BIOA02H3 Lecture : bioa02 chapter 51

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coralmallard31

26 Jun 2011

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Excretory organs control the volume, concentration, and composition of the extracellular fluids of animals. Animal physiologists use the term osmolarity in discussing osmosis: the osmolarity of a solution is the number of moles of osmotically active solutes per liter of solvent. Excretory organs also eliminate the waste products of nitrogen metabolism: the output is called urine. The excretory organs filters extracellular fluid to product a filtrate that contains no cells or large molecules, such as proteins: the composition of the filtrate is then modified to produce urine. In the excretory system, water must be moved either be a pressure difference or by a difference in osmolarity. they have to conserve salts and excrete the water that continuously invades their bodies through osmosis. Most marine invertebrates equilibrate their extracellular fluid osmolarity with the ocean water and are therefore called osmoconformers.

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1) This is a thermodynamics questions

In your body, normal osmolarity of blood serum is just under 0.3 molar. Because cell membranes are permeable to water, the osmolarity of intracellular fluid is approximately equal to that of extracellular fluid (though the intracellular and extracellular composition in terms of specific ions and proteins is quite different). As an aside, measurement of osmolarity of serum is an important clinical test used to check for dehydration or other imbalances of water and electrolytes.

a) In the supplemental information, the osmosis example presented involves sucrose as a solute, but the van't Hoff equation also applies for other solutes. Using this formula (â = cRT, where â is the excess pressure), calculate the osmotic pressure associated with 0.3 molar concentration of osmolytic particles (e.g., ions, proteins, or other dissolved particles) in contact with pure water through a semi-permeable membrane at physiological temperature of 310 K. Express your results in atmospheres of pressure (1 atmosphere of pressure is 1.0x10⁵ Pascal, where 1 Pascal is a Newton/m²).

b) A biological cell membrane is a bilayer of phospholipid molecules, only a few nanometers thick, and can basically be thought of much like a soap bubble, except immersed in aqueous solution. If cells are placed in pure water, they often swell and burst in just a few minutes. Explain why this would happen.

grayporcupine495

Part B - Urine concentration in the kidney

The figure shows how urine concentration occurs in the nephron,the functional unit of the vertebrate kidney.

Active Transport, Passive Transport, Filtrate, Urea, NaCl,Osmosis, Medulla

1. The kidney's ability to cocentrate urine depends on themaintenance of an osmolarity gradient between interstitial of twostructures: the cortex and

2. This osmolarity gradient is maintained by both the passivetransport and the active transport of

3. The osmolarity gradient is also maintained by the passivetransport of

4. Water responds to the osmolarity gradient bymoving from anarea of a lower solute concentration to an area of a higher soluteconcentartion-this process is called

5. Osmosis does not require enery. For this reason, osmosis is aform of

6. The loss of water fromthe result in urine that is highly concentrated.

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How does the homeostatic mechanism regulate osmolarity or solute concentration of the blood in response to a meal high in salt?

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BIOA02H3 Lecture : bioa02 chapter 51

BIOA02H3 Full Course Notes

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