Heart Structure And Function

Question 1

What is the heart?

Answer 1

A four chambered organ, supplied by the coronary circulation, that pumps oxygen-poor blood to the lungs and oxygen-rich blood to the rest of the body

Question 2

What are the 4 chambers of the heart?

Answer 2

Left and right atria and ventricles

Question 3

Where is the heart located?

Answer 3

Located posterior to the sternum, level with the 3rd costal cartilage, down to the 5th costal space, approximately 7.5cm to the left of midline

Question 4

What is the mediastinum?

Answer 4

An area in the chest this is between the lungs and it contains the heart, trachea, oesophagus and major blood vessels

Question 5

What is the heart surrounded by?

Answer 5

The heart is surrounded by the pericardium with about 15-20ml of pericardial fluid in between

Question 6

What are the two layers of the pericardium?

Answer 6

Visceral/epicardial -> a serous membrane that covers the heart, it is in direct contact with the heart
Parietal -> covering over the top of the visceral layer

Question 7

What are the 4 chambers of the heart separated by?

Answer 7

Intratrial and intraventricular septum’s

Question 8

Name the atrioventricular valves

Answer 8

Tricuspid (on right side of heart)
Bicuspid/mitral (on the left side if the heart)

Question 9

What are the valves of the heart tethered down by?

Answer 9

Chordae tendineae which are fibrous connective tissue

Question 10

Where do the fibres of the chordae tendineae originate from?

Answer 10

Parts of the muscle walls of the heart by capillary muscles

Question 11

Name the semilunar valves

Answer 11

Pulmonary valve
Aortic valve

Question 12

What is the trabecular Carneae of the heart?

Answer 12

It is muscular ridges

Question 13

What is the moderator band of the heart?

Answer 13

It is a larger version of a trabeculae carneae but it is heavily involved with the transmission of an impulse to make your heart contract

Question 14

What are cardiac muscles cells connected by?

Answer 14

Intercalated discs

Question 15

What is the importance of intercalated discs in the heart?

Answer 15

At these discs is where two cardiac cells are bound together, this connection means that it stabilises all the cardiac cells. It allows for ions to be transferred and molecules to move from one muscle cell to another

Question 16

What is a syncytium?

Answer 16

A multinucleate mass of cytoplasm resulting from fusion of cells

Question 17

How many syncytiums does the heart have and what is each one composed of?

Answer 17

It has 2
The atria are considered as one syncytium and the ventricles as the other

Question 18

What is the resting potential of cardiac muscle?

Answer 18

It is the same as skeletal muscle (-90mV)

Question 19

What does the action potential in cardiac muscle pass via?

Answer 19

Gap junctions/intercalated discs

Question 20

How long does cardiac muscle action potential last in comparison to skeletal muscle?

Answer 20

0.3 sec (cardiac muscle)
0.001 sec (skeletal muscle)

Question 21

What is the refractory period of contraction of cardiac muscle?

Answer 21

It is the time interval before another contraction can take place

Question 22

What is the purpose of the refractory period?

Answer 22

It means fibres are in relaxation before next contraction can occur
It allows the pumping action of cardiac muscle

Question 23

Why does the action potential need to be coordinated in the heart?

Answer 23

So the heart can act as an effective pump

Question 24

What slows down the rate of APs per minute in the SAN?

Answer 24

Vagus nerve

Question 25

What is the cardiac cycle?

Answer 25

All events associated with one heartbeat

Question 26

What is contraction of the heart called?

Answer 26

Systole

Question 27

What is relaxation of the heart called?

Answer 27

Diastole

Question 28

When the atria contract how much blood do they force into the ventricles?

Answer 28

20-25 mL (30% of ventricles volume as already holding 70%)

Question 29

What is end diastolic volume?

Answer 29

It is the amount of blood the ventricle is holding at the end of its relaxation/before it contracts

Question 30

What is the EDV of the ventricles?

Answer 30

130mL

Question 31

What is isometric contraction in the heart?

Answer 31

An event occurring in early systole during which the ventricles contract with no corresponding volume change

Question 32

What is stroke volume?

Answer 32

The amount of blood that is ejected

Question 33

What is end systolic volume?

Answer 33

The amount of blood left in the ventricles after contraction

Question 34

What is the ESV?

Answer 34

50mL

Question 35

How long does ventricular diastole last?

Answer 35

430msec

Question 36

What is isovolumetric relaxation?

Answer 36

The part of the cardiac cycle between the time of aortic valve closure and mitral opening

Question 37

What is cardiac output?

Answer 37

The total blood volume passing through the lungs and systemic circulation in one minute

Question 38

What is the cardiac output equation?

Answer 38

Cardiac output = stroke volume x heart rate

Question 39

What is stroke volume?

Answer 39

Volume of blood ejected during ventricular systole

Question 40

What 3 factors govern stroke volume?

Answer 40

Preload Contractility After load

Question 41

What is preload?

Answer 41

The stretch on your heart prior to it contracting

Question 42

What is contractility

Answer 42

The strength of the contraction

Question 43

What is afterload?

Answer 43

The pressure that you need before blood will be pushed out into vessels

Question 44

What is the Frank-Starling law of the heart?

Answer 44

The more the heart is filled in diastole, the greater the stretch and the greater the force of systole

Question 45

What are positive inotropic substances?

Answer 45

Certain things that can promote contractility of the heart -> could be drugs or our own internal system

Question 46

What are negative inotropic substances?

Answer 46

Certain things that will decrease contractility of the heart -> drugs like beta blockers, Ca ion channel blockers, stimulation of parasympathetic nervous system, lack of oxygen

Question 47

What does increased afterload result in?

Answer 47

It results in reduced stroke volume because more blood remains in ventricle at end of systole

Question 48

What are the major coronary arteries?

Answer 48

Right coronary Left coronary Left anterior descending Left circumflex

Question 49

What effect does the parasympathetic nervous system have on the heart?

Answer 49

It slows heart rate

Question 50

What effect does the sympathetic nervous system have on the heart?

Answer 50

It increases heart rate

Question 51

What do adrenaline and noradrenaline do to heart rate and contractility?

Answer 51

Increases both

Question 52

What does hyperthyroidism do to the heart?

Answer 52

It gives tachycardia

Question 53

What does increase potassium and sodium ions do to heart rate and contractility?

Answer 53

It decreases both

Question 54

What does a moderate increase of calcium ions do to heart rate and contractility?

Answer 54

Increases both

Question 55

What will happen in the event of SAN disease or damage?

Answer 55

AVN can take over at 40-60bpm

Question 56

What will happen to the heart if both the AVN and SAN are suppressed?

Answer 56

Ventricles will beat at 20-30 bpm from Purkinje fibres

Question 57

What is an electrocardiogram?

Answer 57

A measure of the hearts rhythm and rate through the detection of its electrical activity

Question 58

What causes the P wave on an ECG?

Answer 58

Atrial depolarisation, initiated by the SAN

Question 59

What causes the QRS complex of an ECG?

Answer 59

Ventricular depolarisation which begins at the apex

Question 60

What causes the T wave?

Answer 60

Ventricular repolarisation