2.6 the structure and function of the heart

Question 1

State the definition of cardiac output of the heart.

Answer 1

The cardiac output is a measure of the volume of blood pumped through each ventricle per minute.

Question 2

Calculate the cardiac output of the heart.

Answer 2

Cardiac output is determined by multiplying together heart rate and stroke volume
(CO = HR x SV).

Question 3

Identify differences between the right and left ventricles of the heart

Answer 3

Left ventricle wall is thicker than the right ventricle wall.
Left ventricle pumps oxygenated blood and right ventricle pumps deoxygenated blood

Question 4

Identify the similarities between the right and left ventricles of the heart

Answer 4

The left and right ventricles pump the same volume of blood through the aorta (left) and pulmonary artery (right).

Question 5

Identify the three stages of the cardiac cycle.

Answer 5

diastole
· atrial systole
· ventricular systole

Question 6

Describe diastole

Answer 6

In diastole (relaxation), the higher pressure in the arteries closes the SL valves and blood returning to the atria flows into the ventricles.

Question 7

describe atrial systole

Answer 7

Atrial systole (atrial contraction) transfers the remainder of the blood through the atrio-ventricular (AV) valves to the ventricles.

Question 8

Describe ventricular systole

Answer 8

Ventricular systole (ventricular contraction) closes the AV valves and pumps the blood out through the semi lunar (SL) valves to the aorta and pulmonary artery.

Question 9

Explain the ‘lub’, ‘dub’ sounds of the heart that can be heard using a stethoscope.

Answer 9

The heart sounds are caused by the opening and closing of the AV and SL valves. The valves open and close as a result of the pressure changes in the heart during atrial and ventricular contractions.

Question 10

What does the cardiac conducting system co oridante

Answer 10

The cardiac conducting system co-ordinates the cardiac cycle.

Question 11

What are the two main structures involved in the sioatral node

Answer 11

The two main structures involved are the sinoatrial node (SAN) and the atrioventricular node (AVN).

Question 12

Where is the sinoatrial node located

Answer 12

The sinoatrial node (SAN) is located in the right atrium of the heart and is a region of cells that are auto-rhythmic.

Question 13

where is the electrical impulse spread

Answer 13

These cells generate an electrical impulse called the cardiac impulse which spreads through the atria to the AV node and then through the ventricles. This sets the pace of the heart by determining the rate at which the cardiac muscles contract.

Question 14

Where is the atrioventricular node located

Answer 14

The atrioventricular node (AVN) is also located in the right atrium of the heart close to the central wall.

Question 15

State the name of the technique used to record the electrical impulses generated in the heart.

Answer 15

An electrocardiogram – the electrical impulse is recorded as a wave on a piece of graph paper.

Question 16

Calculate the heart rate from an ECG trace.

Answer 16

An ECG trace is a repeating pattern that corresponds to the heart beating. The heart rate is calculated by measuring the time taken between two repeating points on the graph paper. This tells you the time taken for one heartbeat.

Question 17

Describe the nervous and hormonal regulation of heart rate.

Answer 17

The medulla regulates the rate of the SAN through the antagonistic action of the autonomic nervous system (ANS). Sympathetic nerves of the ANS increase the heart rate and a parasympathetic nerve (the vagus nerve) slows down the heart rate. Sympathetic accelerator nerves release nor-adrenaline and slowing parasympathetic nerves release acetylcholine.

Question 18

Describe the changes in blood pressure that occur during the cardiac cycle.

Answer 18

Blood will always flow from high to low pressure unless a valve prevents this.

Question 19

Describe how a sphygmomanometer is used to measure blood pressure.

Answer 19

An inflatable cuff is placed around the upper arm and then inflated to temporarily stop blood flow through the artery due to the pressure applied. The cuff is then deflated gradually and when the blood starts to flow again this is detected by a pulse at the systolic pressure (higher number on the top of the reading). The blood flows freely through the artery and a pulse is no longer detected when the cuff reaches the diastolic pressure (lower number on the bottom of the reading).

A typical reading for a young adult is 120/70 mmHg.

Question 20

How is blood pressure created

Answer 20

Blood pressure is created by the contraction of the heart. Blood leaving the heart in an artery is under its highest pressure. During systole the walls of the arteries bulge. During diastole the elastic walls recoil, pushing the blood forward through the blood vessel. As the arteries divide into arterioles and then into capillaries, the vessels become narrower

Question 21

What happens when the vessels become narrow

Answer 21

The narrower the vessels become the greater the resistance created by the vessel walls

Question 22

Explain why blood pressure measurement is an important diagnostic tool for medical practitioners.

Answer 22

Hypertension is a chronic long-term condition where the blood pressure in the arteries is higher than normal. Hypertension does not normally cause symptoms (it is an asymptomatic condition), but it is a major risk factor for many diseases including coronary heart disease, so monitoring is a crucial diagnostic tool for other conditions.