8.5 Heart

Question 1

How does the heart work?

Answer 1

2 pumps that are joined together and work together
–> deoxygenated blood from body flows into the right side of the heart and this gets pumped to lungs

–> Oxygenated blood from lungs returns to left side and is pumped to body

Question 2

What is the heart made of?

Answer 2

Made of cardiac muscle, which contracts and relaxes in a regular rhythm- does not get fatigued and need to rest like skeletal muscle

Coronary arteries supply the cardiac muscle with oxygenated blood it needs to keep contracting and relaxing all the time

Heart surrounded by in elastic pericardial membranes (prevents heart from over-distending with blood)

Question 3

How does deoxygenated blood enter the right side of heart

Answer 3

from upper body & head (superior vena cava)

from lower body (inferior vena cava)

–> brought in at low pressure

Question 4

As the right atrium fills, what happens

Answer 4

Slight pressure builds up until the Atrio-ventricular vale (aka tricuspid/ AV valve) opens
blood passes down into the right ventricle

Question 5

Once BOTH right atrium and ventricle are filled with blood, what happens?

Answer 5

atrium contracts
–> forces all blood into right ventricle & stretches ventricle wall

Question 6

What happens to the atrio-ventricular/ tricuspid valve once the right ventricle contracts?

Answer 6

–> as soon as the right ventricle begins to contract, the AV valve closes to prevent back flow (tendinous cord makes sure valves are not turned inside out due to pressure

Question 7

Once right ventricle contracts fully what happens?

Answer 7

deoxygenated blood is pumped through semilunar valves into the pulmonary artery

Question 8

At the same time what is happening on the left side of the heart?

Answer 8

oxygenated blood from lungs enters left atrium from pulmonary vein. Pressure in atrium builds, causing the bicuspid valves to open between left atrium and the left ventricle

—> for ventricle also fills with oxygenated blood

Question 9

Once both left atrium and ventricle are full, what happens?

Answer 9

atrium contracts, forcing oxygenated blood into left ventricle

—> left ventricle contracts and pumps oxygenated blood through semi-lunar valves into AORTA (& around body)

—> as ventricle contracts, tricuspid valve closes to prevent back flow

Question 10

Why is the muscle wall on the left side thicker?

Answer 10

blood is passed at a higher pressure through left due to oxygen saturation being high
–> left side needs to overcome resistance of aorta and arterial systems of whole body & move blood under pressure to all extremities of body

lungs are relatively close to heart= short distance to pump and so right side only has to overcome resistance of pulmonary circulation

Question 11

What is the septum?

Answer 11

Septum: inner dividing wall of heart which prevents mixing of deoxygenated and oxygenated blood

Question 12

How long does one cardiac cycle take?

Answer 12

0.8 seconds

–> atrial systole 0.1 seconds
–> ventricular systole at 0.3 seconds

–> rest is diastole 0.4 seconds

Question 13

What is diastole?

Answer 13

the heart relaxing (atria & ventricles fill=. volume & pressure increases)

Question 14

What is systole?

Answer 14

atria and ventricle contraction
–> pressure inside heart dramatically increases & blood is forced out to either lungs or main body
–> volume & pressure of blood are low at end of systole by blood in arteries is at maximum

Question 15

Cardiac cycle graph: How is aortic pressure represented

Answer 15

Line that never falls below 12kPa (due to recoil action of elastic wall); during atrial systole, the aortic pressure falls slightly

Once semi lunar valves open during ventricular diastole, aortic pressure rises drastically as the ventricle contracts.

At the end of ventricular diastole , the semilunar valve closes and aortic pressure begins to drop

Question 16

Cardiac cycle graph: How is ventricular pressure represented

Answer 16

Low at first but increases as atria contract & fill ventricle with blood
–> once left AV valve closes during ventricular diastole, pressure increases quickly

Pressure rises above aorta so that the blood is forced into aorta
–> pressure falls once semi-lunar valves close

Question 17

Cardiac cycle graph: How is atrial pressure represented?

Answer 17

Always low as wall of atria do not produce much force
–> Highest is during atrial systole and drops when AV valve closes

–> Atria fills with blood during diastole= gradual build up of pressure until slight drop when left AV valve opens

Question 18

Cardiac cycle graph: How is Ventricular volume?

Answer 18

rises as atria contracts
–> ventricle fills with blood but drops suddenly as ventricle is contracted
–> volume increases as AV valve opens

Question 19

How is the basic rhythm of the heart maintained?

Answer 19

via a wave of electrical excitation

SAN –> AVN –> two branches of purkyne tissue
–> apex –> walls of ventricles

Question 20

Rhythm of heart: detailed

Answer 20

wave of electrical excitation begins in pacemaker area (sino-atrial node SAN), causing atria to contract and so initiating heartbeat

2. Atrio-ventricular node AVN picks up electrical activity and imposes a slight delay before stimulating bundle of His
3. bundle of His splits into two branches at the top fo the septum, conducting the wave of excitation to the apex of the heart
4. At apex, purkyne fibres spread out to walls of both ventricle. triggering the contraction starting from the apex
   (from bottom because it is more efficient at emptying ventricles)

Question 21

What is a bundle of His?

Answer 21

bundle conducting tissue made up of fibres called purkyne fibres

Question 22

What is an electrocardiogram

Answer 22

ECG: recording of electrical activity of heart
–> measures tiny electrical differences in skin

Question 23

What is an electrocardiogram

Answer 23

ECG: recording of electrical activity of heart
–> measures tiny electrical differences in skin

Question 24

Parts of an ECG?

Answer 24

P wave= electrical activity during atrial systole
QRS complex= electrical activity during ventricular systole
T wave= ventricular repolarisation

Q-T interval= ventricular contraction time

T-P interval= relaxed ventricles filling with blood

Question 25

Tachycardia

Answer 25

rapid heart beat, over 100 bpm
–> due to exercise, stress or excitement

Question 26

Bradycardia

Answer 26

heart rate slows down to below 60 BPM
–> many people have this because they are fit

Question 27

heart block

Answer 27

separation of P wave and QRS complex
–> pacemaker activity and atrial contraction is normal
–> causes delay in conduction between atria and ventricles

Question 28

hypertrophy

Answer 28

P wave and atrial contraction is normal but
–> QRS complex is distorted due to hypertrophy of one side of the heart

Question 29

atrial fibrillation

Answer 29

arrhythmia (abnormal rhythm of heart
–> rapid impulses that contract very fast but ntot properly