Cardiovascular System

Cardiovascular System Components Circulatory system Pulmonary system Purposes: Transport O2 to tissues and remove waste Transport nutrients to tissues Regulation of body temperature

Circulatory System Heart Arteries and arterioles Capillaries Pumps blood Arteries and arterioles Carry blood away from heart Capillaries Exchange nutrients with tissues Veins and venules Carry blood toward heart

Pulmonary and Systemic Circuits Left side of heart Pumps oxygenated blood to body via arteries Returns deoxygenated blood to right heart via veins Pulmonary Circuit Right side of heart Pumps deoxygenated blood to lungs via pulmonary arteries Returns oxygenated blood to left heart via pulmonary veins

Cardiac Cycle Systole Diastole Contractile phase of heart Electrical and mechanical changes E.g. blood pressure changes E.g. blood volume changes Diastole Relaxation phase of heart Takes twice as long as systole E.g. resting HR = 60 Systole = 0.3 s Diastole = 0.6 s

Arterial Blood Pressure Expressed as systolic/diastolic Normal – 120/80 mmHg High – 140/90 mmHg Systolic pressure (top number) Pressure generated during ventricular contraction Diastolic pressure Pressure during cardiac relaxation

Blood Pressure Pulse Pressure (PP) Mean Arterial Pressure (MAP) Difference between systolic and diastolic PP = systolic - diastolic Mean Arterial Pressure (MAP) Average pressure in arteries MAP = diastolic + 1/3 (systolic – diastolic)

Electrical Activity of the Heart Contraction of heart depends on electrical stimulation of myocardium Impulse is initiated on right atrium and spreads throughout the heart May be recorded on an ECG

Electrocardiogram Records electrical activity of the heart P wave Atrial depolarization QRS complex Ventricular depolarization T wave Ventricular repolarization

Diagnostic use of the ECG ECG abnormalities may indicate coronary heart disease ST-segment depression may indicate myocardial ischemia

Heart Rate Range of normal at rest is 50 – 100 b.m Increases in proportion to exercise intensity Max. HR is 220 – age Medications or upper body exercise may change normal response

Stroke Volume Range of normal at rest is 60 – 100 ml.b During exercise, SV increases quickly, reaching max. around 40% of VO2 max. Max. SV is 120 – 200 ml.b, depending on size, heredity, and conditioning. Increased SV during rhythmic aerobic exercise is due to complete filling of ventricles during diastole and/or complete emptying of ventricles during systole.

Central Circulation Maintenance Important for older or deconditioned adults Moderate, continuous, rhythmic aerobic activity encourages venous return Strenuous activity and held muscle contractions should be avoided Taper or cool down should follow each activity session to encourage venous return

Frank-Starling Law of the Heart The heart will pump all the blood returned to it by the venous system. Central circulation must be maintained and the veins must continuously return blood to the heart.

Features that Encourage Venous Return One-way valves in veins Vasoconstriction of blood flow to inactive body parts Pumping action of skeletal muscles in arches of feet, calves, thighs, etc. Pressure changes in chest and abdomen during breathing Maintenance of blood volume by adequate fluid replacement Siphon action of vascular system

Features that Inhibit Venous return Heat stress requiring additional blood flow to the skin for core temp. maintenance Dehydration from sweating or from limiting fluid intake (dieting, making weight) Held muscle contractions that cause blood to pool in the extremities A Valsalva maneuver which increases pressure in the chest to a high level Changing from a horizontal to a vertical position abruptly

Autonomic Nervous System Control of Heart Rate Sympathetic control Stimulates “fight or flight” response Speeds up heart rate and stroke volume Sympathetic tone > 100 bpm Parasympathetic control Connected to vagus nerves Slows down heart rate Parasympathetic tone 60 – 100 bpm

Skeletal Muscle Pump Rhythmic skeletal muscle contractions force blood in the extremities toward the heart One-way valves in veins prevent backflow of blood

Components of Blood Plasma Cells Hematocrit Liquid portion of blood Contains ions, proteins, hormones Cells Red blood cells Contain hemoglobin to carry oxygen White blood cells Platelets Important in blood clotting Hematocrit Percent of blood composed of cells

Oxygen Delivery During Exercise Oxygen demand by muscles during exercise is many times greater than at rest Increased oxygen delivery accomplished by: Increased cardiac output Redistribution of blood flow to skeletal muscle

Redistribution of Blood Flow Increased blood flow to working skeletal muscle Reduced blood flow to less active organs Liver, kidneys, GI tract

Increased blood flow to skeletal muscle during exercise Withdrawal of sympathetic vasoconstriction Autoregulation Blood flow increased to meet metabolic demands of tissue O2 tension, CO2 tension, ph, potassium, adenosine, nitric oxide