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Flashcards in Blood Vessels Deck (46):

tunica intima
-special in artery

endothelium, basement membrane, subendothelial loose CT
-arteries have internal elastic lamina bordering media (fenestrated layer of elastin)
-forms permeable/semi-permeable barrier


tunica media
-what makes ECM
-what do larger vessels have?
-what replaces it in capillaries and venules?

smooth muscle, variable elastic fibers and lamellae, reticular fibers, proteoglycans
-ECM made from smooth muscle cell
-larger vessels have external elastic lamina
-pericytes replace media
-controls diameter, BP, movement


tunica adventitia
-what do larger vessels have?

fibroblasts, longitudinal collagen, elastic fibers
-larger vessels have vasa vasorum (vessels of vessels to supply with O2)
--more extensive in veins b/c low nutrient and O2 content of venous blood
-provides physical support, attaches vessels to tissue, and carries vessels and nerves



homologous to intima; lining atria and ventricles
-made of endothelium and subendothelium layer of CT



homologous to media; thickest layer of the heart wall
-made of cardiac muscle thicker in ventricles than atria



homologous to adventitia; forms surface of heart and anatomicalloy defined as visceral layer of pericardium
-made of mesothelium and subepicardial layer of loose CT that has nerves, adipose, and coronary blood vessels


large, elastic, conducting arteries location and functions

aorta and main branches, common carotid, brachiocephalic, subclavian, and pulmonary arteries are elastic arteries
-systole distends the elastic arteries, recoil and contract during diastole
--produces more uniform flow


intima of elastic arteries

150 microns thick in adults (1/6 thick)
-scattered smooth muscles in subendothelial layer
-endothelial cells have Weibel-Palade bodies (membrane-bound inclusions) with dense matrix with von Willebrand factor
-endothelial cells are elongate polycons w/ long axes oriented w/ long axes oriented w/ blood flow and cells are connected by occluding junctions


media for elastic arteries

2 mm thick, made of 40-70 layers of fenestrated elastic lamellae with smooth muscle between
-thin external elastic lamina and vasa vasorum of adventitia penetrates outer third to half of it


adventitia of elastic arteries

relatively thin layer with nerve fibers, lymphatics, and vasa vasorum in loose CT


mixed musculo-elastic arteries location and functions

forms parts of terminal abdominal aorta, the iliac arteries, external carotids, axillary arteries, etc.
-these are transitional segments between large and medium arteries


histology of mixed musculo-elastic arteries

tunica media and adventitia are the same thickness
-media has fewer elastic lamellae, and more obvious internal elastic membrane


location and functions of medium muscular, distributing arteries

most named arteries (coronary, renal, etc.)
-distribute blood to tissues and organs regulated by ANS control of media


intima of medium, muscular distributing arteries

thin and has prominent internal elastic lamina that undulates


media of medium, muscular distributing arteries

relatively thick and made of many concentric layers of smooth muscle bound in larger muscular arteries by external elastic lamina that gets thinner and disappears in smaller diameter specimens


aventitia of medium, muscular distributing arteries

as thick as the media
-vasa vasorum and lymphatics are poorly developed


arterioles feneral features and functions

100 microns or less in diamter, invisible to naked eye
-function to maintain normal blood pressure in arterial system, and reduce pressure of blood entering capillaries


intima of arterioles

thin subendothelial layer of reticular fibers and internal elastic membrane is absent in smallest arterioles


media of arterioles

composed of one to five layers of smooth muscles


adventitia of arterioles

moderate to scant



(also precapillary sphincter)
terminal segment from an arteriole before a capillary bed that regulates blood flow into capillaries


structural changes of arteries with age

three tunics are compete during 4th month in utero
-largest arteries grow until age 25
-aging process involves intima and media
-after 30 years, media becomes stiffer from increase in elastic lamellae, and deposition of collagen and proteoglycans


large elastic artery changes with age

change more than muscular arteries
-in media, elastic tissues develop irregular thickenings and elastic fibers can fragment
-plaques from in intima due to noncellular lipid material accumulating in subendothelial layer


muscular artery changes with age

change less than elastic arteries
-undergo calcification of media
-form plaques in intima that reduce diameter as early as 25 years


dimensions and components of capillaries

smallest vascular channels, with average diameter of 5 to 10 microns, 0.05 to 1 mm length
-60,000 miles of capillaries in human body
components: endothelial cells and pericytes


capillary endothelial cells
-life span

cytoplasm w/ Golgi, mitochondria, RER, free ribosomes, pinocytotic vesicles
-structural support from desmin and/or vimentin (intermediate filaments)
-life span of 150-180 days, slowly renewing
-secrete basal lamina, joined by tight and gap junctions\; also makes bioactive substances (collagens I, III, IV, V, fibronectin, laminin, anticoagulants)


capillary pericytes
-what do they share with endothelial cells?

