B1W4: Capillaries/Local Control Blood Flow

Question 1

Components microcirculation

Answer 1

• Arterioles and venuoles with smooth muscle
• precapillary sphincters
• metaarterioles–smooth muscle cells around capillaries

Question 2

Flow in capillaries

Answer 2

Intermittent due to vasomotion (opening/closing of spinchters, contracting); tissue O2 determines this

Question 3

Lymphedema

Answer 3

Edema from tumor restricting blood flow back from veins and causing increasing P

Question 4

Structure of capillary wall

Answer 4

1. slit pores that allow hydrophillic molecules in
2. plasmalemmal vesicles for bigger hydrophillic proteins (at caveolae)
3. endothelium and basement membrane for lipophillic molecules to go through
4. fenestrae/aquaporins for H2O

Question 5

Rate of Flow Determinants

Answer 5

• conc. gradient
• surface area (if capillaries opened or closed)
• diffusion coefficient
  
  • dependent on orga; brain has tight junctions, liver lets anything in, intestines are in the middle and kidney, with fenestrae, lets ionic substances in

Question 6

Components of interstitum between capillaries and cells

Answer 6

• Collagen fiber bundles
• Proteoglycan filaments
• Tissue gel that becomes free fluid in edema

Question 7

Four Capillary Pressures (Starling Forces)

Answer 7

• Capillary pressure (PC): OUT capillary
• Interstial fluid pressure (PiF): IN capillary, normally neg. though and does opp.
• Interstial fluid colloid osmotic pressure (πiF): OUT capillary
• Plasma colloid osmotic pressure (πP): IN capillary, albumin

Question 8

Calculating Net Filtration

Answer 8

(add forces moving out) - (add forces moving in) = net filtration

If answer +: net moving out

If answer -: net moving in

Question 9

Net filtration in body

Answer 9

2 mL/min at .3 mmHg

Lymph catches and restores it so we don’t get edema, up to a point

Question 10

Factors increasing lymph flow

Answer 10

1. elevated capillary pressure
2. decreased plasma COP (drinking too much, liver can’t work)
3. Increased interstial fluid COP
4. Increased permeability capillaries (allergic reactions)
5. Lymph pump

Question 11

Types of local, short-term regulation of blood vessels

Answer 11

• Metabolic autoregulation
• Functional hyperemia
• Reactive hyperemia
• Myogenic autoregulation
• Shear stress regulation

Question 12

Metabolic autoregulation

Answer 12

Maintaining constant blood flow under constant metabolism due to an increase or decrease in pressure

–increase BP, vesels constrict

–decrease BP, vessels dilate

Question 13

Functional hyperemia

Answer 13

Metabolism increases, we need more O2 so we increase blood flow

Intrinsic response

Question 14

The only two ways to increase blood flow using the vessels

Answer 14

1. increase pressure gradient
2. decrease resistance (i.e. dilating)

Question 15

Which organs have the most cardiac output?

Answer 15

Kidneys

Liver

Brain

Skin (thermoregulation–when hot)

Question 16

Metabolic autoregulation theory 1: waste products

Answer 16

If blood flow is too low (i.e. a block upstream), metabolic waste products start to build up and THIS is what the vessel senses it needs to dilate for

Needs to wash these out

i.e. K+, lactic acid, H, CO2, adenosine

Question 17

Metabolic autoregulation theory 2: O2

Answer 17

Due to an occlusion upstream, vessel senses it needs O2 so it dilates

When the blood pressure is getting low, senses it has too much O2, constricts

Both of these maintain blood flow as constant even as pressure changes

Question 18

Reactive hyperemia

Answer 18

Excess tissue flow following occlusion, causing overshoot of blood due to repaying of oxygen debt

–this overshoot is proportional to amount of time the vessel was occluded for

i.e. pushing down on fingers, get white, let go and blood rushes back

Question 19

Raynaud’s phenomenon

Answer 19

Fingers blanch and become numb in coldness

During rewarming, digits become bright red and hurt!

The low blood flow and deoxygenation leads to an overshoot of blood flow, aka reactive hyperemia

Primary: unknown, idiopathic cause

Secondary: scleroderma

Question 20

Myogenic autoregulation

Answer 20

Common in small arterioles

Intrinsic regulation based on stretch of walls due to flow

Not densing flow directly; blood pressure increasing and therefore wall constricts to stop it and keep flow constant

Question 21

Shear stress regulation

Answer 21

NO produced, causing vasodilation

• made from L argininge and activates guanylyl cylase, which makes cGMP (vasodilator)

Question 22

LaPlace’s Law

Answer 22

Wall tension=pressure x radius

Increase radius, increase tension

Hypertrophy occurs (radius increases) in response to increased tension