blood vessels

Question 1

classify blood vessels based on their structure and overall function

Answer 1

they are tubular organs which create a branching network throughout the body that transports and distributes blood. all blood vessels are made of tissue layers surrounding a lumen which blood passes through.

Question 2

what is capillary bed structure

Answer 2

they are capillaries arranged into diving and re emerging networks. they increase the surface area of capillaries throughout the body, ensuring adequate space and time for gas, nutrient and waste exchange.

Question 3

what are the three types of capillaries- they vary in the level of permeability

Answer 3

continuous- slightly permeable. allows small solutes
fenestrated- allows diffusion of medium sized solutes
sinusoid- highly permeable. allows diffusion of large solutes

Question 4

what is the relationship between blood flow, blood pressure and resistance

Answer 4

blood flow is dependant upon pressure and resistance
blood flow= pressure/ resistance
the pressure falls as the heart pumps blood

Question 5

what factors influence blood flow, blood pressure and resistance

Answer 5

influence TPR

• blood viscosity- the thickness of the blood
• blood vessel length (the longer the blood vessel the more resistance)
• blood vessel diameter (the diameter of the blood vessel determines how much space there is in the vessel for the free flow of blood and less hitting the walls)

influence blood pressure
- pressure gradient- as blood flows around the vasculature the pressure continuously drops. BP= CO x TPR

Question 6

what is total peripheral (vascular) resistance and blood pressure and how do they relate to cardiac output

Answer 6

blood pressure is the amount of pressure exerted on the walls of the blood vessels.
total peripheral resistance is the amount of force affecting resistance to blood flow.
CO and TRP influence the blood pressure throughout the vasculature
CO x TPR= BP

Question 7

what are the changes/ differences in blood pressure throughout the vascular system (blood pumping through the heart to the different circuits)

Answer 7

the systemic and pulmonary circuits exhibit differences in blood pressure because

• there is a difference in the total length of blood vessels in each circuit
• force of contraction generated by the ventricles is different between left and right
• blood pressure in either circuit is greatest in the large arteries closest to the ventricles, and then the pressure diminishes as the blood flows further from the heart.
• the pressure gradient influences velocity of blood flow. blood flows faster the greater the difference in pressure between the 2 points .

Question 8

what homeostatic mechanisms regulate systemic blood pressure when it rises

Answer 8

high blood pressure is detected by baroreceptors which send a signal to the cardiovascular centre in the medulla oblongata. the cardiovascular centre responds by decreasing sympathetic signals or increasing parasympathetic signals to
- SA and AV nodes to reduce heart rate
- blood vessels to allow vasodilation
reducing heart rate will drop the CO and vasodilation will reduce the TPR, decreasing blood pressure.
- release of ANP which enhances vasodilation and stimulates diuresis, reducing blood volume and therefore stroke volume and CO

Question 9

what is tissue perfusion

Answer 9

tissue perfusion refers to the blood flow through the capillary beds of body tissues and is reliant on adequate blood volume and blood pressure to deliver enough blood to body tissues

Question 10

what factors regulate or impact tissue perfusion

Answer 10

• sufficient blood volume circulating through the capillary bed based on tissue needs
• adequate time for substances to move between the blood and body tissues

Question 11

what are the different pressures acting on capillaries

Answer 11

hydrostatic pressure- water to move out of the capillary

osmotic pressure- water to flow into the capillary

Question 12

what is the resultant diffusion of water and solutes through capillaries

Answer 12

gases and liquids flow due to a pressure gradient; from high pressure to low pressure

Question 13

what do arteries do

Answer 13

• they carry blood away from the heart towards the body tissues
• they contain all 3 blood vessel layers
• there are 3 types; elastic arterioles, muscular arterioles and arterioles
• high resistance vessels due to thick walls and small lumens

Question 14

what are venules and veins

Answer 14

• venules drain blood away from body tissues into larger veins which transports blood back to the heart
• have all 3 blood vessel layers but the tunica media and tunica externa are much thinner than those of arteries, giving veins a larger diameter
• they have valves which prevent the black flow of blood
• low resistance vessels due to thin walls and larger lumens

Question 15

how does a respiratory pump help blood flow through the venous system back to the heart

Answer 15

the process of breathing alternately increases and decreases abdominal pressure- increasing the pressure against blood vessels in the abdomen, squeezing them and forcing blood in the veins to move towards the heart

Question 16

how does the muscular pumps help blood flow through the venous system back to the heart

Answer 16

when skeletal muscles contract, they also squeeze nearby blood vessels helping to force blood to flow through the veins.

