THE HEART AND CIRCULATION This lesson meets the following DoE Specific Curriculum Outcomes for Biology 11: and 317-1

CIRCULATION Single celled and simple multicellular animals don’t possess a circulatory system – their cells are in direct contact with their external environments. More complex multicellular organisms (including humans) contain millions of cells, most of which are not in direct contact with their external environment.

CIRCULATION The function of a circulatory system is to connect all cells with their external environment, to transport nutrients to the cells and wastes away from the cell.

Types of Circulation in Humans A. Pulmonary Circulation Carries de-oxygenated blood or blood low in oxygen and high in carbon dioxide to the lungs from the right side of the heart Involves the right side of the heart, the pulmonary arteries, both the right and left lungs and the pulmomary veins Carries oxygenated blood back to the left side of the heart

B. Systemic Circulation Carries oxygen to the entire systems of the body Involves the left side of the heart, the aorta, all major arteries, veins and capillaries and the superior/inferior vena cava Carries deoxygenated blood back to the right side of the heart through the vena cava. Blood pressure is at its lowest at this point

C. Coronary Circulation The arteries and veins of the heart itself These blood vessels nourish the heart providing it with its constant need for food and oxygen

COMPONENTS OF A CIRCULATORY SYSTM 1.A fluid in which transported materials are carried (=BLOOD) 2.A network of tubes through whicn the fluid flows (=BLOOD VESSELS) 3.A pump to drive the fluid through the tubes (=HEART)

THE HEART The heart is a muscular organ whose contractions force blood through the blood vessels. Your heart is slightly larger than your fist and located just to the left of the middle of your chest cavity. The outside of the heart is surrounded by a tough protective PERICARDIUM.

THE HEART Internally, the heart is divided into two halves by the SEPTUM and is comprised of four chambers; two ATRIA (left and right) and two VENTRICLES (left and right). This design allows the heart to act as a double pump; the right side sends oxygen-poor blood to the lungs and the left side pumps oxygen rich blood to the rest of the body.

THE HEART CO 2 rich blood returning from the body (systemic circulation) enters the right atrium via the two vena cavas. This blood then moves into the right ventricle where it will be pumped out through the pulmonary arteries to the lungs (pulmonary circulation).

THE HEART Upon its return from the lungs, the 0 2 rich blood enters the left atrium via the pulmonary veins. The blood then moves into the left ventricle where it is pumped out through the aorta to the various tissues and organs of the body (systemic circulation).

THE HEART The flow of blood through the heart is controlled by four valves. Two of these valves, the ATRIOVENTRICULAR VALVES (A-V valves) are located between the atria and the ventricles (one on the left side and one on the right).

THE HEART The other two valves, the SEMILUNAR VALVES (S-V valves) are located between the right ventricle and the pulmonary artery and the left ventricle and the aorta. The function of these valves is to insure that blood flows only in one direction.

THE HEARTBEAT CYCLE Since the heart is mostly muscle, its pumping action results from the alternating contraction and relaxation of the muscles. The periods when the heart muscles are relaxed is called DIASTOLE. The alternate period of contraction is called SYSTOLE.

THE HEARTBEAT CYCLE During diastole, the A-V valves are open allowing blood to pass from the atria to the ventricles. During systole, a muscle contraction in the atria cause these chambers to contract forcing the remaining blood down into the ventricles.

THE HEARTBEAT CYCLE The systole muscle contraction moves in a wave-like manner from the top of the heart to the bottom. As it does, it forces shut the A-V valves and opens the S-V valves of the aorta and pulmonary artery. Finally, as the systole muscle contraction reaches the ventricles; these chambers contract forcing blood out through the aorta and pulmonary artery.

THE HEARTBEAT CYCLE When the ventricles are contracting, the atria are relaxed allowing blood to enter from the veins and the A-V valves open. This marks the beginning of a new diastole period. As the heart valves open and close, they make a “lub-dub” sound that can be heard through a stethoscope. The “lub” sound is made by the closing of the A-V valves. The “dub” sound is made by the closing of the S-V valves.

The Heart’s Electrical System 20 Courtney's First Aid & Safety Training Inc © All Rights Reserved 2011

THE HEARTBEAT CYCLE