Fundamentals: Physiology - General principles of medical physiology Flashcards
Describe the average body composition of a young adult male (in terms of proportions of protein, fat, mineral and water - and the composition of that water)
18% protein
15% fat
7% mineral
60% water (20% ECF with 5% blood plasma and 15% interstitial fluid; 40% intracellular fluid)
I.e. about 1/3 of total body water is ECF and 2/3 is ICF
What % of body weight is the total blood volume?
8%
Describe the differences in fluid and electrolyte composition between extracellular and intracellular compartments (in terms of cation and anion balance)
Extracellular fluid:
- Cation balance largely Na (minimal K)
- Anion balance largely Cl
- Some protein in plasma, not much in interstitial fluid
Intracellular fluid:
- Cation balance largely K
Anion balance largely protein and miscellaneous phosphates
What is interstitial fluid?
Fluid outside of vascular and lymphatic systems which bathes the cells
What bridges the blood plasma and interstitial fluid?
Lymph fluid bridges the two domains
What is a mole?
The gram-molecular weight of a substance
Each mole consists of 6x10^23 molecules
What is a millimole? What is a micromole?
Millimole: 1/1000 of a mole
Micromole: 1/1,000,000 of a mole
How much does 1 mole of NaCl weigh in g?
NaCl = 23g Na + 35.5g Cl = 58.5g/mol
What is the molecular weight of a substance
Ratio of mass of one molecule of the substance to the mass of one-twelfth the mass of a carbon-12 atom
What is the dalton?
Equal to one-twelfth the mass of a carbon-12 atom
What is an equivalent?
One mole of an ionised substance divided by its VALENCE
What is one Eq of sodium? What is one Eq of calcium?
One Eq of sodium (Na+) = 23g
One Eq of calcium (Ca2+) = 40/2 = 20g
What is a gram equivalent?
A gram equivalent is the weight of a substance that is chemically equivalent to 8g oxygen (or 35.5g Cl, or…)
What is normality? Give an example using a 1N solution of HCl
Normality (N) of a solution is the number of gram equivalents in 1L (i.e. g/L)
A 1N solution of HCl contains both H+ (1g) and Cl- (35.5g) equivalents = 36.5g/L
What is pH?
The pH of a solution is the logarithm to the base 10 of the reciprocal of the hydrogen ion concentration
For each pH unit <7, the concentration of hydrogen is increased tenfold and >7, it is decreased tenfold
What is a buffer? Give an example
A buffer is a substance that has the ability to bind or release H+ in solution, thus keeping the pH of the solution relatively constant
Consists of a weak acid and its conjugate base
E.g. carbonic acid, moving the equilibrium point depending on additional H+ or OH-
What makes H2O such an excellent biological fluid? List 3 reasons
- Serves as a solute (has a high surface tension)
- Provides optimal heat transfer (has a high heat of vaporisation and heat capacity)
- Provides optimal conduction of current (has a high dielectric constant)
What are electrolytes?
Molecules that dissociate in water to their cation and anion equivalents
What is the pH of gastric fluid?
3
What is the pH of pancreatic secretions?
8
What is an acid?
A molecule that acts as a H+ donor in solution
What is a base?
A molecule that tends to remove H+ in solution
Describe the isohydric principle
All buffer pairs in a homogenous solution are in equilibrium with the same H+
All buffer systems which participate in defence of acid-base changes are in equilibrium with each other
How is the relationship for dissociation of acid in solution defined mathematically?
According to the laws of mass action, a relationship for dissociation can be defined mathematically as:
Ka = [H+][A-]/[HA]