The heart

Question 1

Where does the heart sit?

Answer 1

In the mediastinum

Question 2

How many layers does the heart have and what are they?

Answer 2

3:
Pericardium, myocardium and endocardium

Question 3

What are the 2 sacs of the pericardium called?

Answer 3

Fibrous (outer sac)
Serous (inner sac)

Question 4

What is the fibrous pericardium attached to?

Answer 4

Continuous with the tunica adventitia of the great blood vessels above and attached to the diaphragm below

Question 5

What is the function of the fibrous pericardium?

Answer 5

Protects the heart and prevents over-distension of the heart.

Question 6

What is the serous pericardium?

Answer 6

A continuous double layer of serous membrane folded over itself creating a double membrane around the heart with an enclosed space in between the layers

Question 7

What is the serious pericardium made up of?

Answer 7

A single layer of endothelial cells

Question 8

What are the 2 membranes of the serous pericardium?

Answer 8

Parietal (outer)
Visceral (inner)

Question 9

What is the visceral pericardium attached to?

Answer 9

The myocardium below

Question 10

What is inside the double membrane of serous pericardium?

Answer 10

20 ml of pericardial fluid (serous fluid)

Question 11

What is the function of the serous pericardium?

Answer 11

Contains the lubricating fluid so that the heart can beat without rubbing against the fibrous pericardium (prevents friction)

Question 12

What is the myocardium?

Answer 12

Specialised cardiac muscle found in the heart

Question 13

What is the structure of the myocardium?

Answer 13

Striated, each fibre has a nucleus and one of more branches, rich in mitochondria to supply its high energy needs

Question 14

How are the cells in the myocardium arranged?

Answer 14

The ends of the cells and their branches are in very close contact with the ends and branches of adjacent cells

Question 15

Why is the arrangement of cells in the myocardium important?

Answer 15

It gives cardiac muscle the functionality of a sheet of muscle rather than individual cells - allows the heart to contract in a coordinated and efficient manner

Question 16

What does the end-to-end continuity of the fibres in the myocardium mean?

Answer 16

Each one does not need a separate nerve supply - when an impulse is initiated, it spreads from cell to cell via the branches and intercalculated discs over the whole ‘sheet’ of muscle

Question 17

What is the endocardium?

Answer 17

A thin membrane that lines the chambers and valves of the heart

Question 18

What does the endocardium consist of?

Answer 18

A single layer of flattened epithelial cells and is continuous with the endothelium lining the blood vessels

Question 19

What is the function of the endocardium?

Answer 19

It minimises friction as the blood flows over it as it is very smooth

Question 20

What are cardiac myocytes?

Answer 20

striated muscle cells , similar to skeletal muscle

Question 21

How do cardiac myocytes allow the heart to contract?

Answer 21

They spontaneously depolarise and are electrically coupled, depolarisation spreads via intercalculated discs and allows Ca2+ ions to enter and causes contraction

Question 22

How is the rate of contraction set?

Answer 22

the sinoatrial node cells depolarise fastest and set the rate of contraction

Question 23

What is the route of depolarisation in the heart?

Answer 23

SA node - atrioventricular (AV) node - bundle of His - left and right bundle branches - purkinje fibres

Question 24

What do the purkinje fibres do?

Answer 24

Carry the electrical activity throughout ventricular myocardium

Question 25

What happens if a major coronary artery gets blocked and why?

Answer 25

Blood supply to the myocardium will be reduced as they are prone to atheroma (narrowing due to build up of plaques)
Not many anastomoses so each artery is very important

Question 26

How does parasympathetic activity affect the heart?

Answer 26

Decreases heart rate through release of acetylcholine

Question 27

How does sympathetic activity affect the heart?

Answer 27

Increases heart rate and force of contraction through release of noradrenaline