Unit IV (14-24) - The circulation

Question 1

What is the effect of vasodilation on peripheral vascular resistance?

Answer 1

Decreased peripheral vascular resistance

Question 2

Increase in which of the following most likely stimulates growth of vessels in a solid tumor? 
A. Plasma glucose concentration
B. Growth hormone
C. Vascular endothelial growth factor
D. Tissue oxygen concentration

Answer 2

C. VEGF

Ch. 17 p.209-210

Question 3

How is the velocity of blood flow calculated?

Answer 3

v=F/A

Question 4

What is the average functional pressure in most vascular beds?

Answer 4

17mmHg

Question 5

What is Ohm’s law?

Answer 5

F = pressure change / resistance

Question 6

How is the tendency for turbulent blood flow measured? How is it calculated? At what level does turbulent flow occur?

Answer 6

Reynolds’ number
Re = v x diameter x density / viscosity
200-400 (branches)
2000 (everywhere)

Question 7

What is conductance?
How is it calculated?

Answer 7

Measure of blood flow through a vessel for a given pressure difference
C = 1/R

Question 8

What is Poiseuille’s law?

Answer 8

F = (pi x pressure change x radius^4)/(8 x viscosity x length)

Question 9

Does arterial pressure affect blood flow? Why?

Answer 9

No. Increase in AP initiates compensatory increase in vascular resistance, reduction initiates decreased VR - blood flow autoregulation

Question 10

How is vascular wall tension calculated?

Answer 10

Laplace law
T = pressure change x (r/wall thickness)

Question 11

What physical force is most important for development and adaption of the vascular system?

Answer 11

Shear stress

Question 12

How is vascular distensibility calculated?

Answer 12

VS = increase in volume / (increase in pressure x original volume)

Question 13

How does the distensibility of veins and arteries differ?

Answer 13

Veins 8x more distensible than arteries

Question 14

How is vascular compliance calculated?

Answer 14

Vascular compliance = increase in volume / increase in pressure

Question 15

How can pulse pressure be calculated?

Answer 15

PP = stroke volume / arterial compliance

Question 16

What is normal RAP?

Answer 16

0mmHg

Question 17

What could cause a RAP of 20-30?

Answer 17

CHF
Massive transfusion

Question 18

What are the constituents of the intestitium?

Answer 18

Collagen fibre bundles
Proteoglycan filaments

Question 19

What is the normal % of free fluid in the interstitium?

Answer 19

<1%

Question 20

What are the theories that explain acute control of tissue blood flow?

Answer 20

Vasodilator theory - adenosine, CO2, ADP, histamine, K+, H+ - cause dilation of met arterioles and pre-capillary sphincters
Oxygen demand theory - oxygen required for muscle contraction, O2 deficiency = muscle relaxation

Question 21

What are the two theories that explain auto regulation of blood flow during changes in arterial pressure?

Answer 21

Metabolic theory - vasodilators washed out => vasoconstriction
Myogenic theory - stretch induced vascular depolarisation and contraction

Question 22

How is acute blood flow regulation different in the brain?

Answer 22

CO2 concentration and H+ play prominent roles in addition to O2

Question 23

What is the most important endothelial derived vasodilator?

Answer 23

Nitric oxide (NO)

Question 24

How is NO produced?

Answer 24

By endothelial-derived nitric oxide synthase, from arginine and O2

Question 25

What is the half life of NO?

Answer 25

6 seconds

Question 26

How does NO cause vasodilation?

Answer 26

Activates guanylate cyclases in vascular smooth muscle - converts cGTP => cGMP - activates cGMP-dependent protein synthase

Question 27

What stimulates NO production?

Answer 27

Shear stress AngII

Question 28

What is the mechanism of action of sildenafil?

Answer 28

PDE-5 inhibitor PDE degrades cGMP, inhibition prolongs action of NO

Question 29

What is the main locally produced vasoconstrictor? What stimulates its production?

Answer 29

Endothelin Released from damaged endothelium

Question 30

What are the 4 vascular growth factors?

Answer 30

VEGF FGF PDGF Angiogenin

Question 31

What determines the vascularity of a tissue?

Answer 31

Its maximum blood flow need

Question 32

What are the humoral vasoconstrictors? Where are they secreted?

Answer 32

Norepinephrine Epinephrine SNS activation - from nerve endings and adrenal medullae Angiotensin II - RAAS activation Vasopressin (ADH) - posterior pituitary

Question 33

What are the humoral vasodilators? Where are they secreted?

