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.
Lymphatic compartment
The lymphatic compartment is largely permeable distally; endothelium acts as one-way valve w/ unrestricted flow from CT to lymphatics while they are at lower P
Specialized vasculature cells
-Aerocytes (lungs)
-Liver Sinusoidal Endothelial Cells (LSECs, liver)
-Pericytes
-Baroreceptors
-Chemoreceptors
Baroreceptors
Sensitive stretch receptors that innervate large vessels and signal the brain stem for baroreflexes. Loss of baroreflex -> orthostatic hypotension (standing posture)
Chemoreceptors
Signal elevated CO2 levels to the brain stem, triggering reflex responses e.g. faster RR
Vasculogenesis vs angiogenesis
Development vs elaboration of vasculature
Start of vasculogenesis
First vasculature forms in extraembryonic mesoderm along the yolk sac as blood islands surrounded by endothelial cells
Angiogenesis triggers
Induced by low tissue oxygen and secreted growth factors e.g. Vascular Endothelial Growth Factor (VEGF)
2 divisions of circulation
- Blood-vascular (CV)
- Lymphatic
Function of elastic artery lining
Elasticity dampens pulsatile flow from heart (flow is more consistent) and also acts as energy/pressure reservoir
Thrombus vs embolus
Thrombus = clot formed in CV
Embolus = anything moving around in CV; -Arterial = away from heart toward smaller vessels
-Venous = toward heart via larger vessels
Anastamosis
Joining of 2 vessels
Pericardium layers
Outer to inner: fibrous pericardium -> parietal serous pericardium -> visceral serous pericardium (epicardium)
Cardiac tamponade
Bleeding into pericardial space, compresses the heart
Coronary arteries
Left and right; arteries supplying the heart. First branches off of the aorta. Blood drains through heart wall to coronary sinus (main vein of heart) which returns to right atrium.
Cardiac skeleton
RIngs around valves which insulate impulse conduction. This enables coordinated, regular contraction. Fibrillation occurs without cardiac skeleton.
Aneurysm
Local one- or both-sided dilation due to wall weakness; bulge creates turbulent flow.
Dissection
Extravasation of blood into the tunica media; offsets intima from vessel wall and creates false lumen. Danger of bursting or shutting of flow to branches
Leukocyte migration points
Post-capillary venules are primary location of diapedesis, which is why large veins are often found near large immune cell depots.
Atherosclerosis pathogenesis
Endothelial injury increases permeability increasing platelet/monocyte adhesion -> LDLs, monocytes enter subendothelium. LDL oxidation, foam cell development, sm. muscle fibers create fatty streaks which calcify. Plaques may ulcerate to create a thrombus.
Grafts vs flaps vs reconstructive flaps
Grafts can be partial or full thickness (partial vs full dermis). Flaps contain subQ vascular plexus for perfusion while grafts can perfuse through fluid alone.
Reconstructive flaps can even include tissue + part of original blood supply.
Flap perfusion
All flaps require adequate arterial inflow and venous outflow (must prevent clotting)
