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MS 1 Physiology Unit 7 > Introduction to Renal Physiology > Flashcards

Introduction to Renal Physiology Flashcards

1
Q

Regulatory Functions of the Kidneys

A
  • extracellular fluid volume
  • extracellular fluid osmolarity
  • extracellular fluid ion composition (Na+, K+, H+, HCO3-)
  • clearance of metabolic end products, toxins and drugs
  • endocrine (erythropoietin, active vitamin D, renin)
  • the regulatory function of the kidney is what it does outside the kidney by doing what it does inside the kidney
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2
Q

Body Fluid Compartments

A
  • Total Body Water (TBW)- 60% body weight, 42L
  • ICF- 40%, 28L
  • ECF- 20%, 14L
  • Intravascular fluid- 7%, 5L
  • Plasma (25% of ECF)- 3L
  • RBC,WBC, Platelets- 2L
  • Extravascular fluid (75% of ECF, interstitial fluid, lymph)- 15%, 10L
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3
Q

Body Fluid Facts

A
  • total body fluid decreases with age from 75% with neonates to 50% BW in aged adults
  • the ECF goes from 50% of TBW in neonates to 33% TBW in adults
  • TBW is inversely proportional to % body fat and TBW decrease as % of BW with an increased % of body fat. For example, puberty increases body fat in women, which decreases TBW as a % of BW
  • whereas the solute composition of the ICF and ECF is different, the solute concentration or osmolarity of the ICF and ECF is essentially the same (300 mOsm/L)
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4
Q

Body Fluid Balacne

A
  • kidneys monitor and maintain plasma volume and osmolarity (solute concentration) which in turn maintains total body water and osmolarity (solute concentration) due to water and solute exchange between the ECF and ICF compartments
  • ICF ECF (plasma) Kidney Urine
  • kidneys are the only effector organs of regulated water and salt excretion. Unregulated water and salt loss from TBW occurs in: sweat, feces, insensible skin and lung loss (H20 only)
  • the kidneys are the effector organ compensating for the effects of variable consumption of solutes and water on ECF volume and osmolarity by increasing or decreasing the excretion of solutes and water in the urine
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5
Q

Fluid and Solute Distribution Between Plasma and Interstitial Fluid

A

-fluid distribution between plasma and ISF is driven by the balance between hydrostatic pressure and osmotic pressure differences across the capillary wall
-opposing forces (Starling forces) of hydrostatic and osmotic pressure, which determine the magnitude and direction of fluid distribution across the capillary wall
-net filtration or reabsorption will occur along the length of the capillary depending on the balance of forces favoring filitration or reabsorption
-arteriole to venous blood flow through the capillaries occurs with filtration of intravascular fluid at the arteriole end where the forces driving filtration (hydrostatic pressure) exceed the forces opposing filtration (oncotic pressure)
-and with reabsorption of extravascular fluid at the venous end
where the forces driving reabsorption (oncotic pressure) exceed the forces driving filtration (hydrostatic pressure)
-it is the filtration of fluid from the intravascular to the extravascular space, which causes a decrease in intravascular hydrostatic pressure as well as the concentration of plasma proteins, which increases intravascular oncotic pressure
-this effect reverses the balance of driving forces favoring reabsorption over filtration at venous end of capillary

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6
Q

Fluid and Solute Distribution Between Plasma and Interstitial Fluid

A
  • filtration of fluid out of the intravascular compartment (plasma) into the extravascular compartment (ISF) and reabsorption of fluid from the extravascular compartment (ISF) into the intravascular compartment (plasma) is driven by opposing forces (starling forces) of hydrostatic and osmotic pressure, which determine the magnitude and direction of fluid distribution across the capillary wall
  • Filtration or Reabsorption Rate = Lp [(Pc-Pi)- PiC-Pi i)] (push out - pull in)
  • net filtration or reabsorption will occur along the length of the capillary depending on the balance of forces favoring filtration or reabsorption
  • solute distribution: solute concentration is similar between the ISF and plasma with the exception of negatively charged plasma proteins, which are impermeable to the capillary wall and remain within the intravascular compartment- oncotic pressure is higher in plasma than ISF due to absence of protein in ISF
  • the presence of negative charged proteins in plasma causes a slightly higher diffusible cation concentration in plasma and a slightly higher diffusible anion concentration in the ISF. The diffusable cation and anion concentration is in a state of electro-chemical equilibrium known as the Gibbs-Donnan equilibrium
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7
Q

