CVPR Week 7: Water & Sodium Balance Flashcards
Objectives

Question 1


Question 2


Question 3


Basic role of the kidneys
Body fluid composition
How do the kidneys change body fluid composition?
- Ideal environment for cellular function
- water and electrolyte excretion and retention controlled
- Composition of extracellular water and plasma tightly regulated by renal function
Primary processes of the kidneys
5 listed
- Filtration
- Reabsorption
- Secretion
- Excretion
- Endocrine function

What structure in the kidney is responsible for filtration?
Bowman’s Capsule
Glomerulus AKA
Bowman’s Capsule
Bowman’s Capsule AKA
Glomerulus
What function is the glomerulus responsible for?
Filtration
What function is the proximal tubule responsible for?
Reabsorption
What function is responsible for reabsorption in the kidney?
Proximal tubule
What function is responsible for descending water reabsorption and ascending solute reabsorption in the kidney?
Loop of Henle
What function is responsible for regulated solute reabsorption in the kidney?
Distal tubule
What function is responsible for regulated water reabsorption in the kidney?
Collecting duct
What function is the proximal tubule responsible for?
Reabsorption
What function is the Loop of Henle responsible for?
- Water reabsorption (descending)
- Solute reabsorption (ascending)
What function is the distal tubule responsible for?
Regulated solute reabsorption
What function is the collecting duct responsible for?
Regulated water reabsorption
Identify


Types of nephrons
- Superficial nephrons
- Juxtamedullary nephrons
Juxtamedullary nephrons
- 10% of nephrons
- Long loop
Superficial nephrons
- Short loop
- 90% of nephrons
Identify


The filtration process
- Blood is “filtered” as it passes through the glomerular capillaries
- ~20% of plasma entering the glomerulus is filtered into Bowman’s Space and enters the proximal tubules
- Plasma is filtered ~60 times/day to control water, sodium and waste product levels
Blood is filtered as it passes through?
The glomerular capillaries
How much filtrate is Reabsorbed
99% of filtrate is reabsorbed
Reabsorbed filtrate moves into
The peritubular capillaries
How is reabsorption regulated?
By hormones
The importance of urine excretion
important route of excretion for many toxic substances
How is secretion in the kidney mediated?
By transporters
Endocrine function of the kidneys
The kidney is an important site of synthesis for three hormones
Renal hormones
3 listed
- Erythropoietin
- 1, 25-dihydroxy vitamin D3
- Renin
1, 25-dihydroxy vitamin D3 AKA
Calcitriol
Calcitriol AKA
1, 25-dihydroxy vitamin D3
Erythropoietin function
Erythrocyte formation
1, 25-dihydroxy vitamin D3 function
Ca2+ homeostasis
Renin function
Na+ and H2O balance
Location of renin synthesis
Synthesized in juxtaglomerular cells (JCC) of the afferent arteriole (granular cells)
What is renin
Renin is an enzyme the regulates the formation of angiotensin II
Renin regulation
Renin is regulated by sympathetic nerves, salt intake and blood pressure
What stimulates the release of renin?
Decreased renal blood flow or sodium delivery stimulates renin release
Renin function
regulates the formation of angiotensin II
Angiotensin II function in fluid composition
it is a sodium-retaining hormone
Identify


EGMC AKA
Extraglomerular mesangial cell
What is erythropoietin?
a glycoprotein hormone
Location of erythropoietin synthesis
Erythropoietin is synthesized and secreted from renal epithelial cells
Erythropoietin function
stimulates erythrocyte synthesis
erythropoietin AKA
EPO
EPO AKA
erythropoietin
Renal failure and erythropoietin
Renal failure decreases erythropoietin synthesis leading to anemia
Location of calcitriol synthesis
- The inactive 25-hydroxyvitamin D (Calcidiol) is synthesized in the skin and liver
- Calcidiol is then taken up by proximal tubule cells hydroxylated to active calcitriol (1, 25-dihydroxy vitamin D)
Calcitriol is reabsorbed
from the proximal tubule into the blood stream
Calcitriol function
increases Ca2+ reabsorption from the gut and from the renal tubules and inhibits PTH release
Calcitriol synthesis pathway

Renal regulation of body fluids: Out
- Urine
- Sweat
- Feces
Renal regulation of body fluids: In
- Food
- metabolism
Renal regulation of body fluids

Body fluid compartments
- Intracellular compartment
- Extracellular compartment
Total body water compartmentalization
40% ICW
20% ECW

Intracellular water % of body weight
40% of the body weight
Extracellular water % of body weight
20%
Intracellular compartment water consists of?
Water inside cells
Electrolyte composition of the intracellular compartment
- High [K+]
- Low [Na+] & [Ca2+]
How does water move in the intracellular compartment
- movement across cell membranes through channels and pumps
- water moves freely in and out of cells
Extracellular compartment electrolyte composition
- Low [K+]
- High [Na+] & [Ca2+]
Extracellular compartment water consists of?
plasma and interstitial water
Extracellular compartment movement of water
- Relatively large changes in volume
- water moves from the plasma to interstitium across capillaries (back in lymph)
Electrolyte distribution in fluid compartments

How to calculate compartment size
Dilution principle

Substances used to estimate body compartment sizes
- Total body water
- Extracellular fluid
- plasma
- Intracellular fluid
- Interstitial water
TBW AKA
Total Body water
ECF AKA
Extracellular fluid
VP
Plasma volume
ICF AKA
Intracellular fluid
Vinst AKA
Interstitial water volume
Vinst =
ECF - VP
ICF =
TBW - ECF
VP =
Evans blue or 131I-albumin
ECF =
Inulin or mannitol
TBW =
Antipyrine
Titrated water (3H2O) or deuterium (D2O)
The simplest and cheapest method for quickly assessing fluid balance
Body weight
Plasma osmolarity =
2 x PNa + [glucose]/18 + BUN/2.8 = plasma osmolarity
Considerations of estimating plasma osmolality
- Protein is ignored since it usually contributes less than 1 mOsm
- [glucose] is divided by 18 and BUN by 2.8 to convert from mg/dL to mmol/L
- PNa is multiplied by 2 to account for the accompannying anion (usually Cl- or HCO3-)
- 2 x PNa gives an estimate of plasma osmolality
- (will give a low value if glucose, BUN or organic acids are elevated)
Na intake alters?
ECF volume

Osmosis description
Solvent moves towards high solute concentration from a lower solute concentration
Osmosis solute considerations
Only non-permeant solute contributes to osmotic pressure
Osmosis rate is dependent on?
osmotic gradient and permeability of the membrane
What determines the final size of a compartment?
the amount of non-permeant solute in that compartment
How is cell volume regulated?
Osmolality regulates cell volume

Types of volume expansion
- Isosmotic
- Hyperosmotic

Hyposmotic volume expansion
