5.THE CARDIOVASCULAR SYSTEM

Control of Blood Pressure

 BP is control in two ways:

1. Short-term control – involves the baroreceptor
reflex, chemoreceptors and circulating
hormones.

2. Long-term control – involves regulation of blood
volume by the kidneys and the renin-angiotensin-
aldosterone system.

Baroreceptors

 Within the aortic and carotid sinuses

 -nerve ending sensitive to stretch (pressure).

1) A rise in BP stimulate baroreceptor,  input to
cardiovascular centre  CVC respond by 
parasympathetic nerve to slow down the heart
activity.

2) At the same time, sympathetic stimulation
inhibited  causing vasodilation  BP .

Baroreceptors

 If pressure within the aortic arch and carotid
sinuses falls, the rate of baroreceptor discharge
also falls.

 CVC responds by  sympathetic drive to speed up
the heart  cause vasoconstriction  BP .

Chemoreceptor

 These are nerve endings situated in the carotid
and aortic bodies, involved in control respiration.

 Changes CO₂, O₂, and the acidity of blood.
 These changes detected by chemoreceptor, they

send signals to the CVC,  sympathetic drive to
the heart and blood vessel.
 Blood O₂ level rise  BP up, respiratory up

Higher centres in the brain

 Input to the CVC is influenced by emotional – fear,
anxiety, pain and anger that may stimulate
changes in blood pressure.

Long term BP regulation

 Slower, longer lasting changes in BP are effected
by the renin-angiotensin-aldosterone system and
the action antidiuretic hormone.

 Atrial natriuretic peptide –released by the heart
itself, causes sodium and water loss from the
kidney and reduces BP.

Pressure in the pulmonary circulation

 Pulmonary circulation is much lower than
systemic circulation.

 If pulmonary capillary pressure exceeds 25mmHg,
fluid is forced out of the bloodstream and into the
airsacs (pulmonary oedema) with very serious
consequences.