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 14 000 liters of blood in a day beats 100 000 times every day transports the blood through vessels with a total length of 100 000 km
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
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; 50-100 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
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 40-60 times per minute Pacing rate of the others is 20-35 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
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