Digestion and absorbtion Flashcards
What are the two main functions of the intestinal barrier
Permeable to nutrients for absorbtion
Impermeable to pathogens and toxins
What builds the functional structure of enterocytes?
cytoskeletal proteins
Name the 3 phases of absorbtion
- luminla phase
- Mucosal phase
- Post absorbative phase
Describe the luminal phase of absorption
Break down of digested food by:
Acid—> stomach
Alkali—–> small intestines
Substrate specific enzymes—-> gastric, small bowel, pancreas
Describe the Mucosal phase of absorption
Pre-digested nutrients is taken up at the brush border of enterocytes and enter intestinal cells
Describe the Post absorbative phase of absorption
Absorbed nutrients is transported in the lymphatics and portal circulation to the rest of the body
What are the functions of water in the gut?
- Hydrolysis reactions of digestion
- Facilitates absorbtion
- Combines with mucin granules to make mucus
Describe the luminal phase of carbohydrate digestion
It is split into small molecules by salivary and pancreatic enzymes (maltase)
disaccharides + limit dextrins
Describe the mucosal phase of carbohydrate digestion
Brush border enzymes complete digestion: Sucrase lactase maltase limit dextrinase glucoamylase
Glucose and galactose enter the cell via sodium-linked secondary active transport
Fructose enters by facilitated diffusion.
Describe the post-absorptive phase of carbohydrate digestion
The sugars exit the cells across the basolateral membrane by facilitated diffusion to the portal vein.
Describe the luminal phase of Lipid digestion
Digestion begins in the mouth with linguinal lipases.
Continues in the stomach with gastric lipase
Bile salts and pancreatic lipase digests triglycerides into free fatty acids, and monoglycerides.
what is the function of bile salts in digestion?
They enhance the activity of lipases via emulsification (smaller droplets)
What absorbs bile salts? What recycles bile slats? What is this system called?
Absorbed- ileum
Recycled- liver
Enterohepatic circulation
What is the function of Commensal bacteria? Describe how it accompanies this function? What is important about the product of its function?
Aid in bile salt production
In the small intestine it de-conjugates bile acids and converts primary bile acids into secondary bile acids
Bile acids produced in this way are diet dependant microbial products as it is linked to diet and digestion
Which type of bile acid, conjugated or unconjugated is better at emulsification and why?
What deconjugates bile acids?
Conjugated because it is more ionized at intestinal PH (more suited for intestinal pH)
Enzymes from commensal bacteria
Describe the Mucosal phase of Lipid digestion
Free Fatty acids and monoglycerides enter the enterocytes by simple diffusion.
Inside the enterocytes they are reassembled into triglycerides and packaged into chylomicrons.
Describe the post-absorptive phase of Lipid digestion
chylomicrons are secreted by exocytosis.
Then they enter the lymphatic capillaries and then the blood stream
Describe the luminal phase of Protein digestion
Begins in the stomach with pepsin
Completed in the small intestines by enzymes from pancreas
How is pepsin made?
Converted from pepsinogen produced by cheif cells which is actvated by HCL, produced by parietal cells
Describe the mucosal phase of Protein digestion
Trypsinogen is converted into trypsin by enterokinase.
Trypsin then activate:
chymotrypsinogen -> chymotrypsin
procarboxypeptidase -> carboxypeptidase
Amino acids enter epithelial cells via sodium-linked secondary active transport across the apical membrane.
Describe the post-absorptive phase of Protein digestion
Amino acids are then transported across the basolateral membrane by facilitated diffusion.
What are the fat soluble vitamins?
vitamins A, D, E and K
dissolve into lipid droplets
What are the fat water vitamins?
B and C
Follows water
Describe the absorption of vitamin B 12
- Binds to haptocorrin (made in salivary glands)
- Complexed with intrinsic factor (IF) from stomach
- Transported in portal circulation.
- Transferred to transcobalamine II
- Absorbed in terminal ileum
