Cardiovascular Physiology Concepts
In simple terms, the purpose of the cardiovascular system is to distribute blood to
the cells of the body in order to provide the cells with sufficient nutrition (glucose, amino
acids, fatty acids, oxygen, ions, etc), remove cellular waste (byproducts of metabolism
such as carbon dioxide, nitrogen), and permit intercellular communication and regulation
via hormones, cytokines and components of immunity.
The heart and blood vessels
function together to create the required pressures and blood flow to meet these needs.
The heart can be considered as a 2 sided pump, i.e. two pumps that are in series
with each other.
The right side is a low pressure system that pumps blood into the
The left side is a high pressure system that pumps blood into the
Thus, the heart receives blood under low pressure, adds energy to
it, and pumps it into a high pressure system.
The higher pressure in the systemic
circulation is necessary for adequate perfusion of the tissues throughout the body.
blood pressure drops too low, as in circulatory shock, tissues are inadequately perfused,
and ischemia and infarction may result.
The blood vessels have important roles in maintaining blood pressure and blood
flow largely through variation in vessel diameter (resistance), and compliance.
Alterations in the diameter of blood vessels determine the amount and direction of blood
flow, and thus the degree to which a tissue is perfused with blood.
Changes in the activity of the cardiac “pump”, and blood vessel “tone” respond to
changes in the internal milieu of cellular metabolism as well as to events in the external
The coordination of the changing activity of the heart and blood vessels is
largely controlled by the autonomic nervous and endocrine systems.
In addition, the
cardiovascular system interacts with the kidneys and lungs in regulating blood volume,
blood gases, electrolytes and pH.
The interdependence of the heart, lungs, kidneys, and
blood vessels is significant when describing the mechanisms of cardiovascular
The primary function of the heart is to generate an arterial blood pressure that is
sufficient to perfuse organs.
A measure of the heart’s function is cardiac output (CO).
Cardiac output is the volume of blood that is ejected from the heart (right or left
ventricle) per minute.
The normal volume/ min at rest in an adult is from 5-6 L/ minute.
Cardiac output will vary with body size, so a volume standardized to body surface area
that provides a more accurate comparison between individuals of different size is known
as the cardiac index, and in an adult is between 2.6 – 4.2 L/min/m
Cardiac output is
dependent on two factors:
heart rate and stroke volume.
CO = HR x SV