Intro to Renal Physiology (5) Flashcards
What are the 5 regulatory functions of the kidneys?
1- Extracellular fluid volume
2- Extracellular fluid osmolarity
3- Extracellular fluid ion composition
4- Clearance of metabolic end products, toxins and drugs
5- Endocrine
What percent of body weight does TBW account for? How many liters is this?
60%
42L
What percent of body weight does intracellular fluid account for? How many liters is this?
40%
28L
What percent of body weight does extracellular fluid account for? How many liters is this?
20%
14L
What are the two main components of ECF? What are their percentages?
Plasma- 25% (3 L)
Extravascular fluid- 75% (10L)
True or False: The solute composition and the osmolarity of the ICF and ECF are same.
False:
The solute composition of the ICF and ECF is different and the ospolarity of the ICF and ECF are the same/
What organ is the only effector organ of regulated water and salt excretion?
Kidneys
Where does unregulated water and salt loss from TBW occur?
Sweat, feces, skin and lungs
What drives fluid distribution between plasma and interstitial fluid?
The balance between hydrostatic pressure and osmotic pressure differences across the capillary wall
Which is higher on the arteriolar side of a capillary….hydrostatic pressure or oncotic pressure?
Hydrostatic pressure
Which is higher on the venous side of a capillary….hydrostatic pressure or oncotic pressure?
Oncotic pressure
What is the equation for filtration or reabsorption rate?
= Lp [(Pc-Pi)- (Oc-Oi)]
Note: O= oncotic pressure
What is Lp?
the hydraulic conductivity coefficient relating the magnitude of fluid volume transfer across the capillary wall per unit of hyrdostatic pressure difference or oncotic pressure difference
What determines of net filtration or reabsorption occurs aloong the length of the capillary?
Balance of forces (hydrostatic and oncotic)
What is the definition for edema?
the excess accumulation of fluid in the interstitial space due to cardiac, renal, hepatic or endocrine dysfunction
What is the cause of edema in congestive heart failure?
Increased hydrostatic pressure on the venous end of the capillary
What is the cause of edema in renal and hepatic dystunction?
Decreased oncotic pressure because of decreased plasma protein concentration.
True or False: Net movement of water between ICF and ECF is driven ONLY by osmotic pressure differences across the cell membrane.
True
Describe the changes in isosmotic fluid expansion
Increase in ECF volume
Dilution of plasma proteins
Decreased Hematocrit
Describe the changes seen in isosmotic volume contraction:
Decreased ECF volume
Concentration of plasma proteins
Increased hematocrit
What are some causes of isosmotic volume contraction?
Diarrhea, isosmotic/isotinic fluid loss from the ECF
What causes isosmotic fluid expansion?
Intravenous isosmotic/ isotonic fluid gain to ECF
Describe the changes seen in hyperosmotic volume contraction:
Decreased ECF volume and Increased ECF osmolarity
This leads to movement of water from ICF to ECF.
Decreased ICF volume and increased ICF osmolarity
What can cause hyperosmotic volume contraction?
Profuse sweating and/ or water deprivation
Describe the changes seen in hyperosmotic fluid expansion:
Increased ECF osmolarity
This leads to movement of water from ICF to ECF
Decreased ICF volume and increased ICF osmolarity
After the movement of water in hyperosmotic fluid expansion, what is the effect on ECF volume?
Increased volume to adjust for the increased osmolarity
What can cause hyperosmotic fluid expansion?
High NaCl intake without fluids. Gain of solute in excess of water in the ECF.
Describe the changes seen in hypoosmotic volume expansion:
Increased ECF volume and decreased ECF osmolarity
This leads to movement of water from ECF to ICF
Increased ICF volume and decreased ICF osmolarity
What can cause hypoosmeotic volume expansion?
Syndrome of inappropriate antidiuretic hormone….gain of water in excess of solute
Describe the changes seen in hypoosmotic volume contraction:
Decreased ECF osmolarity
This leads to water moving from the ECF to ICF
Increased ICF volume and decreased ICF osmolarity
What is the result of the adjustments made for hypoosmotic volume contraction?
Decreased ECF volume
What can cause hypoosmotic volume contraction?
Adrenal (aldosterone) insufficiency and decreased renal NaCl reabsorption (loss of solute in excess of water)
What happens to the cell when there is an increase in ECF osmolarity?
Cell shrinks
What do cells do to compensate for an increase in ECF after they have shrunken?
Cells activate solute uptake mechanisms to increased ICF osmolarity, driving water into cells to restore volume to normal
What happens to the cell when there is a decrease in ECF osmolarity?
cell swelling
What do cells do to compensate for a decrease in ECF after they have swelled?
Cells activate solute efflux mechanisms to decreased ICF osmolarity, driving water out of the cells to restore volume to normal
What is filtration?
anatomical separation of an ultrafiltrate from the blood
What is reabsorption?
the directional movement of solutes and water from the lumen of the kidney tubule to the peritubular surface
What is secretion?
the directional movement of solutes (not water) from the peritubular side (blood side) of the kidney tubule to the lumenal surface
What is synthesis?
Metabolism within kidney cells degrading and creating organic solutes or hormones apprearing in the blood or in the urine
What is excretion?
The final result of filtration, reabsorption, secretion, and synthesis. It is the amount of solute and water eliminated in the urine.
For solutes metabolized by the kidney:
Excretion=
Filtered + Secreted +Synthesized - Reabsorbed
For solutes not metabolized by the kidney:
Excreted=
Filtered + secreted - Reabsorbed
What are the three components of renal function:
1- glomerular filtration
2- Tubular secretion
3- tubular reabsorption
Which is driven by a gradient in hydrostatic pressure…..filtration or osmosis?
Filtration
How many liters a day of water are filtered? Excreted?
Filtered: 180
Excreted: 0.5-12
How much Na is filtered and excreted?
Filtered: 25,500
Excreted: +/- 100
How much HCO3 is filtered and excreted?
Filtered: 1320
Excreted: +/- 4
How much Cl- is filtered and excreted?
Filtered: 18000
Excreted:+/- 100
How much glucose is filtered and excreted?
Filtered: 1100
Excreted:0