Chapter 11 The Cardiovascular System

The Cardiovascular System A closed system of the heart and blood vessels -heart pumps blood -blood vessels - circulate to all parts of body Deliver oxygens & nutrients and to remove carbon dioxide & waste products

The Heart Size of fist In thorax between lungs Pointed apex toward left hip Size of fist

Heart Coverings & Wall Layers Pericardium – double serous membrane Visceral - next to heart Parietal - outside layer Serous fluid fills space between the layers Three layers 1.Epicardium- Outside parietal pericardium Connective tissue 2.Myocardium- Middle Mostly cardiac muscle 3.Endocardium - Inner Endothelium

External Heart Anatomy Figure 11.2a

The Heart: Chambers Right and left act as separate pumps Four chambers 2 Atria - Receiving - Right atrium - Left atrium 2 Ventricles - Discharging - Right ventricle - Left ventricle

The Heart: Valves Allow blood to flow in only one direction Four valves 2 Atrioventricular valves – between atria & ventricles Bicuspid valve (left) Tricuspid valve (right) 2 Semilunar valves - between ventricle & artery Pulmonary semilunar valve Aortic semilunar valve Held in place by chordae tendineae (“heart strings”)

Operation of Heart Valves

The Heart: Associated Great Vessels Aorta - Leaves left ventricle Pulmonary arteries - Leave right ventricle Vena cava - Enters right atrium Pulmonary veins (four) - Enter left atrium

Coronary Circulation Blood in heart doesn’t nourish the heart Heart’s nourishing circulatory system - Coronary arteries - Cardiac veins - Blood empties into the right atrium via the coronary sinus

The Heart: Conduction System Intrinsic conduction system (nodal system) Heart muscle cells contract, without nerve impulses, in a regular, continuous way Sinoatrial node – Pacemaker initiates contraction Sequential stimulation occurs at other autorhythmic cells Atrioventricular node Atrioventricular bundle Bundle branches Purkinje fibers

The Heart: Cardiac Cycle Cardiac cycle – events of one heart beat Terms: Systole = contraction Diastole = relaxation Atria contract simultaneously Atria relax, then ventricles contract

The Heart: Cardiac Output Cardiac output (CO) Amount of blood pumped by each side of the heart in one minute CO = (heart rate [HR]) x (stroke volume [SV]) Stroke volume [SV] Volume of blood pumped by each ventricle in one contraction

Cardiac Output Regulation

The Heart: Regulation of Heart Rate Stroke volume usually remains relatively constant - Starling’s law of the heart: the more that the cardiac muscle is stretched, the stronger the contraction Changing heart rate is the most common way to change cardiac output

Regulation of Heart Rate Decreased Heart Rate 1. Parasympathetic nervous system 2. High blood pressure or blood volume 3. Decreased venous return Increased Heart Rate 1. Sympathetic nervous system Crisis Low blood pressure 2. Hormones Epinephrine Thyroxine 3. Exercise 4. Decreased blood volume