Edema

A
  • the excess accumulation of fluid in the interstitial space due to cardiac, renal, hepatic or endocrine dysfunction
  • a localized or generalized imbalance of hydrostatic and osmotic pressure across the capillary wall, which induces a shift in fluid distribution from the intravascular to extravascular space
  • CHF, nephrotic syndrome, liver disease can cause an isotonic retention of sodium and water as well as decreased circulating volume, which may decreased renal perfusion pressure and activate the R-A-A system, further increasing sodium retention maintaining edema
  • an increase or decrease in edema can be assessed clinically by the patients weight
  • CHF raises capillary hydrostatic pressure
  • nephrotic syndrome and liver disease decrease plasma protein concentration and capillary oncotic pressure
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8
Q

Fluid and Solute Distribution Between ICF and ECF

A
  • net movement of water between ICF and ECF is driven by osmotic pressure differences across the cell membrane
  • permeating and non-permeating solute concentrations (tonicity) in the ICF and ECF determine water movement
  • water moves passively across the cell membrane down its concentration gradient in a direction from the side of higher water concentration (lower tonicity) to the side of lower water concentration (higher tonicity) through the lipid bilayer or through protein water channels (aquaporins) spanning the lipid bilayer
  • the rule of water movement across barriers separating compartments is: passive transport of water follows active or passive transport of solutes
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9
Q

Isosmotic Fluid Expansion

A
  • IV isosmotic fluid gain to ECF
  • increase ECF volume
  • N/C in ECF osmolarity
  • no osmotic driving force between ICF and ECF
  • N/C in ICF volume or osmolarity
  • dilution of plasma proteins and decrease hematocrit
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10
Q

Isosmotic Volume Contraction

A
  • diarrhea, isosmotic fluid loss
  • decrease ECF volume
  • no change in ECF osmolarity
  • no osmotic driving force between ICF and ECF
  • no change in ICF volume or osmolarity
  • concentration of protein and increased hematocrit
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11
Q

Hyperosmotic Volume Contraction- sweating

A
  • profuse sweating and/or water deprivation (loss of water in excess of solute from the ECF)
  • decreased ECF volume and increase ECF osmolarity
  • water moves from ICF to ECF
  • decreased ICF volume and increased ICF osmolarity
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12
Q

Hyperosmotic Volume Expansion

A
  • high NaCl intake without fluids (gain of solute in excess of water)
  • increase ECF osmolarity
  • water moves from ICF to ECF
  • decrease ICF volume and increase ICF osmolarity
  • increase ECF volume
  • ICF Na (and Cl) concentration remains unchanged due to Na-K pump activity (Na extrusion) balancing Na entry
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13
Q

Hypoosmotic Volume Expansion-antidiuretic

A
  • syndrome of inappropriate antidiuretic hormone (SIADH) (gain of water in excess of solute)
  • excess water reabsorption from collecting ducts into ECF causes
  • increase ECF volume and decrease ECF osmolarity
  • water moves from ECF to ICF
  • increase ICF volume and decrease ICF osmolarity
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14
Q

Hypoosmotic Volume Contraction (aldosterone)

A
  • adrenal (aldosterone) insuffiency and decreased renal NaCl reabsorption (loss of solute in excess of water)
  • decrease ECF osmolarity
  • water moves from ECf to ICF
  • increase ICF volume and decrease ICF osmolarity
  • decrease ECF volume
  • salt wasting
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15
Q

Solute Distribution

A
  • the solute composition of the ICF and ECF is different due to the ubiquity of Na-K+ ATPase in the membrane of virtually all cells
  • Na-K+ ATPase exchanges intracellular Na for extracellular K+, thus maintaining intercellular K+ concentration high and intracellular Na concentration low as well as maintaining extracellular K+ low and extracellular Na concentration high
  • desprite differences in intra- and extracellular solute composition, the sum total of different solute concentrations (osmolarity) is essentially equivalent (290 mOsm/L) in the ICF and ECF
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16
Q

