Phys- Lymphatic Function

Question 1

Extravascular circulation is carried out by what system

Answer 1

Lymphatic System

Question 2

Where are lymphatic vessels found

Answer 2

throughout the body EXCEPT: BRAIN, BONE, SKIN

Question 3

composition of lymphatic vessels

Answer 3

single layer of endothelial cells WITHOUT a basement membrane

Question 4

anchoring filaments

Answer 4

loosely teather lymphatic vessels to surrounding tissue

Question 5

lymphatic function

Answer 5

maintain interstitial homeostasis

Question 6

describe the endothelial cells of lymphatic vessels

Answer 6

overlaping edges (rather than tight junctions) form valves that allow movement of water and solutes into the terminal lymphatics

Question 7

where do lymphativ vessels originate

Answer 7

at the capillary bed

Question 8

describe what happens to lymph vessels when interstitial volume increases

Answer 8

tension on anchoring flilaments increases and pulls open the spaces between the endothelial cells lining the terminal lymphatics. This allows fluid and solutes to enter the terminal lymphatics. This allows fluids and solutes to flow into the lymphatics and lymphatic capillaries then back into central circulation

Question 9

can lymphatic vessels contract?

Answer 9

yes- contain smooth muscle in their walls - act like small beating hearts - (as lymph moves segment to segment pressure increaeses in the adjacent segment (increased preload) causing stretch which increaes both the rate and the fource of the contraction and lymph is propelled alon the lymphatic channel)

Question 10

Influence of movement and tissue compression on lymph flow

Answer 10

increases flow in a unidirectional manner (due to valves)

Question 11

After dumping into the throacic duct or the right lymphatic duct lymph returns to ______

Answer 11

systemic circulation (recycle fluid and protein)

Question 12

what is lymph?

Answer 12

fluid that was filtered but not absorbed at the tissue level (net filtration)

Question 13

Lymph node purpose

Answer 13

filter out particulate matter and bacteria picked up from the interstitium so that it does enter systemic circulation

Question 14

To maintain equilibrium, lymph flow must equal what

Answer 14

the net fluid filtration throughout the body (~3L/day)

Question 15

Why is lymph flow important

Answer 15

1.) Maintain dry interstitium (removal of water) 2.) Maintain low interstitial oncotic pressure (picks up plasma proteins that have leaked into the interstitium) 3.) Defense against increased net fluid filtration by maintaining subatmospheric Pi (creates partial vaccum that helps hold tissues together) 4.) Cleansing of the interstitial compartment (collects particulate matter and bacteria) 5.) Absorption of fats (chylomicrons)

Question 16

Relationship between increased Pi and Lymph flow

Answer 16

any factors that increase Pi (interstitial hydrostatic pressure) will increase lymph flow

Question 17

at Pi ~0mmHg how much has lymph flow increased

Answer 17

15 fold (remember Pi normally sits right around -6 and anything that increases Pi will increase lymph flow

Question 18

Intrisic contractions and lymph flow

Answer 18

increased intramural pressure cause intrinsic myogenic contraction sof the smloth muscle in the walls of the lymph vessel which “pumps” lymph form segment to segment (think of it as an increase in preload)

Question 19

Extrinsic influences on lymph flow

Answer 19

sympathetic activation and increases in circulating NE cause increases in lymph flow

Question 20

Lymphatic pump

Answer 20

increasesin Pi and intersitial fluid volume open terminal lymphatics allowing the entry of fluid and solutes into the terminal lymphatics and increasing lymph flow. Tissue compression pushed the contents into the next segment (emptying into terminal lymphatic. Release of teh compression stretches the anchoring filaments and opens the terminal lymphatics again

Question 21

External Compression massage and lymph

Answer 21

external tissue pressure compresses lymph channels (movement, muscle contraction, respiration, intestinal contractions, tissue massage or manipulation) propels lymph along the channels . HOWEVER: excessive compression (tight clothing or bands) can impede lymph flow and lead to distal tissue expansion

Question 22

Respiratory Movements (Thoracic Lymphatic Pump Technique- OMT)

Answer 22

transiently lower intra-thoracic pressure during insiration and increase lymph flow

