6.2 – The Blood System

Blood vessels Arteries Walls of smooth muscle and elastic fibers - Helps maintain and withstand high pressure 2. Branch into arterioles, which branch into capillaries 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 Veins – form from merged 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

The Heart -2 side-by-side pumps that take blood in and pump it out, creating 2 circuits (William Harvey – 1628) 1. Pulmonary – to lungs and back 2. Systemic – to rest of body

-From body, blood enters heart through vena cava -Collects in right atrium -Atria contract and move blood through atrioventricular valve to right ventricle -Ventricle contracts – closes atrioventricular valve to prevent backflow – increase pressure in ventricle and opens semilunar valve, pushing blood into pulmonary artery -Blood goes to lungs where it drops off CO2 and picks up O2-Returns to heart through pulmonary veins -Enters left atrium, through atrioventricular valve to left ventricle, through semilunar valve to aorta -Aorta branches to send blood to rest of body where it drops of O2 and picks up CO2

Blood – NOT blue! Components Plasma – liquid portion, mostly water Erythrocytes – Red blood cells, carry O2 & CO2 Leucocytes – White blood cells Platelets – cell fragments for clotting

B. Transports Nutrients – glucose, amino acids, etc. O2 – reactant for cellular respiration CO2 – waste product of cellular respiration Hormones – transported from glands to target cells Antibodies – proteins for immunity Urea – nitrogenous waster Heat- skin arterioles open/dilate to gain/lose heat

Control of Heart Rate A. Myogenic muscle contractions – contracts and relaxes without nervous system control B. Sinoatrial node (SA node) – mass of tissue located in the right atrium 1. acts as a natural pacemaker 2. initiates contraction of both atria and sends out signals to AV node after .8 seconds

Atrioventricular Node (AV Node) also in right atrium Receives signal from SA node, waits .1 sec and sends out its own signal to ventricles to contract

If there is an increased demand for O2 and to get rid of CO2 (ex If there is an increased demand for O2 and to get rid of CO2 (ex. during exercise), brain gets involved 1. Medulla oblongata senses increase in CO2, sends signal through cardiac nerve to SA node to increase rate at which heart contracts 2. Once demand returns to normal, medulla sends message through vagus nerve for SA node that take back control

Chemicals can also increase heart rate 1. Adrenaline (epinephrine) a. Secreted by adrenal glands (which sit on top of kidneys) when stressed or excited b. Causes SA node to fire more rapidly

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

Heart Health Atherosclerosis – build-up of plaque in the arteries 1. Plaque is composed of lipids, cholesterol, cell debris, calcium 2. Causes arteries to be less flexible

Heart attacks 1. Coronary arteries – 3, branch off aorta, blood supply of heart muscle itself 2. Occlusion – when blood flow in an artery is obstructed by plaque 3. Myocardial Infarction – blood supply to the heart blocked -> dead heart muscle