2.6 Structure & Function of the Heart

Question 1

Cardiac Output

Answer 1

The volume of blood pumped through each ventricle per minute.

Question 2

How to calculate Cardiac Output

Answer 2

CO = HR (heart rate) x SV (stroke volume)

Question 3

Left and Right Ventricles

Answer 3

Pump the same volume of blood through the aorta and pulmonary artery.

Question 4

Systole and Diastole

Answer 4

During the cardiac cycle, systole is the term used to describe the heart
contracting and diastole is used to describe the heart relaxed.

Question 5

Cardiac Cycle Step 1

Answer 5

Atrial and Ventricular Diastole – both atria and ventricles are relaxed and this
allows blood to flow into the atria via the vena cava and pulmonary vein.

Question 6

Cardiac Cycle Step 2

Answer 6

Atrial systole – both atria contract, forcing blood down through the AV valves into the relaxed ventricles.

Question 7

Cardiac Cycle Step 3

Answer 7

Ventricular systole – both ventricles contract, forcing blood through the semi-
lunar valves into the aorta and pulmonary artery. The AV valves close to prevent the backflow of blood. This is the first sound of the heart beat. The second sound of the heart beat is caused by the semi-lunar valves closing when the pressure in the aorta and pulmonary artery exceeds the pressure in the ventricles.

Question 8

The auto-rhythmic cells of sino-atrial node (SAN)

Answer 8

The auto-rhythmic cells of the sino-
atrial node (SAN) or pacemaker, located in the wall of the right atrium, set the rate at which the heart contracts.

Question 9

The atrio-ventricular node (AVN)

Answer 9

Located in the middle of the heart.

Question 10

The Cardiac Conducting System

Answer 10

Controls the timing of heart contraction and therefore controls the cardiac cycle.

Question 11

Steps of the Cardiac Conducting System

Answer 11

• The SA node sends out a wave of electrical impulses which are carried through the walls of BOTH atria. This causes both atria contracting simultaneously. This results in atrial systole.
• The AVN then picks up the electrical impulse from the SAN and it travels down fibres in the central wall of the heart and then up through the walls of both ventricles.
• This causes both ventricles to contract simultaneously. This results in ventricular
systole.

Question 12

Electrocardiogram (ECG)

Answer 12

Impulses in the heart generate currents that can be detected by an
electrocardiogram (ECG). Interpret ECG’s to calculate heart rate and link the waves to atrial systole, ventricular systole and diastole.

Question 13

Electrocardiogram (ECG)

Answer 13

Impulses in the heart generate currents that can be detected by an
electrocardiogram (ECG). Interpret ECG’s to calculate heart rate and link the waves to atrial systole, ventricular systole and diastole.

Question 14

The Medulla

Answer 14

Regulates the rate of the sino-atrial node through the antagonistic action of the autonomic nervous system (ANS).

Question 15

The Parasympathetic Nerve

Answer 15

Decreases heart rate as it releases acetylcholine and the sympathetic nerve increases heart rate as it releases noradrenaline.

Question 16

Blood Pressure

Answer 16

INCREASES during ventricular systole and DECREASES during diastole.
The equipment used to measure blood pressure is a sphygmomanometer.
A typical blood pressure reading for a young adult is 120/80 mmHg (the 120 is
the systolic pressure and the 80 is the diastolic pressure).

Question 17

Hypertension

Answer 17

Prolonged high blood pressure and is a major risk factor for coronary heart disease and many others diseases.