Circulatory System

Circulatory system

Circulatory system is frequently divided into:1. Cardiovascular system, which consists of the heart, blood vessels, and blood.

2. Lymphatic system, which consists of lymphatic vessels and lymphoid tissues within the spleen, thymus, tonsils, and lymph nodes

The cardiovascular system (CVS)

The cardiovascular system consists of the heart, 60000 to 100000 km of blood vessels, and blood.

The main functions of the cardiovascular system are to delivers oxygen and nutrients needed for metabolic processes to the tissues, carries waste products from cellular metabolism to the kidneys and other excretory organs for elimination, and circulates electrolytes and hormones needed to regulate body functions.

The heart pressurizes blood and provides the driving force for its circulation through the blood vessels. Blood is propelled away from the heart in the arteries and returns to the heart in the veins. The exchange of materials between blood and interstitial fluid occurs across capillaries in the microcirculation.

At rest, the blood volume about 5 Liters is distributed as follows:

11% (0.55 L) in the Arteries and Arterioles
5% (0.25 L) in the Capillaries
17% (0.85 L) in the Heart and Lungs
67% (3.35 L) in the Veins


The heart
The heart is hollow cone-shaped four-chambered muscular pump approximately the size of a fist, enclosed in a fibrous sac (the pericardium). It lies in thoracic cavity in the space between the lungs. It lies little more to the left than the right and present a base above and apex bellow



The heart is separated by septum into right and left pump. The right pump consists of right atrium and right ventricle. The right atrium is the reservoir serving the right ventricle, which pumps blood to the pulmonary circulation via the pulmonary artery.

The left pump consist of left atrium and left ventricle. The left atrium is the reservoir serving the left ventricle, which pumps blood, via the aorta, to all other organs in the body through the systemic circulation.

Pericardium

The pericardium or pericardial sac is a double layered closed sac that surround the heart. It consist of fibrous connective tissue outer layer called fibrous pericardium, and a thin transparent inner layer called serous pericardium
The fibrous pericardium prevent over distention of the heart and it is continuous with tunica adventitia of great vessels above and is adherent to diaphragm below
The serous pericardium lining fibrous pericardium is the parietal pericardium. And the part covering the heart surface is the visceral pericardium or epicardium.
The pericardial cavity between the visceral and parietal pericardium is filled with a thin layer of pericardial fluid which help to reduce friction as the heart moves within the pericardial suc .

Heart wall

The heart wall consists of three layers: Epicardium, Myocardium and the Endocardium.
• Epicardium: is a thin serous membrane that constitute the smooth outer surface of the heart.
• Myocardium: is composed of cardiac muscle and is responsible for the ability of the heart to contract.
• Endocardium: this lines the chambers and valves of the heart. It is thin smooth membrane that permits smooth flow of the blood inside the heart.

Heart valves

For the heart to function effectively, blood flow must occur in a one-way direction, moving forward through the chambers of the right heart to the lungs and then through the chambers of the left heart to the systemic circulation. This unidirectional flow is provided by the heart valves:
1. The atrioventricular (AV) valves control the flow of blood between the atria and the ventricles. The thin edges of the AV valves form cusps, two on the left side of the heart
(i.e., bicuspid or mitral valve) and three on the right side (i.e., tricuspid valve)

2. The aortic and pulmonic valves control the movement of blood out of the ventricles. Because of their half moon shape, they often are referred to as semilunar valve .

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