Capillary Exchange & Edema Flashcards
(45 cards)
1
Q
continuous capillaries
A
- uninterrupted endothelium & continuous basal lamina
- seam between adjacent endothelial cells from narrows intracellular clefts w/ tight junctions that only permit small molecules through and exclude proteins
- substances <10nm are permeable
- BBB, most tissues, lung, muscle, skin
2
Q
fenestrated capillaries
A
- have circular pores (60-80nm) that penetrate endothelium
- allows small molecules & some proteins through
- substance <100nm permeable
- SI, Renal glomerulus, pancreas, intestinal mucosa
3
Q
discontinuous (sinusoidal)
A
- a discontinuous basal lamina w/ large gaps
- substance <300nm permeable
- allows free passage of proteins & cells between intersitium & plasma
- in liver, bone marrow, & spleen
4
Q
4 elements of capillary designs, why is it important?
A
- designed for rapid diffusive exchange by optimizing Fick’s Law by
1) close proximity to cells (within 20um)= rapid diffusion
2) large surface/vol ratio, so distance between center of vessel to exchange surface (cap wall) is small= rapid diffusion
3) low blood flow velocity allows effective distribution of nutrients between blood & cells
4) thin walls allow easy/fast permeability of nutrients to the cells from the capillaries
5
Q
what is trancapilalry exchange and was are the 3 routes? What determines rate a substance moves between blood & interstium?
A
- exchange of material between blood and interstium
- the most important way nutrients are delivered to interstium is diffusion
1) transcellular route
2) intercellular route
3) pinocytosis (proteins) - the permeability of the capillary wall determines how rapidly a substance will move between the blood & interstium
6
Q
transcellular route of trans-capillary exchange?
A
- lipid soluble substances like O2& CO2 can diffuse rapid w/ minimal hinderance though lipid membranes of endothelial cells
- so diffuse nutrients between cells
7
Q
intercellular clefts route of trans-capillary exchange?
A
- water soluble substances (glucose, AA, K+, Na+) are limited to diffusion via these clefts
- movement is added by filtration pressure gradient
8
Q
pinocytosis route of trans-capillary exchange?
A
- allows minor amounts of proteins to enter interstium from the blood
- this along with bulk flow are very slow and never occur in the BBB
9
Q
what are 2 ways that transcapilalry exchange can be increased?
A
1) recruiting more capliiaries (at rest have less active capillaries than when exercising)
2) increased tissue conc. gradient (so suck blood into tissue more rapidly)
10
Q
how do tissues remain compact an avoid edema? (regulation of interstitial fluid vol, 3 ways)
A
- balance between 2 competing forces oncotic pressure & hydrostatic pressure
1) microvascular filtration
2) interstitial storage
3) lymphatic return
11
Q
colloid oncotic pressure?
A
- the difference in protein conc. creates this osmotic force
- draws H20 into capillaries since blood has a higher plasma protein conc (albumin) than the interstium does
- helps offset hydrostatic pressure & returns fluid to capillaries
- only ~25mmHG or 1-3mOsm while total plasma osmolarity is 285mOsm; very small fraction of total osmolarity
12
Q
movement of plasma protein?
A
- plasma protein= albumin, usually conc of 7g/100mL at oncotic 25 Torr
- normally leaves vascular compartment & returned via lymphatics in an amount equaling output
13
Q
Starling’s principle of capillary fluid balance?
A
- Filtration= Kf [(Pcap + pi isf)- (Pisf- pi cap)]
- bulk movement of fluid through capillary wall is dependent on balance of these 4 powers
- abroption and filtration values vary greatly from organ to organ
14
Q
filtration? factors that favor it?
A
- the net outward movement across a capillary wall
- when sum of equation is positive
1) capillary hydrostatic pressure (Pcap)
2) interstitial fluid oncotic pressur (pi isf)
15
Q
absorption? factors that favor it?
A
- fluid movement back into the capillaries
- when the sum of equation is negative
1) interstitial fluid hydrostatic pressure (Pisf)
2) capillary oncotic pressure (pi cap)
16
Q
what does apillary hydrostatic pressure (Pcap) depend on (x4)? Why Pcap important?
A
1) distance along capillary (decreases as move in direction of flow)
2) arterial & venous pressure
3) gravity
4) sympathetic vasomotor tone
- Pcap only factor that changes across capillary so is reason why arteriole end if net filtration (13) and venuole end= net absorption (-7)
* gravity and vasomotor tone effect hydrostatic pressure so therefore effect Pcap*
17
Q
interstitial fluid oncotic pressur (pi isf)
A
- draws fluid out of the capillaries intro interstium
- is a very weak force since very low amount of albumin in interstitial fluid
- favors filtration
18
Q
interstitial fluid hydrostatic pressure (Pisf)
A
- sucks fluid into the capillary (favors absorption)
- this value very low since hydrostatic pressure of large insterstium is low
19
Q
capillary oncotic pressure (pi cap)
A
- favors absorption
- draw fluid into capillary from intersitum to balance the large albumin conc gradient in the plasma vs in the interstium
20
Q
pressure changes in the capillaries and how is affects fluid movement?
A
- pressure always drops across resistance
a) when move from artery–> arteriole–> capillary get progressive increase of resistance due to smaller vessel sizes
b) at beginning of capillary hydrostatic > oncotic presser so is FILTRATION
c) at end of capillary hydrostatic pressure < oncotic due to to loss of nutrients & smaller volume so get ABSORBTOPN
21
Q
How does increases in arteriole and venous tone differently affect the capillary filtration?
