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Flashcards in Microanatomy Deck (13):

Organization of blood vessels

-From lumen out: tunica intima, tunica media, tunica adventitia, vasa vasorum (part of adventitia)
-Arteries have large tunica media and veins have large tunica adventitia
-Internal elastic lamina (IEL) separates intima and media (part of intima)
-External elastic lamina (EEL) separates media and adventitia (part of media)


Tunica intima

-Inner most layer consisting of endothelium and its basal lamina, sub endothelial CT (may contain smooth muscle), and IEL (arteries only)
-Smallest layer


Tunica media

-Middle layer composed of circumferential smooth muscle (major site for SM), which secrete elastin and collagen, and there may be EEL
-Largest layer in arteries, mostly SM


Tunica adventitia

-Outer layer composed of collagen (T1) and elastic fibers to anchor to surrounding CT
-Contains vasa vasorum (small arteries that supply blood to the vessel itself)
-Largest layer in veins, mostly CT


Layers of the heart 1

-From in-> out: Endocardium, myocardium, epicardium (AKA visceral pericardium), parietal pericardium, fibrous pericardium
-Endocardium: inside of the heart (where blood is) lined by endothelium (w/ BL) and subendothelial CT. Contains purkinje fibers (modified cardiac muscle) and valves (core of DCT surrounded by endothelium)
-Myocardium: very abundant cardiac muscle cells, inserting in the fibrous cardiac skeleton (part of myocardium, separates atria from ventricles)


Layers of the heart 2

-Epicardium: outer most layer (synonymous w/ visceral pericardium) composed of mesothelium (simple squamous epithelial layer w/ BL) and LCT
-The LCT of epicardium contains coronary vessels, nerves, ganglia, and fat
-Outside of the visceral pericardium is the parietal pericardium, together w/ the visceral pericardium forms the serous pericardium (w/ serous fluid btwn them)
-The entire structure is enclosed in the fibrous pericardium


Conducting arteries

-Conducting (largest) arteries: aorta and its large branches responsible for maintaining a constant BP
-Thin IEL and EEL, but thick tunica media consisting of SM and elastic fibers
-Have thin adventitia w/ vasa vasorum (+ lymphatic vessels and nerves)


Muscular arteries

-Muscular (distributing) arteries display thick tunica media and adventitia w/ scalloped (crescent) lumen
-Contain thick IEL and thin EEL, with the size of media (SM) and adventitia (fibroelastic CT) being about equal
-Adventitia may or may not have vasa vasorum



-Arterioles: Smallest arterial vessels, control BP
-Walls are as thick as the diameter of lumen
-Intima shows endothelial nuclei bulging into lumen, may or may not have IEL (larger ones do)
-One to several layers of SM in media, +/- EEL
-Adventitia is very thin



-Continuous: nonporous endothelial cells w/ tight junction btwn them and complete BL (no leakage)
-Form BBB and BNB
-Fenestrated: capillaries w/ opening to facilitate transport (may be covered by diaphragm to monitor the permeability of pores), w/ continuous BL (some leakage)
-Discontinuous: have wide lumens and large spaces within the capillary (btwn endothelial cells) for most rapid transportation
-Have discontinuous BL and and fenestrated endothelial cells (found in BM)



-Post-capillary venules: principal site of action of vasoactive agents (?), no tunica media or adventitia (highly permeable)
-Site of lymphocyte homing
-Musclular venules: similar to post-capillary venues but contain very thin media and adventitia
-Site of lymphocyte diapedesis/extravasation



-Small veins: tunica intima contains few valves +/- IEL, thin media and thick adventitia +/- vasa vasorum
-Large veins: thick intima w/ IEL, vlaves, and subendothelial CT, thin media w/ little EEL, thick adventitia w/ vasa vasorum and some SMCs
-Compared to arteries, veins have larger lumen, thinner walls and are often collapsed in histological sections


Lymphatic vessels

-Blind-ended tubes lined w/ endothelium w/ large spaces and discontinuous BL
-Allows for transport of larger solutes into lymphatics
-No tunica media or adventitia for lymphatic capillaries
-Lymphatic vessels have thin media (some SMCs) and adventitia (vasa vasorum)
-Vessels empty into ducts (thoracic duct on L or R lymphatic duct) where subclavian + IJV meet