Flashcards in Body Fluids Deck (38):
What is osmolarity?
mOsm (milliosmoles)/L =
concentration of particles per liter of solution.
What is osmolality?
mOsm/kg = concentration of
particles per kg solvent (water in biological systems)
What is an effective osmole?
Refers to a solute that does not easily cross a membrane.
It is an effective osmole because it creates an osmotic force for water.
Proteins are effective osmoles for the vascular compartment
What is the average daily intake of water breakdown?
• Ingestion (fluids or food):
• 2100 ml/day
• 200 ml/day
Total Daily Intake: 2300 ml/day
What is the average daily loss of water breakdown?
• Insensible evaporation:
• 350 ml/day through skin (3-5 liters/day for severe burns)
• 350 ml/day via lungs
• 100 ml/day (5000 ml/day during exercise)
• 100 ml/day
• 1400 ml/day (500 ml/day during exercise)
Total Daily Loss: 2300 ml/day
What is the total body water?
42 liters (70 kg male)
• 50% body weight in females because of more body fat
• 70-75% body weight in premature and newborn
What is the 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)
What are some common things that can elevate the osmolar gap?
• Ethylene glycol
What is the 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
True or false plasma has a higher concentration of proteins because capillaries have a low permeability to plasma proteins.
True or false, ionic composition of plasma and interstitial fluid is similar.
True, because they are separated by highly permeable capillary membranes.
• Applies to measurement of fluid volumes in body
• 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
What are the relative amounts of extracellular fluids in interstitial spaces and plasma determined primarily by?
the balance of hydrostatic and colloid forces across
What is the distribution of fluid between intracellular and
extracellular compartments determined mostly by?
osmotic effects primarily of sodium and chloride
How much osmotic pressure is exerted across the cell membrane for each mOsm concentration gradient of an
about 19.3 mm Hg
What is the percentage of the total osmolarity of the interstitial fluid and plasma due to sodium and chloride ions?
How much of the osmolarity is due to potassium ion for the intracellular fluid?
If the cell membrane is exposed to pure water and the
osmolarity of intracellular fluid is 282 mOsm/L, what is the potential osmotic pressure that develop across the cell membrane?
more than 5400 mm Hg
What happens in an isotonic solution to the extracellular fluid compartment?
• Extracellular osmolarity does not change
• Extracellular volume increases
solutes having an osmolarity of 282 mOsm/L is isotonic
• Water cannot enter or leave the cell
• Examples: 0.9% NaCl or 5% Glucose
What happens in an hypertonic solution to the 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
What happens in an hypotonic solution to the extracellular fluid compartment?
• Volume of both compartments increases
• Osmolarity in both compartments decreases
• A solution of impermeant solutes having an osmolarity
What are the causes and consequences of hyponatremia?
- primary loss of NaCl
- overuse of diuretics
- Addison's disease
- brain cell edema
- headache, nausea, lethargy, disorientation
- seizures, coma, permanent brain damage/injury, death
What are the causes and consequences of hypernatremia?
- loss of water
- excess sodium in extracellular fluid
- excess NaCl added to the extracellular fluid
- intense thirst and secretion of ADH
- depression of the metabolic systems of the tissues
- lack of adequate nutrition to the cells
can also occur in inflammed tissues
- abnormal leakage of fluid from the plasma to the interstitial spaces across the capillaries
- failure to the lymphatics to return fluid from the interstitium back into the blood (lymphedema)
- excessive capillary fluid filtration
True or false, when interstitial fluid pressure is below 0, little fluid accumulates in tissues.
What is the safety factor against edema?
3 mm Hg
True or false, when interstitial fluid pressure rises above 0, free fluid (as opposed to gel fluid) rapidly begins to accumulate in tissues.
What is the anatomical organization of the kidneys?
• Renal cortex:
• Bowman’s capsule
• Proximal and distal convoluted tubules
• Renal medulla:
• Renal pyramids
• Renal pelvis:
• Major and minor calyces
Describe the structure of the nephron.
• 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
• Juxtaglomerular nephrons (20-30% of total) have glomeruli deep in renal cortex near medulla and have long loops of Henle.
• Juxtaglomerular nephrons have long efferent arterioles
associated with peritubular capillaries (vasa recta).
What is the pathway of blood flow to the kidneys?
What is the pathway of blood flow from the kidneys?
True or false, efferent arterioles help regulate hydrostatic pressure in both sets of capillaries.
What percent/amount of the total cardiac output do the kidneys receive?
22% , 1100 ml/min
What does high hydrostatic pressure in glomerular capillaries cause?
rapid fluid filtration
What does low hydrostatic pressure in peritubular capillaries permit?
rapid fluid reabsorption
What is considered high hydrostatic pressure in glomerular capillaries?
~ 60 mmHg