Cell Volume regulation

A
  • cells respond to osmotically driven changes in ECF volume by activatng solute transport mechanisms
  • cell shrinking in response to an increase in ECF osmolarity
  • cell swelling in response to decrease in ECF osmolarity
  • exercise caution in attempting to restore ECF osmolarity to normal. In cells where RVI or RVD has occured in response to an increase and decrease in ECF osmolarity, a rapid correction of ECF osmolarity, by giving hypotonic or hypertonic IV fluids at high rate of infusion, may cause a dangerous cell shrinking if RVD had previously occurred
17
Q

Cell shrinking

A
  • in response to an increase in ECF osmolarity: cells activate solute uptake mechanisms to increase ICF osmolarity, driving water into cells to restore volume to normal (regulatory volume increase RVI)
  • water transport follows solute transport
18
Q

Cell swelling

A
  • in response to a decrease in ECF osmolarity
  • cells activate solute efflux mechanisms to decrease ICF osmolarity driving water out of cells to restore volume to normal (Regulatory Volume Decrease RVD)
  • water transport follows solute
19
Q

Filtration

A
  • the anatomical separation of an ultrafiltration of blood through glomerurlar capillaries excluding cells and large proteins from the filtation
  • not urine
20
Q

Reabsorption

A

-the directional movement of solutes and water from the lumen of the kidney tubule to the peritubular surface (blood side)

21
Q

Secretion

A

-the directional movement of solutes (not water) from the peritubular side (blood side) of the kidney tubule to the lumenal surface

22
Q

Synthesis

A
  • metabolism within kidney cells degrading and creating organic solutes or hormones appearing in the blood or in the urine
  • NH4+, HCO3-, renin erythropoietin and active Vitamin D
23
Q

Excretion

A
  • the final result of the above processes
  • the amount of solute and water eliminated in the urine
  • excretion is not a renal process
24
Q

Renal “Handling” Of solutes and water

A

-excreted= filtered + secreted + synthesized - reabsorbed

  • for solutes not metabolized by the kidney: excreted = filtered + secreted - reabsorbed
  • the renal handling of solutes and water is what the nephron does with filtered water and solutes. The renal handling of each filtered solute is considered individually
25
Q

Components of Renal function

A
  • to acieve its homoestatic functions the kidneys separate the plasma from the blood (filtration) to form a tubular ultrafiltrate, which changes in volume and solute composition, as it passes down the nephron by reabsorption and secretion of solutes and by reabsorption (not secretion) of water
  • nephron is assembly line of cell-specific, solute reabsorptive and secretory processes, beginning with proximal tubule and ending at the collecting duct
  • final product at the end of the assembly line is urine which is excreted
  • urine is formed, collectively, for approximately 1 million nephrons or assembly lines in each kidney
    1. Glomerular filtration
    2. Tubular secretion
    3. Tubular reabsorption
26
Q

Water Filitration

A
  • the movement of water across a permeable barrier driven by a gradient or difference in hydrostatic pressure
  • filtration does not occur across the cell membrane because the cell membrane is unable to withstand a hydrostatic pressure gradient necessary to drive filtration
27
Q

Osmosis

A
  • the movement of water across a permeable barrier driven by an osmotic gradient or difference in water concentration
  • water concentration is higher where solute concentration is lower and water concentration is lower where solute concentration is higher
28
Q

Passive Diffusion

A

-the movement of solutes in a direction across the cell membrane down the solute electrochemical potential gradient across a cell membrane or an epithelial cell layer

29
Q

Active Transport

A
  • the movement of solutes in a direction across the cell membrane up or against the solute electrochemical potential gradient
  • active transport requires direct (primary) or indirect (secondary) coupling to the cell’s metabolic energy (ATP)
30
Q

Renal Handling of Solutes and Water

A
  • the kidneys effect the homeostatic conctrol of ECF osmolarity and volume
  • neural and hormonal signals direct the kidneys to vary filtration and reabsorption of water and solute to maintain ECF osmolarity and volume within normal limits
  • the kidneys vary water reabsorption to regulate extracellular osmolarity and vary solute (primarily NaCl) reabsorption to regulate blood volume/arterial pressure

MS 1 Physiology Unit 7 (11 decks)

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