Circulatory Responses To Exercise PDF

CIRCULATORY RESPONSES TO EXERCISE Chapter 9 Lecture Outline Organization of the Circulatory System. Heart: Myocardium and Cardiac Cycle. Cardiac Output. Hemodynamics. Changes in Oxygen Delivery to Muscle During Exercise. Circulatory Responses to Exercise. Regulation of Cardiovascular...

CIRCULATORY RESPONSES TO EXERCISE Chapter 9 Lecture Outline Organization of the Circulatory System. Heart: Myocardium and Cardiac Cycle. Cardiac Output. Hemodynamics. Changes in Oxygen Delivery to Muscle During Exercise. Circulatory Responses to Exercise. Regulation of Cardiovascular Adjustments to Exercise.  The circulatory system Works with the pulmonary system Cardiopulmonary or cardiorespiratory system Purposes of the cardiorespiratory system Transport O2 and nutrients to tissues Removal of CO2 and wastes from tissues Regulation of body temperature The circulatory system The human circulatory system is a closed loop that circulates blood to all body tissues. Heart Muscular pump that creates pressure to move blood through the system Arteries and arterioles Carry blood away from the heart Capillaries Exchange of O2, CO2, and nutrients with tissues Veins and venules Carry blood back to the heart  Structure of the heart The heart is divided into 4 chambers It is considered to be 2 pumps: Right pump: right atrium and right ventricle Left pump: left atrium and left ventricle The 2 sides of the heart are separated by a muscular wall called the interventricular septum which prevents the blood from the 2 sides of the heart from mixing Blood moves from the atria to the ventricles and from the ventricles it is pumped into the arteries. 4 one-way valves prevent backward flow of blood Right (tricuspid) and left atrioventricular valves (bicuspid or mitral) Prevent flow from the right and left ventricles back to the right and left atria, respectively Pulmonary semilunar and aortic semilunar valves Prevent flow from arteries to ventricles Structure of the heart Figure 9.1 Pulmonary and systemic circuits Pulmonary circuit Right side of the heart Pumps deoxygenated blood to the lungs via pulmonary arteries Returns oxygenated blood to the left side of the heart via pulmonary veins Systemic circuit Left side of the heart Pumps oxygenated blood to the whole body via arteries Returns deoxygenated blood to the right side of the heart via veins Check your understanding ▪ The purposes of the cardiovascular system are the following: (1) _________________________________________________ (2) _________________________________________________ (3) _________________________________________________ ▪ The heart is two pumps in one. The right side of the heart pumps blood through the _________________ circulation, while the left side of the heart delivers blood to the _________________ circulation.  Myocardium The heart wall is composed of 3 layers: Epicardium (outer) Myocardium (middle) Endocardium (inner) The myocardium is the heart muscle responsible for contracting and forcing blood out of the heart Receives blood supply via coronary arteries which branch out of the aorta and circle the heart The coronary veins run along the coronary arteries and drain all deoxygenated blood into a larger vein (coronary sinus) which deposits blood into the right atrium.  Myocardium Heart has a high demand for oxygen and nutrients even at rest Myocardial infarction (MI) Blockage in coronary blood flow results in cell damage The number of heart cells that die from this insult determines the severity of the heart attack A major heart attack seriously impacts the pumping ability of the heart Minimizing the amount of injury during a heart attack is important  Clinical Applications 9.1 Exercise training protects the heart Regular endurance exercise is cardioprotective Reduces incidence of heart attacks Improves survival from heart attack Exercise reduces the amount of myocardial damage from heart attack by: Improving the heart’s antioxidant capacity Altering cardiac mitochondria Refinement of Ca++ handling for ventricular contraction Skeletal muscle vs. heart muscle Cardiac muscle fibers are shorter and connected in a tight series Cardiac fibers are branched whereas skeletal muscle fibers are elongated Heart muscle fibers are connected by intercalated discs Intercalated discs are leaky membranes that allow ions to cross from one fiber to another permitting the transmission of electrical impulses from one fiber to another When one heart fiber is depolarized to contract, all connecting fibers are depolarized and contract as a unit. This arrangement is called a functional syncytium. Skeletal muscle vs. heart muscle Atrial cells are separated from ventricular cells by a layer of connective tissue that does NOT permit the transmission of electrical impulses Atria contract separately from the ventricles Human heart fibers cannot be divided into different fiber types The ventricular myocardium is a homogeneous muscle containing one primary fiber type similar to Type I slow fiber found in skeletal muscle Heart muscle fibers are highly aerobic and contain large numbers of mitochondria, higher than Type I fibers Similarities between skeletal and heart muscle Both striated and contain the same contractile proteins: actin and myosin Both require calcium to activate myofilaments Both utilize the sliding filament model of contraction Heart also alters force of contraction based on degree of overlap of actin- myosin filaments due to changes in fiber length Comparison of cardiac and skeletal muscle The cardiac cycle Cardiac cycle: repeating pattern of contraction and relaxation. Contraction is systole and relaxation is diastole Atrial contraction occurs during ventricular diastole and atrial relaxation occurs during ventricular systole Heart has 2 step pumping action: Right and left atria contract together, which empties blood into the ventricles 0.1 second after atrial contraction, the ventricles contract and deliver blood into both the systemic and pulmonary circuits.  The cardiac cycle A healthy young female may have an average heart rate of 75 beats per minute This means the whole cardiac cycle occurs in 0.8 sec (60sec/75 beats) with 0.5 sec spent in diastole and 0.3 sec spent in systole. During heavy exercise, if the heart rate increases to 180 beats, there is a reduction in the time spent in both systole and diastole. But there is greater reduction in the duration of diastole.  Arterial blood pressure Expressed as systolic/diastolic in mm Hg Normal is