Block 2 Histo Flashcards
Smooth Muscle (involuntary muscle)
Spindle shaped soma and single fusiform nucleus
Eosinophilic cytoplasm because of contractile proteins
Locations: tunica media of non-capillary vasculature, deep to mucosa in respiratory and digestive systems
Skeletal Muscle (striated muscle)
Always under volitional control
Banded, striated, striped appearance
Nuclei are displaced to periphery of cell, and many nuclei per cell
Nuclei are rod-shaped
Cells attached in segmental fashion so contractile force is uni-directional
Cardiac Muscle
Majority of heart muscle
Similar to skeletal (striated), with a few exceptions
Intercalated discs separating cells
Cells have short branches that connect then to adjacent cells, so direction of contractile force is distributed instead of uni-directional
Can be single or multi-nucleated
Nuclei are rounded and in the center of the cell
Heart wall
Epicardium
Myocardium
Endocardium
Endocardium
Simple squamous endothelium
Subendothelial layer
Myocardium
Subendocardial layer (between subendothelial of endocardium and rest of myocardium)
Myocardium (richly vascularized layer of myocytes)
Subendocardial layer
Matrix of fibrous connective tissue
Contains nerves, blood vessels, Purkinje fibers/other components of impulse-conducting system
We will consider it part of the myocardium
Myocyte
Cardiac muscle cells
Multiple short bands extending from central area where nucleus is
Separated by intercalated discs
Plasma membrane called sarcolemma
Contain mitochondria, glycogen granules
Intercalated disc
Transverse portions have desmosomes and fascia adherens (similar to zona adherens)
Longitudinal portions have gap junctions
Epicardium
Epithelium called mesothelium
Subepicardial layer contains blood vessels, nerves, adipocytes
Heart valves
Dense fibrous connective tissue surrounded by epithelium
3 layers of blood vessels
Tunica media (myocardium)
(Outermost) Tunica externa or adventitia (epicardium)
(Innermost) Tunica intima (endocardium)
Tunica intima
Simple squamous epithelium on basement membrane
Subendothelial layer of loose connective tissue with occasional smooth muscle cells
In veins, folds to form a valve
Tunica media
Unlike myocardium, has smooth muscle instead of cardiac muscle
Elastic fibers and reticular fibers of Type III collagen
Thickest layer in aorta, muscular arteries, arterioles
Tunica externa or adventitia
Contains Type I collagen and elastic fibers, blood vessels, and nerves
Thickest layer in vena cava, medium-size veins, and venules
Internal elastic lamina
Elastic fiber ring located in tunica intima
Aorta and muscular arteries have one
Vena cava has interrupted one
External elastic lamina
Elastic fiber ring located in tunica media
ONLY muscular arteries have this
Vasa vasorum
Microvasculature that supplies vessels
Aorta, vena cava, muscular arteries, medium-size veins have vasa vasorum
(Arterioles and venules do NOT)
Nervi vasorum (nerves)
In aorta and muscular arteries, and very thin in arterioles
Fewer in vena cava and medium-size veins, and none in venules
Capillary
Wall is 1 endothelial cell layer thick = tunica intima
No tunica media
Basement membrane is tunica externa or adventitia
3 types: continuous, fenestrated, sinusoidal
Pericytes on continuous capillaries are contractile
Histologically hard to distinguish from postcapillary venule
Have micropinocytotic vesicles to transport materials
Lymph capillary
Wall is 1 endothelial cell layer thin = tunica intima
No tunica media
Incomplete basement membrane = tunica externa or adventitia
Irregular lumen containing lymph, no RBCs
Anchored to surrounding tissue by elastic filaments
What happens to smaller muscular arteries in hypertension?
Hypertrophy of tunica media
Duplication of internal elastic lamina
Fibrotic thickening of tunica externa or adventitia
Where does edema from inflammation come from?
Venules, because they have the loosest endothelial connections
Precapillary sphincter
Rings of smooth muscle where arterioles are about to become capillaries (on precapillary arterioles)
Regulate blood flow to capillary bed
Compare endocardium to epicardium
Endocardium: has single layer epithelium, subendothelial layer is thin and has no adipose tissue
Epicardium: has single layer epithelium, but subepicardial layer is thicker and has adipose tissue, nerves, and blood vessels
Concentric hypertrophy
Due to increased pressure work (aortic stenosis, or increaced BP)
Very thick looking walls, making ventricle hold smaller volume
Eccentric hypertrophy
Due to ventricle being overloaded with fluid
Wall does not become thicker, just creates larger lumen, larger diameter
AKA dilated cardiomyopathy
