LO's:
• describe the uid compartments of the body and their relative volumes
• de ne the processes of osmoregulation and volume regulation
• describe the main structural features of the kidney including the nephron
• outline renal function in terms of ltration, reabsorption, secretion and excretion
• provide an overview of the hormonal control of water (osmoregulation) and salt balance (volume
regulation)
pre-notes:
• osmolarity + osmolality --> same thing = total concentration of osmotically active particles in
solution
• OSMOLALITY can be measured DIRECTLY - units of mOsmol/kg pure water
• values expressed will be slightly di erent --> one litre of solution contains SLIGHTLY LESS water
than one litre of pure water
• electrolytes contribute INDEPENDENTLY to osmolarity
• non-electrolyte solutes - contribution to osmolarity same as molar concentration
body water and uid compartments
• body comp - 60% WATER in MALES, 50% in FEMALES
◦ eg 70kg male: 0.6 x 70 = 42L body water
◦ eg 60kg female 0.5 x 60 = 30L body water
• water distributed in TWO MAIN uid compartments
◦ ICF + ECF
◦ 2/3 body water INTRACELLULAR
◦ 1/3 EXTRACELLULAR
‣ eg 70kg male: 2/3 x 42 = 28 L ICF vol, 1/3 x 42 = 14 L ECF vol
ICF and ECF must be in osmotic equilibrium
• cell membrane SEMIPERMEABLE
◦ PERMEABLE TO WATER
◦ IMPERMEABLE TO MOST SOLUTES
• change in solute concentration in either ICF or ECF --> generate osmotic gradient = results in
SHIFTS OF WATER between compartments
osmolarity must be REGULATED to AVOID osmotic shifts of water
• whatever the plasma osmoloarity is - same interstitial osmolarity
• normal range = 280-300 mOsm/L
◦ large shifts avoided to PREVENT CHANGES IN CELL VOLUME (maintain cell shape, growth,
migration etc)
◦ most serious complications = NEUROLOGICAL
• osmoregulation --> PHYSIOLOGICAL PROCESS THAT MAINTAINS CONSTANT ECF
(extracellular uid) OSMOLARITY
• avoids rupture to cells and further complications
volume regulation: regulation of ECF volume to ensure e ective circulation volume
• i.e. blood volume and blood pressure to obtain tissue perfusion
• ECF compartment subdivided
◦ INTERSTITIAL COMPARTMENT (75% of ECF)
◦ PLASMA COMPARTMENT (25% of ECF)
• volume regulation --> CONTROL OF ECF volume to ensure appropriate plasma volume
• control TOTAL AMOUNT OF SALT AND WATER to maintain plasma volume
• MAINTAINED BY STARLING FORCES
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• describe the uid compartments of the body and their relative volumes
• de ne the processes of osmoregulation and volume regulation
• describe the main structural features of the kidney including the nephron
• outline renal function in terms of ltration, reabsorption, secretion and excretion
• provide an overview of the hormonal control of water (osmoregulation) and salt balance (volume
regulation)
pre-notes:
• osmolarity + osmolality --> same thing = total concentration of osmotically active particles in
solution
• OSMOLALITY can be measured DIRECTLY - units of mOsmol/kg pure water
• values expressed will be slightly di erent --> one litre of solution contains SLIGHTLY LESS water
than one litre of pure water
• electrolytes contribute INDEPENDENTLY to osmolarity
• non-electrolyte solutes - contribution to osmolarity same as molar concentration
body water and uid compartments
• body comp - 60% WATER in MALES, 50% in FEMALES
◦ eg 70kg male: 0.6 x 70 = 42L body water
◦ eg 60kg female 0.5 x 60 = 30L body water
• water distributed in TWO MAIN uid compartments
◦ ICF + ECF
◦ 2/3 body water INTRACELLULAR
◦ 1/3 EXTRACELLULAR
‣ eg 70kg male: 2/3 x 42 = 28 L ICF vol, 1/3 x 42 = 14 L ECF vol
ICF and ECF must be in osmotic equilibrium
• cell membrane SEMIPERMEABLE
◦ PERMEABLE TO WATER
◦ IMPERMEABLE TO MOST SOLUTES
• change in solute concentration in either ICF or ECF --> generate osmotic gradient = results in
SHIFTS OF WATER between compartments
osmolarity must be REGULATED to AVOID osmotic shifts of water
• whatever the plasma osmoloarity is - same interstitial osmolarity
• normal range = 280-300 mOsm/L
◦ large shifts avoided to PREVENT CHANGES IN CELL VOLUME (maintain cell shape, growth,
migration etc)
◦ most serious complications = NEUROLOGICAL
• osmoregulation --> PHYSIOLOGICAL PROCESS THAT MAINTAINS CONSTANT ECF
(extracellular uid) OSMOLARITY
• avoids rupture to cells and further complications
volume regulation: regulation of ECF volume to ensure e ective circulation volume
• i.e. blood volume and blood pressure to obtain tissue perfusion
• ECF compartment subdivided
◦ INTERSTITIAL COMPARTMENT (75% of ECF)
◦ PLASMA COMPARTMENT (25% of ECF)
• volume regulation --> CONTROL OF ECF volume to ensure appropriate plasma volume
• control TOTAL AMOUNT OF SALT AND WATER to maintain plasma volume
• MAINTAINED BY STARLING FORCES
fl
fi
