The Circulatory System

Circulatory System

• The Circulatory System has two major subdivisions:

1. The cardiovascular system: The heart

2. The lymphatic system: Pumpless system of vessels and lymphoid organs that aids the cardiovascular system

Cardiovascular System

Location and Size• Location and size:- Approximately the size

of a person’s fist, the hollow, cone-shaped heart weighs less than a pound

- The heart is located within the bony thorax and is in between the lungs

Location and Size• Location :- Its more pointed apex is

directly toward the left hip and rests on the diaphragm, approximately at the level of the fifth intercostal space

- Its base, from which the great vessels of the body emerge, points toward the right shoulder and lies beneath the second rib

Coverings and wall• The heart is enclosed by a

double sac of membrane, the pericardium:

- The thin visceral pericardium, or epicardium, tightly hugs the external surface of the heart and is actually part of the heart wall

- The fibrous layer, parietal pericardium, helps protect the heart and anchors it to surrounding structures, such as the diaphragm and the sternum

Coverings and wall• A slippery lubricating fluid

is produced by the pericardial membranes:

- This fluid allows the heart to beat easily in a relatively frictionless environment as the pericardial layers slide smoothly across each other

Pericarditis• Inflammation of the

pericardium, often results in a decrease in the amount of fluid

• This causes the pericardial layers to bind and stick to each other, forming painful adhesions that interfere with heart movements

Heart Wall - Myocardium• The heart walls are composed of

three layers:- The outer epicardium, the

myocardium, and the innermost endocardium

• The myocardium consists of thick bundles of cardiac muscle twisted and whorled into ring like arrangement

- It is the layer that actually contracts- It is reinforced internally by a dense,

fibrous connective tissue network called the “ skeleton of the heart”

Heart Wall - Endocardium

• The endocardium is a thin, glistening sheet of endothelium that lines the heart chambers

• It is continuous with the linings of the blood vessels leaving and entering the heart

Lungs

Body cells

Our circulatory system is a double circulatory system.

This means it has two parts parts.

the right side of the system: carries

deoxygenated blood away from the heart, to the

lungs, and returns oxygenated blood back to the heart

the left side of the system: carries

oxygenated blood away from the

heart to the body, and returns

deoxygenated blood back to the

heart

Pulmonary Circulation:

Systemic Circulation

Aorta

right pulmonary artery

Left pulmonary artery

Right atriumLeft atrium

Right ventricle

Left ventricle

Superior VenaCava

Inferior VenaCava

Interventricular septum

right pulmonary veins

Left pulmonary veins

Tricuspid valve

Pulmonary semilunar

valve

Aortic semilunar

valveBicuspid valve

Valves – AV valves• The atrioventricular or AV valves

are located between the atrial and ventricular chambers on each side

• The AV valves prevent backflow into the atria when the ventricles contract

• The left AV valve- Bicuspid (mitral) valve: consist of 2

cusps, or flaps, of endocardium• The right AV valve- Tricuspid valve: has 3 cusps• Tiny white cords, the chordae

tendineae (heart strings), anchor the cusps to the walls of the ventricles

Valves – semilunar valves• The semilunar valves guards the bases

of the two large arteries leaving the ventricular chambers

• Thus, they are known as the pulmonary and aortic semilunar valves

• Each semilunar valve has 3 cusps that fit tightly together when the valves are closed

• When the ventricles are contracting and forcing blood out of the heart, the cusps are forced open and flattened against the walls of the arteries

Stage 1Blood enters the heart through a vein known as the vena cava. The blood is low in oxygen. The first chamber it goes into is the right atrium.

Stage 2The heart pumps the blood from the right atrium into the right ventricle.

Stage 3The heart pumps the blood from the right ventricle through the pulmonary artery towards the lungs.

Stage 4The blood returns from the lungs with lots of oxygen and re-enters the heart through the left atrium.

Stage 5The heart pumps the blood from the left atrium into the left

Stage 6The heart then pumps the blood from the left ventricle out of the heart to the rest of the body through the aorta.

Cardiac Circulation• In reality, blood enters and exits both sides of

the heart at the same time.

blood from the body

blood from the lungs

The heart beat begins when the

heart muscles relax and blood

flows into the atria.

• The atria then contract and

the valves open to allow

blood

into the ventricles.• The valves close to stop blood flowing backwards.

• The ventricles contract forcing the blood to leave the heart.

• At the same time, the atria are relaxing and once again filling with blood.

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