Question 17

how does the sympathetic nervous system help blood flow through the venous system back to the heart

Answer 17

sympathetic innervation of the tunica media of the veins stimulates vasoconstriction, reducing the diameter of the veins and increasing vascular resistance, and consequently blood pressure- facilitating an increase in the pressure gradient to better drive blood back towards the atria

Question 18

how does RAAS (renin-angiotensin aldosterone system) help blood flow through the nervous system back to the heart

Answer 18

it stimulates vasoconstriction to increase vascular resistance and therefore blood pressure to help return blood to the heart

Question 19

what homeostatic mechanisms regulate systemic blood pressure when is falls

Answer 19

low blood pressure results in decreased baroreceptor signalling to the CV center and is also detected by specialised cells of the kidneys. the CV center responds by decreasing parasympathetic signals or increasing sympathetic signals to
- SA and AV nodes to increase heart rate
- myocardium to increase ventricular contractility
- blood vessels to cause vasoconstriction
- adrenal glands to release catecholamines
increasing heart rate contractility increases SV and an increase in both HR and SV increases CO. vasoconstriction increases TRP, therefore BP is increased
- in the kidneys, low blood pressure activates RAAS which results in
- vasoconstriction
- increased sodium and water reabsorption at the kidneys which increases blood volume, therefore increasing SV and CO

Question 20

velocity of blood flow

Answer 20

the velocity at which blood flows through the heart is important as it determines how much time there is for adequate gas, nutrient and waste exchange. it is determined by

• the difference in pressure- the greater the difference, the faster the blood will flow (and vice versa)
• cross sectional area- the total area through which the blood must flow. the greater the cross sectional area, the slower blood will flow (and vice versa)

Question 21

regulation of blood volume through capillaries

Answer 21

the blood available to flow through tissue capillaries is dependant on cardiac output, but local mechanisms can auto regulate to further adapt blood flow through body capillaries, based on the needs of body tissues at any given time

Question 22

what is autoregulation

Answer 22

the ability of body tissues to regulate their own blood flow through the release of local substances affecting local vascular resistance.
- substances released may cause either vasodilation or vasoconstriction of arterioles and may act on the pre capillary sphincters, to alter the amount of blood flowing through the tissues capillary beds at any given time

Question 23

cardiac output with blood volume

Answer 23

cardiac output changes with body needs, through changes in heart rate and stroke volume

Question 24

cardiac output with blood volume

Answer 24

cardiac output changes with body needs, through changes in heart rate and stroke volume. autoregulation and CO will alter the distribution of minute blood volume throughout the body, dependant on individual tissue needs

Question 25

capillary fluid exchange process.

Answer 25

capillary walls have tiny pores that allow water and small solutes to pass between the pores, into and out of the blood vessel. they do not allow protein to pass through. blood pressure (hydrostatic pressure) cause water to move out of the capillary and osmotic pressure which causes water to move into the capillary. at the arteriole end of the capillary bed blood is of high pressure because it has come from the heart. fluid is forced out of the blood, leaving solutes behind which increases the solute concentration of the blood. at the capillary end, blood pressure (hydrostatic pressure) is low because blood has been diverted from the arteriole to many capillaries. solute concentration is high . because osmotic pressure is higher than blood pressure, fluid moves back into the capillaries and the blood becomes dilute.. mid way along the capillary, the 2 forces cancel each other out and there is no net movement of water and solutes diffuse according to their concentration gradient.