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Overview of Urinary System Function

• Blood filtration in kidneys leads to urine formation.

• Main processes involved: filtration, reabsorption, secretion.

Filtration Process

• Filtration Rate: 20% of plasma is filtered in the glomeruli; results in ~125 mL/min or 180 L/day.

• Only solutes and water filtered, with proteins remaining in the blood.

Reabsorption Mechanism

• Reabsorption: Nutrients and water taken back into the bloodstream.

  • Active and passive transport methods used.

• Primary sites of reabsorption: Proximal convoluted tubule, Loop of Henle.

• Important for glucose and amino acids; typically 100% reabsorbed.

Secretion Process

• Secretion: Movement of substances from blood to tubule, often requiring energy.

• Important for excreting excess ions, drugs, and metabolic waste.

Key Hormones in Regulation

• ADH (Vasopressin): Increases water reabsorption in collecting duct.

• Aldosterone: Increases sodium reabsorption, leading to water retention.

• PTH (Parathyroid Hormone): Regulates calcium reabsorption.

Osmotic Considerations

• Water follows sodium due to osmotic gradients, influenced by sodium-potassium pumps.

• High levels of glucose lead to osmotic diuresis, indicating potential diabetes.

Urine Composition & Volume

• Composition: primarily water, urea, electrolytes.

• Average urine output is about 1.5 liters per day.

Concentrated vs Dilute Urine

• Osmolarity of urine is typically around 300 mOsm/L; kidneys can adjust concentration as needed depending on hydration levels.