L1 Endocrinal function of kidney (P2 Hard)

Renal Module Information

• Course code: IMP-07- 20318
• Phase: I
• Year/semester: 2nd year / Semester 3
• Academic year: 2022-2023

Lecture 1: Endocrine Function of the Kidney

• Intended Learning Outcomes (ILOs):
  • Describe functions of the renal system.
  • Identify types of nephrons and their functions.
  • Describe the juxtaglomerular apparatus and its significance.

Structure of the Urinary System

• The urinary system includes the kidney, renal artery, renal vein, ureter, urinary bladder, and urethra.

Kidney Structure

• Composed of 6-18 lobes.

• Each lobe consists of a pyramid of medulla covered by cortex.

• Renal cortex: Outer layer.

• Renal medulla: Inner layer, contains pyramids.

• Renal pelvis: Funnel-shaped structure that collects urine from the pyramids.

• Ureter: Carries urine from the kidney to the bladder.

• Nephron: Functional unit of the kidney (one million nephrons per kidney).

Nephron Structure

• Renal corpuscle:

  • Glomerulus: Ball of capillaries between afferent and efferent arterioles.
  • Bowman's capsule: Expanded blind end of tubules surrounding the glomerulus.

• Renal tubules:

  • Proximal convoluted tubule (PCT): Highly coiled, in the cortex, one cuboidal cell layer, luminal brush border.
  • Loop of Henle: U-shaped, thin descending and thick ascending, in the medulla.
  • Distal convoluted tubule (DCT): Highly coiled, in the cortex, one cuboidal cell layer.

• Collecting tubules (CT): Cross the entire medulla; multiple DCTs empty into each CT, principle cells affected by vasopressin, I cells secrete acids.

Juxtaglomerular Apparatus

• Site: DCT contacts afferent arteriole.
• Components:
  • Macula densa: Modified cells in the DCT that monitor fluid flow rate (NaCl transport).
  • Granular cells: Modified cells in the afferent arteriole wall that monitor flow and secrete renin.

Functions of the Kidney

• 1. Homeostasis of ECF: Regulates water and electrolyte balance, pH, and osmolarity of extracellular fluid (ECF).
• 2. Excretion of metabolic wastes: Eliminates urea, uric acid, creatinine, and foreign compounds (e.g., drugs).
• 3. Gluconeogenesis: Synthesizes glucose from amino acids during prolonged fasting.
• 4. Regulation of arterial blood pressure: Secretions of renin are important
• 5. Endocrine functions:
  • Secretes erythropoietin: Stimulates red blood cell production.
  • Secretes renin: Plays role in salt conservation & controlling blood pressure.
  • Converts vitamin D into active form.(1,25-dihydroxyvitamin D3).
  • Secretes prostaglandins (PGE2 & PGI2): Regulate glomerular filtration rate and renal blood flow..
• 6. Regulation of acid-base balance: Eliminates acids generated from protein metabolism; regulates the body's buffer stores.

Renin-Angiotensin-Aldosterone System (RAAS)

• Renin: Hormone secreted by the juxtaglomerular apparatus, triggered by factors like low blood pressure.
• Converts angiotensinogen to angiotensin I; ACE converts angiotensin I to angiotensin II.

Factors Stimulating Renin Secretion

• Renal ischemia (reduced blood supply).
• Hypotension and hemorrhage.
• Sympathetic stimulation.
• Increased blood catecholamine levels.

Factors Inhibiting Renin Secretion

• Increased blood pressure.
• Increased NaCl or Na reabsorption in the macula densa.
• Angiotensin II.
• Vasopressin (ADH) and aldosterone.

Erythropoietin

• Hormone secreted by peritubular capillaries in response to hypoxia.
• Stimulates red blood cell production in bone marrow.
• Crucial role in erythropoiesis (red blood cell production).
• 85% of erythropoietin in the body synthesized by kidneys; deficiency can lead to anemia in renal diseases.

References for Medical Physiology

• Ganong, William F. Review of Medical Physiology, 23rd edition. McGraw-Hill, 2011, pp. 640-642.
• Guyton, Arthur C., and John E. Hall. Textbook of Medical Physiology, 12th edition. Saunders Elsevier, 2011, pp. 303-306.
• Handbook of the Physiology Department, Faculty of Medicine for Girls, Al-Azhar University, p.1:11.

Test your knowledge on the endocrine function of the kidney, including the structure of the renal system and nephron types. Understand the roles of the juxtaglomerular apparatus and its significance. This quiz is designed for 2nd-year medical students in the Renal Module.