Control of blood flow

Question 1

What is Atherosclerosis

Answer 1

Atheroscelerosis- build up of fat in the blood vessels which can reduce blood flow to the heart

Question 2

What is the equation for flow in Darcy’s law

Answer 2

Flow= Arterial pressure (Pa)/ Central venous pressure (CVP) x Total peripheral resistance (TPR)

Question 3

What does TPR control

Answer 3

TPR controls blood flow and blood pressure
-increase in resistance means need to increase pressure to keep same flow.

Question 4

What controls TPR?

Answer 4

-Darcy and Poisuelle’s laws
-myogenic response (reflexive contraction)
-blood viscosity

Question 5

What is the equation for the G (conductance is the reciprocal of TPR)

Answer 5

G= 1/ TPR

Question 6

What is the equation for the combined flow equation and G equation

Answer 6

Flow= Pa - CVP x G

Question 7

Explain the relationship with normal blood flow with TPR in blood vessels

Answer 7

In the artery, if there is normal BP this will cause normal TPR in the arterioles and will result in normal flow in the capillaries.

-In the artery, if there is a lower BP this will cause decreased TPR in the arterioles so can lead to vasodilation and increased flow in the capillaries

-In the artery, if there is increased BP this will cause an increased TPR in the arterioles so there is vasoconstriction. Therefore there is decreased flow in the capillaries.

Question 8

What does Sedentary brain stem area do for blood flow

Answer 8

Sedentary- involved in the resting process and causes vasodilation

Question 9

What does superior mesentric do

Answer 9

Superior mesenteric which increases flow to the intestines by dilating blood vessels

Question 10

What does the common iliac do

Answer 10

Common iliac causes vasoconstriction of blood vessels causes decreased flow to the legs

Question 11

Explain what the superior mesenteric does whilst exercising

Answer 11

Superior mesenteric, causes vasoconstriction so decreased flow to intestines

Question 12

What does the common iliac do when exercising

Answer 12

common iliac causes vasodilation so increased flow to the legs

Question 13

What is the equation for total peripheral resistance in Poiseuille’s law

Answer 13

TPR= 8 x blood viscosity (h) x Length (L)/ 3.814 x radius of vessel (r)^4

Question 14

What is the equation for conductance

Answer 14

Conductance (G)= 3.814 x r^4/ 8 x blood viscosity (h) x length (L)

Question 15

Explain the r4 effect (radius effect)

Answer 15

Vasocontriction or dilators produce small changes in vessel radius by affecting smooth muscle have large effects on blood flow

Question 16

What is arteriole radius is tightly controlled by

Answer 16

Arteriole radius is tightly controlled by sympathetic nerves providing constant time dilation vs constriction

Question 17

What is TPR controlled by?

Answer 17

TPR is controlled by 3 main parameters:

1) Radius (r4)
2) Pressure difference across vessels (P1-P2)
3) Length (L) arterioles are also long vessels

Question 18

Capillaries have a much smaller radius than arterioles so why do arterioles control TPR?

Answer 18

Capillaries are arranged in parallel formation so have low total resistance. In contrast arterioles are in a series so total resistance is greater

Question 19

What is local blood flow controlled by

Answer 19

local blood flow through individual organs/tissues is mainly controlled by changes in radius of arterioles supplying a given organ/tissues.

Question 20

What are control mechanisms of arteriole radius?

Answer 20

Control mechanisms of arteriole radius:

Intrinsic- factors entirely within an organ or tissue:
-tissue metabolites
-local hormones
-myogenic properties of muscles
-endothelial factors (NO which causes vasodilation)
-hormonal

Extrinsic- factors outside the organ or tissue:
-neural (sympathetic nervous system)
-hormonal (e.g. adrenaline)

Question 21

What is distension

Answer 21

Distension- refers to the act of expanding or swelling due to internal pressure.

