Microcirculation

Question 1

What is microcirculation?

Answer 1

Blood flow through the smallest vessels involves capillaries and lymphatic vessels
Transport of nutrients and removal of waste

Question 2

What are the blood vessels involved in microcirculation from the smallest to the largest?

Answer 2

Vena cava
Aorta
small veins
small arteries
arterioles
venules
capillaries

Question 3

What is the structure of capillaries?

Answer 3

single layer of highly permeable endothelial cells
has pores that allow diffusion
 SA= 500-700m2
 Thin walls
 Modest volume- 5% of body’s blood
 Large cross sectional area amongst all the vessels
 Slowest flow velocity- 2cm/min or 0.3mm/s

Question 4

Why is blood flow slowest in capillaries?

Answer 4

so more time for gas and nutrient exchange

Question 5

What is the role of the capillaries?

Answer 5

allow exchanging of solutes and fluid between plasma and interstitial fluid

Question 6

What is starling’s law of filtration?

Answer 6

A law that governs the flow of filtration across the capillaries

Question 7

What 4 parameters are in the starling equation?

Answer 7

Pc= capillary hydrostatic pressure
Pi= interstitial fluid hydrostatic pressure
Pi c= capillary plasma oncotic pressure
Pi i= interstitial fluid oncotic pressure

Question 8

What does the K in Starling’s equation represent?

Answer 8

Filtration coefficient

Question 9

What is the movement of H2O from plasma to interstitial space called?

Answer 9

filtration

Question 10

What is the movement of H20 from interstitial space to plasma called?

Answer 10

absorption

Question 11

What determines the net flow of fluid across a capillary?

Answer 11

The balance of the 4 starling forces

Question 12

Why is the osmotic effect of capillary fluid greater than the osmotic effect of the interstitial fluid?

Answer 12

the capillary fluid/plasma contains more proteins which generates a higher colloid osmotic pressure and attracts more water via osmosis

Question 13

What is colloid osmotic pressure?

Answer 13

osmotic pressure by proteins in blood plasma or interstitial fluid

Question 14

What solutes move across capillary wall by simple diffusion?

Answer 14

O2, CO2, nutrients and metabolites

Question 15

What 2 pathways do the solutes use to move between blood and interstitial fluid?

Answer 15

transcellular

paracellular

Question 16

What is transcellular movement?

Answer 16

simple diffusion through endothelial cells

Question 17

What is paracellular movement?

Answer 17

simple diffusion through tight junctions or gaps of endothelial cells

Question 18

What are the types of transcellular movement?

Answer 18

simple diffusion
facilitated diffusion
transcytosis

Question 19

What are the 3 types of capillary structures?

Answer 19

continuous
fenestrated
discontinuous/sinusoid

Question 20

Describe the structure of a continuous capillary?

Answer 20

endothelial cells tightly held together
tight junctions between cells
continuous basement membrane
presence of intracellular clefts

Question 21

What types of molecules pass through continuous capillary and what route do they use?

Answer 21

small molecules- water, ions

use paracellular route via intercellular clefts

Question 22

Describe the structure of a fenestrated capillary?

Answer 22

small openings in the cells

leaky

Question 23

What route is used to cross fenestrated capillaries?

Answer 23

use fenestrations and intracellular cleft

Question 24

Describe the structure of a discontinuous/sinusoid capillary?

Answer 24

very leaky
endothelial cells held very loosely 
large gaps between cells 
holes in the basement membrane
large intracellular gaps

Question 25

What route is used to cross discontinuous/sinusoid capillaries?

Answer 25

cross through the holes in membrane and intracellular gasp

Question 26

What is the lymphatic systems role?

Answer 26

scavenger system Drains excess fluid, water, ions, glucose, lipid, WBC, protein, large particles and debris from interstitial space back into blood

Question 27

What is the fluid collected from interstitial space called?

Answer 27

lymph

Question 28

What are lymphatic vessels?

Answer 28

smooth muscle

Question 29

What is the role of the lymph nodes surrounding the lymphatic vessels?

Answer 29

immune function- they have lymphocytes which destroy foreign particles and bacteria present in the lymph

Question 30

What allows the one way flow of lymph from tissues to veins?

Answer 30

lymphatic valves

Question 31

Where is lymph collected from?

Answer 31

All body tissue except brain

Question 32

What are lymphatic ducts?

Answer 32

sites at which lymph empties into large veins

Question 33

What is oedema?

Answer 33

- Swelling caused by excess fluid in tissues/interstitial space - Swelling of skin after damage to local capillaries

Question 34

What causes oedema?

Answer 34

High hydrostatic capillary pressure due to HF, blood clot, cardiac failure, deep vein thrombosis imbalance of starling forces Low blood/plasma protein due to liver failure, poor nutrition and burns Lymphatic failure due to damaged lymphatic vessels, infected lymph nodes, protein accumulated in undrained fluid?

Question 35

What is lymphoedema?

Answer 35

accumulation of lymph which obstructs lymph system

Question 36

What cause can lead to peripheral and pulmonary oedema?

Answer 36

HF

Question 37

Describe the MOA of peripheral oedema?

Answer 37

1. Left ventricle dysfunction= abnormal CO 2. MAP falls due to small CO 3. Reflexes triggered to restore MAP- baroreceptors, salt and water retention by kidneys 4. Salt and water retained 5. Plasma vol increases 6. Venous pressure increases 7. Capillary pressure increases 8. Filtration increases 9. Fluid lot from capillaries to tissue= swelling

Question 38

Describe the MOA of pulmonary oedema?

Answer 38

1. Left ventricular dysfunction 2. Reduced ejection which means reduced SV and CO- so blood is left behind instead of ejected 3. Blood backed up into left atrium 4. Blood build up in pul veins which return blood to heart 5. Pul veins are engorged and swell due to lots of blood and hydrostatic pressure increases 6. Pul capillary pressure increases 7. Increased filtration 8. Fluid leaves capillaries and accumulates in interstitial space of lungs