Histology Flashcards
What are the five layers of the heart wall?
1) Endocardium
2) Myocardium
3) Epicardium
4) Pericardial Cavity
5) Fibrous Pericardium
What are the three sublayers of the endocardium and their components?
1) Endothelium–simple squamous epithelium
2) Subendothelium–mostly areolar CT with elastin and smooth muscle
3) Subendocardium–areolar CT, contains Purkinje fibers
What are the components of the epicardium?
Epicardium is essentially the visceral pericardium; it has a dense adipose layer and some areolar CT. Coronary vessels are found here. On the surface is the serous pericardium (mesothelium) that secretes pericardial fluid
What is the role of the pericardial cavity?
Reduces friction between the pumping heart and the fibrous pericardial sac
What are the two main components of the fibrous pericardium?
A serous pericardial layer that also creates pericardial fluid
A fibrous pericardium made of dense irregular CT that forms the bulk of the gross pericardial sac
With what is the endothelium of the heart continuous?
Endothelium of the vasculature
With what is the fibrous pericardium of the heart continuous?
The tunica adventitia of the great vessels
Of what is the fibrous skeleton made and what are its three main components in the heart?
Dense irregular CT
1) Rings around the valve
2) Trigones that anchor the rings to each other
3) Membranous septa that contains branches of the conducting system
What are the three main jobs of the fibrous skeleton?
1) Anchors the heart valves
2) Serves as attachment site for the myocardium
3) Insulates electrical impulses
What are the three layers of a heart valve?
1) Fibrosa
2) Ventricularis
3) Spongiosa (arterial or auricular [for atria])
Of what are the three layers made?
Fibrosa–dense irregular CT
Ventricularis–HIGH dense irregular connective tissue
Spongiosa–more loose areolar with elastin
What are the external regulators of the heart?
Parasympathetic = vagus nerve Sympathetic = cardiac splanchnics
What are the intrinsic regulators of heart rhythm and what types of cells are they?
SA node cells (pacemaker) AV node cells Bundle of His Purkinje cells All are specialized cardiac cells with high conductivity. Most are thin, small, and wavy except the Purkinje cells which are large
What are the three layers of a blood vessel and their components?
Tunica intima–endothelium, subendothelium, internal elastic lamina
Tunica media–smooth muscle, external elastic lamina
Tunica adventitia—mostly CT, but may have vessels in it
What are the roles of the endothelium?
1) Inhibit coagulation by secreting heparin
2) Promote clotting
3) Change vascular diameter (and resistance) by secreting NO or ACE
4) affect angiogenesis by secreting TNF-beta
5) affect immune response by secreting ILs
6) secreting matrix proteins
How do the layers of major elastic arteries appear?
- Tunica intima does not have much of an internal elastic lamina
- The tunic media is VERY thick with numerous elastin layers
- the tunica adventitia is comparatively thin but does have blood vessels and nerves
How do the layers of muscular arteries appear?
- there is a small or absent subendothelium
- the internal elastic lamina is VERY obvious
- tends to have spiraling smooth muscle
- the external elastic lamina is obvious
- there may be arterioles and venules in the tunica adventitia
How do the layers of arterioles appear?
The elastic lamina appears less obvious as the diameter decreases
tunica media is typically between 1 and 4 cell layers thick
-there is no external elastic lamina
-the tunica adventitia blends with surrounding tissues
How do the layers of a venule appear?
There is no subendothelium nor internal elastic lamina
there is a very thin tunica media and no external elastic lamina
-the tunica adventitia blends in with the surrounding tissue
How do the layers of a medium vein appear?
there is a thin subendothelium and valves may be microscopically present
- the tunica media is thin
- the tunica adventitia is thicker than the other layers
How do the layers of a large vein appear?
- there is a thin subendothelium
- there is a thin circular arrangement of smooth muscle in the tunica media
- the tunica adventitia is very thick and contains longitudinal smooth muscle
What are the three types of capillaries and where can they be found?
1) Continuous-has occluding layers between cells so only small molecules pass; found in muscle, lungs, and central nervous system
2) Fenestrated–has small gaps in the cells but not the basal lamina; found in the glomerulus of the kidney
3) Discontinuous–rather open fenestrations in cells and basal lamina; found in the liver, spleen, and bone marrow
What is a pericyte?
A specialized smooth muscle cell that can occlude a capillary and is proliferative in angiogenesis
