Digestion And Absorption Flashcards
What are the two types of digestion?
- physical/mechanical digestion
- chemical digestion
Describe physical/mechanical digestion
- Starts in the mouth
- Involves Mastication (chewing/
crushing food using molar and
premolar teeth) - Increase the surface area – for
digestive enzyme action (chemical digestion)
Describe chemical digestion
- Starts in the mouth (for Starch)
- Involves the action of digestive
enzymes - Hydrolysis occurs, large insoluble
molecules eventually to small soluble molecules
Define digestion
- large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes
Which enzymes are required to hydrolyse carbohydrates into monosaccharides?
- amylases
- membrane bound disaccharidases
Where is amylase produced?
- pancreas and salivary glands
Describe the role of amylase
- hydrolyses polysaccharides into the disaccharide maltose by hydrolysing glycosidic bonds
Where does carbohydrate digestion begin?
- mouth
Where does carbohydrate digestion continue?
- duodenum
Where is carbohydrate digestion completed?
- ileum
What are some membrane bound disaccharidases that hydrolyse sucrose and lactose into monosaccharides?
- sucrase
- lactase
What does sucrase hydrolyse sucrose into?
- glucose and fructose
What does lactase hydrolyse lactose into?
- glucose and galactose
What are the three types of enzymes that hydrolyse proteins?
- Endopeptidases
- Exopeptidases
- Membrane bound dipeptidases
What do endopeptidases do?
- hydrolyse peptide bonds between amino acids in the middle of a polymer chain
What do exopeptidases do?
- hydrolyse peptide bonds between amino acids at the end of a polymer chain
What do membrane bound dipeptidases do?
- hydrolyse peptide bonds between two amino acids
Where does protein digestion start?
- stomach
Where does protein digestion continue?
- duodenum
Where is protein digestion completed?
- ileum
What enzymes are lipids digested by?
- lipase and action of bile salts
Where is lipase produced?
- pancreas
What is the role of lipase?
- hydrolyse the ester binds in triglycerides to form the monoglycerides and fatty acids
Where are bile salts produced?
- liver
What is the role of bile salts?
- emulsify lipids to form tiny droplets, micelles
What do micelles do?
- increase the surface area for lipase to act on
- deliver fatty acids, glycerol and monoglycerides to the epithelial cells of the ileum for absorption
Why are micelles formed close to epithelial cells?
- allows to make contact and diffuse immediately
What can the epithelial cell also be called?
- mucosal cell
What are micelles?
- water soluble vesicles formed of fatty acids, glycerol, monoglycerides and bile salts
What are the products of digestion absorbed by in mammals?
- cells lining ileum
Adaptations of the ileum
-The lining of the ileum is folded - called villi (finger-like projections) increasing the surface area for absorption
- The villi have thin walls - one epithelial cell layer thick - therefore a short diffusion pathway for the molecules being absorbed
- The epithelial cells also have microvilli, increasing the surface area even more
- The villi have a good blood supply to carry away absorbed monomers (maintaining concentration gradients)
Why is co transport and active transport required for absorption of glucose and amino acids from the lumen to the gut?
- there is higher concentration of glucose or amino acids in the epithelial cells than in the lumen
In what conditions is facilitated diffusion carried out for absorption of glucose and amino acids?
- higher concentration of glucose or amino acids in the lumen compared to the epithelial cell
Describe the process of lipid absorption
- lipids digested into monoglycerides and fatty acids by lipase and bile salts
- form micelles
- when micelles encounter ileum epithelial cells, due to non polar (lipid soluble) nature of fatty acids and monoglycerides, they simply diffuse across cell surface membrane to enter cells of epithelial cells
- once in cell, modified back into triglycerides inside of the endoplasmic reticulum and Golgi body
Describe the reformation of triglycerides
- in the Golgi apparatus and smooth endoplasmic reticulum, Ceylon
Describe the digestion and absorption of lipids
- Presence of bile salts cause emulsification Which increase the surface area
- Micelles contain the bile salts and fatty acids and monoglyceride as the lipase caused hydrolysis of the lipids
3 . Micelles come into close contact with the cells of the ileum and micelles make fatty acids and monoglyceride more soluble - Fatty acids and monoglyceride are absorbed by diffusion into the cell
- Triglyceride are reformed in chylomicrons
- Vesicles from smooth endoplasmic reticulum move to cell membrane and triglyceride enter the lymphatic vessel
Where is lipase secreted?
- small intestine