Question 22

Explain Bayliss myogenic response

Answer 22

This refers to increased distension of a vessel- causing vasoconstriction and vice versa.
Having a linear relationship would entail very large differences in blood flow with differences in pressure.
Maintains blood flow at the same level during changing arterial pressures.
Stretching of the vessel causes ion channels to open (which then depolarise) leading to smooth muscle contraction

Question 23

What does blood flow depend on

Answer 23

Blood flow depends on:
1) Viscosity of blood
2) Vessel diameter
3) Haematocrit

Question 24

What is the definition of viscosity

Answer 24

viscosity- a measure of internal friction opposing the separation of the lamina

Question 25

What is the equation for flow linking blood viscosity

Answer 25

flow= Arterial pressures - Central venous pressure x 3.148 x radius^4/ 8 x blood viscosity x vessel length

Question 26

What are the clinical implications of haemotocrit

Answer 26

Clinical implications: -polycythaemia (high viscosity)- increased TPR + BP and decreased flow -anaemia (low viscosity)- low TPR and BP. High HR

Question 27

What are the clinical implications of tube diameter

Answer 27

Clinical implications: -blood viscosity falls in narrow tubes, cells move to centre reducing friction -decreased resistance, increased flow

Question 28

What are the clinical implications for reduction in red cell deformability

Answer 28

Clinical applications: -Increased blood viscosity, reduced flow

Question 29

What are the clinical applications for the velocity of blood

Answer 29

Clinical applications: -slow venous flow in immobile legs -increased viscosity due to partial clotting

Question 30

Explain characteristics of the veins

Answer 30

Veins: -thin walled, collapsible, voluminous vessels -contains 2/3rd of blood volume -contractile- contains smooth muscle, innervated by sympathetic nerves but thinner arterial muscle and more compliant

Question 31

Explain the volume of blood in veins and contractility

Answer 31

Contraction of vessels- expels blood into central veins: -increases venous return -increases stroke volume

Question 32

Explain venous pressure at different parts of the body

Answer 32

Venous pressure high at the feet so pressure for blood return to the heart. This is helped by thoracic pump, skeletal muscle contraction and one way valves

Question 33

What happens to veins when there is very little pressure

Answer 33

when there is very little pressure, veins just fold up and collapse

Question 34

How can sympathetic nerves cause an increase of CVP, diastolic pressure and preload

Answer 34

Stimulation Of sympathetic nerves causing vasoconstriction shifts blood centrally. -increased venous return, CVP and end diastolic pressure -increased CVP increases preload and so increases stroke volume (Starling’s law)

Question 35

Explain Bernoulli’s theory

Answer 35

Bernoulli Theory- mechanical energy of flow is determined by pressure, kinetic, potential energies (e.g. fluid mass)

Question 36

What is the equation for energy in Bernoulli’s law

Answer 36

energy= pressure (P) + kinetic (pV2/2) + potential energies (pgh)

Question 37

Explain arterial blood flow when standing

Answer 37

Pressure gradient against flow from heart to feet. Ejected blood has greater kinetic energy at the heart compared to the feet. -greater potential energy at heart than feet due to greater height so greater kinetic/ potential energies overcome pressure gradient to maintain flow

Question 38

Explain venous return in cardiac output

Answer 38

Cardiac output- the circulation is a closed system- heart pushes blood further through vascular system. This is via the arterial side of the capillary system into the venules and veins

Question 39

Explain venous return through breathing

Answer 39

Breathing- the pressure in the chest is negative on inhalation at the same time- intra-abdominal pressure rises as the diaphragm moves downwards causing the venous valves in the pelvis to close. The blood moves up into the thorax, during exhalation the intra abdominal pressure decreases and the pelvic veins and inferior vena cava refill

Question 40

Explain venous return through muscle pump

Answer 40

Muscle pump- the deep venous system is embedded within the muscles. Every muscle contraction squeezes the veins to push the column of blood in the direction of the the heart. When muscle relaxes, venous valves prevent the retrograde of blood towards the capillaries

Question 41

Explain venous return through venous tone

Answer 41

venous tone- the blood in the veins exerts pressure on the vein’s wall generating tension and maintaining pressure

Question 42

What are 3 types of drugs related to vasoconstriction/ vasodilation?

Answer 42

1) Nitrates 2) ARBs 3) ACE inhibitors

Question 43

Explain what nitrates do

Answer 43

Nitrates: Vasodilators- lower BP

Question 44

Explain what ARBs do

Answer 44

Angiotensin receptor blockers: Prevents vasoconstriction caused by ACE

Question 45

Explain what ACE inhibitors do

Answer 45

Angiotensin converting enzyme inhibitor: -prevents vasoconstriction caused by ACE