BIOL125 Lecture Notes - Sodium Bicarbonate, Semipermeable Membrane, Solution
10 Jun 2018
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Definitions:
Osmosis: movement of water across a semi-permeable membrane, from a lower solute
concentration to a higher solute concentration
e.g. water moves from a lower solute concentration to a higher sugar concentration (to make
concentrations the same)
Water:
Main component of all body fluids moves by
osmosis, driven by concentration of solutes
Body water content:
-At birth = 70-85%
-Adults = 50-65%
-Old age = 40-45%
As we age, body fat increases and less water
is stored, so more tendency to dehydration
Also gender differences in water content
Fluid compartments- intracellular vs extracellular fluid:
Extracellular fluid (ECF):
-plasma and interstitial fluid
-makes up 1/3 total body water
Intracellular fluid (ICF):
-fluid within cells of the body
-makes up 2/3 total body water
-water can diffuse freely cross most cell membranes
-in health, the osmotic pressure is the same in ECF and ICF- to retain isotonically
Solutes, concentration and solutions:
Solute- dissolved substance
Solution- a mixture of solute and solvent
Electrolytes- chemical substances in the body that dissociate into ions in solution, and have the
capacity to conduct electricity
Ionic bonds break to cations + and anions - e.g. NaCl in water = Na+ Cl-, NaHCO3 = Na+ HCO3-
Non-electrolytes- dissolve in solution but do not dissociate covalent bonds- e.g. glucose, urea,
creatine
Concentration- amount dissolved in solution weight/mL, %, volume/mL, moles/L, osmol/L saline-
0.9% NaCl in water (0.9g/100mL) = isotonic
Molarity- number of molecules of solute in a solution (mmol/L)
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Osmolarity- number of molecules of solute that dissociates in a solution (mosmol/L)- term used for
electrolytes
Osmolarity of cells and ECF maintained at 290 mosmol/L, despite variations in overall composition;
this is because hydrophobic lipid membranes are permeable to water
Fluid intake:
Fluid intake vs fluid output
No receptors directly monitor fluid intake or output (in ml)
Monitored indirectly by:
-blood volume changes
-blood pressure changes
-plasma osmolarity (concentration of dissolved substances in blood eg Na, K)
All are connected
e.g. fluid intake- inc. blood volume- inc. BP- de. blood osmolarity
e.g. fluid output- dec. blood volume- dec. BP- inc. blood osmolarity
Water:
Main component of all body fluids
Moves by osmosis
Driven by concentration of solutes
Fluid balance- electrolyte balance
What is tonicity?
Tonicity of a solution (=solute in ECF solution) is the effect the solution has on cell volume (same,
shrink or swell)
-the cell membrane and capillary endothelium act as selective barriers
-a cell changes shape due to the net movement of water into or out of the cell
-if ECF is isotonic, no net movement
-if ECF is hypotonic, water moves into cells, they will swell and perhaps burst (lysis)
-if ECF is hypertonic, water moves out of cells, they will shrink (crenate)
Water imbalance:
Dehydration
Water loss > water gain
Increase in plasma osmolarity (becomes hypertonic)
Cells shrink-…. cell death
To correct- homeostasis responds to increase water (thirst response) and reduce loss (ADH)
Overhydration:
water gain > water loss
decrease in plasma osmolarity (becomes hypotonic)
Cells swell-…. convulsion, coma, death
To correct, homeostasis responds by excreting water (increase urinary output) and minimising gain
Dehydration:
E.g. fever, burns, vomiting, haemorrhage, diarrhoea
1. Decrease in saliva, dry mucosa in mouth and pharynx
ADH release stimulated from posterior pituitary to give increased water reabsorption back into
renal capillaries
Reduced urine output
2. Decreased in blood volume
BP drops
Renin- angiotensin- adlosterone-system (RAAS) activated to induce production of Angiotensin II- a
powerful systematic vasoconstrictor. Thirst centre activated in hypothalamus
Drink to relieve dehydration: already thirst when activated
Poor thirst response in very young, elderly
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Osmosis: movement of water across a semi-permeable membrane, from a lower solute concentration to a higher solute concentration e. g. water moves from a lower solute concentration to a higher sugar concentration (to make concentrations the same) Main component of all body uids moves by osmosis, driven by concentration of solutes. As we age, body fat increases and less water is stored, so more tendency to dehydration. Water can diffuse freely cross most cell membranes. In health, the osmotic pressure is the same in ecf and icf- to retain isotonically. Electrolytes- chemical substances in the body that dissociate into ions in solution, and have the capacity to conduct electricity. Ionic bonds break to cations + and anions - e. g. nacl in water = na+ cl-, nahco3 = na+ hco3- Non-electrolytes- dissolve in solution but do not dissociate covalent bonds- e. g. glucose, urea, creatine. Concentration- amount dissolved in solution weight/ml, %, volume/ml, moles/l, osmol/l saline-
