Blood Vessels and Hemodynamics Flashcards
what are the 5 main types of blood vessels/
- arteries
- arterioles
- capillaries
- venules
- veins
what do arteries do?
carry blood away from the heart
what are arterioles?
smaller arteries
what are capillaries and what do they do?
thin walled, and accomplosh exchange of substances between blood and body tissues
what are venules?
small veins where capillaries reunite
what do veins do?
convey blood from tissues back to heart
what are the 3 layers of blood vessel walls? describe
- tunica interna/intima: epithelial inner lining
- tunica media: smooth muscle and elastic connective tissue
- tunica externa/adventitia: connective tissue outer covering
what accounts for the 5 types of blood vessels
modifications to the basic three layers provide the structural and functional differences in the 5 types of blood vessels
what does the tunica interna form and what is it in direct contact with?
forms the inner lining of the blood vessel; in direct contact with blood
describe the tunica interna’s contribution to the thickness of vessel walls
minimal contribution to overall vessel wall thickness
what is the innermost layer of the tunica interna? what is it continuous with?
endothelium that is continuous with the endocardial lining of the heart
what is the endothelium that is the innermost layer of the tunica interna made of?
a thin layer of flattened cells that line the inner surface of the entire cardiovascular system
what does the endothelial layer of the tunica intima do?
facilitates efficient blood flow by reducing surface friction
what is the second component of the tunica intima?
the basement membrane
what are the 3 components of the tunica intima, from innermost to outermost?
- endothelium
- basement membrane
- internal elastic lamina
what does the basement membrane of the tunica intima provide? (3)
- provides physical support base for epithelial layer
- provides framework of collagen fibers that gives basement membrane significant tensile strength
- provides resilience for strength and recoil
what does the basement membrane of the tunica intima do? (2)
- anchors endothelium to underlying connective tissue
- regulates molecular movement
describe how the basement membrane of the tunica intima regulates molecular movement
appears to play an important role in guiding cell movement during tissue repair of blood vessel walls
what is the internal elastic lamina?
the outermost part of the tunica intima
what does the internal elastic lamina of the tunica intima form?
forms the boundary between tunica interna and tunica media
what does the internal elastic lamina of the tunica intima do and how?
facilitates diffusion of materials through tunica interna to tunica media via a thin sheet of elastic fibers with window-like openings
what is the tunica media?
a muscular and connective tissue layer
which of the 3 blood vessel layers varies most among the vessel types?
tunica media
describe the tunica media in most vessels (2)
- relatively thick layer
- mainly smooth muscle cells and sustantial amounts of elastic fibers
what is the primary role of the smooth muscle cells in the tunica media?
regulate diameter of the vessel
what stimulates the smooth muscle of the tunica media to contract and what does this result in?
increased sympathetic stimulation stimulates the smooth muscle of the tunica media to contract; resulting in vasoconstriction or narrowing of the vessel lumen
along with increasing vasoconstriction, what does sympathetic stimulation result in relating to the tunica media?
also results in vasodilation and release of nitric oxide and lactic acid
what regulates the rate of blood flow through different parts of the body?
the extent of smooth muscle contractions in walls of vessels
what is crucial in regulating blood pressure relating to the tunice media?
the extent of smooth muscle contraction in a particular vessel type
what happens with the tunica media if an artery is damaged?
smooth muscle contracts (vascular spasm) to limit blood loss
what is the most variable to the tunics?
tunica media
what is the external elastic lamina?
a network of elastic fibers that separates the tunica media from the tunica externa
what is the tunica externa? what is it made of? what does it contain?
the outer covering of a blood vessel, consists of elastic and collagen fiber; contains numerous nerves
what does the tunica externa do?
helps anchor vessels to surrounding tissue
what are the vasa vasorum? (3)
- small vessels that supply blood to tissues of larger vessels
- vessels to the vessels
- can be seen on large vessels including the aorta
describe the compliance of arteries
high; walls stretch/expand easily without tearing in response to small increases in pressure
describe the tunica media of arteries
thick muscular-to-elastic tunica media
what is the largest type of artery in the body?
elastic arteries
give 3 examples of elastic arteries
- aorta
- pulmonary trunk
- branches of aorta
describe the vessel walls of arteries
relatively thin (10% of total diameter) compared with overall size of vessel
describe the tunica media of arteries
thick tunica media, dominated by elastic fibers called elastic lamellae
what do elastic arteries do?
help propel blood downward while ventricles are relaxing
when blood is ejected from the heart into arteries, what happens to accodomate the surge of blood?
artery walls stretch
as elastic fibers stretch, what happens?
they momentarily store mechanical energy are a pressure reservoir
what happens to the thing elastic fibers of arteries as they stretch to serve in the function as a pressure reservoir?
they convert stored energy into kinetic energy of blood so that blood continues to move through arteries even while ventricles are relaxed
what are elastic arteries also called?
conducting arteries
what are the 2 types of arteries?
