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

Chapter 19: Urology

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.

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.

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.

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.

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.

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

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.

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.

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