Question 23

What is edema

Answer 23

presence of excess fluid in the tissues

Question 24

What causes edema

Answer 24

anything that alters the balance of Starling Forces leading to an increased net filtration OR anything that creates an imbalance between the rate of fluid filtration and the capacity to increase lymph flow

Question 25

when does interstitial fluid volume begin to increase/accumulate in the interstitial space

Answer 25

Not until Pi > 0 mmHg

Question 26

Describe what happens to compliance when Pi>0

Answer 26

compliance of the interstitial space increases dramatically as Pi increases above 0 mmHg (due to disruption of the interstitial gel matrix)

Question 27

General terms: why does free flid accumulate

Answer 27

inability of lymphatics to keep up with the rate of fluid filtration and inability of the gel matrix to further trap water (due to increase in compliance)

Question 28

List the edema safety factors

Answer 28

1.) Myogenic compensation 2.) Interstitial compensations 3.) Lymphatic compensation

Question 29

Edema Safety Factors: Myogenic compensation

Answer 29

increases in venous pressure due to venous congestion causes myogenic vascoconstriction of the capillary arterioles. This INCREASES PRECAPILLARY RESISTANCE ans reduces capillary pressure while also DECREASING PERFUSED CAPILLARY SURFACE AREA and decreasing net flow

Question 30

What is the net effect of the “margin of safety” before edema begins to form

Answer 30

12-17 mmHg - BY THE TIME YOU SEE EDEMA, THE SYSTEM HAS EXHAUSTED ALL THE SAFETY FACTORS

Question 31

Edema Safety Factors: Interstitial Compensation

Answer 31

Excessive fluid filtration DILUTES THE INTERSTITIAL PROTEINS which increases net oncotic force to offer some degree of protection resulting in a reduction for the filtration driving force

Question 32

Edema Safety Factors: Lymphatic compensation

Answer 32

small increases in Pi produce marked increases in lymphatic flow (remember: increasing from -6 to 0 resulted in a 15 fold increase in flow) Accelerated lymph flow causes ACCELERATION OF FLUID REMOVAL and WASHOUT OF INTERSITIAL PROTEIN which decreases the oncotic pressure

Question 33

Classifications of causes of edema

Answer 33

1.) Anything that disturbs the balance of Starling forces across the capillary bed resulting in an increase in net fluid filtration 2.) anything that impedes lymph flow

Question 34

How does venous obstruction result in edema

Answer 34

increased venous pressure resulting in increased Pc resulting in increase in net fluid filtration rate (excessive fluid filtration)

Question 35

Impact of increased Pc? What are some conditions that cause this

Answer 35

excessive fluid filtration (results in edema) Conditions: Venous obstruction, cardiac failure, excessive arteriolar vasodilation

Question 36

Impact of reduced plasma protein concentration? What are some conditions that cause this?

Answer 36

reduced absorptive foces (via reduced oncotic pressure- nothing holding water in the vascular system) Conditions: 1.) Severe allergic reactions(increased permeability- lose your plasma proteins) 2.) Nephrosis (protein loss in urine) 3.) Severe malnutrition (low plasma proteins due to low protein intake)

Question 37

Explain why inappropriate arteriolar dilation can increase Pc (capillary pressure)

Answer 37

arterioles are the principal site of vascular resistance protecting the exhange vessels from large hydrostatic pressures.

Question 38

Impact of increased microvascular permeability? What are some conditions that cause this?

Answer 38

Increasing microvascular permeability results in loss of plasma proteins and increased interstitial oncotic pressure Conditions: 1.) Severe burns 2.) Allergic reactions

Question 39

Impact of lymphatic obstruction? What are some conditions that casue this

Answer 39

Lymphatic obstruction impedes lymph flow and leads to an increase in loca interstitial hydrosatic pressure (Pi) and oncotic pressure. Conditions: 1.) Elephantitis (lymphatic filariasis obstruction) 2.) Prolonged extrnal compression

Question 40

Edema in thryoid insufficiency

Answer 40

increase in tissue mucopolysaccharides (have a higher affinity for water) - promotes water retention in the interstitial space and the increased pressure and volume can compromise lymphatic drainage. Results in NON-PITTING EDEMA (especially eyes, hands, and feet) known as MYXEDEMA