Circulatory System

The human circulatory system is composed of three major components:

a. the heart (pump)

b. a system of vessels ( arteries, veins, capillaries, venules and arterioles)

c. fluid (blood)

Every part of the body is made up of tiny units of living matter called cells.

The human body has approximately 50 to 100 trillion cells which require oxygen and nutrients.

These cells must also eliminate waste gases and material.

Nutrients and oxygen are carried to all body cells by the blood.

The blood is pumped by the heart through various vessels.

• Waste material and carbon dioxide are also eliminated from the body by the circulatory system.

As the blood is transported through the body, most of it goes to the muscle cells which remove food materials and oxygen.

Large amounts also go to the brain and smaller amounts to other parts which also require food and oxygen.

There are two basic circulatory patterns in humans:

Systemic circulation

Pulmonary circulation

Systemic circulation carries oxygenated blood from the left ventricle to all parts of the body.

Blood from systemic circulation returns in a deoxygenated form to the right atrium.

•Pulmonary circulation takes deoxygenated blood from the right ventricle to the lungs.

•The blood becomes oxygenated and returns to the left atrium.

The heart must beat constantly to perform these functions.

Approximately 70 beats per minute if the body is relaxed and more beats when the body is active or under stress.

The Heart:The heart is a hollow muscular

pear-shaped organ located in the middle of the chest beneath the sternum and between the lungs.

• The heart pumps blood through the body, supplying cells with oxygen and nutrients and removing carbon dioxide and nitrogen containing waste.

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The heart is held in place principally by its attachment to the great arteries and veins, and by its confinement in the pericardium.

(pericardial sac)

The pericardium is a double walled sac with one layer enveloping the heart and the other attached to the breastbone, the diaphragm, and the membranes of the thorax.

The pericardium protects the heart form friction and trauma.

The adult human heart is approximately the

size of a fist and about the shape of your hand.

In an average adult, it is about fifteen

centimeters long and seven centimeters across

at its broadest part, and it weighs less than one-

half a kilogram. (APPROXIMATELY .43 % OF

THE BODY MASS)

The outside layer of the heart is the epicardium(ectocardium). This is a relatively thin layer but it isextremely important.

The vascular system of the heart is located in thislayer.

Open heart surgery and angioplasty involves bloodvessels found in this layer.

It must continue to beat, pumping blood, no matter the demands placed upon it. This may lead to serious heart problems, including a potentially deadly heart attack.

Unlike other organs the heart is unable to slow down when it does not receive enough nourishment from the blood.

Good coronary circulation is very important. Chest

pain (angina) will occur when the heart is not

receiving enough oxygen. This could possibly be a

result of a blocked artery, inhibiting the flow of

nutrient and oxygen rich blood to the heart. A

complete blockage results in a heart attack.

( coronary occulsion )

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The middle layer of the heart is the thickest layer of the heart and consists mostly of cardiac muscle and small amounts of nerve tissue.

This layer is called the myocardium.

Cardiac muscles are myogenic (self excitable) as they can generate their own electrical impulses.

The inner layer of the heart is the endocardium. In this layer the heart valves are located.

The endocardium lines the atria ( upper chambers) and the ventricles ( lower chambers) in the interior of the heart.The atria have thin walls and function as collection chambers for blood returning from the body.

The atria or upper chambers of the heart have thin walls and function as collection chambers for blood returning from the body.

The ventricles or lower chambers have thick, powerful walls that pump blood to the lungs and organs.

Atrioventricular valves: valves between each atrium and

ventricleAV valves keep blood in the

ventricles from flowing backwards into the atria.

The right AV valve is the tricuspid

The left Av valve is the bicuspid or mitrial.

Semilunar valves: valves between the veins entering the right and left atria and the arties leaving the right and left ventricle.

Heart cycle:

Sequence of events during each heart beat, lasts about 0.8 seconds.

Systole, heart muscles (ventricle) contract and the chambers pump blood in the aorta and the pulmonary artery.

Diastole, the ventricles relax and fill with blood.

• Systole is the upper number in a blood pressure reading .

• Systole readings are usually (young adults)

• 100 + age +_ 10%. • Diastole is the lower number in a blood

pressure reading.• Desirable reading are in the range of 50

to 80.

Stronger hearts have a lower pulse rate and weaker hearts have a higher pulse rate.

Stroke volume = the amount of blood pumped from the ventricles with each contraction of the ventricles

• Cardiac output is the volume (litre) of blood that the heart can pump from the ventricles in a given amount of time ( minute).

• C.O = stroke volume * pulse rate

Cardiac Output• Calculate the the cardiac output for

a student with a pulse rate of 60 beats / min and a stroke volume of 70 ml/ beat.

Stroke Volume

• What is the stroke volume for a person with a pulse rate of 60 beats/min and who requires a cardiac output of 5.25 L/min?

Pulse Rate • A student requires a cardiac output

of 5.8 L/Min and has a stroke volume of 60 ml/ beat. What is the pulse rate for the student?