- elastic arteries
- muscular arteries
describe muscular arteries’ tunica media compared to elastic arteries
muscular artery tunica media contains more smooth muscle and fewer elastic fibers than elastic arteries
describe the walls of muscular arteries compared to elastic arteries
muscular arteries have much thicker walls than elastic arteries
describe the vasoconstriction/vasodialtion capabilities of muscular versus elastic arteries
muscular arteries are capable of greater vasoconstriction/vasodialtion than elastic arteries
describe the range of size associated with muscular arteries
femoral is pencil sized where some are string sized that enter organs
what are muscular arteries also called?
dsitributing arteries
what percentage of total vessel diameter do muscular artery walls comprise?
25%
do muscular arteries recoil like elastic arteries? what does this mean?
do not recoil like elastic arteries, so can’t propel blood
what is primarily responsible for the function of muscular arteries?
the thick, muscular tunica media
what is vascular tone?
the ability of muscle to contract and maintain state of partial contraction
what does the realtively thick walls of muscular arterioles allow for?
not as compliant, so can use vasodilation and vasoconstriction to shift blood to where it’s needed
what does vascular tone do in muscular arteries?
stiffens vessel walls and is important in maintaining vessel pressure and efficient blood flow
what are anastomoses?
unions of branches where 2 or more arteries supply the same body region
what do anastomoses do?
provide alternate routes for blood to reach tissue
what is collateral circulation?
alternate route of blood flow to body part
do end arteries anastomose?
nope
what does obstruction of an end artery result in?
necrosis of the tissue it serves
how might blood supply also be provided (other than anastomoses)?
alternative blood routes
what are arterioles?
small arteries
what do arterioles do?
regulate blood flow into capillary network
describe the wall thickness of arterioles
1/2 vessel diameter
describe the tunica interna and elastic lamina of arterioles
think tunica intima and thin fenestrated elastic lamina
what is the terminal end of arterioles called? what does it taper toward?
metarteriole, tapers toward capillary junction
where are precapillary sphincters located?
at metarteriole/capillary junctions
what do precapillary sphincters do?
monitor blood flow into capillaries
describe the nerves of arterioles
abundant unmyelinated sympathetic nerves
what do the abundant unmyelinated sympathetic nerves of arterioles do?
can alter diameter and therefore rate of blood flow and resistant
what is always needed to maintain blood pressure?
some vascular tone
what does resistance mean in relation to arterioles?
opposition to blood flow
what are arterioles also reffered to as?
resistance vessels
what is the resistance of arterioles mainly due to?
friction between blood and inner walls of blood vessels
how does the diameter of arterioles relate to their resistance?
the smaller diameter of arterioles provides greater friction and contributes to greater resistance
what is contraction of smooth muscle in vessels called and what does this result in in arterioles?
vasocontriction, increases resistance and decreases blood flow into capillaries
what are the smallest blood vessels?
capillaries
what do capillaries connect?
connect arterial outflow to venous return
about how many capillaries do we have in our bodies?
approx 20 billion
what is microcirculation?
flow of blood from metarteriole through capillaries into post-capillary venule
what is the primary function of capillaries and how is this accomplished?
primary function is exchange of substances between blood and intersititial fluid, accomplished through thin-walled exchange vessels
describe the structure of capillaries and what that structure is important for
walls composed of a single layer of eptihelial cells and basement membrane; important for movement of substances into tissues
where does exchange of nutrients occur? (2)
- through capillaries
- through beginning of venules
when is the entire capillary network of a tissue active?
when the tissue is active
what happens in the capillary network when metabolic needs are low?
blood flows through a small part of the capillary network only
what is the capillary bed?
a network of 10-100 capillaries that arise from a single arteriole
where do capillaries move nutrients?
to areas with the highest demand
what are the 3 types of capillaries?
