Heart Flashcards
What are the layers of the heart
Pericardium
Epicardium
Myocardium
Endocardium
Pericardium
Outermost layer of the heart
Single layer of squamous mesothelial cells resting on a thin layer of connective tissue
Visceral pericardium - outer surface of the heart
Parietal pericardium - layer of cells on the inner surface of the fibrous sac containing the heart
Describe epicardium
Immediately underneath the pericardium (sometimes pericardium used but they are different)
- between pericardium and myocardium
Underlying adipose connective tissue - contains mixture of vessels and nerves including coronary arteries
Describe myocardium
Thickest layer of heart muscle
Specialised muscle
Straited - all myofibrils are in register
Single central nuclei
Unique features:
Branching fibres
Intercalated discs
Endomysium - loose fibrous connective tissue between the muscle fibres. May contain very small number of lymphocytes
Describe intercalated discs
Connect actin filaments of adjacent myocytes
Pale areas in between which are specialist connections to form long and branching chains
Contain
- gap junctions
- adhering junctions
- desmosomes
What stain can intercalated discs be seen on
H&E
Where are the largest myocytes found
In the wall of the L Ventricle (myocardium)
Why are atrial myocytes smaller than those in the ventricles
Under much lower pressure
What type of organ is the heart
Endocrine
Contain perinuclear neuroendocrine granules (atrial natriuretic peptide) - ventricles do not secrete
Where can you find Purkinje fibres
In the ventricles immediately below the endocardium
Not easily to see on H&E
What are features of Purkinje Fibres
Glycogen rich cytoplasm
Large vacuolated muscle cells
H&E - shows as pale
Describe the conducting system route
SA
Atrio myocardium
AV
Bundle of His
Purkinje fibres
Describe the endocardium
Innermost layer of heart
Thin layer of fibrous connective tissue
Single flat layer of endothelial cells - simple squamous epithelium
Describe valves
Covered by endothelium
Attach to a central fibrous body
3 separate layers (not identifiable H&E)
- fibrosa - dense fibrous CT (aortic side)
- spongiosa - loose fibrous CT
- ventricularis (collagen and elastin) - ventricular side
Vascular endothelial cells - same line the inside of the blood cells
What is the myocardium compromised of
Specialised form of involuntary striated muscle = cardiac muscle
