Circulatory System

CIRCULATORY SYSTEM

CIRCULATORY SYSTEM Consists of the heart, blood, veins, arteries,

venules, arterioles and capillaries. Purpose of the circulatory system is the

exchange of materials between the blood and tissues.

HEART Located in the thoracic cavity between the

lungs Enclosed in the pericardial membranes, of

which there are three layers. Fibrous pericardium – outermost layer, loose

fitting sac of strong fibrous connective tissue. Parietal pericardium – the is serous and lines the

fibrous pericardium. Visceral pericardium – often called the

epicardium Between the parietal and the visceral

pericardial membranes is serous fluid which prevents friction as the heart beats.

THE HEART – CHAMBERS AND VALVES Not all animals have a four chambered heart Heart muscle is called myocardium The chambers of a four chambered heart are:

Right atrium – the two large caval veins return blood from the body to the right atrium (chamber). The superior vena cava carries blood from the upper

body, and the inferior vena cava carries blood from the lower body.

Blood flows from the right atrium through the right atrioventricular valve (tricuspid valve) into the right ventricle. Valves create a unidirectional flow of blood.

Right Ventricle – Blood is pumped from here into the lungs through the pulmonary artery through the right semilunar valve.

THE HEART – CHAMBERS AND VALVES Left Atrium – Receives blood from the lungs

through the pulmonary veins. Blood flows into the left ventricle through the left

atrioventricular valve (bicuspid valve). Left Ventricle – largest chamber and has the

thickest walls. This enables the left ventricle to contract more forcefully. Left ventricle pumps blood to the body through the

aorta, the largest artery of the body. Blood passes out of the left ventricle into the large artery through the aortic semilunar valve

FOUR CHAMBER HEART

THREE CHAMBERED HEART

ARTERIES AND VEINS Arteries – carry blood from the heart to capillaries

(away from the heart). Smaller arteries are called arterioles. Arteries are involved in the maintenance of normal

blood pressure, especially diastolic blood pressure when the heart is relaxed.

Veins – carry blood from capillaries back to the heart Smaller veins are called venules. Veins do not regulate blood pressure Anastomoses – is a connection, or joining, of vessels,

that is artery to artery and vein to vein. The purpose is to provide alternate pathways for the flow of blood.

CAPILLARIES Carry blood from arterioles to venules. Walls are only one cell in thickness. Some tissues do not have capillaries such as

the epidermis, cartilage and the lens and cornea of the eye.

Most tissues have extensive capillary networks. The quantity or volume in an organ reflects the metabolic activity of the organ.

VEINS, ARTERIES AND CAPILLARIES

PATHWAYS OF CIRCULATION Pulmonary circulation – from the right

ventricle into the pulmonary artery, which divides into the left and right pulmonary arteries, one going to each lung. Exchange of oxygen and carbon dioxide occurs in the lungs. Oxygenated blood travels in the capillaries into venules which merge into veins and finally into tho pulmonary veins from each lung that return to the left atrium. Blood then travels through the systemic circulatory system

PATHWAYS OF CIRCULATION Systemic Circulation – from the left ventricle

blood pumps onto the aorta. The branches of the aorta take blood into arterioles and capillary networks throughout the body. Capillaries merge to form venules and veins. Veins from the lower body take blood to the inferior vena cava; veins from the upper body take blood to the superior vena cava. These two caval veins return blood to the right atrium.

The blood in the systemic veins has a low oxygen content, making them appear blue.

The blood in the systemic arteries carry oxygenated blood, making them appear red.

PULMONARY AND SYSTEMIC CIRCULATION