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Class 5. The Cardiovascular System.docx

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Vanessa Taler

The Cardiovascular System Blood  red blood cells (erythrocytes) carry oxygen to all cells of the body  white blood cells (leukocytes) protect the body from attack by viruses, bacteria, toxins, parasites, and tumour cells  platelets (thrombocytes) are essential for clotting  plasma is the fluid component of blood What does Blood do?  Four major functions: 1. Respiratory: distribution of oxygen from lungs to body tissues, and of carbon dioxide from body tissues to lungs for expulsion 2. Nutritive: transportation of food substances (glucose, fat, amino acids) from storage places to body tissues 3. Excretory: movement of waste products from body cells to excretory organs 4. Regulatory: control of body equilibrium (homeostasis) through hormone distribution, maintenance of water balance, and temperature regulation The Lymphatic System  Two components: lymph: a fluid originating in tissue spaces throughout the body lymph vessels: transport lymph from tissue spaces to lymph ducts, bloodstream and heart Functions of the Lymphatic System  It assists in preventing spread of infection and disease  It filters out foreign particles & bacteria as lymph passes through lymphoid tissue (tonsils, adenoids, and lymph nodes) The Blood-Vascular System  Four major components: The heart The arteries The veins The capillaries The Heart  The heart has four chambers: two atria and two ventricles  The left and right sides are separated by the septum  The aorta leads out of the left ventricle, and the pulmonary artery leads out of the right ventricle  The superior and inferior vena cavae enter the right atrium, and the pulmonary veins enter the left atrium  The bicuspid (mitral) valve separates the left atrium and ventricle  The tricuspid valve separates the right atrium and ventricle  Ventricles and arteries are also separated by valves  Coronary arteries distribute blood to the heart: a blockage results in a heart attack Blood Circulation Pulmonary blood circulation circulates blood through lungs to purify it Systemic blood circulation supplies all body parts Maintenance of Circulation  Circulation is maintained through continuous rhythmic action of heart, which has its own built-in pacemaker mechanism  Excitation begins at the S-A node, passes to the A-V node and then through a bundle of fibres (the bundle of His) to ventricle walls, causing heart to beat Blood Pressure  Contraction of left ventricle forces blood into the aorta with a certain pressure (systolic pressure)  Pressure decreases in following interval (diastolic pressure) Factors Influencing BP 1. age (blood pressure increases with age) 2. pumping action of heart (varies with age & health) 3. blood volume (amount of blood pumped) 4. elasticity of arterial walls 5. thickness of blood 6. peripheral resistance (especially in limbs) Structural Changes in the Cardiovascular system with Age 1. Increase in fatty tissue in outermost layer of heart muscle 2. Increase in collagen and elastin tissues in heart and arteries – vessels become more rigid and thicker 3. Accumulation of lipofuscin 4. Thickening and sclerosis (hardening) of valve flaps 5. Fewer pacemaker cells in S-A node 6. Veins dilate and stretch, and valves in veins function less efficiently 7. Coronary arteries can become dilated, twisted, and calcified 8. Aorta and arterial system lose some elasticity Functional Changes in the Cardiovascular System with Age 1. Longer time to recover after each heartbeat 2. Slight arrhythmias: skipped or extra beats become more common with age 3. Decline in cardiac output (amount of blood pumped from heart in one minute) 4. Increase in atrial fibrillation (arrhythmia involving the atria) due to age- related changes in the conduction system that controls the rate & coordination of the heartbeat. 5. Arteries and veins become more rigid, resulting in diminished regulation of blood pressure Disorders of the Cardiovascular System Age-Related Disorders of the CV System  Arteriosclerosis: hardening of arteries; lessened elasticity & thickening of artery walls, esp. small arteries and arterioles  Atherosclerosis: changes in the inner lining of medium and large arteries, coronary arteries, and arteries supplying the brain, abdomen, and legs Athero & Arteriosclerosis  Usually occur together  They may create occlusions (blockages) in the arteries, and rough surfaces where blood clots may form  They lead to ischemic heart disease and coronary/ cerebral ischemia or infarct (dead tissue resulting from lack of blood supply) Arteriosclerosis: the traditional View Atherosclerosis is a “plumbing problem”: lipids, carbohydrates, and fibrous tissues build up in the artery The New View  Arteries are not inanimate pipes  Cells communicate with one another & with their environment  They participate in the development & growth of atherosclerotic deposits  Deposits occur in vessel walls, not on them  Most heart attacks and many strokes stem from relatively unobtrusive plaques that rupture suddenly, triggering the emergence of a thrombus – blood clot Explanatory Power  Why do so many heart attacks seem to come from out of the blue?  Why do therapies that focus on widening the blood passage in semioccluded arteries (balloon angioplasty or insertion of wire-cage stents) or on surgically creating a bypass can ease angina yet frequently fail to prevent a future heart attack? Understanding Risk Factors  Diabetes elevates blood glucose levels, enhancing the glycation, and thus the inflammatory properties, of LDL.  Smoking causes oxidants to form and may hasten the oxidation of LDL’s constituents, fostering arterial inflammation  Obesity contributes to diabetes and vascular inflammation.  Angiotensin II is responsible for much hypertension and also appears to incite inflammation Viruses & Atherosclerosis  micro-organisms can induce or aggravate atherosclerosis  e.g., C. pneumonia can evoke inflammatory response by macrophages, vascular endothelial and smooth muscle cells  “echo effect”: inflammatory mediators from the body’s response to infection can travel to distant sites via blo
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