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Chapter 12 The Cardiovascular System What is the cardiovascular system? Includes the heart, blood vessels, and blood Brings nutrients to cells and helps get rid of wastes The blood is refreshed in the lung, kidneys, intestine and liver Lymphatic vessels help this system by collecting excess fluid surrounding tissues and returning it to the cardiovascular system Anatomy of the heart A large, muscular organ consisting of mostly cardiac tissue called the myocardium It is surrounded by a sac called the pericardium Consists of two sides, right and left, separated by a septum Consists of four chambers, two atria and two ventricles Blood flow Inferior and superior vena cava (1) dump blood into the right atrium (2) Right ventricle (3) 2 pulmonary arteries (4) that lead to the lungs (5) where blood becomes oxygenated Pulmonary veins (6) bring blood from the lungs back to the left atrium (7) Left ventricle (8) is large and muscular to pump blood into the aorta (9) and to the rest of the body (10) Eventually blood will be pumped back to each vena cava (1) The two cardiovascular pathways in the body Pulmonary circuit: the right side of the heart that brings blood from the body to the heart and the lungs Systemic circuit: the left side of the heart that brings blood to the entire body to deliver nutrients and rid it of wastes All of this requires properly functioning valves 2 sets of valves: semilunar valves and atrioventricular valves (AV valves) The opening and closing of the valves give the resulting “lub” and “dup” sound of the heart Cardiac cycle Diastole is a rest phase, when the chambers relax This is followed by systole when the atria contract together followed by the ventricles contracting together This cardiac cycle, your heartbeat, occurs on average 70 times/minute Control of heartbeat Internal control: o The SA node in the right atrium initiates the heartbeat and causes the atria to contract o This impulse reaches the AV node, also in the right atrium, to send a signal down the AV bundle and Purkinje fibers that causes ventricular contraction o These impulses travel between gap junctions at intercalated disks External control: o Heartbeat is also controlled by a cardiac center in the brain and hormones such as epinephrine and norepinephrine Electrocardiogram (ECG) A record of the electrical changes in the heart muscle during a cardiac cycle o The atria produce an electrical current when stimulated by the SA node called the P wave o The contraction of the ventricles is the QRS complex o The recovery of the ventricles is called the T wave Looking at these electrical changes allows doctors to detect abnormalities Blood pressure The pressure against a blood vessel wall, usually measured in an artery in the arm The highest pressure is during blood ejection from the heart called the systolic pressure The lowest pressure is the diastolic pressure when the ventricles relax Average blood pressure is recorded at about 120/80 mmHg (systolic/diastolic) Blood vessels Heart ➔arteries ➔arterioles ➔capillaries ➔venules ➔veins ➔back to the heart Arteries and arterioles o Carry blood away from the heart o Their walls have 3 layers: Thin inner epithelium Thick smooth muscle layer Outer connective tissue o Arterioles are small arteries that regulate blood pressure Capillaries o Microscopic vessels between arterioles and venules o Made of one layer of epithelial tissue o Form beds of vessels where exchange with body cells occurs o All of them combined form an extremely large surface area Veins and venules o Venules are small veins that receive blood from the capillaries o Venule and vein walls have 3 layers: Thin inner epithelium Thick smooth muscle layer Outer connective tissue o Veins carry blood toward the heart o Veins that carry blood against gravity have valves to keep blood flowing toward the heart Composition of blood o Formed elements: produced in red bone marrow o Red blood cells/erythrocytes (RBC) o White blood cells/leukocytes (WBC) o Platelets o Plasma: o 92% water and 8% salts and organic molecules o Plasma proteins are the most abundant molecules o White blood cells o Derived from red bone marrow o Large blood cells that have a nucleus o Their production is regulated by colony-stimulating factor (CSF) o Can be found in the blood as well as in tissues o Fight infection and are an important part of the immune system o Some live days and others live for months or even years o Red blood cells o They lack a nucleus and have only a few organelles o The biconcave shape increases the surface area available for exchanges o Each contains about 200 million hemoglobin molecules that bind 3 molecules of O2 each o o o o o Lifespan of ~120 days Erythropoiesis is the production of new RBCs ABO blood types Like many body cells, RBCs have surface markers The most common and well-known are the ABO markers It all has to do with which antigens are present on the RBCs The Rh factor is also a surface antigen with a difference The problem arises if a Rh- female has a Rh+ child But it can also be easily avoided Platelets Made of fragments of large cells called megakaryocytes made in the red bone marrow About 200 billion are made per day Function in blood clotting Blood proteins named thrombin and fibrinogen are important for blood clotting by forming fibrin threads that catch RBC’s Cardiovascular disease Cardiovascular disease (CVD) is the most common cause of death in the western world Disorders of the blood vessels o Hypertension/high blood pressure o Atherosclerosis o Stroke o Heart attack o Aneurysm o Hypertension o High blood pressure results when blood moves through vessels at a rate higher than normal often due to arterial plaque o 140/90 mmHg is considered hypertension o A silent killer because there are few symptoms o Can lead to a heart attack, stroke or kidney failure Atherosclerosis o A build up of plaque in blood vessels o Plaque that is stationary is called a thrombus and an embolus when it detaches and can move to distant sites o Associated with stroke, heart attack and aneurysms Aneurysm o A ballooning of a blood vessel o Atherosclerosis and hypertension can weaken a vessel and cause ballooning o The most commonly affected is the abdominal artery or the arteries leading to the brain Stroke o Also known as a cerebrovascular accident (CVA) o Usually occurs when a cranial artery is blocked or bursts o Part of the brain dies dues to lack of oxygen o Symptoms may occur including numbness of hands or face, difficulty speaking and inability to see in one eye Heart attack o Also known as a myocardial infarction (MI) o Part of the heart dies due to lack of oxygen o Can begin with angina pectoris, a pain that radiates down the left arm due to a blockage of a coronary artery