Circulation and Fluid Balance

Question 1

What is the simple system of the amoeba?

Answer 1

• Amoeba are in direct contact with their environment to :
  
  • Obtain nutrients
  • Excrete wastes
• Contractile vacuoles pump water in and out of the amoeba for these exchanges to occur

Question 2

What does the circulatory system do?

Question 3

What are the blood vessels in microcirculation?

Answer 3

• Terminal arterioles
  
  • endothelium, basement membrane, muscle
• Capillaries
  
  • Endothelium, basement membrane
• Post Capillary venules
  
  • Endothelim, basement membrane, muscle

Question 4

What is a Terminal arteriole

Answer 4

• Major resistance vessel of the arterial system
• Terminal arterioles regulate the clow of blood into a capillary bed
• Pressure falls dramatically as blood flows thtrough the arteriole into the capillary

Question 5

What are capillaries?

Answer 5

• The most numerous of all vessels, but generally contain only 5-10% of blood volum
• Blood is directed into a capillary based on tissue needs
  
  • At any given time most capillary beds have minimal blood flowing through them

Question 6

What is a postcapillary venule

Answer 6

• collect blood from a capiillary bed to begin the venous return to the heart
• important site of cellular events associated with inflammation

Question 7

What are the lymphatics in microcirculation?

Answer 7

• Blind-ended lymphatic vessels originate in association with the mircrocirculation
• Important participants in fluid balance at the microcirulatory level

Question 8

What is the interstitium?

Answer 8

• The space between cells and the microcirculation
• Composed of the ECM
  
  • Includes:
    
    • Structural elements
    • Adhesive elements
    • Absorptive elements

Question 9

What is fluid homestasis

Answer 9

• Fluid is in constant flux between compartments of the microcirculatory environment
• Interactions occur between:
  
  • cells and interstitium
  • interstitium and blood vessels
  • interstitium and lymphatic vessels
• Fluid distribution between compartments is controlled by physical barriers, and differences in pressure and concentration of substances within the fluid

Question 10

What is the normal water distribution in the body?

Answer 10

• Total body water (60% body wt)
  
  • Extracellular water (20% body wt)
    
    • Plasma (4-5%)
    • Interstitium (16%)
  • Intracellular water (40%)
    
    • relatively stable compartment

Question 11

How does blood and the interstitium interact?

Answer 11

• Blood vessel wall is the barrier that separates intravascular and teh interstitial compartments
• Capillary wall is semi-permeable membrane that allows selective movement of fluid and molecules
  
  • lipid soluble substanes can move through the endthelil cell
  • Water and water soluble substanes move through inter-endothelial pores

Question 12

How does the intertitium and lyphatic vessels interact?

Answer 12

• Lymph vessel wall separate the lymphatic and interstitial compartments
• Lymph vessel wall functions similar to the capillary wall but is much more permeable
  
  • inter-endothelial gaps are large
• Water moves freely between lymphatic vessel lumens and interstitium based on pressure gradients

Question 13

How is the Intravascular/Interstitial fluid distribution controlled

Answer 13

• Anatomic integrity of the circulation
• Osmotic pressure
  
  • plama
  • interstitium
• Hydrostatic pressure
  
  • plama
  • interstitium

Question 14

How is water flow across the endothelium described?

Answer 14

-K * [P_cap - P_int] - σ [π_cap - π_int]

• K = capillary endothelial permeability constant
• P = hydrostatic ressure
• σ = reflection coefficient
• π = colloid osmotic pressure

Question 15

Intravascular /Interstitial water distribution

Answer 15

• Differences in hydrostatic pressure are determined mainly by teh volume of water in a compartment and any driving force acting on that volume (ex blood pressure)
• Differences in osmotic pressure are determined manly by large protins or protein-disaccharides
  
  • small proteins and electrolytes account for most osmolarity, but are equally distributd between fluid compartments
    
    • 84% of plama osmolality is due to sodium and chloride
    • Less than 1% of plasma osmolality is due to plasma proteins
    • Protein-disaccharides contribute to interstitial osmolality
• Intravascular and interstitial osmotic, and interstitial hydrostatic pressures are relatively constant in the normal microcirculation
• Differences in intravascular hydrostatic pressure between arteriolar and venular ends of the microciculation are teh major actor in driving water exchange between the plasma and interstitium
  
  • Alternatively, water may flow from an entire capillary bed with active blood flow towards abed with minimal flow

Question 16

What controls Fluid dristibution?

Answer 16

• Net filtration pressue:
  
  • plama/interstitium pressue differential at teh arteriole
  • Net flow (nutrients) into the interstitium
• Net absorption pressure:
  
  • Plasma/interstitium pressure
  • differential at the venule
  • Net flow (wastes) into the plams
• Lymphatic vessels pick up excess fluid

Question 17

What are the the mechanism of Edema

Answer 17

• Decreased plama osmotic pressure
• Increased plama hydrostatic pressure
• Decreased lymphatic drainage
• Increased vascular permeability

more than one mechanism is often involved in clinical edema

Question 18

How is plasma osmoic pressure decreased?

