Microcirculation Flashcards
What is microcirculation?
Capillaries, interstitium & lymphatics
Mechanism fir fluid transport: osmosis
Driven by osmotic and hydrostatic pressures
Important 3 elements:
Capillaries & endothelium (permeability)
Interstitium
Lymphatics
Interstium: 40% less proteins than plasma
Electrolytes are found equally in blood and the interstitial fluid - not contribute to fluid exchange
What are the physical factors of microcirculation?
- Hydrostatic pressure: capillary pressures drive fluid out of capillaries into interstitial space.
- Oncotic pressure: capillary oncotic pressures keep fluid in capillaries and drive reabsorption
- Capillary walls: more permeable e,g, inflammation, ischemia, burns
- Lymphatic drainage: remove excess interstitial fluids (related to starling hypothesis)
What is starlings hypothesis?
Under normal cibditiojs, the amount of fluid filtering outward from the arterial ends of the capillaries equals almost exactly the fluid returned to the circulation by absorption
Differntate hydrostatic and oncotic pressures in capillary
Favors filtration from capillary: hydrostatic > oncotic in capillary
Favors Reabsorption onto capillary: hydrostatic< oncotic
What is the Starling-land is equation for net filtration pressure?
Net filtration pressure= 🔼hydrostatic pressure- 🔼oncotic pressure
Capillaries pressures placed first in the equation, as they are normally higher (come back fir image)
Describe starling equation
Positive value= filtration
NFP= (Pc-PIF)-delta (pic-piIF)
At arteriolar end of capillary
Pc= 35 mmHg PIF= -2mmHg
Pic= 25 mmHg oiIF= 0mmHg
NFP= (35-(-2))-(25 -0)= 12 mmHg (positive sign so filtration has taken place)examples
High filtration: glomerulus, retinal Capillaries increase Pc
Lower filtration: lungs decreased Pc to reduce edema
Note: if the sign was negative, oncotic pressure would be higher, absorption would be taking place
Where in calillaries have the best filtration pressure?
Filtration at arteriolar end of capillaries> Reabsorption at venular end
Summarize the basics of lymph flow
Majority of fluid filtered at the arterial end is reabsorbed at the venous end.
Filtration arteriolar end of capillaries > Reabsorption at venous end: about 2-4 L/day. Starling hypothesis a bit off with “filtration almost exactly= Reabsorption”
However fluid doesn’t accumulate in the interstitium
Fluid is not reabsorbed in capillaries is drained by the lymphatic system
- (about 5-10% of filtrate transported out of tissues by lymphatics)
- proteins and bacteria removed
Are there lymphatics in the brain and heart?
Lymphatics are absent in myocardium
Lymphatics AP we’re thought to be absent in brain, lymphatics we’re recently discovered
Describe the movement of lymph
Hydrostatic pressures
Lymphatic (Plymph) < interstitium (Pif) but Plymph can increase due to pumping in lymph vessels (after valves)
- Transient increases in Pif drive fluid into lymphatics. Interstitial volume normally kept relatively corant.
- Pumping action of open terminal ends of lymphatics draw fluid into lymphatics (Lymph P> Pif). Pumping increase when more fluid in Pif
Movement of lymph:
-Valves in lymphatics—> one way movement of lymph
-Contraction/pumping: movement of lymphatics fluids. Pressures in larger lymphatics can be 100 mmHg
Compression: by skeletal muscles, respiratory movements and intestinal movements
What is the lymphatics system?
Lymphatics capillaries merge into the thoracic duct
Thoracic duct drains lymph into the left Subclavian vein
Lymphatic drainage reduces protein in interstitium- controls interstitium colloid pressures.
Fat absorption will be covered in GI system
What are the locations of edema?
Subcutaneous tissue:peripheral edema
Lungs: pulmonary edema
Abdominal cavity: ascites
What are the physical factors of edema?
Hydrostatic pressure
Oncotic pressures
Capillary walls
Lymphatic drainage
How can hydrostatic pressures contribute to edema?
Capillary pressures drive fluid out of capillaries into interstitial space
Pulmonary edema: slight increases in hydrostatic pressures in lung capillaries
Peripheral edema: increase systemic capillary pressures result in increased filtration in lower extremities and intestine
How can oncotic pressure contribute to edema?
Capillary oncotic pressures keep fluid in capillaries and drive Reabsorption
Edema—> reduction of plasma proteins: (protein lost in urine, pregnancy, malnutrition, or reduced albumin production in liver)
How can lymphatic drainage contribute to edema?
Impaired e,g, parasites, surgical lymph node premoval, local edema before blocked nodes
What is albumin?
A major protein contributing to oncotic pressure, produced in the liver
When dies hypoalbunemia occur?
- decreased albumin production: cirrhosis (chronic alcoholism increases risk), hepatitis
- increased albumin clearance: kidneys. Albumin in urine- marker fir kidney disease
- pregnancy
What does hypoalbinemia result in?
- reduced oncotic pressure in capillaries
- less fluid reabsorbed into capillaries
- more fluid in interstitial fluid
Edema: when interstitial fluid volume accumulation> lymph clearance
Summarize edema physical causes
Increased venous pressure—> increased capillary hydrostatic pressure—> increased capillary filtration —> edema
Loss of plasma proteins—> decreased plasma oncotic presssure —> decreased capillary absorption—> edema
Surgery or radiotherapy filariases—> damaged lymph nodes—> defective drainage of lymoh —> lymphedema
How can organ dysfunction lead to cause edema?
Right ventricular failure:
Increased right atrial pressure—. Increased CVP—> increased capillary pressure (systemic) —> increased filtration leads to tissue edema—> ankle swelling (pitting edema)
Left ventricular failure:
Increased left ventricular failure—> increased pulmonary venous pressure —> increased capillary pressure (pulmonary) —> increased filtration —> pulmonary edema —> fluid in lungs
Hepatic Fibrosus : increased hepatic venous pressure
Leads to: ascites: accumulation of fluid in peritoneal cavity
What are the consequences if pulmonary edema ?
Difficult to inflate lung—> dyspnea (difficult/labored breathing)
(LV failure, back up lungs) fluid enters alveoli. O2 and CO2 exchange impaired
What are the consequences of tissue edema?
(Seen when fluid volumevdlubkes in limb about 10% limb vol. right ventricular failure)
Impairs cell nutrition
Causes discomfort and decreased motility
Skin ulcerated and blisters
Prone to infection-cellulitis (bacterial infection)
