The heart Flashcards
Where does the heart sit?
In the mediastinum
How many layers does the heart have and what are they?
3:
Pericardium, myocardium and endocardium
What are the 2 sacs of the pericardium called?
Fibrous (outer sac)
Serous (inner sac)
What is the fibrous pericardium attached to?
Continuous with the tunica adventitia of the great blood vessels above and attached to the diaphragm below
What is the function of the fibrous pericardium?
Protects the heart and prevents over-distension of the heart.
What is the serous pericardium?
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
What is the serious pericardium made up of?
A single layer of endothelial cells
What are the 2 membranes of the serous pericardium?
Parietal (outer)
Visceral (inner)
What is the visceral pericardium attached to?
The myocardium below
What is inside the double membrane of serous pericardium?
20 ml of pericardial fluid (serous fluid)
What is the function of the serous pericardium?
Contains the lubricating fluid so that the heart can beat without rubbing against the fibrous pericardium (prevents friction)
What is the myocardium?
Specialised cardiac muscle found in the heart
What is the structure of the myocardium?
Striated, each fibre has a nucleus and one of more branches, rich in mitochondria to supply its high energy needs
How are the cells in the myocardium arranged?
The ends of the cells and their branches are in very close contact with the ends and branches of adjacent cells
Why is the arrangement of cells in the myocardium important?
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
What does the end-to-end continuity of the fibres in the myocardium mean?
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
What is the endocardium?
A thin membrane that lines the chambers and valves of the heart
What does the endocardium consist of?
A single layer of flattened epithelial cells and is continuous with the endothelium lining the blood vessels
What is the function of the endocardium?
It minimises friction as the blood flows over it as it is very smooth
What are cardiac myocytes?
striated muscle cells , similar to skeletal muscle
How do cardiac myocytes allow the heart to contract?
They spontaneously depolarise and are electrically coupled, depolarisation spreads via intercalculated discs and allows Ca2+ ions to enter and causes contraction
How is the rate of contraction set?
the sinoatrial node cells depolarise fastest and set the rate of contraction
What is the route of depolarisation in the heart?
SA node - atrioventricular (AV) node - bundle of His - left and right bundle branches - purkinje fibres
What do the purkinje fibres do?
Carry the electrical activity throughout ventricular myocardium
