Digestion and absorption Flashcards
Role of the oesophagus?
carries food from the mouth to the stomach
Role of the stomach?
stores and digests food. Has glands which produce enzymes for protein digestion
Role of the ileum (small intestine)?
food is digested by enzymes produced in the walls and glands of the small intestine. Inner walls are folded into villi, with small projections called microvilli which give a large surface area, for rapid absorption into the bloodstream
Role of the large intestine?
absorbs water
Role of the salivary glands?
secrete amylase, which hydrolyses starch into maltose
Role of the pancreas?
secretes pancreatic juice containing protease, lipase and amylase
Why is it necessary to digest polymers?
- need to be small enough to pass into the bloodstream from the small intestine
- need to be soluble for absorption
What are physical and chemical digestion?
physical - large pieces of food are broken down into smaller pieces by physical structures, which increases surface area for chemical digestion
chemical - large, insoluble molecules are broken down into smaller, soluble molecules by enzymes through hydrolysis reactions
What is the substrate of amylase?
starch
What is the substrate of maltase?
maltose
What is the substrate of lactase?
lactose
What is the substrate of lipase?
triglycerides
What is the substrate of sucrase?
sucrose
What is the substrate of exopeptidase?
polypeptides and dipeptides
What is the substrate of endopeptidase?
polypeptides
What is the product of starch?
maltose
What is the substrate of dipeptidase?
dipeptides
What is the product of maltose?
glucose
What are the products of sucrose?
glucose and fructose
What are the products of triglycerides?
glycerol and 3 fatty acids
What are the products of lactose?
glucose and galactose
What are the products of polypeptides?
shorter polypeptide chains and dipeptides
What are the products of dipeptides?
amino acids
Where is amylase produced?
salivary glands and pancreas
Where dissacharidases (maltase, lactase, sucrase) produced?
epithelial lining of ileum
Where is lipase produced?
pancreas
Where is endopeptidase produced?
stomach and pancreas
Where is exopeptidase produced?
pancreas
Where is dipeptidase produced?
epithelial lining of ileum
What is the site of digestion of starch?
mouth and duodenum
What is the site of digestion for disaccharides?
epithelial lining of ileum
What is the site of digestion of triglycerides?
duodenum
What is the site of digestion of short polypeptide chains and dipeptides broken down by endopeptidase?
stomach and duodenum
What is the site of digestion of dipeptides and amino acids broken down by exopeptidase?
dueodenum
What is the site of digestion of amino acids broken down by dipeptidase?
epithelial lining of ileum
How are carbohydrates digested?
- amylase produced in the salivary glands and pancreas will begin to hydrolyse polysaccharides into maltose by hydrolysing glycosidic bonds
- food is swallowed and enters the stomach where conditions are acidic. The acid denatures amylase which prevents further hydrolysis
- maltose is hydrolysed into alpha glucose by maltase produced in the lining of the ileum
How are lipids digested?
- lipids are hydrolysed by lipase enzymes produced in the pancreas which breaks ester bonds found in triglycerides to form monoglycerides and fatty acids
- lipids are firstly split into micelles by bile salts produced in the liver
- this is called emulsification and increases surface area for faster digestion of lipids
How are proteins digested?
- endopeptidases hydrolyse peptide bonds between amino acids in the centre of a polypeptide
- exopeptidase hydrolyse peptide bonds on the terminal amino acids of a peptide molecule
- dipeptidases hydrolyse peptide bonds between 2 amino acids in a dipeptide
- digestion starts in the stomach, continues in the duodenum and fully digested in the ileum
How is the small intestine adapted for efficient exchange?
- microvilli provide a large surface area which accelerates the rate of absorption
- one cell thick epithelial layer/villi for a short diffusion distance
- constant movement of internal medium (blood constantly flowing and good blood supply) and external medium (food in lumen of gut) so concentration gradient remains steep
How is the small intestine specialised for exchange?
- membrane bound disaccharides and dipeptidases
- muscle tissue for contraction to move along food
- elastic tissue for expansion and stretching to fit more food
- lacteals to absorb fat
- lots of mitochondria for active transport and energy release
How are amino acids absorbed into the bloodstream from the epithelial cells?
Through co-transport
- sodium potassium pump - sodium moves out of cell by active transport, low concentration of Na+ inside and high concentration of Na+ in the blood
- sodium ions and amino acids move from the lumen into epithelial cells. Larger di/tripeptides move in by H+ ions - these proteins are not fully digested
- di/endo/exopeptidases break down dipeptides into amino acids
- amino acids move out of epithelial cells into the bloodstream through a carrier protein - they are too large to move out through diffusion
How are lipids absorbed and transported from the ileum into the lymph vessels?
- lipase enzymes hydrolyse lipids into glycerol and fatty acids
- micelles contain bile salts and fatty acids
- micelles make fatty acids more soluble
- micelles come into contact with epithelial cells lining the villi of the ileum and maintain a higher concentration of fatty acids and monoglycerides to the lining of the ileum
- fatty acids and monoglycerides absorbed by diffusion into epithelial cells
- monoglycerides and fatty acids are transported to the endoplasmic reticulum where they are recombined to form triglycerides
- exocytosis of vesicles
What is the role of micelles in the absorption of fats in the ileum?
- micelles include bile salts and fatty acids
- make fatty acids more soluble in water
- carry fatty acids to the lining of the ileum which maintains a high concentration
- fatty acids absorbed by diffusion
