7.6- BLOOD VESSELS AND THEIR FUNCTIONS Flashcards
What are the 4 different types of blood vessels?
arteries
arterioles
capillaries
veins
What do arteries carry?
blood away from heart + into arterioles
What are arterioles?
smaller arteries that control blood flow from arteries to capillaries
What are capillaries?
tiny vessels that link arterioles to veins
What do veins carry?
blood from capillaries back to heart
What is the basic layered structure of arteries, arterioles + veins from outside inwards? (5)
tough fibrous outer layer muscle layer elastic layer thin inner lining (endothelium) lumen
What does the tough fibrous outer layer of the basic layered structure of arteries, arterioles + veins do?
resists pressure changes from both within + outside
What does the muscular layer of the basic layered structure of arteries, arterioles + veins do?
can contract + so control flow of blood
What does the elastic layer of the basic layered structure of arteries, arterioles + veins help do?
helps maintain blood pressure by stretching + springing back (recoiling)
What does the thin inner lining (endothelium) of the basic layered structure of arteries, arterioles + veins do?
smooth to reduce friction + thin to allow diffusion
What is the lumen of the basic layered structure of arteries, arterioles + veins?
not actually a layer but the central cavity of the blood vessel through which blood flows
What differs between the arteries, arterioles + veins?
relative proportion of each layer
How is the structure of arterioles different from arteries?
arterioles smaller in diameter + having relatively larger muscle layer + lumen
What is the difference in structure of arteries, arterioles + veins related to?
differences in function that each type of vessel performs
What is the function of arteries?
transport blood rapidly under high pressure from heart to tissues
How is the structure of arteries adapted to their function? (4)
muscle layer thick compared to veins
elastic layer relatively thick compared to veins
overall thickness of wall great
no valves
What can smaller arteries do as the muscle later is thick compared to veins?
smaller arteries can be constricted + dilated to control volume of blood passing through them
Why is the elastic layer of arteries relatively thick compared to veins?
as it’s important that blood pressure in arteries kept high if blood is to reach extremities of body
What happens to the elastic walls of the arteries during systole + diastole?
elastic wall stretched at each beat of heart (systole)
then springs back when heart relaxes (diastole)
What does the stretching + recoiling action of the arteries help maintain?
helps maintain high pressure + smooth pressure surges created by beating of heart
What does the overall thickness of the wall of arteries being great resist?
resists vessel bursting under pressure
Which arteries do have valves? - they’re an exception
arteries leaving the heart
Why are there no valves in arteries?
blood under constant high pressure due to heart pumping blood into arteries
so tends not to flow backwards
What do arterioles carry?
blood under lower pressure than arteries, from arteries to capillaries
What do arterioles control?
control flow of blood between arteries + capillaries
What structures of arterioles is related to their function? (2)
muscle layer relatively thicker than in arteries
elastic layer relatively thinner than in arteries
What does the contraction of the muscle layer of arterioles allow?
constriction of lumen of arteriole
What does the contraction of the muscle layer constricting the lumen of arterioles do?
restricts flow of blood + so control its movement into capillaries that supply the tissue with blood
Why is the elastic layer of arterioles relatively thinner than in arteries?
as blood pressure lower
What do the veins do?
transport blood slowly, under low pressure, from capillaries in tissues to heart
What structures do veins have that are related to its function? (4)
muscle layer relatively thin
elastic layer relatively thin
overall thickness of wall small
valves at intervals throughout
Why is the muscle layer of veins relatively thin in comparison to arteries?
as veins carry blood away from tissues + so their constriction + dilation cannot control flow of blood to tissues
Why is the elastic layer of veins relatively thin compared to arteries?
as low pressure of blood within veins will not cause them to burst + pressure too low to create recoil action
Why is the overall thickness of vein wall small?
as there’s no need for thick wall as pressure within veins too low to create any risk of bursting
also allows them to be flattened easily aiding flow of blood within them
Why are there valves at intervals throughout veins?
to ensure blood doesn’t flow backwards, which it might otherwise do as pressure is so low
What happens to veins when muscles contract? (valves at intervals throughout veins)
veins compressed, pressuring blood within them
valves ensure this pressure directs blood in one direction only: towards heart
What is the function of the capillaries?
exchange metabolic materials i.e. oxygen, carbon dioxide + glucose between blood and cells of body
How is the flow of blood in capillaries in comparison to the other vessels?
flow of blood in capillaries much slower
What does the flow of blood in capillaries being much slower allow?
allows more time for exchange of materials
How is the structure of the capillaries related to their function? (5)
their walls consist mostly of lining layer
numerous + highly branched
narrow diameter
lumen so narrow
spaces between lining (endothelial) cells
What does the capillary walls consisting mostly of lining layer make them?
