University:
California State University, Northridge
Course:
BIOL 281 | Human Physiology
Academic year:

2024
Views:

139

Pages:

30
Author:

niewszytez7o

CIRCULATORY SYSTEM Structure and Function CIRCULATORY SYSTEMS General Characteristics • There are two basic types of circulatory systems in the animal kingdom. – Open system in which the blood spends a portion of the time in the vessels of the system and the other portion of the time in a modified body cavity usually called a hemocoel. – Closed system in which the blood spends the entire time it is circulating inside the vessels of the system. Vertebrate Circulatory Systems - One Loop In fishes, the heart consists of two chambers and blood flows in a single circuit. The heart forces blood through the gills (where it is oxygenated), then through the arteries to the capillary beds in the body tissues, and finally back to the heart. Vertebrate Circulatory Systems - Two Loop - Type A In amphibians, the heart pumps blood through two partially separated circuits. Some blood is pumped to the lungs, where it is oxygenated. It returns to the heart and mixes with oxygen-poor blood still in the heart; then this partially oxygenated mix is sent to the tissues. Vertebrate Circulatory Systems - Two Loop - Type B In birds and mammals, a four-chambered heart pumps blood through two different circuits. The heart’s right half pumps oxygen-poor, carbon dioxide-rich blood to the lungs, where it is oxygenated and gives off carbon dioxide. Then, the freshly oxygenated blood flows into the heart’s left half; from here it is pumped to the tissues to deliver oxygen and pick up carbon dioxide. Characteristics of Blood Blood volume for average-size adult humans is about 6-to8 percent of body weight. That amounts to about 4 or 5 quarts. If a blood sample is placed in a test tube and kept from clotting, it will separate into two components • a straw-colored liquid (plasma) and • a red-colored cellular portion (red blood cells, white blood cells, and platelets). Components of Blood Plasma normally accounts for 50-to-60 percent of total blood volume, and is mostly water. It functions as • a transport medium for blood cells and platelets, and • as a solvent for a variety of molecules, including simple sugars, oxygen, carbon dioxide, and plasma proteins. Components of Blood Red blood cells (erythrocytes) transport oxygen and carry away some carbon dioxide wastes. • Their red color is due to the presence of hemoglobin, an iron- containing protein pigment that binds oxygen. White blood cells (leukocytes) function as part of the body’s housekeeping and defense systems. • Some engulf old, damaged, or dead cells and anything that is chemically perceived as foreign to the body. • Others target or destroy specific bacteria, viruses, and other agents of disease. Components of Blood The smallest components of the cellular portion of the blood are the platelets. • They are non-nucleated, membrane-bound fragments of large cells called megakaryocytes. Substances released from platelets initiate blood clotting. The following graphics show these components of the blood and explain how they develop. Components of Blood Erythrocytes make up about 99% of the cells in the blood. Components of Blood Components of Blood Components of Blood Human Cardiovascular System Play the Animation on your CD-ROM to show these mechanisms of vascular circuitry. Human Cardiovascular System The heart is located in the thoracic cavity between the lungs. It is surrounded by a protective pericardium—a double-walled sac with fluid between the two layers. Human Cardiovascular System The human heart Human Cardiovascular System Cardiac muscle cells are branched. Adjacent cell membranes meet in folded areas called intercalated discs. These regions are densely packed with gap junctions (pores). Human Cardiovascular System Human heart: its chambers, vessels to and from heart, valves to direct one-way flow of blood. Human Cardiovascular System Heart Valves in action; arrows indicate the direction of blood flow. Human Cardiovascular System Ventricles relax and would draw blood back from the arteries but this backpressure forces semilunar valves closed. Simultaneously, contraction of the atria forces open atrioventricular valves, allowing blood to flow from the atria into the ventricles. Human Cardiovascular System Pacemaker of the heart is a spontaneously active mass of modified muscle fibers in the right atrium called the sinoatrial (SA) node. The signal is spread through the atrioventricular (AV) node and ventricular muscle. Play the Animation on your CD-ROM to show these mechanism of heart contraction Human Cardiovascular System The cardiac cycle. During early diastole, all chambers are relaxed and the ventricles begin filling with blood. At the end of diastole, the atria contract and the ventricles are filled with blood. During systole, the ventricles contract, ejecting blood from the heart. Human Cardiovascular System Blood pressure is the fluid pressure exerted by heart contractions. It is usually measured in the brachial artery and is written as systolic pressure over diastolic pressure (normal is about 120/80). In vessels smaller than arteries, blood pressure drops significantly. Human Cardiovascular System Arteries have a large diameter and present low resistance to flow. Thus, they serve as rapid transporters of oxygenated blood. Their thick, muscular, elastic wall bulges as ventricular contraction forces a large volume of blood into them. Then the wall recoils and forces the blood forward through the circuit while the heart is relaxing. Human Cardiovascular System Track a volume of blood through the systemic route and you find the greatest pressure drop at arterioles, for these offer the greatest resistance to blood flow. Human Cardiovascular System By some estimates, the human body has between 10 billion and 40 billion capillaries. Most capillaries have a diameter so small that red blood cells must flow through in single file. Each capillary is a tube of endothelial cells a single layer thick. Human Cardiovascular System Veins are large-diameter, low-resistance transport tubes to the heart. Some veins (mainly in the limbs) have valves to keep blood from flowing backward in response to gravity. If the valves are damaged, blood pools in "varicose veins. Human Cardiovascular System Arteries can be partially obstructed by atherosclerotic plaques. Accumulation of cholesterol in plaques is related to the concentration of cholesterol-carrying lipoproteins. Your body needs some cholesterol—it is one of the major components of cell membranes. An excess of cholesterol is what causes problems. Human Lymphatic System A portion of the lymphatic system called the lymph vascular system consists of many tubes that collect and transport water and solutes from the interstitial fluid to the circulatory system. The lymph vascular system starts at capillary beds, where fluid enters the lymph capillaries. The capillaries have no obvious entrance; water and solutes move into their tips at flaplike "valves." Human Lymphatic System Valve in a lymph duct.

Circulatory System. Structure and Function

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