- continuous
- fenestrated
- sinusoid
what is the most abundant type of capillary?
continuous capillaries
describe continuous capillaries
a continuous tube interrupted only by intercellular clefts
where are continuous capillaries located? (4)
- CNS
- lungs
- skin
- muscle
what are intracellular clefts?
where exchange of nutrients occurs
describe the cells of fenestrated capillaries
endothelial cells that have many fenestrations (small pores)
where are fenestrated capillaries located? (2)
- kidneys
- villi of small intestines
describe the structure and pattern of sinusoid capillaries
wider and more winding than other capillaries, with large fenestrations
do sinusoid capillaries have a basement membranes?
nope
describe the intracellular clefts of sinusoid capillaries
very large
what do sinusoid capillaries allow for?
allow proteins (like blood cells) to pass from tissue to blood strem
where are sinusoid capillaries found? (3)
- adrenal glands
- liver
- spleen
what is a thoroughfare channel?
where blood can pass from metarterioles to veules without much flow through capillaries
describe the walls of venules and what this means for shape maintenance
thin-walled and do not readily maintain their shape
what do venules do?
drain capillary blood and begin return flow of blood to the heart
what are the 2 types of venules?
- postcapillary venules
- muscular venules
what do the postcapillary venules do? (2)
- initially receive blood from capillaries
- are a significant site of exchange of nutrient and wastes
describe postcapillary venules
very porous
what do postcapillary venules form since they are a significant site of exchange of wastes and nutrients?
form part of microcirculatory exchange unit
describe the walls of muscular venules and what this means?
thicker walls means no exchanges with interstitial fluid
describe the smooth muscle layers of muscular venules (compare to arteries)
1-2 layers of circular smooth muscle
what is the most distensible element of the vascular system? what do they do?
the thin walls of venules; expand and serve as reservoirs for large volumes of blood
describe the walls of veins relative to their total diameter
very thin walled, less than 1/10 of total vessel diameter
compare the tunica intima of veins to arteries
tunica intima of veins is thinner than arteries
compare the tunica media of veins to arteries including descriptions of smooth muscle and elastic fibers
tunica media of veins is much thinner than arteries, with relatively little smooth muscle and elastic fibers
describe the tunica externa of veins and what it includes (2)
tunica externa is the thickest layer of veins; includes collagen and elastic fibers
do veins contain the elastic lamina found in arteries?
no; veins lack the elastic lamina found in arteries
how distensible are veins and what is their limit?
veins are distensible enough to adapt to variations in volume and blood pressure passing through them but not designed to withstand high blood pressure
compare and contrast veins to arteries (4)
- vein lumen is larger than compaarable arteries
- blood pressure in veins is considerably lower than in arteries
- veins contain valves; arteries do not
- veins are more numerous than arteries
how is blood flow from a cut vein different than blood flow from a cut artery?
when you cut an artery, the blood flow will be bright and pulsing from the high pressure; when you cut a vein, the blood flow will be darker and not pulsing due to low blood pressure
describe the valves of veins (4)
- thin folds of tunica interna
- forms flap-like cusps
- project into lumen pointing toward the heart
- aid in venous return by preventing backflow of blood
what are varicose veins?
when veins become dilated and twisted in appearance due to leaky venous valves
where are varicose veins most common? (3) which is the most serious location?
- esophagus- most dangerous
- anal canal
- superficial veins of legs
what is another name for varicose veins?
varices
what causes esophageal varices? what are the symptoms? (2)
when the portal vein is backed up due to scar tissue in the liver and interferes with veinous flow; symptoms are vomiting blood and black stool
what are anal canal varices also known as?
hemorrhoids!
what are the 2 causes of varicose veins?
- congenital
- mechanical stress
what happens with varicose veins due to the leaky valves?
leaking valves may allow backflow of blood from deep veins to less efficient superficial veins causing blood pools
what is DVT?
deep vein thrombosis; a clot in the veins that blocks blood flow or could travel to lungs or brain = bad news bears
what do varicose veins to do surrounding veins and tissue?
create pressure that distends the veins and allows fluid to leak into surrounding tissue
describe the affected vein and surrounding tissue of varicose veins
inflamed and tender
what type of veins are more susceptible to varicose veins? which are less suscetpible and what?
superficial veins like the saphenous vein are more susceptible, while deep veins are less susceptible because they are supported by skeletal muscle
list and describe 4 treatments for varicose veins
- elastic stockings (compression socks)
- sclerotherapy: inject tissue with compound to induce necrosis
- laser occlusion: shut down a section of the vein
- stripping: removing part of the vein
describe blood distrubution at rest (but rly just know the first one)
- 64% in veins and venules
- 13% in systemic arteries and arterioles
- 7% in systemic capillaries
- 9% in pulmonary blood vessels
- 7% in the heart
what serves are the blood reservoir of the body? what can it do with this reservoir?
