Microcirculation and Lymphatic System

Question 1

Capillary Wall

Answer 1

Composed of unicellular layer of endothelial cells surrounded by a basement membrane

Question 2

How do solutes and water move across the capillary wall?

Answer 2

By intercellular cleft (space in between cells = movement of water and water soluble molecules) OR by plasmalemma vesicles (plasma membrane invaginations and associated vesicles = endocytosis)

Question 3

Flow of Blood through Capillaries

Answer 3

Driven by vasomotion (change in diameter or tone of blood vessels) = intermittent contraction of metarterioles and precapillary sphincters

Regulated by precapillary sphincters
Primary regulator = oxygen-tissue concentration (drop = sphincters open = more oxygentated blood to these tissues and stay there for longer)

Intermittent = NOT CONTINUOUS

Question 4

Why don’t all tissues always get blood flow?

Answer 4

Precapillary sphincters

Question 5

Capillary Exchange

Answer 5

Most important means of exchange = diffusion between plasma and interstitial fluid (lipid soluble substances

Water soluble substances (water, sodium, chloride, glucose, etc.) = cross walls through water-filled intercellular clefts = FAST (makes up for not many clefts)

Question 6

Permeability of Capillary Walls

Answer 6

Solubility AND concentration difference betweeen the two sides of the membrane AND size of molecules (sizes of intercellular slit pores vary from tissue to tissue)

Question 7

The net rate of diffusion of water soluble substances across capillary walls is dependent on…

Answer 7

…the concentration difference between the two sides of the membrane (can be very small to cause lots of movement), the size of the molecule, and the size of the pore

Question 8

Special characteristics of pores in capillaries of the:

1) Brain
2) Liver
3) GI capillary membranes
4) Glomerular capillaries of the kidney

Answer 8

1) Blood Brain Barrier - tight junctions (SMALL)
2) Gaps are very wide to allow almost all dissolved substances through
3)Midway between the muscle and liver
4) Fenestrae that penetrat through middle of endothelial cell
Filtering of large amounts of water, small molecules (glucose) but not proteins

Question 9

4 Primary Forces Determine Net Fluid Movement through Capillary Membrane

Answer 9

1) Capillary Hydrostatic Pressure (Pc) - forces fluid outward through the membrane
2) Interstitial Fluid (Hydrostatic) Pressure (Pif) - opposes filtration when the value is positive AND increases it when negative (inverse effect)
3) Plasma Colloid Osmotic Pressure (πp) - opposes filtration causing osmosis of water inward through the membrane due to plasma proteins (helps prevent too much liquid being lost from the blood)
4) Interstitial Fluid Colloid Osmotic Pressure (πif) promotes filtration by causing osmosis of fluid outward through the membrane

Question 10

Net Filtration Pressure

Answer 10

Influenced by the primary forces determining net fluid movement through the capillary membrane

Net Filtration Pressure (NFP) = Pc - πp - Pif + πif

Slightly positive in normal situations = fluid to interstitial space

Question 11

Rate of fluid filtration in a tissue is determined by…

Answer 11

Number and size of pores in each capillary

Number of capillaries in which the blood is flowing

Question 12

Measure of the capacity of a capillary membrane to filter water for a given net filtration P

Answer 12

Filtration = Kf x NFP

Kf = capillary filtration coefficient (number and size of pores)

Question 13

Interstitial Fluid

Answer 13

In between cells

Gel = diffusion in order for movement to occur (not as fast as flow through free fluid BUT rapid transport for short distances)

Small amounts of free fluid exists as well

Question 14

Hydrostatic Pressure

Answer 14

1) Capillary Hydrostatic Pressure (Pc) - forces fluid outward through the membrane
2) Interstitial Fluid (Hydrostatic) Pressure (Pif) - opposes filtration when the value is positive AND increases it when negative (inverse effect)

Derermined by:

1) Capillary P - Arterial end P = 30 mmHg
Venous end P = 10 mmHg

2) Interstitial Fluid P = -3 mmHg in most tissues
due to Lymphatic System

Question 15

Plasma Colloid Osmotic P

Answer 15

opposes filtration causing osmosis of water inward through the membrane due to plasma proteins (helps prevent too much liquid being lost from the blood)

Caused by proteins in the plasma
Do Not travels through membrane typically
Normal concentration = 7.3 g/dL

Plasma colloid Osmotic P = +28 mmHg
75% due to albumin and 25% due to globulins

Question 16

Interstitial Fluid Colloid P

Answer 16

promotes filtration by causing osmosis of fluid outward through the membrane

Due to small amounts of protein leaking out of capillaries in to interstitial space

Plasma protein Conc = 3g/dL
Pressure - 8 mmHg

Question 17

Arterial End of Capillary

Answer 17

Filtration

Forces pushing fluid out = capillary P, Negative Interstitial Free Fluid P, Interstitial fluid colloid osmotic P

Forces pushing fluid in = Plasma colloid osmotic P

Net OUTWARD Force = 13 mmHg

Question 18

Venous End of Capillary

Answer 18

Reabsorption

Inward = Plasma Colloid osmotic P

Outward = capillary P, Negative Interstitial Free Fluid P, Interstitial fluid colloid osmotic P

Net INWARD Force = 7

Question 19

Most of fluid that leaves from the arterial end of capillaries…

Answer 19

…reabsorbed at the venous ends

excess fluid goes into the lymphatic system

Question 20

Normal Rate of Net Filtration in the Body

Answer 20

2 ml/min

Question 21

Importance of the Lymphatic System

Answer 21

1) Preventing edema
2) Returns protein and high molecular weight substances that cannot be reabsorbed in the blood
3) Major route of absorption from the GI tract
4) Important role in the immune system

Question 22

Factors that increase interstitial lymph pressure and lymph flow

Answer 22

1) Elevated capillary P (bc pushing more fluid OUT of the capillaries)
2) Decreased plasma colloid osmotic pressure (bc less fluid is flowing back into the capillaries)
3) increased interstitial fluid colloid osmotic P (bc same as 1)
4) Increased permeability of capillaries (bc allows more fluid and substances such as porteins to leave the capillaries)

LYMPHATIC SYSTEM WILL REACH MAXIMAL LYMPH FLOW RATE DUE TO COMPRESSED OUTSIDE SURFACES OF LARGER LYMPHATICS BECAUSE OF PRESSURE