8.5- The Heart

Question 1

What is the heart made up of?

Answer 1

Cardiac muscle:
-contracts and relaxes in a regular rhythm.
- does not get fatigued or need to rest like skeletal muscles.
- coronary arteries supply the muscle with the oxygenated blood needed to keep contracting and relaxing.
The heart is surrounded by inelastic pericardial membranes which prevent it from over distending with blood.

Question 2

Structure of the right side of the heart?

Answer 2

• superior vena cava
• right pulmonary artery and vein.
• right atrium
• tricuspid valve (right atrioventricular valve)
• right ventricle.
• inferior vena cava.

Question 3

Structure of left side of heart?

Answer 3

• left pulmonary artery and veins
• left atrium.
• bicuspid valves (left atrioventricular valves).
• left ventricle.
• thick muscular wall of left ventricle.

Question 4

Structure of middle of the heart?

Answer 4

• Carotid arteries.
• aorta.
• semilunar valves.
• septum. (Inner dividing wall which prevents mixing of oxy and deoxy 🩸)

Question 5

What is diastole?

Answer 5

In diastole:

• the heart relaxes.
• atria and then the ventricles fill with blood.
• volume increases.
• pressure decreases.
• blood pressure in arteries is at minimum.

Question 6

What is systole?

Answer 6

• atria contract (atrial systole).
• ventricles contract (ventricular systole).
• pressure in heart increases dramatically as blood is forced out the right side towards the lungs and out of the left to the rest of the body.
• volume and pressure of blood are low at the end of systole.
• blood pressure in arteries is at maximum.

Question 7

SAN and its role?

Answer 7

A wave of electrical excitation begins in the pacemaker area called the sino-atrial node (SAN).

• causes the atria to contract and so initiating a heartbeat.
• a layer of non-conducting tissue prevents the excitation passing directly to the ventricles.

Question 8

AVN and its role?

Answer 8

The electrical activity from the SAN is picked up by the atrio-ventricular node (AVN).

• the avn imposes a slight delay which allows the atria to fully contract and pass maximum blood to ventricles before they start contracting.
• it then stimulates the bundle of his.

Question 9

What is the bundle of His and its role?

Answer 9

A bundle of conducting tissue made up of purkyne fibres which penetrate through the septum between the ventricles.
- the bundle of His splits into 2 branches and conducts the wave of excitation to the apex (bottom) of the heart.

Question 10

What happens at the apex (electrical impulse)?

Answer 10

• The purkyne fibres spread out through the walls of the ventricles on both sides.
• the spread of excitation triggers the contractions of the ventricles, starting at the apex.
• contractions starting at the apex allows more efficient emptying of ventricles.

Question 11

Explain the route of blood when it enters the heart till it leaves.

Answer 11

1. Deoxy 🩸enters right atrium from the vena cavas. As it flows in, pressure builds up till tricuspid valve opens and allows blood into right ventricle.
2. When atrium and ventricle are filled, atrium contracts, blood all forced to r ventricle.
3. R ventricle starts contracting, t valve closes. Pumps deoxy 🩸through semilunar valves into pulmonary artery (takes to lungs).
4. At same time, oxy🩸from lungs enters left atrium from pulmonary vein. As pressure builds b valve opens. L ventricle also fills with 🩸.
5. Atrium contracts, forces all blood into L ventricle. L ventricle contracts, b valve closes, oxy 🩸 pumped through s valves into aorta to whole body.

Question 12

Role of tendinous cords in heart?

Answer 12

Make sure that when the atrioventricular valves close they aren’t turned inside out by the pressures exerted when the ventricles contract.

Question 13

What is an electrocardiogram?

Answer 13

Measures the spread of the electrical excitation through the heart in order to record what happens when it contracts.
This recording of electrical activity = ECG.
Used to help diagnose heart problems.

Question 14

How does an ECG work?

Answer 14

Doesn’t directly measure the electrical activity of your heart.
It measures tiny electrical differences in the skin which result from the heart’s electrical activity.
- to pick up these tiny changes, electrodes are stuck painlessly to clean skin to get the good contacts needed for reliable results.
- signals from each electrode are fed into a machine that produces the ECG.

Question 15

Normal ECG.

Answer 15

Beats evenly spread.

Rate = 60-100 / min.

Question 16

Tachycardia.

Answer 16

Heart beat is very rapid.
Over 100 bpm.
- often normal during exercise, fever, fright or anger.
- when abnormal may be caused by problems in the electrical control of the heart.

Question 17

Bradycardia.

Answer 17

Heart rate slows down to below 60bpm.

• many people have bradycardia due to being fit. Training makes the heart beat slowly and more efficiently.
• severe bradycardia may require a pacemaker to keep the heart beating steadily.

Question 18

Ectopic heart beat.

Answer 18

Extra heart beats that are out of rhythm.
Most people have atleast one a day.
- usually normal but can be linked to serious illness when frequent.

Question 19

Atrial fibrillation.

Answer 19

Is an example of arrhythmia (abnormal rhythm of the heart).

• rapid electrical impulses generated in the atria.
• they contact very fast (fibrillate) up to 400 times/min.
• however don’t contract properly and only some impulses are passed to ventricles which contract less often.
• as a result heart does not pump blood effectively.