the systemic venous system; can divert blood when needed
what happens involving blood distribution during exercise?
the cardiovascular center in the medulla oblongata sends sympathetic impulses to veins causing venoconstriction and allowing greater blood flow to muscles
what happens to blood volume and pressure during hemorrhage?
blood volume and pressure decrease
what happens to counteract the drop in blood pressure during hemorrhage?
venoconstriction
what are principle blood reservoirs?
veins in abdominal organs (like the liver and the spleen) and the skin
what is bulk flow?
a passive process where large numbers of ions, molecules, or aprticles in fluid move together in the same direction
how is bulk flow different from diffusion?
bulk flow movement occurs at a much faster rate than can be accounted for by diffusion alone
where and when does bulk flow occur?
from areas of higher pressure to areas of lower pressure as long as a pressure difference exists
what is bulk flow more important for than diffusion?
bulk flow is more important for regulation of relative volumes of blood and interstitial fluid
what is diffusion more inportant for than bulk flow?
diffusion is more important for solute exchange between blood and interstitial fluid
what is filtration?
the pressure-driven movement of fluid/solutes from blood capillaries into interstitial fluid
what is reabsorption?
pressure-driven movement from interstitial fluid into capillaries
what 2 pressures promote filtration?
- blood hydrostatic pressure (BHP)
- interstitial fluid osmotic pressure (IFOP)
what 2 pressures promote reabsorption?
- blood colloud pressure (BCOP)
- interstitial fluid hydrostatic pressure (IFHP)
what is hydrostatic pressure?
pressure from water component of fluid
what is osmotic pressure?
pressure from water moving to where solutes (proteins) are
what is net filtration pressure? what does it determine?
balance of pressures that are constantly opposing each other in capillaries; determines whether volumes of blood and intersitital fluid change
what is Starling’s law of the capillaries?
normally, the volume of fluid and solutes reabsorbed is almost as large as volume filtered
what is BHP? describe
blood hydrostatic pressure due to the pressure that the water in blood plasma exerts against blood vessel walls
what does BHP do?
pushes fluid out of capillary into interstitial fluid
give values for BHP at arterial and venous ends of capillaries
arterial: 35 mmHg
venous: 16 mmHg
what is IHP? describe
interstitial hydrostatic pressure; opposing pressure of interstitial fluid
what does IHP do?
pushes fluid from interstitial spaces back into capillaries
describe IHP contribution to net filtration pressure
close to 0; minimal contribution
what is the difference in pressure across capillary walls due to?
presence of plasma proteins in blood that are too large to move through fenestrations or gaps between endothelial cells
what is BCOP? describe
blood colloid osmotic pressure; the force caused by suspension of large proteins in plasma
what does BCOP do?
pulls fluid from interstitial spaces into capillaries
what is the average BCOP in most capillaries?
26 mmHg
what is IFOP? describe
intersitial fluid osmotic pressure; opposes BCOP
what does IFOP do?
pulls fluid out of capillaries
describe the level of IFOP/contribution to net filtration pressure and why
very small; only tine amounts of protein in interstitial fluid
what determines if fluid leaves or enters capillaries?
balance of pressures
when does filtration occur in capillaries?
in pressures pushing fluid out of capillaries exceed those pulling fluids in
when does reabsorption occur in capillaries?
if pressures pushing fluid out of interstitial space into capillaries exceeds those that pull fluids out of capillaries
what is the equation to find net filtration pressure (NFP)?
NFP = (BHP + IFOP) - (BCOP+IFHP), or pressures promoting filtration minue pressures promoting reabsorption
what is the average NFP aat the arterial end of capillaries and what does this mean?
avg is 10 mmHg; so net outward pressure, fluid moves out of capillary
what is the average NFP at venous end of capillaries; what does this mean?
avergae is -9 mmHg, so net inward pressure and fluid moves into capillary from interstitial spaces
on average, what percentage of blood filtered out of capillaries is reabsorbed?
85%
how much blood is filtered daily? how much of that is reabsorbed and where does the rest go?
20L filtered daily; 17L reabsorbed and 3L enter lymphatic capillaries
a person who has liver failure can’t synthesize a normal amount of plasma proteins. How does a deficit of plasma proteins affect blood colloid osmotic pressure and what is the effect on capillary exchange?
there will be less reabsorption because fewer plasma proteins decreases BCOP; the buildup of fluid in the tissue can lead to edema
