COMPONENTS OF THE CIRCULATORY SYSTEM: Components Human Cardiovascular System

Circulatory System
COMPONENTS OF THE CIRCULATORY SYSTEM OPERATION AND FUNCTION Systemic Circulation Pulmonary Circulation Additional Functions Blood Pressure

HEART Anatomy Arrhythmias Cardiac Cycle Cardiac Output Congenital Heart Defect Control Of The Heart Rate Coronary Arteries Coronary Heart Disease Diseases Of The Heart Endocardium Function Of The Heart Generation Of The Heartbeat Heart Failure Heart Valves History Of Heart Research Myocardium Pericardium Heart Structure Heart Valve Malfunction Other Forms of Heart Disease
Blood INTRODUCTION ROLE OF BLOOD COMPOSITION OF BLOOD Plasma Red Blood Cells Blood Type White Blood Cells Platelets and Clotting PRODUCTION AND ELIMINATION OF BLOOD CELLS Red Blood Cell Diseases White Blood Cell Diseases Coagulation Diseases BLOOD BANKS Blood Transfusion Blood Count Blood donation and registry Blood gas analysis Blood sugar tests Blood typing and crossmatching Blood urea nitrogen test Blood-viscosity reducing drugs Blood Culture Blood Clot in the Legs Causes Blood Clot in the Legs Symptoms Blood Clot in the Legs
Digestive system Esophagus Gall bladder Large intestine Lips, cheeks and palate Salivary glands Serous membranes Small intestine Stomach Tunics
Teeth Tongue Digestive Process in Mouth Sleep Right Mouth Guard
Respiratory system
Endocrine system Glandular Structure Gonads Hormones Pancreas Parathyroid Glands Pineal Gland Pituitary Gland Pituitary Hormones Thymus Thyroid Gland


COMPONENTS OF THE CIRCULATORY SYSTEM: Components Human Cardiovascular System

 In an average healthy person, approximately 45 percent of the blood volume is cells, among them red cells (the majority), white cells, and platelets. A clear, yellowish fluid called plasma makes up the rest of blood. Plasma, 95 percent of which is water, also contains nutrients such as glucose, fats, proteins, and the amino acids needed for protein synthesis, vitamins, and minerals. The level of salt in plasma is about equal to that of sea water. The test tube on the right has been centrifuged to separate plasma and packed cells by density.

 The heart, blood, and blood vessels are the three structural elements that make up the circulatory system. The heart is the engine of the circulatory system. It is divided into four chambers: the right atrium, the right ventricle, the left atrium, and the left ventricle. The walls of these chambers are made of a special muscle called myocardium, which contracts continuously and rhythmically to pump blood. The pumping action of the heart occurs in two stages for each heart beat: diastole, when the heart is at rest; and systole, when the heart contracts to pump deoxygenated blood toward the lungs and oxygenated blood to the body. During each heartbeat, typically about 60 to 90 ml (about 2 to 3 oz) of blood are pumped out of the heart. If the heart stops pumping, death usually occurs within four to five minutes.

 Three types of blood vessels form a complex network of tubes throughout the body. Arteries carry blood away from the heart, and veins carry it toward the heart. Capillaries are the tiny links between the arteries and the veins where oxygen and nutrients diffuse to body tissues. The inner layer of blood vessels is lined with endothelial cells that create a smooth passage for the transit of blood. This inner layer is surrounded by connective tissue and smooth muscle that enable the blood vessel to expand or contract. Blood vessels expand during exercise to meet the increased demand for blood and to cool the body. Blood vessels contract after an injury to reduce bleeding and also to conserve body heat.

 Arteries have thicker walls than veins to withstand the pressure of blood being pumped from the heart. Blood in the veins is at a lower pressure, so veins have one-way valves to prevent blood from flowing backwards away from the heart. Capillaries, the smallest of blood vessels, are only visible by microscope—ten capillaries lying side by side are barely as thick as a human hair. If all the arteries, veins, and capillaries in the human body were placed end to end, the total length would equal more than 100,000 km (more than 60,000 mi)—they could stretch around the earth nearly two and a half times.

 The arteries, veins, and capillaries are divided into two systems of circulation: systemic and pulmonary. The systemic circulation carries oxygenated blood from the heart to all the tissues in the body except the lungs and returns deoxygenated blood carrying waste products, such as carbon dioxide, back to the heart. The pulmonary circulation carries this spent blood from the heart to the lungs. In the lungs, the blood releases its carbon dioxide and absorbs oxygen. The oxygenated blood then returns to the heart before transferring to the systemic circulation. ©2016.