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- - series of efferent vessels that become
- smaller as they branch
carriers the blood (with nutrients and oxygen) to the tissues
smallest blood vessels that anastomose profusely
through walls blood and tissues interchange substances
- convergence of capillaries result in a
- system of channels
- become larger as approach heart
returns tissue fluid to the blood
what is in the microcirculatory bed?
arterioles - controls how much gets into capillary beds, capillary network, and postcapillary venules - where neutrophils (most WBC) leave and go into the CT
layers of vascular wall: (lumen outward)
- tunica intima - squamous epithelial cells (endothelium), basal lamina of endothelial cells, subendothelial layer (loose connective tissue, also layer that has internal elastic membrane)
- tunica media- layers of smooth muscle cells
- tunica adventitia- CT layer on the outside - collagenous tissue and a few elastic fibers
controls how much blood gets into cap bed, it is like a shunt, direct conduit, if you want less to get into capillaries
Basics of Arteries
- internal elastic lamina - layer of elastic fibers that are inbetween intima and media (fenestrated - holes in it) that are important for exchange/diffusion of materials (glucose and oxygen)
- - variable amounts of smooth muscle cells and elastic depending on where in body the artery is
- adventitia layer- continous with CT of the organ through which it runs. contains the vaso vasorum - where you find blood vessels that supply the vascular walls and also the nervi vascularis which controls contraction of smooth muscle in the vascular walls
classification of arteries:
- large (elastic) - pulmonary arteries (associated with the heart)
- medium (muscular) - most of the named arteries in the body
- small - up to 8 layers of smooth muscle
- arteriole - 1 or 2 layers of smooth muscle
what is the thickness of the tunica adventitia in arteries and veins?
- arteries- thin
- veins - thick
what is the vaso vasorum and what layer does it belong to?
- supplies blood to the vascular walls
- it is in the tunica adventitia
describe vascular endothelium
- simple squamous cells lined up in the direction of blood flow - good for gas exchange!
- junctional complexes - tight junctions/gap junctions between cells
- apical surface - cell adhesion molecules and diff receptors (part of homeostasis)
what is major function of endothelial cells?
maintain homeostasis for the body!! very importnat - they know what is up and transport signals to the rest of the body!
what is an example of a cell adhesion molecule on the endothelial cells?
post capillary venule - selectin and integrin for neutrophils
what are the ways exchange occurs between tissues and blood? and what kind of molecules do each thing?
- simple diffusion - small molecles/lipids (oxygen, carbon dioxide)
- transcellular pathway - (water and hydrophilic molecules - glucose) actively transported through transporters
- paracellular pathway - through zonula occludins, between 2 epithelial cells
- receptor mediated endocytosis - LDLs
How is the non-thrombogenic barrier maintained?
blood platelets and subendothelial tissue need to have a barrier between them - so they produce anticoagulant factors (so that platelets dont bind)
but... damaged epithelium produce PROTHROMBOGENIC AGENTS to induce clotting (von willebrand factor)
how does von willebrand factor work?
binds to one of the enzymes in the cascade, produces plasminogen activator, maintain and activates clot
functions of endothelial cells?
- selective permeability barrier
- maitenance of a non thrombogenic barrier
- activation of clotting
- modulation of blood flow and vascular resistance - secretion of vasodilators and vasoconstrictors
- regulation of immuno responses (secrete interluekins to activate immune system)
- hormone synthesis (blood pressure, blood cell differentiation, maintain homeostasis)
- modification of lipoproteins - too much fat in the blood stream is bad, so they will take up the lipids and break them up through oxidation (good)
how does an atherosclerotic plaque form?
too many LDLs enter tunica intima - get reactive oxygen species (O2-) because of oxidation, overwhelm the healthy system - activates immune and inflammatory response - increased permeability so more fat comes in - monocytes come in and differentiate into macrophages that eat up the fat - turns them into foam cells which accumulate and become fatty streaks, then they die which activates even more of an inflammatory response - endothelial layer gets even more leaky - endothelial cells get damaged so you get blood clots forming, smooth muscle cells come in to make a protective capsule around the area turning the fatty streaks turn into fibrofatty plaques - so the tunica intima thickens! and depositoin of cholesterol in smooth muscle cells and macrophages. can be regional... or just general thickening
what part of cardiovascular system is predisposed to getting plaques?
coronary arteries - causes strokes or heart attacks
what is function of elastin in arteries?
- helps minimize force so it can snap back quickly when the heart beats
- stabilize blood flow and make it more uniform
what happens to elastic arteries during systole and diastole?
systole - elastic lamina are stretched and reduce pressure change
diastole - ventricular pressure drops and elastic rebound maintains arterial pressure
elastic arteries - describe the layers
intima: endothelium, subendothelial tissue, inconspicuous internal elastic membrane (inner most layer of elastic wall, it is continous with the rest of the elastic layers)
tunica media: thickest layer, has elastin in the form of fenestrated sheets or lamellae, smooth muscle cells, collagen and ground substance
tunica adventitia: relatively thin, collagen fibers, elastic fibers (loose network and unorganized) - fibroblasts and macrophage
nerve supply in the tunica media of elastic arteries
how is the tunica media organized in elastic arteries?
