Digestion And Absorption Flashcards
Definition of digestion
The process where large, insoluble molecules are hydrolysed into small, soluble molecules
What are the 2 types of digestion
- Physical
- Chemical
What is physical digestion
Large food pieces being broken down into smaller pieces to make it possible to swallow and increase surface area
What is chemical digestion
Hydrolyses large, insoluble molecules into smaller, soluble ones (hydrolysis uses water to break down a substance)
Describe starch digestion at the mouth (carbohydrate)
Salivary amylase hydrolyses starch into maltose (saliva contains mineral salts to maintain neutral ph)
Describe starch digestion at the stomach
The acid in the stomach denatures amylase so hydrolysis of starch is stopped
Describe starch digestion at the small intestine (1st part)
Pancreatic amylase hydrolyses the remaining starch to maltose (alkaline salts are produced to maintain a neutral ph)
Describe starch digestion at the small intestine (part 2)
Maltase hydrolyses the maltose to alpha-glucose (membrane bound disaccharide so not released into lumen)
What does maltase do
Hydrolyses maltose into alpha glucose
What does sucrase do
Hydrolyses sucrose into glucose and fructose
What does lactase do
Hydrolyses lactose into glucose and galactose
Describe lipid digestion part 1
Large fat droplets, emulsified by bile salts, are broken down into micelles - smaller fat droplets (increases sa)
Lipid digestion part 2
Triglycerides are hydrolysed by lipases (produced in pancreas) to form fatty acids and a monoglyceride (lipase hydrolysed ester bond)
What enzymes break down proteins (protein digestion)
Are complex molecules so are hydrolysed by a group of enzymes called peptidases
What does endopeptidase do (part 1)
Hydrolyses peptide bonds between amino acids in central region of a protein - form a series of peptide molecules
What does exopeptidase do (part 2)
Hydrolyse the peptide bonds on terminal amino acids of the peptide molecules formed by endopeptidases - form dipeptides and a single amino acid
What does dipeptidase do (part 3)
Hydrolyses the peptide bond between 2 amino acids. These enzymes are membrane bound - part of cell surface membrane of epithelial cells lining the ilium
Definition of absorption
Products of digestion are taken into cells from the lumen of the gut
What are the products of digestion that need to be absorbed
- Amino acids
- Monosaccharides
- Monoglycerides and fatty acids
How are the cells lining the ilium adapted for efficient absorption
- Villi increase sa for diffusion
- Villi are thin-walled (1 cell thick) - decreases diffusion distance
- Contain muscle so are able to move and maintain diffusion gradients as contents of ilium can mix
- Well supplied with blood vessels so blood can carry away absorbed molecules and maintain the diffusion gradient
- Epithelial cells lining villi have microvilli to increase sa even more
Describe absorption of triglycerides into the epithelial cells
Micelles include bile salts and fatty acids which help to make fatty acids more soluble in water (as are non polar). They bring the fatty acids to the lining of the ilium + therefore maintain a higher conc of fatty acids so they can be absorbed by diffusion
Describe absorption of triglycerides inside the epithelial cells
The short fatty acid chains within the cell can move directly into the blood via diffusion. But the longer fatty acid chains recombine with monoglycerides and fatty acids in the endoplasmic reticulum. These are packaged into lipoproteins called chylomicrons
Describe the absorption of triglycerides out of the epithelial cells
These droplets are transported to a lacteal (a lymph vessel within the villus) via exocytosis, eventually chylomicrons enter the bloodstream. The triglycerides in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of blood capillaries from where they diffuse into cells
Describe how products of carbohydrate or protein digestion are absorbed in the ileum
- Potassium moves into the epithelial cell from the capillary via active transport (against conc gradient
- at the same time sodium moves out of the epithelial cell into the capillary by active transport (causing a low conc of sodium in the cell)
- sodium and glucose move into the cell via active transport (using energy form gradient created)
- glucose then moves into capillary by facilitated diffusion (along gradient)
