6.2 – The Blood System

Essential Idea: The blood system continuously transports substances to cells and simultaneously collects waste products. 6.2 The Blood System Understandings: Arteries convey blood at high pressure from the ventricles to the tissues of the body   Arteries have muscle cells and elastic fibers in their walls The muscle and elastic fibers assist in maintaining blood pressure between pump cycles Blood flows through tissues in capillaries. Capillaries have permeable walls that allow exchange of materials between cells in the tissue and the blood in the capillary Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart Valves in veins and the heart ensure circulation of blood by preventing backflow There is a separate circulation for the lungs The heart beat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node The sinoatrial node acts as a pacemaker The sinoatrial node sends out an electrical signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain Epinephrine increases the heart rate to prepare for vigorous physical activity Applications: William Harvey’s discovery of the circulation of the blood with the heart acting as the pump Pressure changes in the left atrium, left ventricles and aorta during the cardiac cycle Causes and consequences of occlusion of the coronary arteries Skills: Identify blood vessels as arteries, capillaries or veins from the structure of their walls Recognize the chambers and valves of the heart and the blood vessels connected to it in dissected hearts or in diagrams of heart structure

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

C. 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

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, O2 poor blood received on right side and pumped to the lungs 2. Systemic – to rest of body and back, O2 rich blood received on left and pumped to the 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 waste 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 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 Artherosclerosis – 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