Anatomi & Fysiologi The cardiovascular system (chapter 20) The circulation system transports; What the heart can do;

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1 The cardiovascular system consists of; The cardiovascular system (chapter 20) Principles of Anatomy & Physiology 2009 Blood 2 separate pumps (heart) Many blood vessels with varying diameter and elasticity The circulation system transports; Nutritive substances from the digestive system to the tissues Rest products from the tissues O 2 from the lungs to the tissues CO 2 from the tissues to the lungs hormones (chemical messingers) heat from the tissues to the skin surface More; Protect against infection (white blood cells and antibodies) stabilize the inner milieu of the body (ph, ions, amount of water and osmotic pressure) deliver 25% of the blood volume to the digestive system and the liver each minute What the heart can do; Transverse section of thoracic cavity Start to beat when the fetus is 3 weeks old pump 5 liters blood every minute pump liters of blood in a day beats times every day transports the blood through vessels with a total length of km

2 Pericardium and heart wall 1. The fibrous pericardium (inelastic connective tissue) prevents overstretching, provides protection and anchors the heart 2. The serous pericardium forms a double layer around dthe heart The cone-shaped heart is; - 12 cm long - 9 cm wide - 6 cm thick - weight; 250g (females), 300g (males) The slippery liquid (a few milliliters) in the pericardial cavity reduces the friction between the membranes as the heart moves The endocardium (endothelium & connective tissue) covers the valves and is continous with the endothelial lining of blood vessels Overview chambers & valves Structure of the heart Mitral Valve = Bicuspid valve Anterior view Structure of the heart The fibrous skeleton of the heart The left chamber wall is thicker then the right wall - contains four fibrous rings - foundation to which the heart valves attach - prevents overstreching of the valves - acts as an electrical isolator between the atria and ventricles

3 Valves Semilunar valves - Valves open and close in response to pressure changes as the heart contracts and relaxes - The valves ensure one-way flow of blood Coronary circulation * * Anastomoses Autorhytmic muscle cells (fibers); Cardiac muscle fiber; μm long 14 μm in diameter Act as *pacemakers, setting the rhythm (frequency) of electrical excitation that causes contraction of the heart Form the conduction system, which ensures that cardiac chambers become stimulated to contract in a coordinated manner (effective pump) * self-excitable

4 The conduction system of the heart Ectopic pacemaker; The SA node is the normal pacemaker of the heart = 100 times per minute Nerve impulses from ANS and blood-borne hormones modify the timing A site that developes abnormal self-excitability It operates only occasionally as extra beats or may pace the heart for some period The AV node has a spontaneous depolarization of times per minute Pacing rate of the others is beats per minute Triggers of such activity may be caffeine, nicotine, electrolyte imbalances, hypoxia and toxic reactions to drugs such as digitalis Action potential in a ventricular contractile fiber ECG (Electrocardiogram) and interpretation larger P wave:enlargement of an atrium Lead II record; right arm to left leg larger R wave:enlarged ventricles flatter T wave:coronary artery disease (insufficient oxygen) longer P-Q interval:coronary artery disease elevated S-T segment: acute myocardial infarction longer Q-T interval:myocardial damage or ishemia Cardiac Cycle 0.1 s Atrial systole 0.3 s Ventricular systole Heart Sounds 0.4 s Relaxation period S1; closure of the AV valves S2; closure of the semilunar valves

5 Cardiac output (CO) CO = sv (stroke volume) HR (heart rate) (ml/min) (ml/beat) (beats/min) Ex.1: CO = 70 ml/beat 75 beats/min = 5,25 L/min = resting value Ex.2: CO = 130 ml/beat = 19,5 L/min 150 beats/min Frank-Starling law of the heart; The heart will pump out all the blood that entered its chambers during the previous diastole Cardiac reserve= difference between a person s maximal CO and CO at rest Factors that regulate stroke volume: Preload; degree of stretch on the heart before it contracts Contractility; strength of contraction at any given preload Afterload; the pressure that must be exceeded before ejection of blood Preload and Afterload Preload=depends on the end-diastolic volume (EDV). The greater the EDV the more forceful contraction Afterload=the pressure that must be overcome before a semilunar valve can open Nervous system control of the heart