Fisiología Renal - Reabsorción y secreción tubular renal (Túbulo Proximal) (IG:@doctor.paiva)
Introduction to Renal Physiology
Overview of Proximal Tubule Function
- Eduardo Paiva introduces the topic of renal physiology, focusing on reabsorption and secretion in the proximal tubule.
- The proximal tubule, also known as the contorted proximal tubule, has a unique structure that facilitates its functions.
Structural Characteristics
- The proximal tubule features high metabolic activity with numerous mitochondria and an extensive brush border on the luminal membrane, enhancing reabsorption surface area.
Key Substances Reabsorbed and Secreted
- Major substances reabsorbed include sodium, chloride, bicarbonate, potassium, water, glucose, and amino acids; while hydrogen ions and organic bases are secreted.
Mechanisms of Sodium Reabsorption
Active Transport Processes
- Sodium-potassium ATPase pumps sodium out into the interstitium against its concentration gradient while bringing potassium into cells. This process is crucial for maintaining low intracellular sodium levels.
Coupled Transport Mechanisms
- Glucose and amino acids are co-reabsorbed with sodium through specific transporters in the luminal membrane due to sodium's gradient created by active transport.
Water Reabsorption Dynamics
Osmotic Balance
- The proximal tubule maintains osmolarity equal to plasma by reabsorbing water alongside solutes like sodium. This balance is essential for urine concentration mechanisms discussed later.
Reabsorption Patterns in Proximal Tubule
Segmental Differences
- The first half of the proximal tubule primarily reabsorbs glucose and amino acids; whereas the second half focuses more on chloride along with continued absorption of sodium and water.
Bicarbonate Handling in Proximal Tubule
Bicarbonate Reabsorption Mechanism
- A significant amount (85%) of bicarbonate is reabsorbed via countertransport mechanisms involving hydrogen ions facilitated by carbonic anhydrase enzymes.
Secretion Functions in Proximal Tubule
Organic Acid/Base Secretion