makes them extremely thin, so distance over which diffusion happens is short
What does the distance over which diffusion happens being short allow? (capillaries- walls consisting mostly of lining layer)
allows for diffusion of material between blood + cells
What does the capillaries being numerous + highly branched provide?
provide large SA for exchange
What does the capillaries having a narrow diameter mean?
permeate (spread throughout) tissues, which means that no cells far from capillary + there’s short diffusion pathway
What happens as the lumen of the capillaries are so narrow?
red blood cells squeezed flat against the side of capillary
What does the lumen of capillaries being narrow and red blood cells being squeezed flat against the side of capillary mean?
brings red blood cells even closer to cells to which they supply oxygen
reduces diffusion distance
What do the spaces between the lining (endothelial) cells of the capillary allow?
allow white blood cells to escape to deal with infections within tissues
Although capillaries are small, what can they not do?
cannot serve every single cell directly
Where is the final journey of metabolic material made in?
liquid solution that bathes the tissues called tissue fluid
What is tissue fluid?
watery liquid that contains glucose, amino acids, fatty acids, ions in solution + oxygen
What does tissue fluid supply?
supplies substances in it to tissues
What does tissue fluid receive from tissues?
receives carbon dioxide + other waste materials from tissues
What is tissue fluid the means of?
means by which materials exchanged between blood + cells, and, as such, bathes all cells of body
What is tissue fluid formed from?
from blood plasma
What is the composition of blood plasma controlled by?
various homeostatic systems
What sort of environment does tissue fluid provide?
mostly constant environment for cells it surrounds
Where does blood pumped by heart pass along? (formation of tissue fluid)
arteries, then narrower arterioles + finally even narrower capillaries
What pressure does the pumping of the heart create? (formation of tissue fluid)
hydrostatic pressure at arterial end of capillaries
What does the hydrostatic pressure at the arterial end of the capillaries cause? (formation of tissue fluid)
cause tissue fluid to move out of blood plasma
What factors is the outward pressure opposed by? (2) (formation of tissue fluid)
hydrostatic pressure of tissue fluid outside capillaries, which resists outward movement of liquid
lower water potential of blood, due to plasma proteins, that causes water to move back into blood within the capillaries
What is the combined effect of all the forces to create? (formation of tissue fluid)
to create overall pressure that pushes tissue fluid out of capillaries at arterial end
What is the overall pressure of the combined forces only enough to do? (formation of tissue fluid)
only enough to force small molecules out of capillaries leaving all cells + proteins in blood as these are too large to cross the membrane
What is the type of filtration of small molecules out of capillaries leaving all cells + proteins in blood as these are too large to cross the membrane under pressure called?
ultrafiltration
What happens to tissue fluid once it has exchanged metabolic materials with the cells it bathes? (return of tissue fluid to circulatory system)
it’s returned to circulatory system
How does more tissue fluid return to the blood plasma? (return of tissue fluid to circulatory system)
directly via capillaries
Return of tissue fluid to blood plasma directly via capillaries: #1 hydrostatic pressure
loss of tissue fluid from capillaries reduce hydrostatic pressure in them
Return of tissue fluid to blood plasma directly via capillaries: #2 venous end
by the time blood has reached venous end on capillary network its hydrostatic pressure usually lower than that of tissue fluid outside it
Return of tissue fluid to blood plasma directly via capillaries: #3 tissue fluid
tissue fluid forced back into capillaries by higher hydrostatic pressure outside them
Return of tissue fluid to blood plasma directly via capillaries: #4 what does the plasma still contain
plasma has lost water + still contains proteins
so has lower water potential than tissue fluid
Return of tissue fluid to blood plasma directly via capillaries: #5 what happens to water
water leaves tissue by osmosis down water potential gradient
Cab all the tissue fluid return to the capillaries?
no
Where is the remainder tissue fluid carried back by?
via lymphatic system
What is the lymphatic system?
system of vessels that begin in tissues
initially resemble capillaries (except thy have dead ends), but gradually merge into larger vessels that from network throughout body
What do the larger vessels of the lymphatic system do?
drain their contents back into bloodstream via two ducts that join veins close to heart
Are the contents of the lymphatic system (lymph) moved by the pumping of the heart?
no
What is the contents of the lymphatic system (lymph) moved by? (2)
hydrostatic pressure of tissue fluid that has left the capillaries
contraction of body muscles that squeeze lymph vessels
What do the valves in the lymph vessels ensure?
that fluid inside them moved away from tissues in direction of heart
