The Transport System
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Describe the action of the heart in terms of collecting blood, pumping of blood, and opening and closing of valves

In mammals, with double circulation, the heart is divided into right and left sides with 2 atria and 2 ventricles. This division of the heart prevents the oxygenated blood on the left side from mixing with the deoxygenated blood on the right side. The muscular heart pumps the blood into a system of arteries, which branch into arteries. Within the tissues the arterioles branch into capillaries where exchange of materials between blood cells takes place. From the capillaries blood is collected up into a series of venules which join up to form veins which the blood returns to the heart. Blood returning to the heart from all parts of the body, except the lungs, enters the right atrium, whence it passes into the right ventricle, and then via the pulmonary artery to the lungs. The walls of the arteries and veins are elastic,. and the heart and veins are equipped with valves which prevent blood flowing in the wrong directions. Blood returning via the venae cavae enters the right atrium. The resulting pressure in this chamber forces open the flaps of the tricuspid valve. The result is that blood flows through the tricuspid opening into the right ventricle. When the atrium ad ventricle is full of blood, the atrium suddenly contracts, propelling the blood into the ventricle. The contraction spreads from the right atrium over the rest of the heart. Atrial systole s relatively weak but the ventricles, whose thick walls are especially well endowed with muscle, contract more powerfully. As a result, blood is forced from the right ventricle into the pulmonary artery.

Draw a diagram of the heart showing all four chambers, and associated vessels and valves.

Outline the way the heart beats and is regulated in terms of its myogenic nature, nerve and hormone situation

Cardiac muscle (i.e. the heart) is myogenic: its rhythmical contractions arise from within the muscle tissue itself. The heart is made to slow up or down, under involuntary control, by means of nerves and hormones. Myogenic means that cardiac cells are self-excitable: they can contract without any signal from the nervous system. The sinoatrial (SA) node/pacemaker is located in the wall of the right atrium. It is composed of specialised muscle tissue. Each time the SA node contracts, it.initiates a wave of excitation that travels through the wall of the heart; the two atria contract in unison. The atrioventricular node is located at the bottom of the wall separating the 2 atria. When the wave of excitation reaches the AV node, it is delayed for about 1 second. After this delay, the wave of excitation spreads upward through the ventricular walls. The pacemaker is controlled by both nerves and hormones. The hormones are secreted into the blood by the glands.

Explain the relationship between the structure and function of arteries, capillaries and veins

• Arteries

o        flow away from heart.

o        thickest vessels

o        thin passage (to maintain pressure

o        fast flow