Lecture 9 Flashcards
What does each part of the small intestine absorb and secrete?
The Jejunum reabsorbs Na+, K+, Cl- and H2O.
The Ileum secretes HCO3- and absorbs H2O.
Colon reabsorbs Na+, Cl- and H2O and it secretes K+ and HCO3-.
What does the proximal small intestine absorb and secrete
Tight Junctions more permeable
Absorption: Nutrients Vitamins Na Cl Water K
Secretion:
HC03-
What does the colon absorb and secrete
Absorption:
Na
Cl
Water
Secretions
K
HC03-
Discuss the two types of chyme related to water
Chyme hypoosmotic (diluted)- water is absorbed through intestinal musoca into the blood of the villi
Chyme hyperosmotic –
water transferred by osmosis to make chyme isoosmotic with the plasma
What are the four major types of epithelial cells making up the intestinal mucosa
enterocytes, endocrine cells, goblet cells, and Paneths cell
Describe the structural properties of enterocytes
Epithelial cells are polarised:
Apical side faces lumen, apical membrane has microfilms
Basal side communicate with blood stream and lymphatic lacteals
Lateral side is in contact with neighbouring cells
Apical and basolateral membranes are separated by TJ.
TJ are key for the regulation and transport of ions and liquids.
What do TJs do?
Intracellular TIGHT JUNCTIONS restrict passive flow of solutes after secretion or absorption
(i.e. serve as stopgaps preventing water and solute transport across the membrane)
Describe transcellular transport
Employs membrane transporters to move molecules and water through cells (think motor of the intestinal luminal activity)
Their activity drives ion flux and establishes concentration gradients, which dictates passive transport of water and solutes.
May work against electrochemical gradient
Requires energy/ATP
What are the three transport proteins that determine transepithelial transport
Channels, carriers and pumps
discuss channels
Hydrophobic outside, hydrophilic inside, allowing the transport of ions
Gated, have a part of protein that opens and closes and regulates entrance of ions.
ion specific
transport based on electrochemical gradient
Discuss carriers
Proteins that facilitate the movement of specific solutes across the membrane through conformational changes
Facilitated diffusion or active transport
Transport of single molecule, co transport or exchange.
Discuss pumps
Transports proteins that move ions and other solutes across membrane against electrochemical gradient
they’re ATPases
Exchange
What are the types of transepithelial transport
Passive transport
Solvent drag
Active transport
