Lecture 13: Circulatory System Flashcards
3 basic layers of circulatory vessels
- Tunica intima
- Tunica media
- Tunica adventitia
Tunica intima
Inner epithelium + associated CT. Smooth and non-thrombogenic
Tunica media
Between intima and adventitia; vessel-associated muscle and supporting CT (esp. elastic fibers)
Tunica adventitia
Adventitial CT
Heart “vessel” layers
Inner to outer:
-Endocardium
-Subendocardium
-Myocardium
-Subepicardium
-Epicardium aka visceral layer pericardium
-Parietal pericardium
-Fibrous pericardium
Major artery features
Aka elastic arteries: tunica media has lamellar units. Also has internal/external elastic laminae + scattered media elastic fibers
Lamellar units
Alternating elastin/sm. muscle lamellae
Arteriole features
Similar to elastic arteries but smaller, roughly 1-3 smooth muscle layers. Primary resistance modulator via dilation/constriction
Capillary features
No smooth muscle, no tunica media. Always v. small, 1 RBC diameter or less. Can exchange via pinocytosis.
Venules
Look the same as capillaries (no tunica media, no sm. muscle), but slightly larger, ~5-6 RBCs across
Veins
Usually travel with companion arteries. Have a smaller tunica media and one-way valves
Large veins (vena cava type)
Contain longitudinal adventitial smooth muscle, controlling compliance and thus capacitance
Smooth muscle innervation
Sympathetic innervation (v. little parasymp.); nervi vascularis contained in tunica adventitia. Main NTs are NE and neuropeptide Y (NPY). Symp. stim. increases Ca++ influx via GPCRs increasing contraction.
Vasa vasorum
Vessels supplying outer vessel walls
Compounds mediating vasoconstriction
Endothelin, thromboxane, angiotensin II, ADH (vasopressin) are all common vasoconstrictors
Compounds mediating vasodilation
NO, ANP via cGMP, adenosine, prostacyclin, β-receptor agonists via cAMP are common vasodilators
Endothelial vasodilator secretion
The endothelium itself locally secretes many vasodilators e.g. NO; dysfunction can lead to reduced dilation capacity
Capillary types
Based on wall opening width
1. Continuous
2. Fenestrated
3. Sinusoidal
Continuous capillaries
No passive transport across endothelium; active transport via caveolae; e.g. lung, placenta, muscle, CNS
Fenestrated capillaries
Contain openings for free passage of small molecules; e.g. endocrine glands, kidney, gall bladder, intestinal tract
Sinusoidal capillaries
Contain large openings, sometimes large enough for cells; e.g. liver, spleen, bone marrow
Pericytes
Cells often associated w/ basal small vessel surfaces; almost 1:1 w/ endothelial cells in brain. Contractile role in slow modulatory blood flow control. Organ specific w/ high plasticity.
Lymphatic vessel features
Minimal structure/layers. Contain one-way valves and lymph fluid.
Vascular compartment
Systemic vasculature is separated from CT space. Epithelia especially is avascular and the basement membrane prevents angiogen./migration. Vascular-CT transport is regulated by endothelial cells and usually occurs only in thin-walled vessels; large tunica media limits transport.
