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Flashcards in Cardiovascular Histology Deck (30)
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caval system

the venous side of the systemic circulation as it returns blood to the heart via the superior and inferior vena cavae


What is the distribution of blood in the body's blood vessels?

15% in the systemic arteries, 5 % in capillaries, and over 60% in the veins

the rest is in the heart and pulmonary circulation


mean pressure in the large arteries

about 90 mmHg


three basic layers of arteries and veins

tunica intima

tunica media



tunica intima

consists of the endothelium (simple squamous epithelium) and a thin layer of connective tissue


tunica media

the thickest layer containing smooth muscle



an outer layer of connective tissue that blends with the surrounding tissue


elastic arteries

greater than 10 mm in diameter

biggest tributaries designed to expand during ventricular systole and then recoil to maintain blood flow downstream during diastole when no pressure is generated by the heart

tunica intima contains the endothelium, connective tissue plus smooth muscle cells and a thin internal elastic membrane

tunica media is thick and has alternating layers of smooth muscle cells and fenestrated elastic lamellae

the connective tissue adventitia is relatively thin and contains fibroblasts, macrophages, and vasa vasorum, collagen fibers help prevent distention of the artery beyond its limits during systole


muscular arteries

medium sized arteries 2-10 mm

characterized by prominent smooth muscle tunica media and internal and external elastic laminae

tunica intima has the endothelium, a thin layer of connective tissue, and a prominent internal elastic membrane

tunica media is almost entirely smooth muscle arranged as circular, spiraling layers that reduce the diameter of the lumen when contracted

very little elastic material

adventitia is thick compared to elastic arteries, and collagen fibers are the predominant extracellular component

often there is an external elastic membrane adjacent to the tunica media



smallest vessels, 10-100 um

control blood flow int he capillary beds in response to local conditions of the tissue interstitium like PO2, PCO2, and pH

large aggregate diameters of many small vessels result in continuous flow of blood at a very slow rate

very compliant, can dilate to as much as 100% of their resting diameter

can remain nearly 50% constricted for long periods of time

tunica intima consists of endothelium and a very thin layer of subendothelial connective tissue

tunica media has one or two layers of smooth muscle cells in a circular arrangement aroudn the vessel

slight thickening of the circular smooth muscle at the entry of the capillary beds

precapillary sphincters control blood flow into the beds

metarterioles bypass the capillary beds by connecting directly to venules (an arteriovenous anastomosis)

specialized arterioles from AV shunts are important for thermoregulation in the skin of the fingertips and nose as well as erectile tissue blood flow

these muscular, spiraling, innervated arterioles encapsulated by connective tissue are called glomus bodies



arterioles that bypass the capillary beds by connecting directly to venules


glomus bodies

muscular, spiraling, innervated arterioles encapsulated by connective tissue - specialized for thermoregulation int he skin of the fingertips and for erectile tissue blood flow



4-10 um, about the diameter of a single red blood cell

site of metabilic exchange, primarily of endothelial cells that are elongated with their nuclei in the direction ob blood flow

often have pericytes that surround them

three types: continuous, fenestrated, and discontinuous (sinusoids)



cells that surround the endothelium of capillaries and are within the basal lamina

provide mechanical and metabolic support and are morphlogically similar to mesenchymal stem cells

during wound healing and angiogenesis in general, pericytes can differentiate into both endothelial and smooth muscle cells


continuous capillaries

found in skeletal muscle, the lungs, CNS, and other places

tight junctions restrict passage of all but the smallest molecules


fenestrated capillaries

present in endocrine organs and sites where the extensive passage of fluid and metabolites occurs (GI tract, gall bladder, kidney)

80-100 nm fenestrations are channels spanning the entire endothelial cell

also have pinocytotic vesicles


discontinuous capillaries

sinusoids of the liver, spleen and bone marrow that have the greatest degree of "leakiness"

they are larter in diameter than the other capillaries and have a more irregular profile

many fenestrations are larger in size, and there are gaps between the endothelial cells


How is venous blood moved back to the heart?

through compression from skeletal muscle contraction and movement of GI organs

negative intrathoracic pressure sucks blood into the thorax, and valves in the limbs prevent retrograde flow



receive blood from capillary beds

sites of action of vasoactive substances such as histamine

where fluid and white blood cells leave the bloodstream to enter the interstitium during inflammation and allergic reactions


types of venules

postcapillary venules

muscular venules

high endothelial venules


postcapillary venules

have scant smooth muscle and are characterized by the extensive presence of pericytes


muscular venules

distal to the postcapillary venules and represent the transition to small veins in that they have one or two layers of smooth muscle, the beginning of a tunica media

much larger in diameter than corresponding arterioles, few if any pericytes


high endothelial venules

found in lymph nodes

simple cuboidal epithelium and are the sites of migration of lymphocytes from blood into the lymphatic tissue


medium veins

up to 10 mm in diameter

like the larger veins of the extremities

have many layers of circular smooth muscle plus collagen and elastic fibers of the tunica media

wall is much thinner than the corresponding artery

adventitia is thick, has collagen and elastic fibers, and there are usually some bundles of loongitudinal muscle at the interface between the tunica media and adventitia


large veins

like the superior and inferior venae cavae and hepatic portal vein have a relatively thin tunica media and thick adventitia with prominent longitudinal bundles of smooth muscle


functions of the simple squamous endothelial cells

maintenance of selective permeability barrier

control of blood flow and vascular resistance

prevention of blood cell coagulation and blood clot formation

growth factor synthesis and secretion

response to epithelial injury and sites of infection

responseresponse to epithelial injury and sites of infection


Weibel-Palade bodies

organelles containing von Willebrand factor that results in platelet adhesion to the site of endothelial cell injury

also contain P-selectin, a cell adhesion molecule that, when expressed, leads to the migration of neutrophils across the epithelium to their site of action

P-selectin binds to neutrophils to slow their flow until stronger adhesions are formed



a focal enlargement of an artery due to congenital weakening of the wall or inflammation that causes protease to degrade the collagen/elastin in the wall


aortic dissection

results from a tear in the endothelium

blood enters the tunica media and splits its layers for a distance, narrowing the orignal lumen of the artery

usually occurs in the aortam, but can happen in other arteries as well



a fatty/fibrous build-up within the tunica intima of the arteries after endothelial injury with numerous risk factors