Week 5: Disturbed Blood Flow Flashcards
Normal Fluid Balance
60% of our bodies is water!
-2/3 = intracellular
-1/3 = extracellular (15% interstitial, 5% plasma)
Depends on:
-Starling’s law
-Systemic factors (Intact circulation, overall fluid balance, salt retention)
-Physiologic ranges of intravascular pressure, osmolarity
What does the extracellular component of the body consist of?
Interstitial + blood vessels
What does intracellular refer to?
Within cells
Lymphatic System
Products are deposited in the venous side of circulation
-50% of total blood proteins leak out of capillaries into the tissue fluid and return to the blood via lymphatic vessels EVERY DAY
-Under NORMAL circumstances, only a small amount of fluid leaks from vessels to form interstitial fluid
-Fluid is removed by lymphatic vessels
Starling’s Law
Movement of fluid between vascular and interstitial spaces (at capillary level) is controlled by 4 forces:
1. Hydrostatic pressure (HP)
2. Plasma oncotic pressure (OP)
3. Interstitial/tissue fluid osmotic pressure
4. Interstitial/tissue fluid oncotic pressure (tissue tension)
**Focus on OP and HP
Hydrostatic Pressure
Force exerted by a fluid against the capillary wall (pushing force)
In vessels: Fluid contains oxygen and nutrients that move into the surrounding tissue, where they are less concentrated
In tissues: Fluid contains waste products
MOVE WITH DIFFUSION
Mean of 25mmHg between arterial and venous ends (32 arterial, 12 venous)
Oncotic Pressure
Pressure created by the presence of large molecules/particles that cannot diffuse and are prevented from moving through capillary membrane
Large molecules = plasma proteins (e.g. albumin)
Encourage osmosis, draw water towards them
Because capillary blood has a high content of plasma proteins, capillary has a HIGH oncotic pressure = 26 mmHG
Oncotic pressure does not vary from one end of capillary to another
Direction of Fluid Flow
NFP calculated: HP vs. OP in capillaries
If HP > OP, fluid will leave
If HP < OP, fluid will enter
Under normal conditions, 10% of fluid enters lymphatic capillaries. 90% re-enters the capillary.
Arterial End (under normal conditions)
HP = 32
OP =26
NFP = +6
Water moves OUT
Venous End (under normal conditions)
HP = 12
OP = 26
NFP = -14
Water moves IN
Edema
Accumulation of abnormal fluids in the interstitial/subcutaneous tissue (tissue under epithelium, the outermost layer of the skin) → swelling
Interstitial Pressure (Tissue Tension)
3-4 mmHg
Causes of Edema
- Congestive heart failure
- Deep venous thrombosis of lower legs
- Hypoproteinemia (liver disease, renal failure, malnutrition)
- Lymphatic obstruction (cancer, inflammation, blockage)
- Inflammation
- Sodium retention (heart/kidney failure)
- Tumours, radiation
Hydrostatic Edema
An increase in intravascular (whole system) hydrostatic pressure due to increased venous pressure (one area).
Reabsorption is decreased (fluid build-up in interstitial tissue) and lymphatics drain
Clinical Examples:
1. Congestive Heart Failure (CHF)
-Right side failure → peripheral edema and pitting edema (due to
increased HP in the venous circulation)
- Left side failure → lung edema (due to increased
HP in the arterial circulation)
2. Deep venous thrombosis of lower legs
- Obstruction of veins (blood clot - localized)
- Increased interstitial fluid buildup because the hydrostatic pressure exerted by the clot pushes all the fluid out)
Oncotic Edema
(Hypoproteinemia)
Fall in colloid osmotic pressure of plasma. Due to loss of albumin or other proteins.
Oncotic pressure decreases and fluid goes to tissues. We can decrease the fluid amount but this is not enough.
Clinical Examples:
1. Liver disease as cirrhosis (liver failure): decrease synthesis of albumin
-Hepatic ascites (Because increased HP in portal veins increases the fluid in the abdominal cavity)
If you have fewer proteins occupying/IMF bonding to the fluid/water molecules, more water molecules will be free to exert pressure on the vasculature
- Decreases fluid in circulation after it leaves for the insterstitium; increases oncotic
pressure
2. Renal failure: loss of albumin in urine
3. Malnutrition: if you don’t eat enough protein in meals
Lymphatic Obstruction
Increases interstitial oncotic pressure (with normal OP and HP).
Accumulation of interstitial fluid because of insufficient reabsorption and deficient removal of proteins → increasing the oncotic pressure of the fluid in the interstitial space
Proteins cannot go back into the circulation through lymphatics
Clinical examples:
1. Cancer (tumour on lymphatics)
2. Inflammation
3. Postsurgical lymphedema
4. Postradiation
Inflammatory and Traumatic Edema
Local or systemic
Vascular bed becomes leaky following injury to the endothelium (cells lining blood vessels)
Sodium Retention (Edema)
Causes both increase in hydrostatic pressure and reduced vascular osmotic pressure
Sodium is a MAJOR cation that determines the osmolarity of the extracellular fluid volume
Increased total body sodium must be balanced by more extracellular water to maintain constant osmolarity
Clinical examples:
1. Kidney diseases
2. Heart diseases
-CHF → decreased blood perfusion to kidney →
triggers renin-angiotensin-aldosterone complex
3. Increase intake of sodium
- Increases water retention
- Increases plasma volume: Hypervolemia
(increases HP or expansion of intravascular fluid
volume, decreases OP or dilution of protein)
Localized Edema
Due to:
-Increased hydrostatic pressure due to vascular/venous obstruction (local)
-Inflammation (epithelial injury)
-Lymphatic obstruction (lymphedema): compression by tumour or inflammation (local)
-Tumour
-Inflammation
-Postsurgical
-Postradiation
-Burns (edema by disrupting local permeability of local vasculature)
Generalized Edema (Anasarca – swelling of the whole body)
Affects the visceral/internal organs (think visceral fat) and skin of trunk and lower extremities.
Due to:
-Increased hydrostatic pressure: i.e. heart failure.
-Decreased oncotic pressure (colloid osmotic pressure) due to:
-Loss of albumin in renal failure (nephrotic
syndrome)
-Decreased synthesis of albumin in liver failure
(Ascites)
-Malnutrition
-Sodium retention → Kidney disease (can start around the eye)
Hydrothorax (Pleural Effusion)
Fluid in chest cavity
Hydropericardium
Fluid in the pericardium
Hydroperitoneum (Ascites)
Fluid in the abdominal cavity (e.g. due to liver failure)
Transudate
Results from disturbances in Starling Forces
Protein < 3 g/dl
Specific gravity < 1.012
