Homeostasis Flashcards
Water
- 60% of the body
- Highly reactive
- Unusual properties
- Very polar
- Interacts will with ions and other dipoles
Which types of substances tend to dissolve readily in water?
- Ionic
- Polar-neutral
Hydrophilic/water soluble compounds
Non-water soluble
Lipophilic
Water determines the structure and biological properties of…
- Proteins
- Nucleic acids
- Lipids
- Biological membrane
Water has a tendency to ionise into…
Hydrogen and Hydroxide Ions
H+/OH-
The amount of hydrogen and hydroxide ion in a solution is related to which equation?
[H+] x [OH-] = 10-14 mol/l
Give the pH of water
7
What did Claude Bernard famously state?
Maintenance of life is guaranteed by the constancy of the fluid matrix or ‘milieux interieur’.
Homeostasis was first discovered by…
Walter Bradford Cannon
Constant conditions which are maintained in the body are known as…
Homeostasis
Formerly: “Equilibria”
ICF comprises…% of the body’s mass
40%
ECF represents…% of the body’s mass
20%
The ECF is a solution comprising of…
- Water
- NaCl
- NaHCO3
ISF comprises…% of the body’s mass
15%
IVS comprises…% of the body’s mass
5%
TCF comprises…% of the body’s mass
1-2%
Dehydration is defined as…
A decrease in ECF of <20%
Overhydration is defined as…
An increase in ECF of >20%
Hypovolaemia
Decreased volume of blood plasma
Hypervolaemia
Increased volume of blood plasma
Oedema
Increased volume of ISF
What can lead to dehydration?
- Vomiting
- Diarrhoea
- Sweating
- Drinking less
What can lead to hypovolaemia?
Bleeding
Isoosmosis
The constancy of osmotic pressure of ECF
dependent on osmotic concentration
How can osmotic conc. of blood plasma be determined?
Measurement of freezing point
1 osmol of solute dissolved in 1 L solution depresses freezing point by…
-1.86°C
The freezing point of blood plasma…
-0.56°C
The concentration of physiological saline
0.9% NaCl
0.3 osmol/L
RBC in Hypotonic solution
- Swells and Disrupts
- Haemolysis
RBC in Hypertonic solution
Shrinks
All isotonic solutions are…
Isoosmotic
Not all isoosmotic solutions are…
Isotonic
Give the concentrations of the anions in blood plasma
- Cl- = 110 mmol/l
- HCO3- = 27 mmol/l
- Protein = 17 mmol/l
- Phosphate = 2 mmol/l
- Sulphate = 1 mmol/l
- Organic acids = 4 mmol/l
Give the concentrations of the cations in blood plasma
- Na+ = 140 mmol/l
- K+ = 4 mmol/l
- Mg2+ = 1.5 mmol/l
- Ca2+ = 1.25 mmol/l
Isohydria
The constancy of pH in the ECF
pH of the ECF
7.4
Give the Henderson-Hasselbalch equation
pH=pKa+log[A-]/[HA]
Weak acids have…pKa values
High
Strong acids have…pKa values
Low
Blood [H+] concentration
2.5x10-7
pH value between 7.35 and 7.0 is called…
Acidosis
pH value between 7.45 and 7.8 is called…
Alkalosis
Which organs regulate acid-base balance…
Respiratory centres in the brain stem and the kidneys
Buffer systems/Buffer pairs tend to resist…
Changes in pH
Buffer capacity
Measure of the efficiency of a buffer in resisting changes in pH
Acidic components of buffer systems…
Give H+
Basic components of buffer systems…
Bind H+
Location of the bicarbonate buffer system
Mainly in the ECF
Which molecules are involved in the bicarbonate buffer system?
- Carbonic acid (H2CO3)
- Sodium bicarbonate (NaHCO3)
pKa value of the bicarbonate buffer system
pKa = 6.1
Calculate pH of the bicarbonate buffer system
- pH = pKa + log[HCO3-]/[H2CO3]
- pH = 6.1 + log 20/1 = 6.1 + 1.3 = 7.4
How is carbonic acid (H2CO3) excreted from the body?
Excreted by the lung in the form of CO2
Chemicals involved in the phosphate buffer system
- Dihydrogen phosphate (H2PO4-)
- Monohydrogen phosphate (HPO42-)
pKa value of the phosphate buffer system
pKa = 6.8
Location of the phosphate buffer system
Mainly in the ICF
Calculate the pH of the phosphate buffer system
- pH = pKa + log[HPO42-]/[H2PO4-]
- pH = 6.8 + log 4/1 = 6.8 + 0.6 = 7.4
What determines the acid-base behaviour of native intact globular proteins?
Ionisable groups of -R, -amino, and -carboxyl gorups
pKa value of plasma proteins
pKa = 4.9-6.4
Give the pKa value of a haemoglobin buffering system
pKa = 6.5-7.8
