AP2 - Day 11 - Ch 19 pt 2_student.pdf

Chapter 19: Urology

19.5 Reabsorption

• Urine Formation: Understand the critical processes involved in urine formation, including filtration, reabsorption, secretion, and excretion.

• Key Concept: 180 L/day of fluid is filtered from glomerular capillaries, but only approximately 1.5 L is excreted as urine.

• Filtrate Concentration: The filtrate from Bowman’s capsule entering the proximal tubule has the same solute concentration as blood plasma.

19.6 Secretion

• Function of Secretion: Enhances the excretion of various substances actively, moving them against concentration gradients.

• Active Transport Mechanisms: Utilizes primary active transport and two forms of secondary active transport.

• Transport Specificity: Organic solute transporters like OAT can handle a broad range of organic anions.

19.7 Excretion

• Output and Functionality: Urine output reflects all renal processes and provides insight into body elimination but doesn’t explain renal functioning.

• Clearance: Clearance of a solute indicates the rate it disappears from the body, calculable using glomerular filtration rate (GFR) along with blood and urine samples.

• Case Study - Inulin:

  • 100% excretion and neither reabsorbed nor secreted.

  • GFR maintained at 100 mL/min with inulin clearance also at 100 mL/min.

19.8 Micturition

• Definition: A spinal reflex controlled by the higher brain, facilitating bladder control.

• Mechanics of Micturition:

  • Bladder at Rest: Internal sphincter (smooth muscle) contracted; external sphincter (skeletal muscle) remains contracted.

  • Firing of Stretch Receptors: Marks the sensation of bladder fullness.

• Process: 1. Stretch receptors activate. 2. Parasympathetic neurons stimulate contractions of the smooth muscle. 3. Internal sphincter opens and external sphincter relaxes.

Detailed Breakdown of Reabsorption

6-4 Reabsorption

• Mechanisms: Utilizes both secondary active transport and passive mechanisms for anion and water movement.

• Process Overview: Na+ reabsorption through active transport creates electrochemical gradients. This drives passive movement of other substances and water.

  • Key Players:

    • Na+: Actively transported, primary force for renal reabsorption.

    • Anions: Driven by electrochemical gradients.

    • Water: Moves via osmosis following solute reabsorption.

    • Diffusion: Permeable solutes are accessible through membrane transporters or paracellular pathways.

6-4 Sodium-Linked Reabsorption

• Example: Co-transport of glucose, amino acids, and organic metabolites along with sodium ions, showcasing an integrated approach to nutrient reabsorption.

Reabsorption of Proteins

• Proteins that manage to pass the filtration barrier are reabsorbed via endocytosis in the proximal tubule, through:

  1. Endocytosis at Apical Membrane: Large proteins enter proximal tubule cells.

  2. Digestion in Lysosomes: Proteins are broken down, and their constituents (amino acids) are released to the interstitial fluid for absorption.

Micturition Control

• Conscious vs. Unconscious Control: Influenced by higher CNS input that can either facilitate or inhibit the reflex based on the physiological demands.

• Reflex Mechanism: Stretch receptors detect fullness, signaling nervous and muscular responses contributing to bladder emptying.

Conclusion and Reviews

• Emphasis on revising all discussed topics before the upcoming problem set and exam. Focus on Chapter 20 for further understanding.