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8/12/2019 kitar kardiak

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CARDIAC CYCLE

WHAT IS CARDIAC CYCLE?


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The series of events that occur during onecomplete heartbeat including

Contraction (systole)

Relaxing (diastole)

Of both the atria and the ventricles

1 systole and 1 diastole equal to 1 heartbeat (0.8

sec)


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The pumping of the heart generates sufficientforce to move the blood through the arteries,arterioles and capillaries.

When the blood reached the veins, the pressureproduces by the heart is insufficient to force itback into the heart

When the body move,

- skeletal muscle contract and press the veins- the veins constrict and the blood pressureincreases, forces open the valves and pushedthe blood towards the heart


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The heart rate increase when:

An increase in the secretion of hormone (e.g

adrenaline) when a person is excited An increase in partial pressure of carbon

dioxide in the blood

Body temperature is elevated (higher thannormal)


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REGULATORY

MECHANISM OF BLOOD

PRESSURE


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Blood pressure (bp) is the force of the bloodexerted on the wall of the arterial blood vessels.

Arterial bp : Highest during ventricular systole

Lowest during diastole (ie resting phase of the

heart) Bp regulated bybaroreceptors located in the

wall of the aorta and carotid arteries branch outfrom the aorta

baroreceptors - monitor the pressure ofblood flowing to the body and to the brain


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Stretches the baroreceptors

Impulses are sent to the cardiovascular controlcentre (in medulla oblongata)

Impulse then sent via the parasympatheticnerve to the heart.

- slow down the heartbeat and decrease the

bp


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Baroreceptor are inhibited

Increase stimulation of the sino-atrial (SA)node by the sympathetic nerve

This increases the contraction of the

- cardiac muscles hence increase in heart rate

- smooth muscles of the arteries, hence

decrease the diameter Bp increase and returns to its normal level.


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Bp can increase because of increase in heartbeat, resistance fo blood vessel, viscosity of

blood and stress Bp can be measured by using

sphygmomanometer


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CIRCULATORY

SYSTEMS IN FISH,AMPHIBIANS AND

HUMAN


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CIRCULATORY SYSTEM

Open Circulatory System Close Circulatory System

Double Single

Complete incomplete

Eg. Fish

Eg. Insect

Eg. Human Eg. Amphibian


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Heart consists of 2 separate

chambers, an atriumand a ventricle The deoxygenatedblood enters the

atrium and then the ventricle The ventricle pumps the blood to the

capillaries in the gills where gaseous

exchange occurs The oxygenatedblood leaves the gills

and flows directly to the body tissues. In the systemic capillaries, oxygen

diffuses into the tissues while carbondioxide diffuses out of the tissues andinto the capillaries.

The deoxygenated blood then flowsback to the heart.

The blood flows through the heartonly once in complete cycle.


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Humans have a four-chamberedheart :two atria and two ventricles. The four-chambered heart prevents the

mixing of the oxygenated anddeoxygenated blood.

Humans have a double closed circulatory

system due to the pulmonary andsystemic circulatory systems arecompletely separated.

In the pulmonary circulation system,deoxygenatedblood in the right ventricleis pumped into the pulmonary arteries to

the lungs and oxygenatedblood from thelungs returns to the left atrium. In the systemic circulation, blood is

carried from the heart to the other parts ofthe body except the lungs and transportedback to the heart.

The blood enters the heart twice duringone complete cycle.


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THE MECHANISM OFBLOOD CLOTTING

Learning outcomes:

Explain the necessity for blood clotting at the site of

damaged blood vessels.

Explain the mechanism of blood clotting

Predict the consequences of impaired blood clotting in anindividual


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When you get cut, blood vessels around thewound immediately constrict to reduce bloodloss.

The platelets in the blood exposed to airbecome sticky and clump together to plug thewound.

Thrombokinase and other clotting factors arereleased by platelets.


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In the presence of calcium ions, thrombokinaseconverts prothrombin into thrombin.

Prothrombin, a plasma protein is synthesizedin the liver and requires vitamin k.

Thrombin converts soluble plasma protein,fibrinogen into insoluble fibrin fibres which

form a meshwork of threads over the wound. As the blood flows out, erythrocytes and

platelets are trapped in the fibrin fibres and a

blood clot forms. It dries to form scab. When the wound heals, new skin is formed

and the scab peels off.


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Problem related to bloodclotting:

Haemophilia

Thrombosis


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Haemophilia is a hereditary disease due to thelack of certain gene for the production ofcertain clotting factors.

This is an impaired clotting mechanism whichcauses serious bleeding particularly in the

joints.

The afflicted person may die as a result ofexcessive bleeding from even minor cuts andbruises because blood clotting cannot takeplace.


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Sometimes a local blood clot (thrombus) is

formed on the damaged or rough inner wall ofthe artery, a condition known as thrombosis.

When the thrombus dislodges and is carriedaway by blood circulation, it is known as anembolus. The embolus may be trapped in asmall artery where it blocks the blood flow.This condition is called embolism.

If the thrombosis occurs in coronary artery(vessel that carries blood to the heart) thesupply of oxygen and nutrients to the heartmuscles is cut off, hence causes heart attack.

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