output
Mechanisms to counteract the RAA
system
• Several mechanisms in place to control RAA
system
• Atrial Natriuretic Peptide (ANP)
• A cardiac hormone released in response to
atrial distension
• It has vasodilatory and diuretic properties
• Its naturetic properties encourages the
excretion of sodium and water and inhibits
activation of RAA system
Summary of Neurohumoral activation
• Increase in heart rate; due to the sympathetic
stimulation
• Increase in afterload; due to vasoconstriction
• Increase in preload; due to the retention of
Na+ and water
• Increase in contractility; due to the
sympathetic stimulation