The Circulatory System Blood Vessels and the Heart

Blood vessels Arteries – carry blood away from the heart Walls of smooth muscle and elastic fibers - Helps maintain and withstand high pressure 2. Branch into arterioles, which branch into capillaries

B. Veins – carry blood to the heart 1. Form from merged venules 2 B. Veins – carry blood to the heart 1. Form from merged venules 2. Have valves to prevent backflow due to low pressure and gravity

B. Capillaries Form “beds” to allow gas exchange in all areas of the body - diffusion of O2 and CO2 from high concentration to low Merge to form venules

Arteries Capillaries Veins Carry blood away from heart Exchange of gases with tissues Carry blood back to the heart Thick walled 1 cell thick Thin walled No exchange All exchange No valves Valves High pressure Low pressure Small lumen Lumen 1 cell wide Larger lumen

II. The heart

Two side-by-side pumps O2 poor blood received on right side and pumped to the lungs O2 rich blood received on left and pumped to the body Creates two circuits Pulmonary circuit – heart to lungs and back Systemic circuit – heart to rest of body and back

Blood flow through the heart 1. Controlled by valves – opened by pressure, prevent back flow a. Atrioventricular valves - between atria and ventricles (left – mitral/bicuspid, right – tricuspid) b. Semilunar valves – between ventricles and arteries (right - pulmonary, left – aortic)

-From body into vena cava -Right atrium -Right ventricle -Pulmonary artery -Lungs -Pulmonary vein -Left atrium -Left ventricle -Aorta -Body

Control of heart rate 1. Myogenic muscle contractions – no input from nervous system 2. Sinoatrial (SA) node acts as a natural pacemaker – fires every .8 seconds, causing both atria to contract and sending a message to AV node 3. Atrioventricular (AV) node – receives signal from SA node, pauses .1 seconds, fires to contract both ventricles (message goes through bundle branches and Purkinje fibers)

During exercise, medulla oblongata senses increase in CO2 a. Sends message to SA node through cardiac nerve to increase rate of firing b. When CO2 levels return to normal, sends message to SA node through vagus nerve to tell SA node to take back over normal pace 5. Adrenaline/epinephrine – speed up heart rate

E. Pressure & Volume in the heart A. Diastole – not contracting B E. Pressure & Volume in the heart A. Diastole – not contracting B. Systole – contracting

C. As blood enters the atria, the atrioventricular valves are closed C. As blood enters the atria, the atrioventricular valves are closed. The increase in volume increases pressure. D. Systole of atria pushes open atrioventricular valves and moves blood into ventricles E. Systole of ventricles forces atrioventricular valves closed to prevent backflow (“lub”) F. As ventricle contracts, pressure increase until semilunar valves are forced open, pushing blood into aorta/pulmonary artery G. As contraction finishes, semilunar valve closes (“dub”)

Blood supply to the heart First branching of aorta results in 3 coronary arteries that supply the heart muscle itself with blood 2. Artherosclerosis – build-up of plaque in the arteries a. Plaque is composed of lipids, cholesterol, cell debris, calcium (Causes arteries to be less flexible) b. Occlusion – when blood flow in an artery is obstructed by plaque

3. Myocardial Infarction – (heart attack) blood supply to the heart blocked -> dead heart muscle