4. Cardiac wall (endocardium, myocardium, epicardium) - structure. Fibrous skeleton.

What are the three layers of the heart's outer wall?

- Epicardium (also called the visceral pericardium)
- Myocardium (middle muscle layer responsible for contraction)
- Endocardium (inner layer that lines heart chambers and valves)

What is the role of the endocardium?

- Lines heart chambers and valves
- Composed of epithelial and connective tissue
- Merges with the inner lining of blood vessels
- Contains three layers:
- Endothelium (simple squamous epithelium)
- Smooth muscle cell layer
- Connective tissue layer

Describe the composition of the myocardium.

- Contractile myocytes (cardiac muscle) form the bulk of the atria and ventricles.
- Myocytes adapted for electrical conduction from pacemaker regions.
- Histology of cardiac muscle:
- Cells (fibers) are branched, connected by intercalated discs
- Discs link cells mechanically (maculae adherens) and electrically (gap junctions).

What is the epicardium, and what does it cover?

- Epicardium is the deeper layer of the serous pericardium.
- Covers the surface of the heart, passing into the grooves of the heart.
- Ensheaths coronary vessels and parasympathetic ganglia.

What are the components of the heart's fibrous skeleton, and what is its function?

- Components:
- Fibrous rings (annuli) around the atrioventricular canals.
- Extensions to the origins of the aorta and pulmonary trunk.
- Fibrous annuli of the mitral, tricuspid, pulmonary, and aortic valves.
- Fibrous trigones (left and right), connecting the valve rings.
- Functions:
- Electrically isolates atria from ventricles.
- Provides rigidity to prevent valve dilation.
- Attachment points for valve leaflets and myocardium.

Describe the right fibrous trigone of the heart.

- Right fibrous trigone is the largest thickening of the fibrous skeleton.
- Connects the aortic, mitral, and tricuspid valves.
- Often referred to as the central fibrous body.

What layers make up the endocardium, and what do they contain?

- Endothelium: simple squamous epithelium.
- Smooth muscle cell layer: middle layer.
-Subendocardial layer: outer layer, merges with myocardium.

What structures does the fibrous skeleton of the heart support?

- Valves: mitral, tricuspid, pulmonary, aortic.
- Electrical isolation**: separates atria from ventricles.
- Attachment points: for valve leaflets and myocardium

What is the significance of the left and right fibrous trigones?

- Left fibrous trigone: point of attachment for the aortic and mitral valves.
- Right fibrous trigone: connects aortic, mitral, and tricuspid valves, largest thickening (central fibrous body).