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SF3 - Test 1 > 3 - Microcirculation > Flashcards

3 - Microcirculation Flashcards

1
Q

What following substances move across capillary endothelia using the following:

Diffusion

Bulk Flow

Vesicles

Active Transport

A

Diffusion - O2, CO2, lipid-soluble substances (lipid bilayer!)

Bulk Flow - H20, Electrolytes, small molecules

Vesicles - Macromolecules

Active Transport - Ions, small molecules

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2
Q

Equation: What law govern’s movement of a substance via diffusion?

What is the equation?

A

Fick’s First Law of Diffusion (Gases, Lipid-Soluble substances)

J = DA(ΔC/ΔX)

J = Flux (moles/sec)

D = Diffusion constant of specific substance

A = Surface area available for diffusion

ΔC = Concentration gradient

ΔX = Diffusion distance

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3
Q

What are the three types of capillaries?

A

Continuous

Fenestrated

Discontinuous

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4
Q

Where does bulk flow occur?

What substances use this method?

A

Intercellular clefts between endothelial cells

Water, Lipid-soluble, electrolytes

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5
Q

Continuous Capillaries

A

Have very tight endothelium and continuous basement membrane

Reduces bulk flow across capillar

Found in Skeletal muscle, skin, lung, and brain

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6
Q

Fenestrated Capillaries

A

Have perforations (fenestrae) in the endothelium, resulting in relatively high permeability and bulk flow

Example: Exocrine glands, renal globeruli, intestinal mucosa

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7
Q

Discontinuous Capillaries

A

Large intercellular gaps, as well is gaps in basement membrane–highest permeability

Liver, Spleen, Bone Marrow

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8
Q

What two types of transport likely play a smaller role in movement of substances across capillaries?

A

Vesicular Transport (proteins), Active Transport (ions, glucose, amino acids)

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9
Q

What law governs oxygen diffusion?

How can you increase this rate?

A

Fick’s Law of Diffusion: J = DA (ΔC/ΔX)

You can increase capillary blood pO2 (breathe pure oxygen)

You can decrease tissue pO2

You can increase the surface area available for oxygen diffusion (increasing number of flowing capillaries)

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10
Q

What law governs carbon dioxide diffusion?

How does it compare to oxygen?

What does the removal of CO2 from the tissue primarily depend on?

A

J = DA(ΔC/ΔX)

Diffusion constant 20x > Oxygen

Removal depends on blood flow

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11
Q

Transcapillary Fluid Exchange:

Fluid Filtration / Reabsorption

Lymph Flow

What does total filtration equal?

A

A steady state of volume is filtered to interstitium, and returned to vasculature (reabsorbed)

Anything left over is taken up by terminal lymphatics, and transport them to larger lymphatics

Filtration = Reabsorption + Lymph Flow

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12
Q

What physical mechanisms govern fluid exchange?

What are the Starling forces?

A

Hydrostatic and Oncotic Pressure

  1. Capillary Pressure (Pc) - tends to force fluid outward
  2. Interstitial Fluid Pressure (Pi) - Tends to force fluid in through cap. membrane
  3. Capillary Plasma Colloid Osmotic (oncotic) Pressure (πc) - Cause osmosis of fluid inward through cap membrane
  4. Interstitial fluid colloid osmotic (oncotic) pressure (πi) - Tends to cause osmosis of fluid outward through cap membrane

Summary:

Pc/πi = Out

Pi/πc = In

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13
Q

What is the reflextion coefficient?

A

Factor to reprsent the permeability of a capillary to the proteins respnsible for generating oncotic pressure

1 = Impermeable

0 = Freely permeable

0 > a > 1 ; Somewhat permeable

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14
Q

Equation: What is method to calculate net fluid flux?

A

J = Kf x A (NDF)

NDF = (Pc-Pi) - a(πc-πi)

J = Net flux

Kf (constant) = Capillary filtration constant (permeability)

A = Surface area for exchange

NDF = driving force (4 components + constant)

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15
Q

How does filtration constant vary among the different types of capillaries?

