Medicosa's Biology Lecture on Kidney Physiology

Introduction

• Continuation of the kidney physiology series.
• Focus on:
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
• Previous videos cover embryology, anatomy, and basic physiology.

Functions of the Kidney

• Regulation
• Excretion
• Secretion
• Gluconeogenesis
• Focus on regulation of water and electrolytes.

Blood Flow to the Kidney

• Oxygenated blood pathway: Left ventricle -> Aorta -> Renal artery -> Kidney
• Blood consists of plasma and cells.
• Only plasma (without proteins and cells) should be filtered.

Filtration and Reabsorption

• Good Stuff (reabsorbed): Sodium, glucose, amino acids, most water.
• Bad Stuff (excreted): Urea, ammonia, protons, potassium.
• Metabolism secretes acids (pyruvic acid, lactic acid, etc.)
• Proton removal: Ammonium compounds like ammonium chloride.

Renal Blood Flow and Filtration

• Renal blood flow: 20-25% of cardiac output.
• Renal plasma flow: 55% of renal blood flow.
• Glomerular filtration rate (GFR): ~20% of renal plasma flow.
• Filtration fraction = GFR / Renal plasma flow.

Filtration Process

• Blood flows through capillaries - glomerulus.
• Filtration membrane layers:
  1. Endothelium
  2. Glomerular basement membrane
  3. Podocytes
• Non-filterable: Plasma proteins and cells.

Nephron Structure

• Bowman's capsule -> Proximal convoluted tubule -> Loop of Henle -> Distal convoluted tubule -> Collecting tubules -> Urinary system.
• Filtration: Blood -> Tubule.
• Reabsorption: Tubule -> Blood.
• Secretion: Blood -> Tubule.

Detailed Nephron Segment Functions

Proximal Tubule

• Primary Active Transport: Sodium-potassium ATPase.
• Secondary Active Transport: Sodium-glucose co-transporter (SGLT2).
• Reabsorption: Glucose, amino acids, calcium, bicarbonate.
• Secretion: Uric acid, oxalic acid, bile salts, etc.
• Acid-Base Balance: Carbon dioxide + water -> bicarbonate and protons.

Loop of Henle

• Descending Limb: Permeable to water, concentrates urine.
• Ascending Limb: Permeable to salt, dilutes urine.
• Carrier Protein: Sodium-potassium-2 chloride co-transporter.

Distal Convoluted Tubule and Collecting Ducts

• Principal Cells: Respond to aldosterone and ADH.
• Intercalated Cells: Manage acid-base balance, reabsorb bicarbonate, secrete protons.
• Aldosterone: Reabsorbs salt and water, secretes potassium and hydrogen.
• ADH (Vasopressin): Reabsorbs free water.

Clinical Implications

• Nephrotic Syndrome: Protein loss in urine, leads to edema.

Conclusion

• Further details available in Medicosa's renal physiology and pharmacology courses.
• Encouraged to review previous videos for foundational concepts.