Describe Osmolarity.
It is the concentration of osmotically active particles present in a solution.
Units are osmol/l or mosmol/l (the latter is used for body fluids as these are weak salt solutions).
Can be calculate if:
1) The molar concentration of the solution is known.
2) The number of osmotically active particles present is known.
Compare osmolarity and osmolality with relation to body fluids.
For weak solutions (such as body fluids) osmolarity and osmolality are interchangeable.
Osmolality has units of osmol/kg water.
Osmolarity has units of osmol/l.
Describe tonicity.
Is the effect a solution has on cell volume, it also takes into consideration the ability of a solute to cross the cell membrane.
A solution can be:
- hypertonic = a decrease in cell volume as less water and higher salt concentration causes cell shrinkage.
- isotonic = no change in cell volume.
- hypotonic = an increase in cell volume as more water and lower salt concentration causes cell lysis (bursting).
Briefly describe TBW.
TBW -> total body water.
Males = ~60% of body weight
Females = ~50% of body weight (as they have higher body fate %)
Exists as two main compartments; intracellular fluid and extracellular fluid.
Describe the two compartments of TBW.
Intracellular fluid - 67% of TBW.
Extracellular fluid - 33% of TBW.
Includes:
Plasma (~20% of ECF)
Interstitial fluid (~80% of ECF)
Lymph and transcellular fluid (however, both male up such a low amount of ECF that they are negligible)
Describe the use of tracers in TBW.
We use ‘tracers’ to measure these by obtaining the ‘distribution volume’ of a tracer.
TBW = ECF + ICF
(therefore ICF=TBW-ECF)
TBW tracer - 3H2O
ECF tracer - Inulin
Plasma tracer - labelled Albumin
Describe the dilution principle.
V (litres) = Dose (D) / sample concentration (c)
Summary:
1) Add a known quantity of tracer X (Qx; mol or mg) to the body.
2) Measure the equilibration volume of X in the body ([X]).
3) Distribution volume (litres) = Qx (mol) / [X] (mol/litre)
Give an example of a water balance table.
Input (ml/day)
Fluid intake 1200
Food intake 1000
Metabolism 300
Output (ml/day)
Insensible loss:
Skin 350
Lungs 350
Sensible loss:
Sweat 100
Faeces 200
Urine 1500
Input=Output therefore homeostasis.
Give an example table of the effects of environment temperature on water loss.
Normal Temp
Skin 350
Lungs 350
Sweat 100
Faeces 200
Urine 1500
TOTAL = 2500
High Temp
Skin 350
Lungs 250
Sweat 1400
Faeces 200
Urine 1200
TOTAL = 3400
Prolonged Exercise
Skin 350
Lungs 650
Sweat 5000
Faeces 200
Urine 300
TOTAL = 6700
Explain what maintains water balance
Decreased excretion of water by the kidneys is insufficient to maintain water balance.
Water balance is maintained by increased water ingestion.
Give the overall ionic composition of ECF and ICF.
(values may differ between tissues)
ICF (mM)
Na+ 10
K+ 140
Cl- 7
HCO3- 10
ECF (mM)
Na+ 140
K+ 4.5
Cl- 11.5
HCO3- 28
Why can cells maintain different environments intracellularly to extracellularly?
The cell membrane and membrane transport mechanisms enable cells to maintain internal environments that differ in composition compared to their external surroundings.
Main ions in ECF are Na+, Cl-, HCO3-
Main ions in ICF are K+, Mg2+, -vely charged proteins
Why is the regulation of fluid balance and electrolyte balance intertwined?
Changes in solute concentrations lead to immediate changes in water distribution, therefore fluid balance and electrolyte balance are tightly intertwined.
Describe fluid shift.
Fluid shift; movement of water between the ICF and ECF in response to an osmotic gradient.
Explain challenges to fluid homeostasis.
Gain or loss of water = change in fluid osmolarity, similar changes in ICF and ECF volumes.
Gain or loss of NaCl = change in fluid osmolarity.
- Na+ ‘excluded’ from ICF
- Osmotic water movements
-> These two factors combine to produce opposite changes in ICF and ECF volumes:
ECF NaCl gain; ECF increase, ICF decreases.
ECF NaCl loss; ECF decreases, ICF increases
Gain or loss of isotonic fluid (0.9% of NaCl solution) = no change in fluid osmolarity. Change in ECF volume only.
-> Kidneys alter composition and volume of ECF. Regulation of ECF volume is vital for long term regulation of blood pressure.
Explain why electrolyte balance is important.
Total electrolyte concentrations can directly affect water balance (via changes in osmolarity).
The concentrations of individual electrolytes can affect cell function.
Na+ and K+ are particularly important:
- they are major contributors to the osmotic concentrations of the ECF and ICF (respectively).
- they directly affect the functioning of all cells.
Describe sodium balance.
More than 90% of the osmotic concentrations of the ECF results from the presence of sodium ions.
The amount of sodium in the ECF represents a balance between two factors (input and output).
Na+ is mainly present in the ECF therefore it is a major determinant of ECF volume.
Therefore it is vital to regulate Na+.
Describe Potassium balance.
Minor fluctuations in plasma [K+] can have detrimental consequences.
K+ plays a role in establishing membrane potential.
More than 95% of body K+ is intracellular; small leakages or increased cellular uptake may severely affect concentration of plasma K+ leading to:
- muscle weakness, in severe cases paralysis
- cardiac irregularities, worst case scenario cardiac arrest
Summarise the salt balance table (g/day).
Input
Fluids and Food 10.5
Output
Sweat and Faces 0.5
Urine 10
Input=Output therefore homeostasis.
Describe the impact of salt balance.
Salt imbalance is manifested as changes in extracellular fluid volume.
Regulation of ECF volume is important for long term regulation of blood pressure.
List Kidney functions.
1) Water balance
2) Salt balance
3) Maintenance of plasma volume
4) Maintenance of plasma osmolarity
5) Acid-base balance (regulate the concentrations of bicarbonate [HCO3-] and H+ ions)
6) Excretion of metabolic waste products
7) Excretion of exogenous/foreign compounds
8) Secretion of Renin (control of arterial blood pressure)
9) Secretion of erythropoietin (to stimulate red blood cell production)
10) Conversion of vitamin D into active form
State the primary function of the kidney.
Its primary function is to regulate the volume, composition and osmolarity of the body fluids.
The kidney’s role is the controlled excretion of substances.
Describe the composition of the urinary system.
The urinary system consists of the kidneys, that produce urine, and the structures that store and carry the urine from the kidneys to the outside for elimination from the body.
Each kidney receives 20-25% of the cardiac output.
Describe the nephron.
The nephron is the functional unit of the kidney - the smallest structural component of a system/organ/tissue capable or performing that systems/organs/tissues primary function.
Each kidney is composed of ~1 million nephrons.
It is the loop of Henle of each nephron that gives rise to the striated appearance of the kidney medulla cross section.
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Renal System81
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Endocrine Control of Body Fluid37
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Acid-Base Balance46
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The Physiology and Pharmacology of Asthma24
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Drugs to Treat Asthma25
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COPD & Emphysema17
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Epithelial Fluid Homeostasis16
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Treatment for Cystic Fibrosis32
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Dysrhythmias and Antidysrhythmic Drugs44
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Ischaemic Heart Disease and Hypertension41
