Functional organization of Cardiovascular system

Learning Objectives:

Describe the functional organization of cardiovascular system

Describe the main function of arteries, capillaries and veins

Describe the flow of blood through the chambers of the heart and through the systemic and pulmonary circulations.

Compare and contrast the systemic and pulmonary circulation.

Explain flow, pressure and resistance relationships

Describe the relationship between blood flow, pressure and resistance

List the functions of cardiovascular system.

Dr. Rasha El-Deeb

MB BCh., MSc., MD.

Component of Cardiovascular System

The cardiovascular system is composed of the heart (pressure pump) and a group of blood vessels (arteries, arterioles, capillaries, venules and veins)

Cont.,.

The heart is made up of two halves

right and left. Each half is made up of an atrium and a ventricle with an atrioventricular (AV) valve in between allowing blood to pass only in one direction; from the atrium to the ventricle

The main function of the atrium is an entry to the ventricles and to act as a reservoir that accommodates the blood received from the veins

The main function of the ventricle is a pump, left ventricle pump to systemic circulation and right ventricle pump to pulmonary circulation.

Cont.,.

The valves of the heart

Any admixture between arterial and venous blood should be prevented.

This means that the circulation must be strictly one way directed. This is the action of valves.

There are four valves in the heart. The right atrioventricular opening is guarded by tricuspid valve (three cusps) and the left opening by the mitral or bicuspid valve (two cusps). The openings of the aorta and pulmonary artery are guarded by semilunar valves (three cusps).

To Understand How the Heart Perform its function as a Pump You should Know :Properties of cardiac muscle

Excitability

It is the ability of cardiac muscle to respond to appropriate stimulus by generating an action potential followed by contraction

Rhythmicity

It is the ability of the cardiac muscle to initiate its beats regularly and continuously. Cardiac rhythmicity is myogenic in origin

Conductivity

It is the ability to transmit the excitation wave (cardiac impulses) originated in the SA node to all parts of the heart

Cardiac Contractility

Cont.,.

Blood Vessels

Form a closed delivery system that

begins and ends at the heart

There are three types of blood vessels:

o Arteries which carry blood away from the heart.

o Veins which carry blood towards the heart.

o Capillaries which carries blood from the arterioles to the venules

Cont.,.

The arteries

Are large-diameter vessels with thick walls composed mainly of circular smooth muscles with a good proportion of elastic tissue (i.e. highly elastic).

This permits stretching during systole and recoil during diastole and preventing systolic blood pressure from rising too much (as the elastic elements will be stretched).

Also it prevents diastolic pressure from decreasing too much (as the elastic elements recoil during diastole).

Called Windkessel vessels

Function as pressure reservoir help propel blood forward while ventricles relax and Conduct blood to medium sized arteries

Cont.,.

The arterioles

From small arteries the blood flows into the arterioles whose walls contain a thick layer of smooth muscles and much less elastic tissue than arteries.

This permits control of the diameter of the arterioles and therefore, the peripheral resistance to blood flow.

For this reason the arterioles have been called the resistance vessels.

Sympathetic tone controls this peripheral resistance as increased tone causes arteriolar constriction and rise the arterial blood pressure

Local chemical mediators can alter diameter and thus blood flow

Remember:

Cont.,. The capillaries Blood flows from the arteriole to the

capillaries, which have thin walls, made of one layer of flat endothelial cells leaving pores in between and based on a basement membrane.

They are very permeable ,this favors the exchange of nutrients, water , O2 and CO2 to take place between the interstitial fluid and blood therefore the capillaries are called exchange vessels

Have highly branched network creating a huge surface area . They have the largest total cross sectional and surface area.

3 types of capillaries:

o Continuous (brain)

o Fenestrated (Intestinal , Renal)

o Discontinuous ( Liver, Spleen)

Cont.,.

The veins and venules

Are thin-walled vessels with much less muscle coat than the arteries.

However they are still capable of a certain degree of contraction.

The venules and veins together hold more than 60% of the blood volume. This is why they are called the capacitance vessels.

Has a low pressure , low resistant and it has valves that prevent the back flow of the blood.

Cont.,.

Normally, the fluid leaving the capillaries is more than that returning to them.

The extra-fluid does not accumulate because it is drained by the lymphatic.

Lymph flows back through the thoracic duct into the great veins in the thorax. The lymph is propelled by rhythmic contractions in the walls of the right lymphatic duct and the thoracic duct. The respiratory pump helps the flow of lymph and by the muscle pump in the same way they help the venous return. The lymph vessels and the large ducts also have valves, which prevent backflow

Distribution of blood in different parts of circulatory system

Pulmonary circulation Systemic circulation

Starts at right

ventricle

Ends at left atrium

Receives blood

from right side of

heart

Carries blood

between heart and

lungs

Blood perfusing the

lungs is partially

deoxygenated

All blood flows

through lungs

Low pressure, low

resistance

Starts at left ventricle

Ends at right atrium

Receives blood from

left side of heart

Carries blood

between heart and

other organ systems

Blood perfusing the

organ systems is

oxygenated

Part of the blood go

to different organ

systems

High pressure, high

resistance 14

Cont.,.

Relationship Between

Pressure, Flow, and Resistance Blood flow through a blood vessel is determined by

two factors:

Pressure difference of the blood between the two ends of the vessel, also sometimes called “pressure gradient” along the vessel, which is the force that pushes the blood through the vessel

Vascular resistance: resistance occurs as a result of friction between the flowing blood and the intravascular endothelium all along the inside of the vessel.

∆P F = --------- R Contraction of ventricles generates blood pressure

Systolic BP : highest pressure attained in arteries during systole

Diastolic BP : lowest arterial pressure during diastole Blood pressure also depends on total volume of blood

Pressure profile in blood vessels

As blood flows through the systemic circulation, pressure decreases progressively because of the resistance to blood flow.

Thus pressure is highest in the aorta and large arteries and lowest in the vene cavae

The largest pressure decrease occurs across the arterioles because they are the site of highest resistance

Function of Cardiovascular System

Transport of nutrients, oxygen, and hormones to cells throughout the body and removal of metabolic wastes (carbon dioxide, nitrogenous wastes, and heat).

Protection of the body by white blood cells, antibodies, and complement proteins that circulate in the blood and defend the body against foreign microbes and toxins. Clotting mechanisms are also present that protect the body from blood loss after injuries.

Regulation of body temperature, fluid pH, and water content of cells.

Circulates blood throughout the body so;…..

Sources:

Guyton, Arthur C. Textbook of

medical physiology / Arthur C.

Guyton, John E. Hall.—11th ed.,

Ganong's Review of Medical

Physiology/Kim E. Barrett, Susan M.

barman, Scott Boitano and Heddwen

L.Brooks,23rd ed.,

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