Cardiac/Vascular Histology Flashcards
Myocardium
Thickest layer of heart
Contains: cardiocytes (contractile), nodal cardiocytes (in AV/SA nodes), myoendocrine cardiocytes
Characterized by: striations, intercalated discs, lipofuscin granules
Intercalated discs
Interdigitating junctions b/w cardiocytes
At sites were cells meet end to end, coincide with Z lines
Bind cells, transmit forces of contraction, allow spread of excitation
Transverse region (perpendicular) of intercalated disc junction
Fascia adherens: actin filaments at ends of terminal sarcomeres insert into junction
-transmit contractile forces b/w cells
-most predominant
Desmosomes: provide anchorage for the intermediate filaments of the cytoskeleton
Longitudinal region (parallel) of intercalated disc junction
Gap (nexus) junctions: sites of low electrical resistance
- allows excitation to pass b/w cells
Diad T-tubules
In heart, T-tubules form diad with 1 t-tubule and 1-SR cisterna
Found at Z-lines
Permits uniform contraction of myofibrils within a single cardiocyte
Nodal cardiocytes
Modified cells w/in SA/AV nodes that initiate/relay electrical signals
Parasympathetic and sympathetic fibers terminate in the nodes
Only MODIFY rate of intrinsic cardiac muscle contraction
Purkinje fibers
Specialized cardiac muscle cells
Conduct electrical impulses that allow coordinated contraction
Fewer myofibrils, but increased glycogen
Larger and typically seen at periphery of myocardium
Mostly lack T-tubules
Atrial granules
Myoendocrine cardiocytes: atrial cells that contain membrane bound granules. Smaller quantities are found in the left atrium and the ventricles
Contain precursor of atrial natriuretic factor ANF- which targets kidneys to decrease Na and H2O retention
Cardiac skeleton
Contributes to interventricular and interatrial septa
Extends into the valve cusps and chorea tendinae
Dense irregular CT located in the endocardium
Anchors valves and surrounds AV canals to maintain shape
Heart valves
Core of fibroelastic CT (lamina fibrosa) covered by endothelium
Continuous with the cardiac skeleton
Fibroelastic layer of endocardium condenses to forma a valve ring
-creates a central portion of the valve
Tunica intima layers
Endothelium- single layer of squamous epithelium
Basal lamina- thin EC layer of collagen/glycoproteins
Subendothelial layer- loose CT - consists of internal elastic membrane in arteries/arterioles
Tunica media
Circumferentially arranged layers of smooth muscle
Thickest in arteries
Extends from internal to external elastic membrane
Tunica adventitia
Longitudinally arranged collagenous tissue
Will merge with loose CT surrounding vessels
Thin in arterial system, thick in veins
Vasa vasorum- vessels of TA that supply blood to the tunics- found in large arteries and veins
Nervi vasorum- ANS input that controls contraction of vascular smooth muscle
Large (elastic) arteries
Elastin forms concentric sheets b/w muscle cell layers
No fibroblasts, smooth muscle synthesizes collagen, elastin
No internal elastic membrane
Medium arteries
Prominent internal elastic membrane becomes apparent
Recognizable external elastic membrane
Thick tunica adventitia, about same size as tunica media
Pericytes
Perivascular contractile cells
Controlled by NO
Promote stability of capillaries and postcapillary venules
Discontinuous/sinusoidal capillaries
Located where exchange of b/w blood and tissue must openly occur
Larger fenestrations than fenestrated capillaries
Large cell movements allowed through membrane
Discontinuous basement membrane
Found in bone marrow, liver, spleen
Fenestrated capillaries
Have tight junctions among endothelial cells
Greater exchange than continuous capillaries, but limited to size of molecule
Continuous basement membrane
Found in endocrine glands like kidney
Continuous capillaries
Tight, occluding junctions sealing off clefts
All molecular exchange via diffusion or transcytosis
Continuous basement membrane
Located throughout body
Precapillary sphincters, metarterioles, true capillaries
Metarterioles are first branch off arteriole supplying tissues
True capillaries branch from metarteriole, LACK smooth muscle, must have pericytes
Precapillary sphincters regulate blood flow through capillaries
Thoroughfare channel
Distal end of metarteriole, lacks smooth muscle
Connects to postcapillary venule
Arteriole
Tunica media only has one-two layers of smooth muscle
Thin tunica adventita
Vein vs artery
Veins have thinner walls, lumen is larger and often collapsed
Venules
Receive blood from capillaries, subclassified as postcapillary and muscular venules
Postcapillary–>muscular–>small vein
Postcapillary have no true tunica media
Muscular have 1-2 layers of smooth muscle in tunica media and a thin tunica adventitia
Medium veins
Travel with muscular arteries
Thicker tunica media and adventitia
Contain valves
Large veins
Tunica adventitia is thickest layer, contains collagen, elastic fibers, fibroblasts and smooth muscle cells
Tunica media is thin w/smooth muscle cells, collagen and fibroblasts
Tunica intima is thin and blends with media
