General Anatomy & Embryology Circulatory System PDF

# General Anatomy & Embryology # Circulatory System By the end of this course, each student should be able to describe the circulatory system, heart and blood vessels, lymphatic system, lymph vessels, lymph nodes, lymphoid tissues, spleen. The blood moves inside a closed system formed of a pump (h...

# General Anatomy & Embryology # Circulatory System By the end of this course, each student should be able to describe the circulatory system, heart and blood vessels, lymphatic system, lymph vessels, lymph nodes, lymphoid tissues, spleen. The blood moves inside a closed system formed of a pump (heart) and tubes (arteries, veins and capillaries). ## (A) Heart: ### Site & Size: The heart is a muscular organ lying in the thorax behind the sternum between the lungs and on the diaphragm and its apex directed to the left, for about 8-9 cm from the median plane in the left fifth intercostal space. It has the size of a closed fist. The heart ejects about 70 c.c. of blood per beat and 5 liters of blood per minute. ### Shape: The heart has 4 borders (upper, lower, right and left) and divided into four chambers (Rt & Lt atria and Rt & Lt ventricles). ### The Pericardium: The heart is completely covered by the pericardium which is formed of two layers: - Fibrous pericardium - Serous pericardium (it is formed of two layers a thin film of fluid is present between the two layers to facilitate the heart movement). ## Structure: The heart is a hollow organ divided into two halves right (venous) and left (arterial). Each is subdivided into a thin walled atrium and a larger thick wall ventricle. 1. **Right atrium:** It receives (venous blood from the lower 1/2 of the body through inferior vena cava (I.V.C) and from the upper 1/2 of the body through superior vena cava (S.V.C). The blood passes from right atrium to right ventricle through the tricuspid valve. 2. **Right ventricle:** It receives the venous blood from the right atrium and pumps it through the pulmonary valve to the pulmonary arteries to the lungs. 3. **Left atrium:** It receives the arterial (oxygenated) blood from the lungs by means of four pulmonary veins and pumps it to the left ventricle through the mitral valve. 4. **Left ventricle:** It receives the oxygenated blood from the left atrium and pumps it to the aorta (through aortic valve) to all parts of the body. ## Blood supply: The myocardium gets its blood supply from the right and left coronary arteries. The heart pumps the blood into the arteries, then the capillaries in the tissues to be collected by small veins then larger veins and finally back to the heart. ## The blood circulation: can be divided into: 1. **Pulmonary circulation:** It occurs between the heart and lungs. The deoxygenated blood in the right ventricle is pumped to the lungs through the pulmonary arteries, then to the alveolar capillaries. The blood passes through venules after gas exchange, then to large veins and finally to the left atrium through 4 pulmonary veins as oxygenated blood. 2. **Systemic circulation:** The blood (oxygenated) is pumped from the aorta to all parts of the body, deoxygenated blood return to the right atrium through S.V.C & I.V. C. and then to the right ventricle. 3. **Portal Circulation:** The venous blood from the stomach, intestine, pancreas and spleen is collected through a separate venous channel to end in the liver via the portal vein. The blood is then collected by the venules of hepatic veins to end in I.V. ## (B) Blood vessels: 1. **Arteries:** They carry blood from the heart to all parts of the body, they have thick and elastic wall and they rebranch into arterioles that end in the capillaries. The wall of the artery is formed of smooth lining endothelium, smooth muscle fibers & elastic tissue and outer thin layer of connective tissue fibers. 2. **Veins:** They carry blood from different parts of the body to the heart, the vein has thin wall and the lumen is wider than that of the accompanying artery. The wall of the vein contains less amount of smooth muscle fibers and elastic tissue than the arterial wall. 3 **Capillaries:** They are the networks of microscopic vessels connecting the arterioles and the venules. The walls of the capillaries are formed of a single layer of flat endothelium to allow exchange of substances between the blood and tissues. ## Blood vessels - **Endothelium** - **Smooth muscle & elastic tissue** - **Connective tissue** **Artery** **Vein**