Cardiac Output

• Calculate the the cardiac output for a student with a pulse rate of 72 beats / min and a stroke volume of 60 ml/ beat.

Stroke Volume• What is the stroke volume for

a person with a pulse rate of 70 beats/min and who requires a cardiac output of 5.50 L/min?

Pulse Rate• A student requires a cardiac

output of 6.2 L/Min and has a stroke volume of 70 ml/ beat. What is the pulse rate for the student?

Types of blood vessels

• Arteries( arterioles)

• Veins ( venules)

• Capillaries

Arteries and veins contain 3 layers of tissue.

1. Outer layer (epithelial layer)

2. Middle layer - smooth muscle and elastic fibers,

3. Inner layer - endothelium

The internal opening in the blood vessel through which blood passes is called the lumen.

• Vasoconstriction = smaller lumen size

• Vasodilation = larger lumen size

Arteries and veins

• Carry blood from the heart

• Deep in the body tissue

• Carry oxygenated blood

• Carry blood to the heart

• Close to the surface

• Carry deoxygenated blood

• Arteries lack valves

• Arteries have small lumens

• Veins contain valves to prevent the back flow of blood on its way to the heart

• veins have large lumens

• Arteries have spherical lumens

• Arteries are under pressure

• Veins have oval lumens

• Veins are not under pressure

• Arteries have thick layers of muscle and elastic fibers

• Veins have thin layers of muscle and elastic fibers

Capillaries

• Unlike the arteries and veins, capillaries are very thin and fragile.

• The capillaries are actually only one epithelial cell thick.

• Blood cells pass through capillaries in single file.

• Despite the small size capillaries are essential to survival.

• The exchange of oxygen and carbon dioxide between the body cells and the circulatory system takes place through the thin capillary walls.

Capillaries connect veins to arteries. It is here that any and all exchanges take place between the blood and the body cells.

Capillaries are one cell thick.

• The red blood cells inside the capillary release their oxygen which passes through the wall and into the surrounding tissue.

• The tissue releases its waste products, like carbon dioxide, which passes through the wall and into the blood vessel.

• The arteries pass their oxygen-rich blood to the capillaries which allow the exchange of gases within the tissue.

• The capillaries then pass their waste-rich blood to the veins for transport back to the heart.

• Capillaries are also involved in the body's release of excess heat.

The major form of heart disease in Western countries is atherosclerosis.

In this condition fatty deposits called plaque, composed of cholesterol and fats, build up on the inner wall of the coronary arteries.

Gradual narrowing of the arteries throughout life restricts the blood flow to the heart muscles.

Symptoms of this restricted blood flow can include shortness of breath, especially during exercise, and a tightening pain in the chest called angina pectoris

The plaque may become large enough to completely

obstruct the coronary artery, causing a sudden decrease in

oxygen supply to the heart. Obstruction, also called

occlusion, can occur when part of the plaque breaks away

and lodges farther along in the artery, a process called

thrombosis. These events are the major causes of heart

attack, or myocardial infarction, which is often fatal

Heart Beat

• The heart has two nerve masses that initiate muscular contraction: 

• 1. the SA or sinoatrial node, 

• 2. the AV or atrioventricular node. 

The sinoatrial node (S-A Node or the pacemaker) which controls the rate of contraction of the heart is located in the right muscle of the atrium wall.

• More specifically the SA node (sinoatrial node) is located in the wall of the right atrium, near the junction of the atrium and the superior vena cava.

The atrio-ventricular node (AV node) is also located in the myocardium but lower in the atrial wall.

•  The AV node (atrioventricular node) is located near the bottom centre of the right atrium slightly above the right ventricle.  

• The nerve cells in the SA node are connected to the medulla oblongata by nerves.

• The medulla oblongata is the section of the nervous system which controls body functions which occur automatically.

• Impulses from this region of the brain (Medulla Oblongata) end up in the SA node.

• The SA node in turn regulates the contraction of the cardiac muscle cells in the right and left atrium.

• Nerve fibers extend through the R. and L. atrium causing simultaneous contractions of the upper chambers.

• The SA node is commonly refered to as the pacemaker of the heart.

• When the SA node initiates a contraction, fibers rapidly conduct the impulse to a large bundle of nerve fibers called the AV node.

• Here the impulses move quickly through Purkinje fibers (Bundle of His) via the septum that divides the two ventricles in the ventricles themselves.

• From here, fibers run in two pathways one running to the right ventricle, and one running to the left toward the posterior apex of the heart.

• The result is that while the atria are contracting, the impulse is carried quickly to the ventricles.

• With the AV node holding up the impulse just enough to let the atria finish their contraction before the ventricles begin to contract, blood can fill the ventricles.

• Since nerve fibers have carried the electrochhemical impulse to the (atrioventricular node) , the next impulse generated by the heart proceeds into the ventricles where the blood leaves through the pulmonary arteries and the aorta.