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Flashcards in Histology Deck (46):

Describe smooth muscle physical characteristics

swollen in the center w/ finely tapered ends; central nucleus that is typically a little elongated but doesn't get flattened down; no visible striations; interconnected by gap junctions


What is the purpose of dense bodies?

equivalent to Z discs that anchor to actin and myosin in smooth muscle cytoplasm


What is the purpose of caveolae?

equivalent to T-tubles; small indentations that allow Ca signaling into the cell to create contraction


Describe cardiac muscle physical characteristics

short, branched, Y shaped cells w/ extensive capillaries and centrally located nucleus


What is the purpose of intercalated discs?

transverse junctions between cardiac muscle cells (where cells meet end to end) that allows for the passage of electrical current


What is unique about the organelles in cardiac muscle cells?

organelles and cell fibers loop around the centrally located nucleus to protect it from damage w/ intense cell contraction


Describe the layers of the pericardium

Fibrous - outer covering of dense CT
Parietal serous - lines inner surface of fibrous
Visceral serous - covers outer surface of heart (epicardium)
Pericardial cavity - space between parietal and visceral layers


Describe the layers of the heart wall

mesothelium - simple squamous epithelium (outer layer)
underlying layer of loose CT and adipose tissue (where coronary vessels usually found)
Myocardium - heart muscle
Endocardium - loose connective tissue and endothelium (simple squamous)


What makes up the epicardium?

mesothelium + underlying layer of loose CT and adipose tissue -> much thicker than endocardium


Function of fascia adherens?

actin based filaments at ends of sarcomeres that transmit contract forces between cells in a way that prevents damage (most prevalent)


Function of desmosomes?

provide anchorage for intermediate filaments of cytoskeleton (prevent tearing of myocardium)


Function of gap (nexus) junctions?

sites of low electrical resistance; allows excitation to pass between cells


What makes up a Dyad T-tubule? What is its function?

1 T-tubule + 1 SR cisterna (fewer number compared to triad T tubule in skeletal muscle; permits uniform contraction myofibrils within single cardiomyocyte


What are lipofuscin granules?

small bodies that accumulate around the nucleus w/ age; material from residual bodies after lysosomal digestion


What cells contains ANF and BNF? What is the purpose of ANF?

myoendocrine cells (atrial cardiomyocytes) - ANF targets kidneys to increase filtration rate (decreases Na and H2O retention)


What makes endocardium thicker in ventricles compared to atria?

ventricles have subendocardial layer - thin layer of CT w/ smooth muscle that contains Purkinje fibers between myocardium and endocardium


Describe the physical characteristics of Purkinje fibers

more rounded than cardiac muscle cells; larger cell and nucleus; some intercalated discs (not many) and mostly lack T tubules


What does the cardiac skeleton consist of? What is its purpose?

4 rings (one around each valve) and 2 trigones (broader areas that connect rings to valve; anchors valves and surrounds AV canals to help maintain shape


What are heart valves?

extensions of endocardium on either side of opening between chambers that is continuous w/ cardiac skeleton


Where is the tunica intima?

layer most closely exposed to the vessel (most internal layer)


What are the layers of tunica intima?

endothelium - single layer of squamous epithelial cells
Basal lamina of endothelial cells
Subendothelial layer of loose CT


Where would you find the internal elastic membrane (lamina)?

in the subendothelial layer of tunica intima of arteries and arterioles; links tunica intima to tunica media


What is found in the tunica media? In what vessels is this layer thick?

circumferentially arranged layer of smooth muscle; relatively thick in arteries


Where would you find the external elastic membrane (lamina)?

on the outer border of the tunica media; links tunica media to tunica adventitia


What makes up tunica adventitia? How thick is it in arteries and veins?

collagenous loose CT w/ few elastic fibers; relatively thin in arteries and thick in veins/venules


What is vasa vasorum and where is it found?

vessels of tunica adventitia; supply blood to vascular walls (vessels of vessels)


What is nervi vasorum and where is it found?

ANS input that controls contraction of vascular smooth muscle (nerves of vessels); found in tunica adventitia


Describe large (elastic) arteries and the physiology behind its structure

thick tunica media w/ elastin forming sheets/lamellae between muscle cell layers -> elastin allows arterial wall to expand due to high pressures during systole


What is prominent in medium (muscular) arteries?

internal elastic membrane is prominent (folds down on itself and looks wrinkly); also has recognizable external elastic membrane


How thick is tunica media in muscular arteries compared to elastic arteries?

more smooth muscle and less elastin present in tunica media (less BP); relatively thick tunica adventitia - about same thickness as tunica media


How would you distinguish small arteries from arterioles?

small arteries have up to 8 layers of smooth muscle and internal elastic membrane

arterioles have 1-2 layers of smooth muscle and internal elastic membrane may not be present


What are pericytes and what is their function?

perivascular contractile cells/ branching processes found in capillaries; they are controlled by NO produced by endothelial cells and promote stability of capillaries


Describe continuous capillaries

continuous layer of endothelial cells surrounded by basal lamina; only small substances (gases etc.) can diffuse


Describe fenestrated capillaries

endothelial cells have pores that allow larger material to diffuse but with restrictions; basal lamina continuous; located in places we want filtration (kidneys)


Describe sinusoidal capillaires

no regulation; pores are large enough for full cells to fit through and basal lamina is discontinuous; found in bone marrow and liver


Where would you find endothelial cells? What are their functions?

innermost layer of tunica intima (lining vessel wall); they support basement membrane and produce collagen; also involved in coagulation and local vasodilation/constriction


What is a metarteriole?

first branch off arteriole to capillary bed


What is a true capillary?

branch from metarteriole that lacks smooth muscle but may have pericytes


What is a thoroughfare channel?

distal end of metartiole that connects to post capillary venule; lacks smooth muscle


What is the function of precapillary sphincters?

to regulate blood through true capillaries; when contracted, they shunt blood flow away from capillary bed -> forces blood to enter venous return quickly


What are 2 classifications of venules?

postcapillary - drains capillaries; no true tunica media
muscular - 1-2 layers of smooth muscle in tunica media


How would you describe small veins?

continuous w/ muscular venules but they have all 3 layers w/ a thicker tunica adventitia


What do medium veins travel with? What makes them different from venules/small veins?

they travel w/ muscular arteries and contain valves


What are examples of large veins? What is their thickest layer?

superior/inferior vena cava, hepatic portal vein; their thickest layer is tunica adventitia but overall, wall is thinner than arteries


Describe the internal structure of lymphatic capillaries

closed-ended tubes in the capillary bed; overlapping endothelial cells form a 1-way valve for collecting lymph


What is the flow of lymphatics?

lymphatic capillaires -> vessels -> trunks -> right lymphatic duct -> thoracic duct drains into brachiocephalic veins