1. Which of the following is NOT a correct match of cardiac cycle event and its

Question

1. Which of the following is NOT a correct match of cardiac cycle event and its description?

a. ventricular diastole: SL valves are open

b. atrial systole: AV valves are open

c. ventricular systole: increased pressure closes AV valves

d. atrial diastole: atria fill with blood

2. Which situation would increase cardiac output?

a. all of the answers are correct

b. low blood pressure

c. increased blood volume

d. increased sympathetic activity

3. What is a key difference between arteries and veins?

a. arteries have valves

b. veins have thicker smooth muscle layers

c. arteries have elastic lamina layers

d. all of the answers are correct

4. Which part of artery allows it to (1) contract or dilate and (2) withstand the pressure originated from ventricular contractions?

a. (1) endothelium, (2) valves

b. (1) basement membrane, (2) endothelium

c. (1) smooth muscle, (2) elastic tissue

d. (1) elastic tissue, (2) smooth muscle

Explanation / Answer

Reason:

Cardiac cycle comprises of two major events namely systole which is the contraction of the heart chambers and the diastole which is their relaxation.

Semilunar valves are present around the aorta and the pulmonary artery which arises from the left and right ventricle respectively and are meant to prevent the backflow of the blood.

During the ventricular diastole the ventricles relaxes and pumps out all their blood to the aorta and pulmonary arteries through the semilunar values. they are open during ventricular diastole.

During the atrial systole, the atrias are contracted while the ventricles are relaxed; which thus forces the flood flow movement from the atrias to the ventricles and this commnucations are maintained through the pace setter which the AV (Atrio Ventricular) node. This remains open.

During the venricular systole, the ventricles contracts and the pressure inside them increases. The blood should not flow back to the atrium. And the bllod flows to the lungs from the heart . During this period the AV vales remains closed.

The phase atrial diastole signifises the relaxations of the artria. In this phase the blood from this chamber would move from atria to the ventricles. They thus remains emtptyied.

2. Option D:

Reason:

Cardiac optput is defined as the amount of the blood pumper by heart per minute.

We know our hart beats 72 times every minute and the stroke volume( volume which is pumped out of the blood) is approximately 70ml.

Hence cardiac output=stroke volume* number of times a heart beats.

This equals to around 5040 ml blood/min which is approximately the total amount of blood in our body which is around 5 litres.

There are several factors affecting the cardiac output.

Increase in the blood presuure(hypertension) increases the arterial pressure due to which our body detects the changes and the sympathetic activity gets reduced. Due to the decrease in the sympathetic canges the heart rate and thus the stroke volume decreases.

A dip in the blood pressure(hypotension) results in the lower venous activity and lower return due to which the stroke volume decreases, However this dip in the body stimulates the activation of the sympathetic activity which maintains the notmal heart rate.and thus the cardiac output is maintained.

Increase in the sympathetic stimulation results in the release of the flight or the fight hormone named adrenaline. It increases the heart rate . It is also responsible for the increase in the contractility of the chambers due to which stroke volume also increases. It thus is responsible for the increased cardiac output

3. option C.

Reason: Arteries carries pure oxygenated blood under high pressure. It does not requires any valves . However as veins carry deoxygenated blood and the blood pressure in them is less so it requires the presence of valves so as to prevent the backflow of blood.

Walls of the arteries are thick and muscular.This is because the blood pressure in the arteies is very high and it has to be supported by the arteies. This is facilitated by the thick muscular walls which allows the arteies to withstand such a high pressure without getting collapsed.

Arteries have an elastic lamina layer. This layer is the underlying layer of the connective tissue and the function is to help arteries bear the changes in the volume of the blood during the regular contraction and relaxation of the heart.

4. option C

Reason: Arteries have a thick muscular wall made of smooth muscles. In order to maintain the continuous blood flow which is under a high pressure, the smooth muscles undergoes repeated contraction and relaxations thus allowing the arteries to withstand a high pressure and mainaining the continuous blood flow.

The thick elastic membrane of tunica interna with more elongated endothelial cells helps in bearing the changes in the blood volumes during systole and diastole. Thus it helps to withstand the pressure originated due to ventricular contractions.

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