Answer 33

Bradykinin - produced from alpha2-globulins in plasma by kalikrein - activated by maceration of blood and tissue inflammation Histamine - mast cells in damaged tissue

Question 34

What are the effects of increased concentrations of the following on vascular tone? a - Ca b - K c - Mg d - H+ e - Acetate/citrate f - CO2

Answer 34

a - vasoconstriction b - vasodilation c - vasodilation (+++) d - vasodilation e - vasodilation f - vasodilation (marked in brain)

Question 35

Describe the anatomy of the SNS

Answer 35

Sympathetic vasomotor nerves leave the spinal cord through all thoracic and first 2 lumbar spinal nerves, pass into sympathetic chains. Pass to sympathetic nerves and peripheral portions of spinal nerves

Question 36

Describe the structure of the vasomotor centre?

Answer 36

1. Vasoconstrictor area (acts on all levels of the spinal cord) 2. Vasodilator area (inhibits VCA) 3. Sensory area (input from vagus/GP nerves - controls VCA and VDA)

Question 37

What is the sympathetic vasoconstrictor neurotransmitter? Where does it act?

Answer 37

NEpi Alpha-adrenergic-r of vascular SM

Question 38

How does SNS activation affect the circulation?

Answer 38

1 - arterioles contracted => ^TPR => ^ABP 2 - veins constricted => ^SV 3 - direct adrenergic stimulation of heart

Question 39

Where are baroreceptors found?

Answer 39

Carotid arteries and aortic arch

Question 40

How are signals transmitted from the different baroreceptors?

Answer 40

Carotid arteries => Hering's nerves => GP nerves => nucleus tractus solatarius (brainstem) Aortic arch => vagus nerve => NTS (medulla)

Question 41

What is the effect of baroreceptor stimulation?

Answer 41

Inhibits vasoconstrictor centre Excites vagal parasympathetic centre Causes vasodilation, decreased HR and force of contraction

Question 42

Are baroreceptors important in long term regulation of arterial pressure?

Answer 42

No - reset after 1-2 mins However, may influence sympathetic nerve activity of the kidneys

Question 43

Where are the chemoreceptors?

Answer 43

Carotid and aortic arch

Question 44

What activates the chemoreceptors?

Answer 44

Low O2, high CO2/H+

Question 45

When are the chemoreceptors important?

Answer 45

At lower pressures than baroreceptors

Question 46

How do the atrial and pulmonary artery reflexes affect arterial pressure?

Answer 46

Low pressure receptors Minimise arterial blood pressure change after blood loss

Question 47

What is the volume reflex?

Answer 47

Stretch of atria activates low pressure atrial receptors => reduced renal sympathetic nerve activity => decreased tubular reabsorption and afferent arteriole dilation Signals also transmitted to hypothalamus to reduce ADH Results in increased fluid loss

Question 48

What is the Bainbridge reflex?

Answer 48

Atrial pressure increase = increased HR

Question 49

What is the CNS ischaemic response?

Answer 49

When blood flow to brain reduced enough to cause ischaemia, vasoconstrictor centre becomes strongly excited Increase in BP Vasoconstriction so intense some peripheral vessels totally occluded

Question 50

How does anaemia impact cardiac output?

Answer 50

Anaemia => peripheral vasodilation + reduced blood viscosity => reduced TPR => increased CO

Question 51

What factors influence venous return?

Answer 51

RAP Degree of filling of the systemic circulation Resistance to blood flow between peripheral and RA

Question 52

What factors increase mean circulatory filling pressure?

Answer 52

Increased blood volume SNS stimulation

Question 53

What is the formula for calculating venous return?

Answer 53

VR = Pdf - PRA / RVR

Question 54

Which blood vessel receptors are associated with vasodilation and vasoconstriction?

Answer 54

Alpha - constriction Beta - dilation

Question 55

Following cardiac infarction, what 4 factors contribute to the risk of fibrillation?

Answer 55

1 - potassium depletion and accumulation in the ECF - increases irritability 2 - ischameia causes injury current 3 - SNS stimulation 4 - ventricular dilation => circus movements

Question 56

What is the MOA of digitalis?

Answer 56

Increase calcium in muscle fibres by inhibition of Na-K ATPase = ^Intracellular Na = slowing of Na-Ca exchanger

Question 57

What 4 effects do SNS stimulation have on fluid balance?

Answer 57

1 - Constriction of renal afferent arteriole = water retention 2 - Activation of alpha-adrenergeric receptors on tubular epithelial cells => na/H2O retention 3 - stimulation of renin release 4 - Stimulation of ADH release

Question 58

Where are a) ANP and b) BNP released from? What are their effects?

Answer 58

a - atria b - ventricles Increase na excretion

Question 59

What are the 3 stages of circulatory shock?

Answer 59

1 - nonprogressive 2 - progressive 3 - irreversible

Question 60

What mechanisms engage in nonprogressive shock?

Answer 60

Baroreceptor reflex CNS ischaemic response Reverse stress relaxation of the circulatory system RAAS activation ADH secretion Increased epinephrine and norepinephrine secretion

Question 61

In which kinds of shock is sympathomimetic therapy valuable?

Answer 61

Neurogenic and anaphylactic