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21 Cards in this Set
- Front
- Back
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1. What are the primary cellular/tissue elements in the endocardium?
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Endothelial cells (simple squamous epithelium) overlying variable layer of loose connective tissue
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. What are the primary cellular/tissue elements in the myocardium?
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Bundles of cardiac muscle cells surrounded by connective tissue.
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. What are the primary cellular/tissue elements in the epicardium?
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Mesothelial cells (simple squamous epithelium) overlying loose connective tissue containing adipose cells, blood vessels and nerves.
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. Where are Purkinje fibers seen?
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In the deep portion of the endocardium, near the border with the myocardium. Fibers extend approximately 1/3 of the way into the myocardium but are most visible, along with Purkinje cell bodies, in the deep portion of the endocardium, near the border with the myocardium.
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. What types and sizes of blood vessels can be identified in each layer of the heart wall? What feature of the coronary circulation may provide (some) protection from ischemic damage in the case of occlusion of small coronary vessels?
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The largest arteries and veins are present in the epicardium. Smaller arteries extend into the myocardium, where numerous arterioles, capillaries and venules are apparent. The smallest arterial vessels (as well as capillaries) are present in all layers and extend into the endocardium. Anastomoses among the penetrating vessels of the myocardium provide some protection from ischemia in the case of occlusion of small arterial branches.
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Describe the distribution, orientation and relative amounts of smooth muscle, collagen bundles and elastic fibers in the aorta.
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The subendothelial connective tissue of the tunica intima is collagenous and elastic with bundles of fibers oriented largely longitudinally. Smooth muscle, collagen bundles, and elastic lamellae all are found in the media, all running circumferentially. More longitudinally oriented collagenous (and some elastic) tissue is apparent in the adventitia.
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. How might the appearance of the aorta differ if it were fixed (instantly) during systole versus during diastole?
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When the heart contracts blood is forced into the aorta under great pressure and the vessel expands – diameter increases, wall thins, and the sheets of elastic tissue stretch. Between contractions the vessel recoils – diameter decreases and the elastic tissue relaxes (so it appears wavy in a cross section).
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How does the relative thickness and definition of the three tunics differ between muscular arteries and the larger elastic arteries?
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The tunica intima is thinner in muscular arteries than in elastic arteries because of the paucity of subendothelial connective tissue. The tunica media appears particularly well-defined in muscular arteries because of the smooth muscle in the media and the prominent and distinct internal and external elastic lamellae (those lamellae are less distinct in elastic arteries since they are just the innermost and outermost of many layers of elastic tissue in the media). The tunica adventitia in the largest, elastic arteries contains numerous blood vessels (vaso vasorum) and nerve bundles (nervi vascularis) and often is more prominent than in muscular arteries, where the adventitia may not be very distinct from surrounding tissue.
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How do the components of each layer of the vessel wall differ between elastic and muscular arteries?
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Intima: endothelial cells and distinct subendothelial connective tissue in elastic arteries, endothelium with little, if any, connective tissue in muscular arteries
Media: mix of collagen bundles, much elastic tissue and a little smooth muscle in elastic arteries; collagen and smooth muscle (and less elastic) in muscular arteries Adventitia: collagenous connective tissue (and some elastic) in both types |
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. How does the relative thickness and definition of the three tunics differ between arteries and veins?
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Generally the tunics are better defined in arteries than in veins. In arteries the tunica media predominates; in smaller veins the tunics are more similar in thickness and in larger veins the adventitia predominates.
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How does the relationship between luminal diameter and wall thickness differ between arteries and veins?
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For arteries and veins of similar luminal diameter the arteries generally will have much thicker walls. Similarly, for arteries and veins with walls of similar thickness the vein will have a larger luminal diameter.
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How does the appearance of the internal and external elastic membranes differ between arteries and veins?
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Generally both are more distinct in arteries. In medium and larger veins the internal elastic lamella often is evident but the external is scant, if seen at all.
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13. From what portion(s) of the wall of the vein are valves formed (when present)? In what veins are valves most common?
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Valves form as extensions of the tunica intima and are most common in the medium veins of the lower extremities.
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What are the unique structural features of the large veins relative to smaller veins and to arteries?
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The presence of bundles of longitudinally oriented smooth muscle in the adventitia.
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15. What characteristics distinguish arterioles from venules?
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Arterioles have thicker walls for their diameter and 1-2 layers of smooth muscle in the tunica media. Venules have thin walls with spaces among the endothelial cells to increase permeability; only the largest venules have smooth muscle in their walls.
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How do the structural differences between arterioles and venules relate to their functional properties?
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Arterioles must be able to constrict and regulate flow into distal portions of the vasculature. Venules need walls that are more permeable to permit easier movement of substances, and even cells, into and out of the vessels.
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How does the range of sizes of venules compare to the range of sizes of arterioles?
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There is a somewhat greater range in the diameter of venules than arterioles. The diameter of venules increases pretty rapidly as you move away from the capillaries.
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what layer are the purkinje fibers located?
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between the endocardium and the myocardium
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purkinje fiber histo findings
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larger (larger than myocardium cells), no intecalated disks
single nucleus no intercalated disks, instead gap junctions |
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what is the connective tissue of the heart valves made of
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collagen and elastin fibers
acidophillic, extracellular |
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where is the internal elastic membrane located in the aorta
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between the intima and media
circumferential layers produced by smooth muscle....not fibroblasts |
