Circulatory Adaptations to Exercise

Prepared By: Fritzie B. Talidano

MPE 1-A

Organization Of Circulatory System

HEART

Arteries

Arterioles

Capillaries

Venules

Veins

Structure of the Heart• The heart is divided into four chambers and is

often called to be two pumps.– The right atrium and right ventricle form the right

pump, while the left atrium and left ventricle combine to make the left pump.

• Blood movement within the heart is from atria to the ventricles, and from ventricles blood is pumped into the arteries. To prevent backward movement of blood, the heart contains four one-way valves.

Pulmonary and Systemic Circuits• The right side of the heart pumps blood that is

partially depleted of its oxygen content and contains an elevated carbon dioxide content as result of gas exchange in the various tissues of the body. This blood is delivered from the right heart into the lungs through the pulmonary circuit. At the lungs, oxygen is loaded into the blood and carbon dioxide is released. This oxygenated blood then travels to the left side of the heart and is pumped to the various tissues of the body via systemic circuit.

• Purpose of the Cardiovascular System– Transport of Oxygen to tissues and removal of

wastes.– Transport of nutrients to tissues.– Regulation of body temperature.

Heart: Myocardium and Cardiac Cycle

Myocardium– Or heart muscle is responsible for

contracting and forcing blood out of the heart.– It receives blood supply via the right and left

coronary arteries. Characteristics – Heart muscles are all interconnected via

intercalated discs-permit transmission of electrical impulses from one cell to another.

– Thought to be rather homogeneous muscle containing one primary fiber type that is similar in many ways to slow-twitch fibers found in skeletal muscle.

– Highly aerobic in nature, contain an extensive capillary supply, and have large numbers of mitochondria.

– Heart muscle is striated (contains actin and myosin protein filaments).

– It can alter its force of contraction as a function of the degree of overlap between actin myosin filaments.

Cardiac Cycle– Refers to the repeating pattern of contraction and

relaxation of the heart. • Contraction phase is called systole• Relaxation period is called diastole

– Atrial systole and diastole• Atrial contraction occurs during ventricular diastole and

atrial relaxation occurs during ventricular systole. – A healthy 21-year old female might have an average

resting heart of 75 beats per minute • The total cardiac cycle lasts 0.8 sec., with 0.5 sec. spent in

diastole and remaining 0.3 sec. dedicated to systole .• If the heart rate increases from 75 bpm to 180 bpm (heavy

exercise), there is a reduction in the time spent in both systole and diastole.

• 3D echocardiogram showing the mitral valve (right), tricuspid and mitral valves (top left) and aortic valve (top right). The closure of the heart valves causes the heart sounds.

Systole Diastole Rest HR=75 beats/min.

0.3 seconds 0.5 seconds

Systole Diastole Heavy exercise HR=180 beats/min.

0.2 seconds 0.13 seconds

Note: A rising heart rate results in a greater time reduction in diastole, while systole is less affected.

Arterial Blood Pressure– Blood pressure is the force exerted by blood

against the arterial walls and is determined by how much blood is pumped and the resistance to blood flow.

– It can be estimated by the use of sphygmomanometer. • The normal blood pressure of an adult male is 120/80,

while that of adult females tends to be lower (110/70). • The larger number in the expression of blood pressure

is the systolic pressure and the lower number is the diastolic pressure both expressed in millimeter of mercury(mm Hg).

– Pulse pressure• The difference between systolic and diastolic pressure

– Mean arterial pressure• The average pressure during a cardiac cycle.• It is important because it determines the rate of blood flow

through the systemic circuit.• Mean arterial pressure can be estimated in the following way:Mean arterial pressure= DBP=.33 (pulse pressure)Example, suppose an individual has a blood pressure of 120/80 mm Hg. The men arterial pressure would be:

MAP = 80 mm Hg+.33(120-80) = 80 mm Hg + 13 = 93 mm Hg

Electrical Activity of the Heart• Sinoartrial Node (SA node)– Serves as the pacemaker for the heart.

• Atrioventricular Node (AV node)– Located in the floor of the right atrium, connects

the atria with the ventricles by a pair of conductive pathways

• Electrocardiogram (ECG)– A recording of the electrical changes that occur in

the myocardium during the cardiac cycle.

Cardiac Output• Cardiac output (Q) is the product of the heart

rate (HR) and the stroke volume (SV)(amount of blood pumped per heart beat.

Q = HR x SV • It can be increased due to a rise in either heart

rate or stroke volume. During exercise in the upright position( e.g. running or cycling ). The increase in cardiac output is due to both an increase in heart rate and stroke volume.

Regulation of Heart RateDuring exercise the quantity of blood pumped by

the heart must change in accordance with the elevated skeletal muscle oxygen demand.• The two most prominent factors that influence heart

rate are:– Parasympathetic nervous system– Sympathetic nervous system

• The parasympathetic fibers that supply the heart arise from neurons in the cardiovascular control center in the medulla oblongata and make up a portion of the vagus nerve.

• Parasympathetic– Acts as a braking system to slow down heart rate.– Studies have shown that the initial increase in

heart rate during exercise, up to approximately 100 beats per minute, is due to withdrawal of parasympathetic tone.

• Sympathetic fibers reach the heart by means of the cardiac accelerator nerves, which innervate both the SA node and the ventricle.

• ExampleAn increase in resting blood pressure above

normal stimulates pressure receptors in the carotid arteries and the arch of aorta, which in turn send impulses to cardiovascular control center.

In response, the cardiovascular control center increases parasympathetic activity to the heart to slow the heart rate and reduce cardiac output.

This reduction in cardiac output causes blood pressure to decline back to normal.

• Another regulatory reflex involves pressure receptors located in the right atrium. – An increase in right atrial pressure signals the cardiovascular

control center that an increase in venous return has occurred.

– The increase I the cardiac output lowers right atrial pressure back to normal and venous blood presure is reduced

• A change in body temperature can influence heart rate. – An increase in body temperature above normal results in an

increase in heart rate, while lowering of the body temperature below normal causes a reduction in heart rate.

Regulation of Stroke Volume–Stroke volume , at rest or during

exercise, is regulated by three variables:• (1) The end-diastolic volume (EDV), which

is the volume of blood in the ventricles at the end of diastole• (2) The average aortic blood pressure • (3) The strength of ventricular

contraction

• The end-diastolic volume (EDV),– A rise in cardiac contractility results in an

increase in the amount pumped per beat. The principal variable that influences EDV is the rat of venous return to the heart. An increase in venous return results in a rise in EDV and therefore an increase in stroke volume. Increased venous return and the resulting increase in EDV plays a key role in the exercise in stroke volume observed during upright exercise.

• Factors that regulate venous return during exercise – Three principal mechanism s for increasing

venous return during exercise.• (1) constriction of the veins (venoconstriction)• (2) pumping action of contracting skeletal

muscle (muscle pump)• (3) pumping action of the respiratory system

(respiratory pump)

• The average aortic blood pressure – (mean arterial pressure called afterload)– Stoke volume is inversely proportional to the

afterload; that is, in an increase in aortic pressure produces a decrease in stroke volume. However, it is noteworthy that afterload is minimize during exercise due to arteriole dilation. This arteriole dilation in the working muscles reduces afterload and makes it easier for the heart to pump a large volume of blood.

• The final factor that influences stroke volume is the effect of circulation epinephrine/norepinephrine and direct sympathetic stimulation of the heart by cardiac accelerator nerves.