MCB 135E Discussion

MIDTERM II Review

• Monday the 7th of November• 2040 VLSB• 6-8pm• E-mail questions regarding exam

well in advance

The Kidney and Urinary System

• Anatomy• Function• Hormones• Circulation• Development

Kidney Functions

• Regulates – Water– Electrolyte balance– pH

• Removes– Waste

• Secretes Hormones– Erythropoiten– Renin– Vitamin D3

Metabolic and Excretory Functions

• Glomerular Filtration– Selective filtration of blood

• Tubular Reabsorption – Takes up some solutes from filtrate and

delivers them to peritubular capillaries

• Tubular Secretion– Adds some of its own products to the

filtrate, passes filtrate on to bladder as urine

Water Metabolism

• Osmotic Pressure – – Force driving or pulling a solvent from lesser

to greater concentration on either side of a selectively permeable membrane

• Regulation of solute exchange– Selective permeability of membrane– Influence of hormones and metabolites on

membrane– Simple and exchange diffusion across

membrane– Active secretion by the membrane

Acid Base Balance

• Determined By:– Hydrogen Ion Concentration (pH)

• Normal 7.3-7.5• Max 7.0-7.8

– Alkali reserve• CO2 combing power of plasma

• Normal 50-70% Volume

– Both vary due to exercise and metabolism

Acid-Base Regulation• Buffers, Ventilation, Kidney• Buffers

– Cellular proteins, phosphate ions, Hemeglobin (Chloride Shift)

• Ventilation– Rate and depth of respiration controls CO2 release in

lungs – Increased respiration in a respiratory compensation

for acidosis

• Kidney– Excretes H+

– Reabsorbs HCO3-

Urine Acidification Mechanisms

• Reabsorption of Filtered Bicarbonate– In proximal tubule: H+ exchanged for Na+– In distal tubule and collecting duct

• CO2 and HCO3(-) are transported into cell and form H2CO3 by carbonic anhydrase

• Dissociation of H2CO3 releases H+ which is then exchanged for Na+

• Secretion of Ammonia– In distal tubule

• NH3 + H- NH4 (Ammonium) [formation of a titrable acid]

Mechanism for Renal Acid/Base Balance

1. Apical Na(+)/H(+) antiporter2. Basolateral Na(+)/HCO3(-)

symporter3. H(+) ATPase4. H(+)/K(+) ATPase5. NA(+)/NH4(+) antiporter

Proximal Tubule Acid/Base Balance

1. H(+) is secreted into the lumen in exchange for Na(+)

2. Secreted H(+) then combines with the filtered bicarbonate to form CO2 in the lumen

3. CO2 diffuses into the proximal tubule cell and combines with water to form carbonic acid, this dissociates to form H(+) and HCO3(-) in the cytoplasm (Involves carbonic anhydrase)

4. The H(+) is secreted again by the antiport in step 15. The HCO3(-) is transported out of the cell by a

NA(+)/HCO3(-) symporter where it can function as a buffer