Answer 18

• Hypoalbuminemia is a common underlying factor in decreased plama osmotic pressure
  
  • Albumin is the major plasma protein that contributes to intravascular osmotic presure

Question 19

What causes hypoalbuminemia?

Answer 19

• starvation
  
  • inadequate protein intake
• Liver disease
  
  • Decreased protein production
• Renal disese (nephrotic syndrome)
  
  • glomerular loss of albumin
• GI disease
  
  • malabsorption
  • parasitis
• Severe burns

Question 20

How is Edema caused by decreased plasma osmotic pressure characterized?

Answer 20

• Due to systemic nature of hypoalbuminemia, edema tends to be generalized
  
  • Manifestations of generalized edema sometimes tnd to be localized (bottle jaw, brisket edema)

Question 21

How does increased plasma hydrosttic pressure cause edema?

Answer 21

• Creates a net outflow of fluid from teh vessel to the intrstitium
  
  • the normal absoptive pressue at teh venule becomes a filtration pressure
    
    • high venula hydrostatic pressure prevents reentry of fluid from teh intersittium

Question 22

What causes increased plasma hydrostatic pressure?

Answer 22

• Increased blood flow
  
  • accute inflammation
• Passive blood accumulation
  
  • Venous obstruction
    
    • thrombi
    • Masses - inflammatory or neoplastic
    • Organ torsions
  • Heart failure

Question 23

How does heart failure cause fluid maldistribution?

Answer 23

• Fluid maldistribution can vary depending on the nature of the failure
• Right heart failure: blood backs up in the portal circulation
  
  • Fuid accumulates in the abdominal catity (ascites)
• Left heart failure: blood backs up in pulmonary circulation
  
  • Fluid accumulates in the alveoli of teh lung (pulmonary edema)
• Generaized edema from generalized heart failure can result in reduced circulating blood volume
  
  • ADH and aldosterone stimulate water andsodium retention to contribute to hypervolemia and increased plasma hydrostatic pressure

Question 24

How does increased plasma hydrostatic pressure cause edema?

Answer 24

• Fluid maldistribution can be generalized or localized depending on the underlying cause
  
  • Generalized - heart failure
  • Local - venous obstruction

Question 25

How does Decreased lymphatic drainage cause edema?

Answer 25

• Any decreasse in lymphatic flow prevents remol of the slight excess of fluid that normally presist in the interstitium during intravascular/interstitial fluid exchange
• Fluid maldistribution is almost almost always localized for acquired defects in drainage
• Congenital defects can be manifested by generalized edema

Question 26

What casues decreased lymphatic drainage

Answer 26

• Lymphatic obstruction
  
  • compression from inflammatory or neoplastic masses
  • intralumenal obstruction by thrombi or emboli
• Lymphatic anomalies
  
  • Congnital anasarca/lymphedema

Question 27

How does increased vascular permeability caus edema?

Answer 27

• Decreased structual integrity alows water to move out of a vessel into teh interstitium more freely

Question 28

What causes increased vascular permeability?

Answer 28

• Inflammation
  
  • endothelial contraction and cytoskeletal rearrangement results in expansion of interendothelial junctions and fluid movement to the interstitium
  • Inflamatory Meditors:
    
    • Immediate transient response: histamine, bradykinin, leukotrienes, C₄D₄E₄, Platelet activating factor, substance P
    • Delayed sustained response: TNF, IL-1, gamma-IFN
• Immunologic stimuli
  
  • many of the same events of inflammation are initiated
• Direct endothelial injury
  
  • toxins, chemicals, or infectious agents

Question 29

How is edema caused from increased vascular permeability characterized?

Answer 29

• Usually localized
  
  • increased intravscular hydrostatic pressure and increased extravascular osmotic presure also contribute to fluid loss associated with inflammation
• In cases of systemic hypersensitivity, there can be more widespread fluid loss/edema

Question 30

What is the morphology of Edema?

Answer 30

• Gross:
  
  • clear, gel-like fluid within tissue
  • tends to gravitate to ventral areas
  • Can occur in body cavities
    
    • Ascites - abdomen
    • hydrothorax - thoracic cavity
    • hydropericardium - pericardial sac
• Histological:
  
  • Eosinophilic amorphous material within a tissue

Question 31

What is the significance of Edema?

Answer 31

• Can be insignificant to fatal
  
  • SQ edema has little functional significance
  • Cerebral or pulmonary eedema are life-threatening
• Clinical classification
  
  • nutritional
  • renal
  • cardic
  • parasitic