Vasculature, Arterial Blood Flow and Peripheral Resistance

Question 1

Laminar fluid flow

Answer 1

Vessels lined with endothelial cells
Fluid molecules touching wall adhere move slowly 
– Next layer slips over these
• Next layer over these...
–Middle most layers move the most rapid

Question 2

Turbulence

Answer 2

disrupts flow, increases resistance.

• Poiseuille’s law doesn’t hold true during turbulence

Question 3

Reynold’s number (Re)

Answer 3

used to indicate whether flow is laminar or turbulent.

Question 4

Re increases with

Answer 4

– High velocity flow
– Large diameter vessels
– Low blood viscosity
– Abnormal vessel wall

Question 5

Thixotropic fluids

Answer 5

Flow affects viscosity

– Static blood has 100x the viscosity of flowing blood

Question 6

Korotkoff sounds

Answer 6

Artificially generated turbulence

– Ausculatory measurements using a sphygnomanometer cuff

Question 7

LaPlace’s Law

Answer 7

Distending pressure (P) produces an opposing force or tension (T) in the vessel wall, proportional to the
radius (R) of the vessel

Question 8

Practical consequences of LaPlace’s Law - control of blood flow

Answer 8

– Low tension required to oppose blood pressure in arterioles
– Smooth muscle control of arteriole and precapillary sphincters are
the sites of tissue blood flow regulation

Question 9

Practical consequences of LaPlace’s Law - capillaries

Answer 9

– Can be extremely thin and still withstand the pressure

– Thin walls essential for exchange processes

Question 10

Practical consequences of LaPlace’s Law - Aneurysm

Answer 10

rupturing of a blood vessel, can’t oppose the pressures within so the region expands and becomes weakened and can’t create the same tension so stretches and bulging occurs (radius then increases and gives brief normalisation of pressure but this quickly balances out) and then ruptures (blows up)

Question 11

Regulation of blood flow - arterioles

Answer 11

– Control regional distribution (Local and extrinsic controls)

Question 12

Regulation of blood flow - Metarterioles

Answer 12

– Links arterioles to venules, discontinuous smooth muscle

Question 13

Regulation of blood flow - Precapillary sphincters

Answer 13

– When a true capillary branches from a metarteriole

– Vasodilation produced by local factors

Question 14

tissue blood flow - Vasomotion

Answer 14

– Spontaneous oscillating contraction of blood vessels

Question 15

tissue blood flow - Active and reactive hyperemia

Answer 15

– Local factors associated with metabolic activity of tissues

ACTIVE
– If tissue is highly active, the rate of flow will increase
– E.g.byupto20xin skeletal muscle

REACTIVE
– When blood supply blocked (few s to h)
– Blood flow increases to 4-7x normal

Question 16

tissue blood flow - Flow autoregulation

Answer 16

– In response to changes in arterial pressure
• Arterial pressure↑, arterioles constrict to reduce flow •Arterial pressure↓, arterioles dilate to increase flow
– Myogenic response
• Stretch-activated Ca2+channels

Question 17

tissue blood flow - Response to injury

Answer 17

– E.g. endothelin-1 released from endothelial cells •Potent vasoconstriction

Question 18

Role of the endothelial cells in regulating vascular tone

Answer 18

Nitric oxide vasodilator

Question 19

Local vasoconstrictor

Answer 19

myogenic response

endothelian 1

Question 20

local vasodilator

Answer 20

decrease in o2, potassium and carbon dioxide and hydrogen
adenosine
nitric oxide
bradykinin

Question 21

neural vasocontrciter

Answer 21

sympathetic nerve s

Question 22

neural vasodilator

Answer 22

no releasing nerves

Question 23

hormonal vasoconstrictor

Answer 23

adrenaline
angiotensin II
vasopressin

Question 24

hormonal vasodilator

Answer 24

adrenaline

atrial - natriuretic peptide

Question 25

Blood flow through capillaries

Answer 25

s intermittent, turning on/off every few seconds or minutes

– At rest, only ~5% of total cardiac output is in the capillaries

Question 26

Acute regulation of local blood flow

Answer 26

– Rapid changes within seconds or minutes
– Vasodilator theory widely accepted (“local factors”)
• E.g.↑PCO2,↓PO2,↑H+,↑K+,↑lacKcacid,↑adenosine,↑ histamine

Question 27

Long term regulation of local blood flow

Answer 27

– Change in physical size or number of blood vessels

Question 28

Specialised flow (lungs)

Answer 28

Decreased alveolar O2 reduces local alveolar blood flow
– Opposite to effect observed in systemic vessels
– Mediator unknown