The Circulatory System

1) The circulatory system is a system consisting of the heart, blood and blood vessels that pump blood throughout the body. The lymphatic system (lymph and lymphatic vessles) can also be considered part of the circulatory system.

2) The purpose of the circulatory system is to transport oxygen throughout the body and to remove carbon dioxide and other wastes. The circulation of blood also is needed to transport cells and components of the immune system to sites of infection

The Circulatory System

3) The heart is of course a central component of the system and functions to pump blood throughout the body. Oxygenated blood is pumped out to the body- and de-oxygenated, carbon dioxide rich blood returns to the heart. The heart is connected to the lungs through the pulonary circulation to exchange oxygen and carbon dioxide.

Pulmonary Circulation Labelled Figure

4) The heart is located between the lungs, angled down towards the left hip and is about the size of a human fist.

5) The heart is surrounded my a serous membrane called the pericardium. The pericardium consists of two layers- the parietal pericardium (the outside layer), and the visceral pericardium (or epicardium) which is the inside layer touching the heart. The two layers are filled with serous fluid.

6) There are three layers of the heart wall: the epicardium (outer layer), the myocardium (middle layer) and the endocardium (inner layer).

7) The heart is divided into four chambers. The right atria and left atria (receiving chambers) and the left ventricle and right ventricle (pumping chambers).

Heart Anatomy

8) Blood is pumped from the right side of the heart to the lungs, and returns oxygenated to the left side of the heart.

Labelled Figure of the Circulation of Blood Through the Heart

9) Deoxygenated blood returns from the body through the superior vena cava and inferior vena cava to the right atrium. Blood then flows from the right atrium through the tricuspid valve to the right ventricle. From the right ventricle, blood is pumped through the pulmonary artery to the lungs in the pulmonary circuit.

10) Blood leaving the heart in this step is deoxygenated, but the pulmonary artery is still called an artery (vessels leaving the heart are arteries).

11) Blood then return from the lungs to the left atrium of the heart. Blood then flows through the mitral valve to the left ventricle.

12) Blood is then pumped from the left ventricle through the aorta and out to the rest of the body to deliver oxygen.

13) Arteries pump oxygenated blood to the body. Arteries branch of into smaller capillaries into capillary beds where the exchange of oxygen and carbon dioxide with tissues occurs.

14) Venules and veins transport blood back to the heart.

Labelled Figure of the Venous System

15) Blood vessels have three layers. The tunica intima is the innermost layer. The tunica media is the inner muscular layer (smooth muscle) and the tunica externa is the outermost layer.

Labelled Figure of the Layers of Blood Vessels Artery Structure

16) The tunica media of arteries is thicker than veins to withstand higher pressures. Veins have valves which prevent backflow of blood.

17) Blood is supplied to the brain through the carotid arteries. Several arteries meet in the brain to form a structure called the cerebral arterial circuit or the circle of Willis

. Circle of Willis Diagram