stellate cells around capillaries and post-capillary venules
-extensive branching processes with large nuclei rich in heterochromatin, small Golgi, mitochondria, RER, and filaments extending into processes
-share basal lamina of endothelial cells
-contract to regulate blood flow, and serve as stem cells for endothelial and smooth muscle cells after injury


types of capillaries



continuous capillary location and structure/function

L: most common, in muscle, nervous, CT, and exocrine pancreas
S/F: endothelial lining and basal lamina are complete (sealed by tight junctions for passage of small molecules)
-cytoplasm has vesicles to transport large molecules


fenestrated capillaries location and structure/function

L: pancreas, intestines, endocrine glands
-those with no diaphragm are only in renal glomerulus
S/F: continuous (thin) endothelium and basal lamina
-endothelial cells have small pores (60-80 nm) covered by diaphragm
-specialized for rapid interchange of substances between blood and tissue


sinusoid capillaries structure/function

irregular blood channels that conform to shape of structure they line
-continuous basal lamina and fenestrae with diaphragms much larger than fenestrated capillaries
-the discontinuous types have absent/discontinous basal lamina with large gaps between endothelial cells that allows enhanced exchange between blood/tissue


three types of sinusoid capillaries and locations

sinusoidal capillaries: endocrine glands
discontinuous sinusoids: liver and bone marrow
venous sinusoids: spleen


capillary permeability (2 types)

small: 9-11 nm; gaps between cell junctions that allow water and small hydrophilic molecules to pass (moreso during inflammation)
large: 50-70 nm; transcytosis by pinocytotic or trans-Golgi derived vesicles


traits of veins VS arteries

-greater variation in size and structure
-larger caliber and more numerous (contain 70% of total blood volume)
-more extensive vasa vasorum and lymphatics
-more collagen and less elastic susbstance and smooth muscle
-most thickness is from adventitia
-small and medium veins have valves that are formed from infolding of intima with elastic CT core


large veins structure

intima: continuous endothelium and basal lamina, but no IEL
media: incomplete or absent
adventitia: largest, best developed (95% thickness)
-thick bundles of longitudinally oriented smooth muscle, collagen, and elastic fibers
-well-developed vasa vasorum and lymphatics


what kinds of vessels are superior and inferior vena cava and portal vein?

large veins


small and medium vein structure

intima: continuous endothelium and basal lamina
-complete IEL is only in leg, with some valves
media: poorly developed except in limbs; smooth muscle is circumferential
adventitia: thickest tunic and has no smooth muscle
-has collagen, elastic fibers, fibroblasts, lymphatics, and vasa vasorum


two classes of venules

pericytic and muscular


venule function

continue exchange of materials that begin in capillaries
-preferred location for leukocyte emigration
-become leaky in response to histamine and serotonin


pericytic venules

post-capillary venules 10-50 microns in diameter
-resemble large capillaries b/c they have a pericyte


muscular venules

reccieve blood from pericytic venules and accompany arterioles
-media has 1-2 circular layers of smooth muscle cells
-thin adventitia of loose CT


portal system specializations and examples

carry blood from one capillary bed to another
-hepatic portal vein between intestines and liver
-hypophyseal portal veins of pituitary
-efferent arterioles of renal cortex


arteriovenous anastomoses and examples

direct cross connections between arterioles and venules
-smooth muscle cells form sphinchter that regulates blood flow and allows bypass of a capillary bed


characteristics of lymphatic vessels

large lumen, thin wall, irregular shape, extensive branching that runs parallel to blood capillaries and veins


functions of lymphatic vessels

collect lymph from extracellular spaces and return it to blood vascular system
-aid in circulation of lymphocytes


structure of lymphatic vessels

lymphatic collecting vessels are like veins (endothelium intima, incomplete media, and longitudinal bundles of smooth muscle in adventitia), but more irregular in shape and size
-discontinuous or absent basal lamina, held open by elastic anchoring filaments