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