Regulation of Arteriolar Resistance + pressure and flow

Question 1

How is arterial pressure measured

Answer 1

auscultation of korotkoff (blood flow) sounds using Sphygmomanometer (cuff) and stethoscope

Question 2

Describe what you should hear in a healthy person

Answer 2

at rest - you should not hear anything as should be smooth laminar flow pressure above systolic pressure - silence as blood flow is cut off pressure just below systolic pressure - tapping sound - large obstruction to blood flow pressure below systolic pressure - more blood moving through arteries - more turbulent so longer thumping sounds (less constriction) pressure = diastolic pressure - muffled sounds as the cuff is still constricting the artery a little as pressure decreases below diastolic - normal smooth laminar flow again so should be silence again

Question 3

What is systolic pressure?

Answer 3

pressure of the blood in the arteries when the heart pumps/contracts. It is the higher of the two numbers in the blood pressure.

Question 4

What is diastolic pressure?

Answer 4

pressure in your blood vessels when your heart rests between beats

Question 5

Describe pressure and flow in arteries

Answer 5

elastic arteries act as pressure reservoir as ventricular relaxation occurs, the energy being stored in the walls of the aorta is released and this pushes blood out through the arterioles

Question 6

why would it be hard to push blood through arterioles?

Answer 6

if the arterioles are constricted - increased total peripheral resistance

Question 7

what on average is normal blood pressure values?

Answer 7

120/80 however now looking a bit higher in our current ageing population ie 130/80

Question 8

arterial pressure increases with what?

Answer 8

age and individually

Question 9

describe the variety in pressure within the vascular tree

Answer 9

pressure falls throughout the vascular tree aorta - pressure stays high due to elastic walls retaining it capillaries - very low pressure - thin walled and fragile

Question 10

value for the drop in pressure through arteries

Answer 10

95-90 mmHg

Question 11

value for the drop in pressure through arterioles

Answer 11

90-40 mmHg

Question 12

value for the pressure difference pushing blood back through the veins to the heart?

Answer 12

20 to 5 mmHg

Question 13

what does blood flow depend on?

Answer 13

total cross-sectional area ie aorta has the highest velocity of blood flow but there is only one in the body so it has the lowest cross sectional area along with venae cavae. However there are loads of capillaries in the body so these have the highest total cross-sectional area but lowest velocity of flow - allows time for exchange of gases and nutrients

Question 14

Describe pressure and flow in veins

Answer 14

pressure is low. There is a small decrease in pressure required to push blood back through the veins to the heart. Veins are susceptible to being compressed by pressure but can also expand easily and carry a lot of blood.

Question 15

what external influences can affect blood flow in veins (5)

Answer 15

• gravity
• skeletal muscle pump
• respiratory pump
• venomotor tone
• systemic filling pressure

Question 16

How does gravity affect blood flow in veins?

Answer 16

when you stand up blood is pushed down to your feet due to gravity which increases the pressure there. Blood is sucked out of the brain so blood pressure decreases there. Standing up leads to a decrease in EDV, preload, SV, CO and MAP Gravity causes venous distension (dilatation) in legs and venous collapse in the neck (less blood flows through it - jugular vein shouldn’t be visible)

Question 17

what does gravity not affect?

Answer 17

the driving pressure from arteries to veins

Question 18

what is orthostatic hypotension

Answer 18

low blood pressure that continues after standing up common in the elderly

Question 19

what can the height of jugular vein collapse be used to estimate?

Answer 19

central venous pressure

Question 20

describe pressure and jugular vein

Answer 20

pressure in the vein gets smaller as you go up as gravity is pulling blood down pressure outside the vein is always about 0 so at some point the pressure outside will be higher than inside and this constricts the vein in a healthy person it will collapse below the clavicle

Question 21

why might you see a healthy person’s jugular vein? for example in a footballer celebrating after scoring a goal

Answer 21

higher BP means higher central venous pressure and a higher point of colla[se in the neck so the JV is visible.

Question 22

What is the skeletal muscle pump

Answer 22

mechanism that alters venous blood flow Every time you contract the muscle in your leg it pushes blood out of the vein and this blood gets pushed back towards the heart even though it wouldn’t normally. Increased venous return, preload, EDV

Question 23

in what type of exercise does skeletal muscle pump occur

Answer 23

in rhythmic exercise in static exercise the muscle length doesn’t change - wight lifting

Question 24

why might a person faint?

Answer 24

if blood is sent to periphery as your EDV gets smaller and smaller.

Question 25

What is the respiratory pump

Answer 25

when you inhale you draw more blood back to your heart as your diaphragm contracts and pressure decreases in the thorax. This causes an increase in the pressure gradient that is pushing blood back to the heart.

Question 26

what is venomotor tone?

Answer 26

state of contraction of the smooth muscle surrounding the venules and veins alters blood flow by mobilising capacitance of vessels

Question 27

what is systemic filling pressure?

Answer 27

pressure created by ventricles and transmitted through vascular tree to the veins changes during exercise

It is an indicator of how full the circulatory system is (i.e. the volume of blood in the system compared to the capacity of the system)

influenced by the vol of circulating blood and the smooth muscle tone in the walls of the venous system (which determines the capacity of the system)

Question 28

describe the anti-clotting mechanisms of the endothelium of vessels.

Answer 28

blood flows so slowly through capillaries that it is in danger of clotting so your endothelium has to work hard to prevent inappropriate clotting:-

• 1. It stops blood contacting collagen - no platelet aggregation
• 2. produces prostacyclin and NO which both inhibit platelet aggregation and are vasodilators
• 3. Produces tissue factor pathway inhibitor TFPI which stops thrombin production so will stop fibrin from being produced
• 4. Expresses heparin - also inactivates thrombin - natural anticoagulant
• 5. secretes tissue plasminogen activator (t-PA) - plasminogen turns to plasmin and digests clot

Question 29

define dicrotic notch

Answer 29

a secondary upstroke in the descending part of a pulse tracing corresponding to the transient increase in aortic pressure upon closure of the aortic valve

Question 30

what are the anacrotic and catacrotic limbs?

Answer 30

the ascending and decending parts of pressure wave