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HIS2 Body fluid compartments, osmolality- Learning Outcomes

Describe the distribution and composition of body fluids

  Male: 60% Water, 40% Solids (Fats, carbs, proteins, minerals)  Water (60%)

o  40% intracellular fluido  20% extracellular fluid (5% plasma and 15% interstitial fluid)

  Also consist of electrolytes, small quantities of amino acids/glucoseo  ICF: Na+, Cl-, HCO3- o  ECF: K+, PO43- 

Discuss how the composition of body fluids is maintained at a constant level

  The composition is essential for cell function (ECF= homeostasis ICF= cell mechanisms)  ECF = Glucose increases after a meal = increased secretion of insulin which decreases the

amount of glucose in the plasma. Other examples: blood pressure, pH, temperature 

  ICF has a selectively permeable cell membrane to water and small but not large ions/small solutes. Na/K transporter pump where K is pumped back in the cell and kept constant

Explain how the osmotic pressure of body fluids is determined

  Water moves down its concentration gradient, from area of low solute concentration to ahigh solute concentration, water will always move to dilute a solution.

  Typically ECF is similar to ICF in osmotic pressure, because there's no net movement ofwater into or out of the cells, it remains relatively constant.

Differentiate between osmolarity and osmolality

  Osmolarity = A concentration of a solution is expressed in Osmol/L of solutiono  Body fluid is 283 mOsmol/L because of ECF: K+, PO43- ICF: Na+, Cl- 

  Osmolality= A concentration of a solution expressed in Osmol/kg of solventExplain how the tonicity of solutions is determined

  Tonicity is the measure of the osmotic pressure gradient of two solutions separated by asemi permeable membrane.

  Effected by solutes that cannot pass the membrane (Na, K, etc.)  Hypertonic = Shrink and shrivel (Water escapes the cell, ECF < ICF )  Isotonic= No net effect (5% glucose or 0.9% saline ECF = ICF)  Hypotonic= Swell and burst (Water enters the cell, ECF > ICF)

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Describe the effects of water balance disturbances

  Water balance disturbances associated with changes in body fluid osmolarity.o  Osmotic movement of water into or out of the cell

  Water moves from low osmolarity to a high osmolarity.Diabetes mellitus Type 1 and Type 2

  Results from absolute or functional deficiency of circulating insulin (hyperglycemia)  Glucose is osmotically active (↑ ECF osmolarity = water shift ECF to ICF = dehydration)   Urinary glucose excretion (glycosuria) and kidney glucose excretion.  Symptoms: polyuria, intra/extracellular dehydration, increased thirst.

Dehydration:

  Insufficient H2O intake (desert travel, difficulty swallowing.  Symptoms mainly neurological as water lost from brain cells leads to shrinkage of cells.

Mild cases Moderate cases Severe cases  Non-neural

symptoms

Dry skin and

tongue, sunken

eyeballs

Mental confusion

and irrationality

Delerium,

convulsions, coma

Circulatory

disturbances (vary

from slight lower

BP, circ shock, and

death

Underhydration

  Excessive H2O loss (heavy sweating, vomiting, diarrhea, diseases such as cholera, diabetesinsipidus)

Overhydration

  Any surplus of water is excreted so it does not generally occur.  Patients with renal failure (cannot excrete dilute urine and become hypotonic upon

consuming more water than solutes)

  Low body mass infants  Marathon runners who only drink water  Over-heating (overexertion/MDMA-Ecstacy)  Syndrome of inappropriate vasopressin/ADH secretion (SIADH)  Excess water dilutes ECF → ECF osmolarity decreases → water moves by osmosis throughcell membrane → ICF osmolarity decreases → disrupts cell function   Symptoms: Related to water entering brain cells / swelling of brain cells leading to a

decrease in cell fluid osmolarity. = confusion, lethargy, headache, dizziness, vomiting and

severe cases coma/death. Also weakness (muscle cell swelling) and plasma volume increase 

Diabetes Insipidus

  Deficiency in vasopressin (ADH/antidiuretic hormone)   Normal for reduction in urine output, conserves water in the body.  Patients can produce up to 20 L of urine (normal is 1.5L)

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Relate the clinical use of IV solutions 

  Chemically prepared solutions for patients, by injection or infusion to blood.  Used to replace lost fluid and aid in IV medication delivery

Colloid

solutions

High molecular weight solutions Ex: albumin or other which do not

readily cross the semi-permeable membrane.

They stay longer than crystalloid (3-6h). Reduces abnormal

accumulation of fluid in interstitial compartment (edema) because

they draw fluid from interstitial/intracellular to vascular components.

Crystalloid

solutions

Clear solutions consisting of sterile water and electrolytes which

cross a semi-permeable membrane into interstitial space and achieve

equilibrium in 2-3 hours. The principle one for IV therapy and

classified based on tonicity.

Given to patients undergoing surgery (IV drip of saline), used to

rehydrate or admin drugs. Isotonic saline can also be given to patients

with low ECF volume (dehydrated).

Hypertonic: 3% - 5% saline which may be given to patients with low

 plasma osmolarity and as a result water has moved into the cells

Hypotonic: 0.45% saline which may be given to patients whose body

fluids are hyperosmotic or with renal disease and cannot rehydrate

 but do not need additional sodium.

Blood products