Physiology Of Microcirculation And Lymphatics

Question 1

What makes up the microvascular bed

Answer 1

Terminal arterioles, capillary bed and the post capillary venules

Question 2

Thoroughfare channels vs true capillaries

Answer 2

Both are found in the capillary bed within the microvascular bed

Thoroughfare = larger arterioles that have continuous flow

True capillaries = smaller capillary where blood flow is intermittent these focus more on nutrient and gas exchange)

Question 3

At rest, how many capillary beds are fully open?

Answer 3

25%

this number increases during exercise to meet metabolic needs of muscles

Question 4

Pericytes

Answer 4

Cells found around some capillaries which control vasoconstriction and vasodialation through contractile filaments

Question 5

General make up of capillary walls

Answer 5

1-3 endothelial cells connected w/ tight junctions

• usually are 50 micrometers in length, 0.2 micrometers thick and 8-10 micrometers in diameter

Question 6

3 groups of capillaries

Answer 6

Continuous

Fenestrated

Discontinuous

Question 7

Continuous capillaries

Answer 7

Most common form of capillary

Have no gaps or fenestrations, but do possess clefts (except in BBB)

Found in

• lymph nodes
• all muscles
• the CNS

Function

• feed BBB
• lymphocyte homing
• metabolic exchange

Question 8

Fenestrated capillaries

Answer 8

Have thin perforated walls with very small circles with a diaphragm called fenestrations

Found in

• endocrine glands
• GI
• choroid plexus
• kidney glomeruli

Function:

• secretion
• absorption
• filtration

Question 9

Sinusoidal (discontinuous) capillaries

Answer 9

Rarest type of capillaries

Have fenstrations and large gaps between endothelial cells

Found in

• liver
• bone marrow
• spleen

Functions:

• promote haematopoesis
• filter blood cells
• exchange particles

Question 10

Structural characteristics of capillary flow

Answer 10

Decreased blood pressure compared to other vessels
- lack resistance due to structure

Decreased blood velocity

Increased exchange surface are
- occupy the most surface area of all vessels

Possess vasomotion

all allow for sufficient surface area and time for efficient exchange of gases and nutrients

Question 11

Epinephrine vaso effects

Answer 11

Small doses produce vasodilation

Large doses produce vasoconstriction

norepinephrine elicits only vasoconstriction regardless of doseage

Question 12

Endocrine and neural mechanisms that increase peripheral resistance (vasoconstriction)

Answer 12

Epinephrine/norepinephrine

Angiotensin- 2

Increased renin secretion

Sympathetic activity

Question 13

Endocrine and neural mechanisms that decrease peripheral resistance (vasodialate)

Answer 13

Decreased renin secretion

Parasympathetic innervation

Question 14

Laplace law

Answer 14

Describes the relationship of tension in vessel wall with respect to transmural pressure.

T = (change in pressure) x (radius)

change in pressure is (intravascular pressure - tissue pressure)

Question 15

Ways that material are exchanged across the capillary wall

Answer 15

Pinocytosis (larger molecules such as proteins)

Bulk flow via junctions and fenstrations via blood pressure (mild-moderate molecules that aren’t lipid soluble)

Diffusion via junctions “facilitated diffusion” (for small molecules and gasses that aren’t lipid soluble)

Diffusion directly through cells (gasses that are lipid soluble)

Osmosis ( water only)

Question 16

What are starling force pressures

Answer 16

Capillary Hydrostatic pressure (Blood pressure)

tissue Interstitial pressure (plasma protein content)

Capillary oncotic pressure

these forces determine the rate of blood flow through the capillary wall

Difference between hydrostatic pressure and osmotic pressures = net pressure

Question 17

Difference between hydrostatic and osmotic pressures

Answer 17

Hydrostatic

• due to fluid pushing against a boundary
• “pushes” the fluid across the boundary
• caused by blood pressure in blood vessels

Osmotic

• due to non diffusable solutes that cant cross a boundary
• “ pulls” the fluid towards the solute to even it out
• caused by plasma proteins in blood vessels

Question 18

Startling forces equation

Answer 18

JV = Kf x Pnet

• Kf = hydraulic conductance (water permeability of the capillary wall)
• Pnet = net pressure (difference of hydrostatic pressures vs oncotic pressures)

Question 19

What does excess filtration cause?

Answer 19

Edema
- due to inability to recover filtered fluid and can in return compromise preload and compromise LV preload

Causes 2 changes in body pressures

1) increases capillary hydrostatic pressure (BP)
- can lead to heart failure

2) decreases oncotic pressure or plasma proteins
- can leads to liver failure or kwashiorkor disease

Question 20

Precapillary sphincters

Answer 20

Found between true capillaries and metarterioles

- control amount of blood flowing into capillaries

Question 21

What does histamine do to the starling forces?

Answer 21

Increases permeability of capillaries to proteins = increases interstital colloid osmotic pressure
- causes fluid to move out of capillaries easier

Also increases hydraulic conductance

Question 22

What happens if JV is >0? What happens when it is <0?

Answer 22

JV> 0 = filtration from capillary to interstitial tissue

JV < 0 = resorption from interstital tissue to capillaries

Question 23

When does interstitial fluid move into lymphatic freely

Answer 23

When the pressure in the interstitum is greater than the pressure in the lymphatic

fluid always moves from high -> low concentrations of pressure

Question 24

What is the most common cause of interstital fluid accumulation?

Answer 24

Excessive capillary fluid filtration

Question 25

Three conditions that from intracellular edema

Answer 25

Hyponatremia

Depression of metabolic systems

Lack of nutrition to cells

Question 26

Two conditions that causes extracellular edema

Answer 26

Abnormal leakage of fluid from plasma into interstitial spaces

Failure of lymphatic is to return fluid from interstitium back into the blood

Question 27

What drugs may cause edema? What drugs cure it?

Answer 27

Cause:

• steroids
• estrogens
• CCBs
• NSAIDs
• thiazolidinediones

Cure:
- diuretics (flurosemide)

Question 28

Jugular vein distention (JVD)

Answer 28

Occurs when central venous pressure is above the normal level

If JVD does not fall when inspiration occurs = Kussmaul’s sign and usually indicative of constrictive pericarditis