WATER AND BODY FLUIDS Lecture 4 and 5  

How does vasopressin reduce water loss?

Three Basic Processes in urine formation  

∙ Glomerular filtration 

o where the blood is filtered by the nephron by the glomerulus into the Bowman’s  capsule 

∙   Tubular reabsorption

o Materials that need to be in the blood are reabsorbed into the blood stream  through osmosis and with carrier mediated transport

o Renal threshold­ the maximum amount of solute that can be transported using  carrier mediated transport

o After this point glucose, blood proteins, ketone bodies and bile among other  things should not be in the filtrate

∙   Tubular Secretion 

o Removal of waste through renal tubule to be excreted in urine 

What is the primary cation in extracellular fluid?

o Hydrogen, Potassium and other selected solutes 

o When worrying about renal failure the kidneys fail to properly secrete solutes so  things like potassium intake need to be closely monitored

Fluid Balance 

∙ Hypothalamus has the thirst center which regulates fluid intake 

∙ Vasopressin/ Anti­diuretic hormone­ reduce the amount of fluid lost in the urine o ADH released when the body has higher demand for water and creates more  concentrated urine 

o Alcohol inhibits ADH

Taking apart electrolytes 

∙ Primary extracellular ions are Na+(cation) and Cl­(anion)

∙ Primary intracellular ions are K+(cation) and HPO42­(anion)

How does aldosterone affect sodium reabsorption?

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∙ Hypo­prefix meaning low 

∙ Hyper­ prefix meaning high

∙ Nat­pertaining to sodium

∙ Kal­ pertaining to potassium 

∙ Phos­ pertaining to phosphate  Don't forget about the age old question of What is the role of public health in the identified health issues in your community?

Electrolyte Balance

∙ Aldosterone stimulates sodium reabsorption and prevents excessive loss of sodium  o Helps maintain the small acceptable range of sodium in the blood

o Reabsorption of sodium causes excretion of potassium 

Acid/Base Balance 

∙ Acids are proton DONORS

∙ Bases are proton ACCEPTORS

∙ Blood has a narrow pH range in which life can be sustained of 7.35­7.45 o Alkalosis­ pH too high in blood

 Respiratory­ too much CO2 expulsion

 Metabolic­ too much acid is lost

o Acidosis­ pH too low in blood

 Respiratory­ too much CO2 retention

 Metabolic­ too much acid bicarbonate loss  If you want to learn more check out What is the relationship between cause and effect?
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∙ Buffers help maintain narrow pH goal and avoid pH fluctuation 

o Bicarbonate is the most important

 H2CO3H+ + HCO3­

 Carbonic acid Hydrogen ions and bicarbonate

 Used to avoid excess CO2 in the blood (acidosis)

 Acidic blood is neutralized with secretion of hydrogen ions and alkaline  blood is neutralized with bicarbonate 

o Phosphate and plasma proteins act as buffers as well