A
- they will act on the capillary filtration in opposing ways
a) vasoconstriction: will decrease BV in capillaries, decrease pressure, and net absorption
b) vasodilation: will increase BV in capillaries, increase pressure, net filtration
c) venoconstiction: will increase BV in cap, increase pressure, net filtration
d) ventilation: will decrease BV in cap, decrease pressure, net absorption
22
Q
what has greater effect on capillaries filtration vs absorption?
A
-venous pressure changes (venoconstrction/dilation) has greatest effects on capillary filtration’s absorption than arteriole pressure changes do
23
Q
how does regional circulation of extracellular fluid work?
A
- moment to moment, capillaries change from open to closed depending on local accumulation of metabolic vasodilators
- means capillaries change between net filtration & absorption
- means that the open capillaries favoring filtration will release their filtrate and it will be absorbed by surrounding (closed) capillaries who are favoring absorption
- is how sealed capillary neighbors can still receive nutrients to do metabolic cellular work
24
Q
What is edema? What re the 4 types?
A
- accumulation of excess interstitial fluids causing tissue to no longer be dry/condensed (tissue swelling)
1) inflammatory edema
2) venous edema
3) hydroproteinemic edema
4) lymphatic edema
25
conditions that promote edema?
a) increased arterial or venous pressure (venous thrombis)
b) decreased oncotic pressure of plasma
(kwashikor, rapid IV saline infusion, glomerulonephrotitis)
*both conditions cause filtration>>absorption so increased interstitial vol*
26
inflammatory edema & causes
- increases permeability of endothelial layer
1) burns
2) ischemia
3) inflamm
4) venous valve incompetency
27
venous edema & causes
- due to increases in venous pressure & venous pooling
1) CHF
2) prolonged standing
3) thrombosis of vein
4) venous valve incompetency
28
hypoproteinemic edema & causes
- result of decreases plasma albumin concentration
1) poor nutrition
2) glomerulonephritis:
3) rapid saline infusion (diffuses/pushes out albumin)
4) liver cirrhosis (liver makes albumin)
29
what is glomerulonephritis?
- when glomerulus leaky to protein so pee out protein and loose oncotic gradient
- get increased filtration and selling in tissues
30
what is lymphatic edema?
- due to lymphatic obstruction comes as a result of
1) surgery
2) elephantitis etc
31
Kwashiorkor
- condition due to severe protein malnutrition
- body starts to eat own albumin when have no dietary protein, means loose oncotic gradient and fluid fills the most easily distensible place (the belly)
- get huge swollen abdomens
- edema tends to start in feet then work way up body
32
what is transcapilalry fluid shift?
- in cases of hypovolumia, interstitial fluid can be mobilized to vascular space to restore vascular volume
- intersitial fluid compartment acts as backup reservoir that can supply fluid to plasma or receive excess fluid in times of need
- possible cuz interstitial fluid ~10L which is ~3x as much as plasma
33
when does transcapilalry fluid shift occur?
1) decreased arterial pressure (due to hemorrage)
- transfer of ISF to blood to help restore circulating blood flow
2) increased plasma oncotic pressure (due to dehydration, diarrhea, sweating, vomiting)
- transfer of ISF to blood to help restore the plasma oncotic pressure
34
transudate
- inreased permeability of fluid (membrane remains intact)
- due to increased hydrostatic pressure (CHF or venous obstruction)
- or decreased oncotic pressure due to decreased protein synthesis or increased protein loss
35
exudate
- break down of endothelial wall (low permeability now)
| - allows proteins to leak across & loose oncotic pressure gradient
36
2 ways fluid moves across capillaries?
a) transudate
| b) exudate
37
What is the lymphatic system?
- unidirectional drainage system for clearance of excess interstitial fluid & transport of immune cells to lymph nodes
- a second circulation, lacks a pump; uses extravascular pressure to move contents
- helps removes the 3L of fluid loss to the interstium each day to prevent swelling/edema, extent of fluid loss can increase w/ disease & exercise
38
Functions of the lymph system?
1) returns excess interstitial fluid to the blood (keeps tissues compact)
2) returns interstitial protein to blood (maintains oncotic gradient)
3) transports cells (immune system)
4) transports large molecules & debris
39
how fluid flow through lymph?
- lymph system is an open system that drains blood into subclavian vein & has no special pump uses
1) pressure gradient
2) one way valves (lymph capillaries)
3) external compression
to push fluid to subclavian vein
40
what does external compression mean in the lymph system?
- helps "milk" lymph fluid to the subclavian vein by using
1) surrounding sk. muscle
2) smooth muscle in collecting lymphatics
3) resp. movements
4) one way lymph valves
41
What are the lymphatic capillaries?
- blind ended ducts within the collecting lymphatic ducts that collect excess interstitial fluid
- thin capillary walls have clefts that act as one-way valves, open under low lymph pressure, close under high pressure
42
what is extravascular compression and how does it work?
- is the main driving force of lymph fluid back to the subclavian vein, has 2 pumping actions
a) recurrent compressions of lymph vessels by surrounding skeletal muscle
b) periodic compression of smooth muscle in walls of collecting lymphatic ducts that have one way valves to prevent backward flow (similar to veins)
- resp movements also help move fluid to subclavian vein
43
What happens if have a condition that impedes normal lymph flow?
- it will cause peripheral edema due to one of below:
1) fluid escaped capilalries & remains in interstitial space (not cleared)= swelling
2) protein escapes cap & not returned, collapse of oncotic gradient, promotes fluid absorption along cap
44
Filariasis (Elephantisis)
- is due to a parasitic worm (nematode threadworm) transmitted by mosquitos
- as worm grows it occludes the lymph vessels
- lymph drainage is blocked & causes swelling of body (mostly lower limbs (due to gravity) and soft tissues (scrotum))
45
surgical edema?
- removal of lymph nodes in testicular cancer surgery to prevent spread of disease
- loose lymph nodes/drainage in affected limb causes severe edema
