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
Where is the only place vitamin B 12 can be absorbed?
Terminal ileum
What does cholera cause?
Secretory diarrhoea
How is cholera treated? What is the mechanism of treatment?
Oral rehydration solutions contain sodium, glucose and amino acids.
Enables sodium and water absorption by the coupled uptake of sodium with glucose or amino acids
What is the name of the absorbative and secretory cells in the intestines?
Villus- absorptive
Crypt- secretory
What causes general malabsorbtion in the mucosal phase? Give examples
Small intestinal mucosal disease = reduced absorptive area
Examples- Coeliac disease
Post-infectious malabsorption
Crohn’s disease
What is the morphology of the small intestines when someone has coeliac disease?
Complete villous atrophy
Crypt hyperplasia
Increased IEL’s
What is specific malabsorbtion? Give an example
Failure of the processes which control the absorption of 1 or more nutrient types
Genetic or acquired failure to absorb dissacharide sugars or vitamin B12 (perciniouse anemia)
Give an example of a Disaccharidase deficiency
lactase deficient
lactose- intolerance
What is the cause of lactase deficiency?
mutation in the LCT gene
Affecting the ‘mucosal phase’ of dissacharides absorption
What causes Glucose-galactose malabsorption?
Mutations in SLC5A1 gene.
Codes for Sodium dependent GLucose Transporter one SGLT1 transporter
mucosal phase” of glucose absorption is affected
What is a consequence of Unabsorbed disaccharides
Increases osmotic load in colon causing watery diarrhoea
Where does 95% of nutrient absorption occur?
Small intestines
What is broken down and absorbed in the duodenum?
- Triglycerides are broken down by bile salts and lipases to form monoglycerides and fatty acids
- proteases break downprotein is broken down to amino acids and absorbed
- Amylase breaks down carbohydrates into disaccharides then monosaccharides which is absorbed
- Ion is absorbed
What is absorbed in the jejunum?
- Calcium
- Folate
- Fat soluble vitamins
- Free fatty acids
- Monoglycerides
- B12 (small amounts)
- Water (moderate)
- Sodium (small amounts)
What is absorbed in the Ilium?
- Water and sodium (moderate amounts)
- B12
- Intrinsic factor
- Bile acids reabsorbed to recycle to the liver
What is absorbed in the colon?
- water (small amount)
- Electrolytes (small amounts)
- Bile acids reabsorbed (small amounts)
What is the name for a pro-enzyme?
Zymogen
