Cardiovascular Histology Flashcards
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
adventitia
tunica intima
consists of the endothelium (simple squamous epithelium) and a thin layer of connective tissue
tunica media
the thickest layer containing smooth muscle
adventitia
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
arterioles
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
metarterioles
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
capillaries
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)
pericytes
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
venules
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
aneurysm
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
atherosclerosis
a fatty/fibrous build-up within the tunica intima of the arteries after endothelial injury with numerous risk factors
