General Renal Function and Body Fluids

Major functions of the kidney - filtration

1. Filtration

• Clearance of metabolic waste products, especially nitrogenous wastes, excess ions

• Drugs

• Toxins

Major waste products produced by body

Nitrogenous metabolic waste

• Ammonia from protein catabolism

  • Extremely toxic and soluble in water

  • Converted to urea: breakdown of amino acids

  • Converted to uric acid: breakdown of nucleotides

• Creatinine

  • Continuously produced during muscle breakdown

  • Serum creatinine used a test of kidney function

  • Serum creatinine levels high if kidneys don’t work

Major function of the kidney - production

2. Production

• Renin - blood pressure

• Erythropoietin - RBC maturation

• Prostaglandins - blood flow within the kidney

• Vitamin D (calcitriol)

Production functions of the kidney summary

Major functions of the kidney - regulation

3. Regulation

• Body fluids

  • Volume of extracellular fluid

  • Osmolality of body fluids

  • Concentration of electrolytes

  • pH of blood - acid/base balance

  • Blood pressure

  • Red blood cells

The body fluids

• Regulated by the kidneys with help from adrenal glands (aldosterone release) and brain (ADH release)

• Mechanisms exist in our body to increase water gain when we don’t have enough

Why regulate body fluids?

Volume

• 40L of water in women and 45L of water in men

• Can’t be dehydrated or overhydrated with water

• Kidneys control urine volume and thus concentration

• Increase in water in the body: kidneys remove water - dilute urine

• Decrease in water in the body: kidneys conserve water - concentrated urine

Osmolality

• Osmolality of body fluids is very critical

• Extreme variation in Osmolality causes cells to shrink, swell and even burst

• Damages cell structure and disrupts normal cell function

• Normal body Osmolality is 275-295mOsm/Kg water

Fluid compartments - Location

Fluid compartments - Boundaries (barriers)

Fluid compartments - Movement of fluid

Composition of body fluids and movement across compartments