Chapter20 - Blood Vessels Flashcards
Blood vessels
hollow tubes that direct blood.
Blood vessel types
Artery
Vein
Capillaries
Capillaries-
microscopic permeable vessels that allow the exchange of substances between blood and surrounding tissues
Artery-
away from the heart
Vein-
take blood to the heart
Blood vessel structure
Walls are composed of layers, tunics, that surround the inner space ,lumen.
tunic intima
(connective tissue for support and protection)
tunic media
(smooth muscle layer +/- elastic fibers)
tunic externa
(endothelium + connective tissue)
Artery
lumen, thickest layer, shape,pressure, valves
L: narrower TL:tunica media S: maintain shape and better resistant to high-pressure (more elastic and collagen fibers) P: 100-40 mm Hg V: no
Vein
lumen, thickest layer, shape,pressure, valves
L: narrower TL: Turnica externa S: collapses without blood and less resistant to have pressure (less elastic and collagen fibers) P:20-0 mm Hg V:yes
Arteries
Branch into smaller vessels:
Elastic arteries
Muscular arteries
Arterioles
Elastic arteries
Or conducting
conduct blood from the heart. Large proportion of elastic fibers allows them to stretch and recoil assisting in propelling blood
Muscular arteries
Or distributing
distribute blood to various body regions
Arterioles
Or resistance vessels
Smallest
can dilate and constrict thus, regulating blood flow to tissues and systematic blood pressure
Atherosclerosis
Progressive disease of elastic and muscular arteries characterized by formation of plaques narrowing already arterial limit and obstructing bloodflow
Aneurysm
Part of the arterial wall thins and balloons out, prone to rupture leaving to massive bleeding and death
Capillaries
Smallest vessel (just larger than a single erythrocyte) Consist of endothelial layer on the basement membrane
Why does the capillaries consist of endothelial layer on the basement membrane?
Optimal for exchange of substances between blood and surrounding tissues
Types of capillaries
- Continuous capillaries
- Fenestrated capillaries
- Sinusoids
Continuous capillaries
Least permeable (only small molecules pass) most common (muscle, skin, lungs)
Fenestrated capillaries
Endothelium with thin areas(fenestrations) that allow movement of small plasma proteins
-small intestine endocrine glands
Sinusoids
Have openings that pass large substances (formed elements, large plasma proteins)
- in bone marrow liver spleen
Capillary bed
Groups of capillaries functioning together
- true capillaries
- vascular shunt
Vascular shunt
=metarteriole
Proximal part with scattered muscle cells) + thorough fare channel (distal part with no muscle cells
True capillaries
Vessels branching from metarteriole
Precapillary sphincters
(Smooth muscle rings)
regulate blood flow into the true capillaries. they contract and relax at a rate 5-10 cycles/min: 1/4 open at a time
Perfusion
Amount of blood entering capillaries per unit time per gram of tissues
(Varies)
Function of capillaries
Allow exchange of substances between blood and surrounding tissue
Diffusion
Movement of substances from high to low concentration
Vesicular transport
Endothelial cells perform endocytosis to transport large molecules
Bulk flow
Movement of large amounts of fluids with a dissolved substances in one direction down a pressure gradient through pores in intercellular clefts
Includes
Filtration
Movement of fluid out of the capillaries
Reabsorption
Movement of fluid in the capillaries
Hydrostatic pressure
Force exerted by a fluid on a structure “pushing”
Up
Colloid osmotic pressure
Pull of water by tissues proteins
Net filtration pressure (NFP)
Difference between HP and net COP determines movement of fluid
Veins
Merge into the larger vessels as they extend from the capillaries to the heart
Venules
Smallest
-drain capillaries merge to form veins
Small and medium sized veins
Are companion vessels to muscular arteries;
contain numerous valves that prevent blood from pulling in the limbs
Large veins
Travel along elastic arteries contain numerous valves
Systemic veins function as blood
_________________
(55-60%).
-reservoirs
If necessary, blood can be:
-moved into circulation via vaso________ (if more blood is needed, ex.during exertion)
-shifted back into reservoirs via vaso___
(if less blood needed, ex. during rest)
- constriction
- dialation
There is_____enough blood in the body to fill all the capillaries at the same time, so blood can be __________ to the organs and tissues where it is most needed.
- not
- directed
Low blood flow
–amount of blood delivered to capillaries of a specific tissue.
It depends on:
1.degree of tissue vascularization
2.local regulatory factors altering blood flow
3.total blood flow
Degree of Vascularization
determines potential ability of blood delivery
high vascularization in brain, skeletal muscle, heart, liver
;
little vascularity in tendons, ligaments
Angiogenesis
formation of new blood vessels in tissues, stimulated by:
- aerobic training(in skeletal muscle)
- weight gain(adipose tissue)
- tumor development
Regression
return to the previous state of blood vessels, stimulated by:
- sedentary style of life
- losing weight
Local regulation
Involve surrounding tissues altering the bloodflow in response to changes in the metabolic activity or damage
Perivascular tissues release a variety of vasoactive chemicals:
1 vasodialators
2 vasoconstrictors
Vasodialators
Dilate Arterioles and relaxed precapillary sphincters -> increased flow into the capillaries
Ex: histamine released by leukocytes in response to infection (part of the inflammatory response)
Ex: low levels of O2 & nutrients, high levels of co2 anaphylactic acid as a result of intense exercise or disrupted bloodflow
Vasoconstrictors
Cut straight arterio lace in precapillary sphincters -> increased flow into the capillaries
Ex: release of thromboxyne x2 by thrombocytes causes vasoconstriction to reduce blood loss through the damaged vessel
Total blood flow
Amount of blood transported through the cardiovascular system per unit time (min)
Total blood flow equation
Pressure gradient (established by the heart) / Resistance (experience by blood as it moves through the vessels)
