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

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 Systemic Circuit

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

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)

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

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