Microcirculation

Question 1

What is microcirculation?

Answer 1

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

Question 2

What are the physical factors of microcirculation?

Answer 2

1. Hydrostatic pressure: capillary pressures drive fluid out of capillaries into interstitial space.
2. Oncotic pressure: capillary oncotic pressures keep fluid in capillaries and drive reabsorption
3. Capillary walls: more permeable e,g, inflammation, ischemia, burns
4. Lymphatic drainage: remove excess interstitial fluids (related to starling hypothesis)

Question 3

What is starlings hypothesis?

Answer 3

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

Question 4

Differntate hydrostatic and oncotic pressures in capillary

Answer 4

Favors filtration from capillary: hydrostatic > oncotic in capillary

Favors Reabsorption onto capillary: hydrostatic< oncotic

Question 5

What is the Starling-land is equation for net filtration pressure?

Answer 5

Net filtration pressure= 🔼hydrostatic pressure- 🔼oncotic pressure

Capillaries pressures placed first in the equation, as they are normally higher (come back fir image)

Question 6

Describe starling equation

Answer 6

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

Question 7

Where in calillaries have the best filtration pressure?

Answer 7

Filtration at arteriolar end of capillaries> Reabsorption at venular end

Question 8

Summarize the basics of lymph flow

Answer 8

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

Question 9

Are there lymphatics in the brain and heart?

Answer 9

Lymphatics are absent in myocardium

Lymphatics AP we’re thought to be absent in brain, lymphatics we’re recently discovered

Question 10

Describe the movement of lymph

Answer 10

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

Question 11

What is the lymphatics system?

Answer 11

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

Question 12

What are the locations of edema?

Answer 12

Subcutaneous tissue:peripheral edema

Lungs: pulmonary edema

Abdominal cavity: ascites

Question 13

What are the physical factors of edema?

Answer 13

Hydrostatic pressure

Oncotic pressures

Capillary walls

Lymphatic drainage

Question 14

How can hydrostatic pressures contribute to edema?

Answer 14

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

Question 15

How can oncotic pressure contribute to edema?

Answer 15

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)

Question 16

How can lymphatic drainage contribute to edema?

Answer 16

Impaired e,g, parasites, surgical lymph node premoval, local edema before blocked nodes

Question 17

What is albumin?

Answer 17

A major protein contributing to oncotic pressure, produced in the liver

Question 18

When dies hypoalbunemia occur?

Answer 18

• decreased albumin production: cirrhosis (chronic alcoholism increases risk), hepatitis
• increased albumin clearance: kidneys. Albumin in urine- marker fir kidney disease
• pregnancy

Question 19

What does hypoalbinemia result in?

Answer 19

• reduced oncotic pressure in capillaries
• less fluid reabsorbed into capillaries
• more fluid in interstitial fluid

Edema: when interstitial fluid volume accumulation> lymph clearance

Question 20

Summarize edema physical causes

Answer 20

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

Question 21

How can organ dysfunction lead to cause edema?

Answer 21

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

Question 22

What are the consequences if pulmonary edema ?

Answer 22

Difficult to inflate lung—> dyspnea (difficult/labored breathing)

(LV failure, back up lungs) fluid enters alveoli. O2 and CO2 exchange impaired

Question 23

What are the consequences of tissue edema?

Answer 23

(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)