The Circulatory System A & P - Mr. Carlson

Major Structures of the Circulatory System Heart Blood Vessels Blood Lymph Nodes Lymph Lymph Vessels

The Heart The heart is the central organ of the cardiovascular system. Beats more than 2.5 billion times in an average lifespan. Lies within the thoracic cavity, behind the sternum, and between the lungs.

Heart Parts The pericardium is a tough sac-like membrane that surrounds the heart and functions to secrete a fluid that reduces friction as the heart beats. The septum vertically divides the heart into two sides. Right side pumps blood to lungs. Left side pumps blood to other parts of the body.

Heart Chambers The heart is divided into upper & lower chambers. Each upper chamber is called an atrium. Each lower chamber is called a ventricle. There are four total chambers.

Heart Valves Atrioventricular valves separate each atrium from each ventricle. AV valves consist of flaps of tissue that open in only one direction. The AV valve on the right is called the tricuspid valve. The AV valve in the left is called the mitral valve.

Heart Valves Semilunar valves separates the ventricles from large blood vessels on each side of the heart. SL valves are also one-way valves. The SL valve on the right is known as the pulmonary valve. The SL valve on the left is known as the aortic valve.

Patterns of Circulation The heart and blood vessels from one continuous, closed system of circulation. This system also consists of two primary subsystems: Pulmonary Circulation – Blood travels between heart and lungs. Systemic Circulation – Blood travels between the heart and all other body tissues.

Circulation of Blood in the Heart Deoxygenated blood from the body returns via the superior & inferior vena cava to the right atrium. The right atrium pumps blood through the tricuspid valve to the right ventricle. The muscles of the right ventricle contract and force the blood into the pulmonary arteries, which lead to the lungs. In the lungs, carbon dioxide diffuses out and oxygen diffuses into the blood.

Circulation of Blood in the Heart Oxygenated blood from the lungs returns via the Pulmonary Veins to the left atrium. From the left atrium, blood passes through the mitral valve into the left ventricle. Contraction of the muscular walls of the left ventricle force the blood into a large blood vessel called the aorta. From the aorta, blood is distributed to the rest of the body except the lungs.

Whew!!! Have you had enough yet? I didn’t even include the SL Valves in the last description! Almost there!

Control of the Heartbeat The heart consists of muscle cells that contract in waves. When the first group of muscle cells is stimulated it sets off a chain reaction that travels across the heart. The sinoatrial (SA) node is a group of specialized heart- muscle cells located in the right atrium that is stimulated first. The SA node is called the pacemaker because it regulates the rate of contraction of the entire heart. The atrioventricular (AV) node is located in the septum between the atria and relays the electrical impulse to the muscle cells that are located in the ventricles.

Heart Disease The end result of untreated heart disease is a heart attack. Heart disease is one of the leading causes of death in the United States. Elevated cholesterol levels is a major factor in creating heart disease. The CDC estimates the number of americans that are overweight or obese is currently at 61%.