Lecture 15: Body Fluids

Question 1

Review slide 4-6 and do what it says

Answer 1

Do it.

Question 2

How much daily intake of fluid is recommended daily?

Fluid Loss?

Answer 2

• Fluid Intake
• Ingestion (fluids or food): 2100 ml/day
• Metabolism: 200 ml/day
• Fluid Loss:
  -Insensible evaporation:
  350 ml/day through skin (3-5 liters/day for severe burns)
  350 ml/day via lungs
• Sweat: 100 ml/day (5000 ml/day during exercise)
• Feces: 100 ml/day
• Urine: 1400 ml/day (500 ml/day during exercise)

Total: 2300 mL/day both in And out

Question 3

Review image on slide 8

What is the water composition in the average person?

Answer 3

• Extracellular:
• Interstitial (≈ 11 liters)
• Plasma (≈ 3 liters)
• Transcellular

*Intracellular: 28 liters (40%)

• Total:
• 42 Liters in a 70 kg male
• 50% body weight in females because of more body fat
• 70-75% body weight in premature and newborn

Question 4

Describe the Osmolar Gap

Answer 4

Osmolar Gap: (helps to narrow the differential diagnosis)

• Difference between the measured osmolality and the estimated osmolality (Normal ≤ 15)
• ECF Effective osmolality = 2(Na+) mEq/L + (glucose mg%/18) + (urea mg%/2.8)
• Common things that can elevate the osmolar gap:
• Ethanol
• Methanol
• Ethylene glycol
• Acetone
• Mannitol

Question 5

Describe the body fluid compartments

Answer 5

• Ionic composition of plasma and interstitial fluid is similar because they are separated by highly permeable capillary membranes.
• Higher concentration of proteins in plasma because capillaries have a low permeability to plasma proteins.
• Intracellular fluid composition:
• Small amounts of sodium and chloride ions
• Almost no calcium ions
• Large amounts of potassium and phosphate ions
• Moderate amounts of magnesium and sulphate ions

Question 6

Describe the indicator dilution principle

Answer 6

• Applies to measurement of fluid volumes in body fluid compartments.
• Requirements for an indicator:
• Disperses evenly throughout compartment
• Disperses only in compartment being measured
• Not metabolized or excreted
• Not toxic

Vol B = Vol A x conc. A / conc. B
- See Slide 13

Question 7

Describe Fluid Distribution and Amounts

Answer 7

• Relative amounts of extracellular fluids in interstitial spaces and plasma are determined primarily by balance of hydrostatic and colloid forces across capillary membranes.
• Distribution of fluid between intracellular and extracellular compartments is determined mostly by osmotic effects primarily of sodium and chloride ions.

Question 8

What is the difference between Osmolality and Osmolarity?

Answer 8

• The total number of particles in a solution is measured in osmoles.
• Osmolal concentration of a solution =
• Osmolality when concentration is expressed as osmoles/Kg of water
• Osmolarity when concentration is expressed as osmoles/liter

Question 9

How does one calculate the potential osmotic pressure of a solution?

Answer 9

• About 80% of the total osmolarity of the interstitial fluid and plasma is due to sodium and chloride ions.
• For intracellular fluid, about half the osmolarity is due to potassium ion.
• If the cell membrane is exposed to pure water and the osmolarity of intracellular fluid is 282 mOsm/L:
• The potential osmotic pressure that can develop across the cell membrane is more than 5400 mm Hg.

Question 10

Define the term Isotonic

Answer 10

• Note that the terms isotonic, hypotonic, and hypertonic refer to whether or not solutions will change the volume of a cell. Refer to Figures 25-5 and 25-6.
• Addition of isotonic saline to extracellular fluid compartment:
• Extracellular osmolarity does not change
• Extracellular volume increases
• A solution of impermeant solutes having an osmolarity of 282 mOsm/L is isotonic
• Water cannot enter or leave the cell
• Examples: 0.9% NaClor 5% Glucose

Question 11

Define the term Hypertonic

Answer 11

• Addition of hypertonic saline to extracellular fluid compartment:
• Intracellular volume decreases
• Extracellular volume increases
• Osmolarity in both compartments increases
• A solution of impermeant solutes having an osmolarity > 282 mOsm/L = hypertonic
• Water will diffuse out of the cell

Question 12

Define the term Hypotonic

Answer 12

• Addition of hypotonic saline to extracellular fluid compartment:
• Volume of both compartments increases
• Osmolarity in both compartments decreases
• A solution of impermeant solutes having an osmolarity < 282 mOsm/L = hypotonic
• Water will diffuse into the cell
• See Slides 24-25

Question 13

• Need to figure out:
• What are the causes and consequences of hyponatremia and hypernatremia?
• Compare and contrast intracellular and extracellular edema.
• Name the three conditions especially prone to cause intracellular swelling.
• Review causes of extracellular edema:
• Refer to page 297

Answer 13

Have to look this one up on own.

Question 14

Review Slides 27-33

Answer 14

Do It

Question 15

Describe the anatomical organization of kidneys

Answer 15

• Capsule
• Renal cortex:
• Bowman’s capsule
• Proximal and distal convoluted tubules
• Renal medulla:
• Renal pyramids
• Renal pelvis:
• Major and minor calyces
• See Slides 36

Question 16

Describe the structure of a nephron

Answer 16

• 800,000 –1,000,000 nephrons/kidney
• Decrease by 10% every year after the age of 40
• Each large collecting duct (≈ 250/kidney) receives urine from 4000 nephrons
• Cortical nephrons have glomeruli located in outer cortex and have short loops of Henle
• Juxtamedullary nephrons (20-30% of total) have glomeruli deep in renal cortex near medulla and have long loops of Henle.
• Juxtamedullary nephrons have long efferent arterioles associated with peritubular capillaries (vasa recta)
• See Slide 38

Question 17

Describe Blood Flow to the Kidney

Answer 17

• Kidneys receive about 22% of total cardiac output:
• 1100 ml/min.
• Efferent arterioles help regulate hydrostatic pressure in both sets of capillaries:
• High hydrostatic pressure in glomerular capillaries (≈60 mm Hg):
• • Causes rapid fluid filtration.
• Low hydrostatic pressure in peritubular capillaries (≈13 mm Hg):
• • Permits rapid fluid reabsorption.
• See Slides 40-44