- smooth muscle cells are between the elastic fibers - they make the elastic fibers!
- elastic fibers are little squiggles
- tunica intima = elongated cells
are there fibroblasts in the tunica media?
no! smooth muscle cells secrete ECM material!
what is pattern that happens in arteries with age?
high blood pressure? proper term?
- number of elastic layers increases
- barely any elastic lamallae when you are born
high blood pressure (hypertension) - have more smooth muscle cells which accumulates lipids
Describe layers of muscular/medium arteries?
- tunica intima - thinner than in elastic, prominent internal elastic membrane (little squiggly line), thickens with age bc of fatty streaks
- tunica media - smooth muscle cells among collagen fibers with little elastin, SMC arranged in spiral formation, no fibroblasts
- tunica adventitia - relatively thick, separated from media by external elastic membrane, has fibroblasts, collagen, elastin, has nerves and small blood vessels
describe transition from large to small arteries
how do you distinguish small arteries from arterioles?
what do they share?
- number of smooth muscle cell layers in the tunica media
- 1-2: arterioles
- up to 8 in small arteries
- arterioles may not have obvious internal elastic membrane
both: tunica adventitia not well defined and thin
fucntion of arterioles
- direct blood flow to particular tissue through vaasodilation and constriction
- - have a resting diameter that can dialate or constrict
what is the precapillary sphinctor?
it is in the arterioles and it is a slight thickening of the smooth muscle - regulate flow
What is the structure of capillaries?
- single layer of endothelial cells + basal lamina
- diameter is just enough for a RBC to pass through
which tissues have more capillaries?
the most metabolically active ones
how many miles of capillaries in body?
Three types of capillaries?
- 1) continuous - absence of fenestrae in wall (muscle, lungs, CNS), lots of pinocytotic vesicles, occluding junctions
- 2) fenestrated - large fenestrae walls of endothelial cells, found in tissues where rapid interchange of substances occur (kidney, intestinal tract, endocrine), pinocytotic vesicles too
- 3) discontinous - larger in diameter, irregularly shaped, also fenestrae, endothelial cells and basal lamina are discontinuous (not as tightly controlled so you find macrophages, (liver, spleen, bone marrow)
what is fx of pinocytotic vesicles?
aid in transport between lumen and connective tissue and vice versa
what are the pressures that cause exchange of fluid?
hydrostatic pressure (causes flow OUT of capillary into interstitial fluid)
osmotic pressure (causes flow INTO capillary), increases as you get to venous end
role of metarterioles?
more direct passage from artery to vein
what is the other name for AV shunts? and what/how is their function?
where are they found?
- Arteriovenous Anastomosis
- thermoregulation (conserve body heat)
- they bypass capillaries, bring blood straight from arteries to veins (act as a shunt)
- when they contract the blood goes to a capillary, when they are relaxed then the bypass happens
would be in the kidney, rolled up in ball, involved in filtration
capillary bed between two veins (ex: liver)
how is the lymph involved?
it picks up the fluid that doesnt go back inside the veins
- at various locations in caps and postcapillary venules
- mesenchymal origin (same precurser as endothelial cells)
- long cytoplasmic processes that surround endothelial cells
- basal lamina continous with endothelial basal lamina
- myosin, actin, and tropomyosin - suggests that have contractile function
- fx: relationship with the endothelial cells, both synthesize growth factors
comparison of veins and arteries?
veins have thinner walls and wider lumens and veins have less distinct tunic layers
2 types of venules?
- Postcapillary venules - endothelial linining with basal lamina and pericytes, histamine and serotonin
- muscular venules - have tunica media that poscaps dont, lack of pericytes
- contains valves (to prevent backflow, common in lower half of body)
- three tunics are the most evident for these ones
- diameter greater than 10 mm
- thin tunica media
- thick tunica adventitia
- ex: portal vein, venae cavae
effect of nitric oxide (NO)?
what happens if too much?
- shearing stress on endothelial cells - synthesis of VEGF and eNOS (ca2+ dependent) which oxidizes l-arginine into NO (gas) - diffuses out through cell to tunica media and through cascade decreases concentration of Ca2+ causing smooth muscle relaxation
- if too much - inflammatory response so it is tightly regulated
relax of smooth muscle cells - increase luminal diameter - decrease vascular resistance - and decrease systematic blood pressure
effect of prostacyclin (PGI2)?
- caused by metabolic stress of endothelial cells
- - relaxes smooth muscle cells and also inhibits platelet aggregation
- - PGI2 binds to receptors on the smooth muscles - stimulates camp activated protein kinase A - phosphorylates myosin light chain kinase - prevents activation of the calcium - calmodulin complex (occurs without changing intracellular ca2+)
contraction of smooth muscle - reduces luminal diameter - increases vascular resistance - increases systemic blood pressure
what are modes of vasoconstriction?
- O2- inhibits NO - contraction
- angiostensin II and thrombin bind to endothelial cells - stimulate endothelins (prstoaglandin H2 synthesizes thromboxane A2) that bind to own receptors and increase Ca2+ -> contraction!
how does angiostensin 1 turn into angiostensin 2?
- angiostensin 1 is secreted by liver and is turned into A2 by RENIN (Secreted by kidney)
- renin can tell what the blood pressure is like