Phys- Lymphatic Function Flashcards
Extravascular circulation is carried out by what system
Lymphatic System
Where are lymphatic vessels found
throughout the body EXCEPT: BRAIN, BONE, SKIN
composition of lymphatic vessels
single layer of endothelial cells WITHOUT a basement membrane
anchoring filaments
loosely teather lymphatic vessels to surrounding tissue
lymphatic function
maintain interstitial homeostasis
describe the endothelial cells of lymphatic vessels
overlaping edges (rather than tight junctions) form valves that allow movement of water and solutes into the terminal lymphatics
where do lymphativ vessels originate
at the capillary bed
describe what happens to lymph vessels when interstitial volume increases
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
can lymphatic vessels contract?
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)
Influence of movement and tissue compression on lymph flow
increases flow in a unidirectional manner (due to valves)
After dumping into the throacic duct or the right lymphatic duct lymph returns to ______
systemic circulation (recycle fluid and protein)
what is lymph?
fluid that was filtered but not absorbed at the tissue level (net filtration)
Lymph node purpose
filter out particulate matter and bacteria picked up from the interstitium so that it does enter systemic circulation
To maintain equilibrium, lymph flow must equal what
the net fluid filtration throughout the body (~3L/day)
Why is lymph flow important
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)
Relationship between increased Pi and Lymph flow
any factors that increase Pi (interstitial hydrostatic pressure) will increase lymph flow
at Pi ~0mmHg how much has lymph flow increased
15 fold (remember Pi normally sits right around -6 and anything that increases Pi will increase lymph flow
Intrisic contractions and lymph flow
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)
Extrinsic influences on lymph flow
sympathetic activation and increases in circulating NE cause increases in lymph flow
Lymphatic pump
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
External Compression massage and lymph
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
Respiratory Movements (Thoracic Lymphatic Pump Technique- OMT)
transiently lower intra-thoracic pressure during insiration and increase lymph flow
What is edema
presence of excess fluid in the tissues
What causes edema
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
when does interstitial fluid volume begin to increase/accumulate in the interstitial space
Not until Pi > 0 mmHg
Describe what happens to compliance when Pi>0
compliance of the interstitial space increases dramatically as Pi increases above 0 mmHg (due to disruption of the interstitial gel matrix)
General terms: why does free flid accumulate
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)
List the edema safety factors
1.) Myogenic compensation 2.) Interstitial compensations 3.) Lymphatic compensation
Edema Safety Factors: Myogenic compensation
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
What is the net effect of the “margin of safety” before edema begins to form
12-17 mmHg - BY THE TIME YOU SEE EDEMA, THE SYSTEM HAS EXHAUSTED ALL THE SAFETY FACTORS
Edema Safety Factors: Interstitial Compensation
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
Edema Safety Factors: Lymphatic compensation
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
Classifications of causes of edema
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
How does venous obstruction result in edema
increased venous pressure resulting in increased Pc resulting in increase in net fluid filtration rate (excessive fluid filtration)
Impact of increased Pc? What are some conditions that cause this
excessive fluid filtration (results in edema) Conditions: Venous obstruction, cardiac failure, excessive arteriolar vasodilation
Impact of reduced plasma protein concentration? What are some conditions that cause this?
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)
Explain why inappropriate arteriolar dilation can increase Pc (capillary pressure)
arterioles are the principal site of vascular resistance protecting the exhange vessels from large hydrostatic pressures.
Impact of increased microvascular permeability? What are some conditions that cause this?
Increasing microvascular permeability results in loss of plasma proteins and increased interstitial oncotic pressure Conditions: 1.) Severe burns 2.) Allergic reactions
Impact of lymphatic obstruction? What are some conditions that casue this
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
Edema in thryoid insufficiency
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
