Function of the Nephron

Introduction

• Tutorial focuses on the function of the nephron.
• Recommended prerequisite: Renal Anatomy series from handwrittentutorials.com.
• Overview of the nephron's physiology.

Nephron Structure and Blood Flow

• Blood Flow: Blood enters the glomerulus via the afferent arteriole and exits via the efferent arteriole.
• Blood elements are filtered into and out of the nephron system.

Filtration, Reabsorption, Secretion, and Excretion

• Filtration (F): Main method of removing substances from blood into the nephron.
• Reabsorption (R): Movement of substances back into the blood.
• Secretion (S): Movement of substances from the blood into the nephron.
• Excretion (E): Urine on its way to the bladder.

Filtration

• Filtrate should not contain large proteins (e.g., albumin) or red blood cells; their presence indicates a disease.
• Normal Filtrate Composition: Water, sodium, chloride, potassium, bicarbonate, glucose, amino acids, creatinine, and urea.
• Waste products (e.g., creatinine, urea) are removed to prevent toxicity.
• Filtration Rate: Approximately 90 mL/min per 1.73 m² body surface area.

Proximal Convoluted Tubule

• Reabsorbs: Potassium, sodium, chloride, water, amino acids, glucose, bicarbonate.
• Percentage Reabsorbed: 65% of sodium chloride and water, nearly 100% of amino acids and glucose, 90% of bicarbonate.
• Secreted: Uric acid, organic acids (including many antibiotics).

Loop of Henle

• Function: Concentration of urine.
• Descending Limb: Reabsorbs water (highly water-permeable).
• Ascending Limb: Reabsorbs 25% of filtered sodium chloride.
• Results in higher concentration of waste products (e.g., urea).

Distal Convoluted Tubule

• Reabsorbs: 5% of filtered sodium chloride, some water.
• Secretes: Potassium, hydrogen ions.
• Main site for fine-tuning reabsorption and secretion.

Collecting Duct

• Reabsorbs: Some urea, 5% of filtered sodium chloride, some water.
• Excretion Components: Water, sodium chloride, potassium, bicarbonate, creatinine, urea.
• Creatinine: Not reabsorbed or secreted; used as a marker for glomerular filtration rate.

Hormonal Control of Water Excretion

• Aldosterone: Part of the renin-angiotensin-aldosterone system (RAAS); increases water reabsorption in distal tubules.
• Antidiuretic Hormone (Vasopressin): Released from posterior pituitary; increases water reabsorption in collecting ducts.
• Both hormones act during under-hydration to retain water.

Conclusion

• Overview of the nephron’s function.
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