pack Flashcards
(30 cards)
What is the primary function of the jejunum?
The jejunum is primarily involved in the absorption of nutrients and electrolytes.
What are the key mechanisms of Na⁺ absorption in the jejunum?
- Na⁺/Glucose Co-transport (SGLT1): Na⁺ is absorbed with glucose or galactose.
- Na⁺/Amino Acid Co-transport: Na⁺ is absorbed with amino acids.
- Na⁺/H⁺ Exchange (NHE3): Na⁺ is absorbed in exchange for H⁺, maintaining pH balance.
How is Cl⁻ absorbed in the jejunum?
- Passively through paracellular pathways due to the electrochemical gradient created by Na⁺ absorption.
- Via Cl⁻/HCO₃⁻ exchange, where Cl⁻ is absorbed in exchange for HCO₃⁻ secretion.
How is water absorbed in the jejunum?
Water follows the osmotic gradient created by Na⁺ and nutrient absorption.
What is the primary function of the ileum?
The ileum absorbs electrolytes, water, bile salts, and vitamin B₁₂, and can secrete Cl⁻.
How is Na⁺ absorbed in the ileum?
- Via Na⁺/glucose co-transport and Na⁺/H⁺ exchange (similar to the jejunum).
- Na⁺/Bile Salt Co-transport: Na⁺ is absorbed with bile salts via the ASBT transporter.
How is Cl⁻ secreted in the ileum?
- Via the CFTR channel, regulated by cAMP.
- Cl⁻ secretion is coupled with HCO₃⁻ secretion to neutralize acidic chyme.
How is K⁺ absorbed in the ileum?
K⁺ is absorbed passively through paracellular pathways due to the electrochemical gradient.
What is the primary function of the colon?
The colon absorbs water and electrolytes, concentrating fecal material.
How is Na⁺ absorbed in the colon?
- Via Epithelial Sodium Channels (ENaC), driven by the Na⁺/K⁺-ATPase pump.
- Via Na⁺/H⁺ Exchange (NHE3).
How is Cl⁻ absorbed in the colon?
- Via Cl⁻/HCO₃⁻ exchange, where Cl⁻ is absorbed in exchange for HCO₃⁻ secretion.
- Passively through paracellular pathways.
How is K⁺ transported in the colon?
- Absorption: Passively through paracellular pathways.
- Secretion: Via apical K⁺ channels, driven by the electrochemical gradient created by Na⁺/K⁺-ATPase.
How is HCO₃⁻ transported in the colon?
HCO₃⁻ is secreted in exchange for Cl⁻ absorption, neutralizing acidic byproducts of bacterial fermentation.
How is water absorbed in the colon?
Water absorption is driven by the osmotic gradient created by Na⁺ and Cl⁻ absorption.
What role does aldosterone play in electrolyte transport?
Aldosterone increases Na⁺ absorption and K⁺ secretion in the colon by upregulating ENaC and Na⁺/K⁺-ATPase.
What is the role of VIP in electrolyte transport?
VIP stimulates Cl⁻ and HCO₃⁻ secretion in the ileum and colon.
How do SCFAs affect electrolyte transport?
SCFAs, produced by bacterial fermentation in the colon, enhance Na⁺ and water absorption.
Where is iron primarily absorbed?
Iron is absorbed primarily in the duodenum and upper jejunum.
How is non-heme iron absorbed?
- Found in plant-based foods and supplements as Fe³⁺.
- Reduced to Fe²⁺ by duodenal cytochrome B (DcytB) on the brush border of enterocytes.
- Fe²⁺ is transported into enterocytes via the divalent metal transporter 1 (DMT1).
How is heme iron absorbed?
- Found in animal-based foods (e.g., hemoglobin, myoglobin).
- Absorbed intact via the heme carrier protein 1 (HCP1) on enterocytes.
- Inside the enterocyte, heme is broken down by heme oxygenase to release Fe²⁺.
What happens to iron inside enterocytes?
- Fe²⁺ can be stored as ferritin or exported into the bloodstream via ferroportin.
- Export requires oxidation to Fe³⁺ by hephaestin or ceruloplasmin.
- Fe³⁺ binds to transferrin in the blood for transport to tissues.
How is iron absorption regulated?
- Hepcidin: A liver-derived hormone that inhibits ferroportin, reducing iron absorption when body iron stores are high.
Where is calcium primarily absorbed?
Calcium is absorbed primarily in the duodenum and jejunum.
How does transcellular calcium absorption occur?
- Occurs in the duodenum when calcium intake is low.
- Calcium enters enterocytes via TRPV6 or TRPV5 channels.
- Inside the cell, calcium binds to calbindin-D9k to prevent precipitation.
- Calcium is actively pumped out of the cell into the bloodstream via PMCA and NCX.