What effect does histamine hace on KF?

A

Discontinuous > Fenestrated > Continuous

Increase

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16
Q

What determines capillary hydrostatic pressure? (Pc)

How do changes in this effect capillary hydrostatic pressure?

A

Arterial/Venous Pressure, Precapillary (arterioles) and Postcapillary (venules) Pressure

Increase in Arterial/Venous Pressure = Increase Capillary Hydrostatic Pressure

Increase in Arteriolar Resistance reduces capillary pressure; Increase in Venule Resistance increases capillary pressure

(like a hose, blocking the begininng lowers pressure, blocking the end builds pressure)

17
Q

Provide The Effect on Capillary Pressure of the Following, and provide examples:

Arteriole Dilation

Arteriole Constriction

Venous Dilation

Venous Constriction

Increased Arterial Pressure

Decreased Arterial Pressure

Increased Venous Pressure

Decreased Venous Pressure

A

Arteriole Dilation - Increase - Decreased sympathetics (parasympathetics increase)

Arteriole Constriction - Decrease - Increased Sympathetics

Venous Dilation - Decrease - Increased metabolism of tissue

Venous Constriction - Increase - Physical compression

Increased Arterial Pressure - Increase - Increase C.O.

Decreased Arterial Pressure - Decrease - Hemorrhage/dehydration

Increased Venous Pressure - Increase - Congestive heart failure (blood backing up, not being moved from venous circulation)

Decreased Venous Pressure - Decrease - Hemorrhage/dehydration

18
Q

(Equation) What is interstitial compliance?

What are examples of high vs low compliance?

High = Subcutaneous Tissue

Low = Brain (your brain can’t swell!)

A

C = ΔV / ΔP

Or–slope of these two plotted

ΔPi = ΔVi / C

ΔP = Change in interstitial fluid pressure

ΔV = Change in interstitial fluid volume

C = Interstitial Compliance

(C = ΔV / ΔP )

19
Q

What determines capillary plasma oncotic pressure? (piC)

What determines tissue (interstitial) fluid oncotic pressure? (pi-i)

A

Presence of proteins within the capillary

Albumin generates majority

Interstitial protein concentration

20
Q

What type of substances can enter lymphatic capillaries easily?

A

High MW, like proteins

“Saloon-Door” one way valves allow this to occur

21
Q

What factors can increase lymph flow?

What slows this down?

A

Anything that increases interstitial fluid pressure

  • Elevated capillary pressure
  • Decreased plasma colloid osmotic pressure
  • Increased interstitial fluid colloid osmotic pressure
  • Increased permeability of the capillaries
    • -

Increased compression from more fluid impedes lymph flow

22
Q

What is the Lymphatic Pump?

A

Lymph vessels beyond the terminal lyphatic capillaries surrounded by smooth muscle.

When stretched, the smooth muscle automatically contracts

Major intrinsic for propelling lymph

23
Q

How can external intermittent compression effect lymphatics?

A

Pumping

Contraction of muscles, movement, pulsations of arteries, compression of tissue from outside

very active during exercise

24
Q

Clinical: Edema Formation

A

When fluid in interstitial compartment increases beyond filtration/reabsorption rate

Can result in tissue death, impair gas exchange

25
Q

What are four major categories which cause edema?

A
  1. Increased Capillary Pressure (heart failure, increased blood volume, thrombosis, gravity, hypertension, vasodilation)
  2. Increased Capillary Permeability (vascular damage, burns, trauma)
  3. Decreased Plasma Oncotic Pressure (Malnutrition)
  4. Lymphatic Blockage (Lymphedema) (Tissue injury, parasites)
26
Q

Clinical: Elephantiasis

A

Parasites block lymph collection

27
Q
A

SF3 - Test 1 (28 decks)

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