Histology Flashcards
The three layers of blood vessel walls?
Tunica intima
- Endothelium & it’s basal lamina
- Thin layer of sub-endothelial Connective Tissue.
Tunica media
- Circular layers of smooth muscle & elastic CT
Tunica adventitia
- CT with loosely arranged elastic and collagen fibres & scattered smooth muscle cells
Function of endothelial cells?
Selective barrier
Secrete vasodilators and vasoconstrictors
Secrete anticoagulants
Secrete immune modulators e.g. Interleukins
Examples of elastic arteries?
Conducting: Aorta, pulmonary. carotid
Features of elastic arteries? (5)
Large diameter
T. Media is thick
Lots of elastic laminae & smooth muscle cells in between.
T. adventitia is relatively thin
Fibroelastic CT with scattered smooth muscle cells & vasa vasora.
What is vasa vasora?
Vessels with the CT of larger vessels to feed inner smooth muscle.
Examples of Large/collecting Veins?
Vena cavae
Features of Large/collecting veins? (5)
Large, often collapsed
T. media is very thin
Very few layers of elastic laminae & smooth muscle cells
T. adventitia relatively thick
Fibroelastic CT occupying longitudinal bundles of smooth
muscle & vasa vasora
Examples of muscular arteries?
Radial, femoral & splenic
examples of medium veins?
Renal & hepatic
Features of muscular arteries?
Medium diameter
T. Media is Thick
Multiple concentric smooth muscle and fibro-elastic cartilage in between media and adventitia
T. Adventitia is relatively thick
Fibro-elastic CT with scattered smooth
muscle & .Vasa vasora
Internal & external elastic laminae
Features of medium veins?
Medium diameter
T. Media is thin
2-3 concenric smooth muscle layers
T. Adventitia is relatively thick
Fibro-elastic CT with scattered smooth muscle & Vasa vasora
Valves
Differences/similarities in arterioles and venules?
Arterioles have a small lumen and thick wall, venules are the opposite.
Both have thin T. intima
T.Media: Arterioles have 1/2 layers of smooth muscle in fibroelestic CT, venules may have some cells but not layers.
T. adventitia is very thin in both
Arterioles may have internal elastic lamina whereas venules may have valves
What vessels are there in the microcirculation?
The vessels between the arterioles and venules:
- Metarterioles - Terminal arteriole branches, regulate the blood flow through capillaries
- Capillaries, lined by epithelial cells
- Arterio-venous shunts, link arterioles directly to venules, to divert blood away from capillaries.
Three types of capillaries?
Continuous:
- Most common
- Lined by endothelium
- Limited permeability
Fenestrated:
- Located in intestine and kidney mostly
- continuous but have fine trans-endothelial channels
- Highly permeable and allow large molecules through
Discontinuous:
- Found in liver, bone marrow and lymph nodes
- Wide irregular lumens
- Highly permeable to large molecules and even blood cells.
Features of the epicardium?
analogous to T. adventitia
consist of visceral pericardium & fibrous adipose tissue CT beneath
Thickness varies with amount of adipose tissue
Occupies branches of Coronary vessels and nerves