3.3.3 Digestion and Absorption Flashcards
Oesophagus
transports food from mouth to stomach
Stomach
muscular sac, inner layer produces enzymes, stores and digests food (particularly protein)
ileum (small intestine)
where further enzyme digestion occurs
Large Intestine
mostly absorbs water and nutrients
Salivary glands
a duct in the mouth containing amylase
Pancreas
contains pancreatic juices which contain various enzymes
What are the exchange features in the ileum? (5)
- Villi and microvilli increase surface area
- Villi lining and capillary endothelium are one cell thick
- Ileum contain muscle which contracts.
- Well supplied with blood vessels.
- Epithelial cells are dense with carrier proteins for amino acids and glucose
How is many villi and microvilli in the ileum beneficial?
creates a large SA:V ratio
How is the villi lining and capillary endothelium of the ileum being one cell thick beneficial?
Shorter diffusion distance
How is the ileum containing muscles that contract beneficial?
This movement mixes the contents of the ileum and so maintains concentration gradients.
How is the ileum being supplied with blood vessel beneficial?
Blood circulates to maintain concentration gradient
How is the epithelial cells being dense in the ileum with carrier proteins for amino acids and glucose beneficial?
selectively permeable
Role of carbohydrases
Hydrolyses polysaccharides to disaccharides
Role of disaccharidases
Hydrolyse disaccharides to monosaccharides
Role of Lipases
Hydrolyses lipids into monoglycerides and fatty acids
Role of Proteases/ Peptidases (2)
Hydrolyses polypeptides to dipeptides
Hydrolyses dipeptides to amino acids
Where are all these digestive enzymes found?
in the epithelial surface membrane
Outline the process of Carbohydrate digestion (7)
- Saliva enters mouth and is mixed with food.
- Salivary amylase starts hydrolysing starch to maltose.
- Mineral salts in the saliva maintain the pH at neutral.
- The food enters the stomach and amylase is denatured.
- The food is passed into the small intestine and mixed with pancreatic juices (containing pancreatic amylase)
- Epithelial lining of small intestine produces maltase.
- Maltase hydrolyses maltose to alpha glucose.
Describe how a molecule of starch is digested into glucose (4 marks)
- Salivary amylase hydrolyses starch into maltose
- Pancreas makes pancreatic amylase which further hydrolyses starch into maltose
- Membrane-bound maltase hydrolyses maltose into glucose
- Glycosidic bonds are broken
Role of the disaccharidase Sucrase?
breaks the glycosidic bond in a sucrose molecule, producing glucose and fructose.
Role of the disaccharidase Lactase?
breaks the glycosidic bond in a lactose molecule, producing glucose and galactose.
What happens when you add lipids in water? Why?
An emulsion is formed.
Fatty acids are hydrophobic – insoluble in water.
Outline the process of triglyceride digestion (7)
- Emulsification must occur to aid digestion
- Bile salts are produced by the liver and stored in the gall bladder
- Large lipid droplets are split up into tiny droplets called micelles by bile salts.
- This increases the lipids surface area, increasing the activity of lipases
- Now lipid digestion can occur at an increased rate
- Lipases in pancreatic juice hydrolyse triglycerides into monoglycerides and fatty acids. Break ester bond.
- Micelles carry monoglycerides/fatty acids to the epithelial cell membrane
What is a micelle?
an association of bile salts, monoglycerides and fatty acids
Describe what happens during emulsification.
Large insoluble lipid droplets are split into smaller molecules called micelles
How do micelles increase the digestion and absorption of lipids? (2 ways)
Increase SA for action of lipases
carry them to epithelial lining and make them soluble
What are the three types of peptidases?
endopeptidases, exopeptidases and dipeptidases
endo
in
exo
out
Outline the process of protein digestion (3)
- Endopeptidases hydrolyse the central region of a protein molecule forming a series of peptide molecules.
- Exopeptidases progressively release dipeptides and single amino acids by breaking peptide bonds on terminal amino acids
- Dipeptidases break the bond between the 2 amino acids of a dipeptide
What is the function of endopeptidase?
hydrolyses the central region of a protein molecule
What is the function of exopeptidases?
progressively release dipeptides and single amino acids by breaking peptide bonds on terminal ends of the polypeptide chain
What is the function of dipeptidases?
break the bond between the 2 amino acids of a dipeptide
Where are peptidases produced in the body? (3 organs)
stomach, small intestine and pancreas
How are glucose and amino acids absorbed?
co transport
Outline the process of cotransport of glucose absorption in the ileum (4)
- Sodium ions are actively transported out of ileum epithelial cell into blood. There are now less Na+ ions inside the cell.
- This forms a diffusion gradient for sodium to enter epithelial cell from the lumen.
- As sodium moves into cell, glucose enters by facilitated diffusion with sodium ions via the co-transporter protein.
- Glucose moves into blood via facilitated diffusion through a channel protein.
Outline the process of cotransport of amino acid absorption in the ileum (4)
- Sodium ions are actively transported out of ileum epithelial cell into blood. There are now less Na+ ions inside the cell.
- This forms a diffusion gradient for sodium to enter epithelial cell from the lumen.
- As sodium moves into cell, amino acids enter by facilitated diffusion with sodium ions via the co-transporter protein.
- Amino acids move into the blood via facilitated diffusion through a channel protein.
What is lacteal?
Tiny lymphatic vessels
Transport fat and slowly release them into the bloodstream
What do epthelial cells make?
Chylomicrons.
These lipoproteins are adapted for transporting dietary lipids from intestines to other parts of the body.
Describe how triglycerides/lipids are absorbed (6)
- Micelles come into contact with epithelial cell membrane and break down, releasing the monoglycerides and fatty acids.
- MGs and FAs diffuse across the phospholipid bilayer into the epithelial cells.
- MGs and FAs move to endoplasmic reticulum where they are recombined to form triglycerides.
- Triglycerides move to Golgi apparatus, where they associate with cholesterol and lipoproteins to form chylomicrons.
- Chylomicrons move out of epithelial cells by exocytosis.
6. Chylomicrons enter lacteals (lymphatic capillaries) and are transported away from intestine.
what is the role of micelles in the absorption of lipids. (5)
- Micelles include bile salts and fatty acids
- Make the fatty acids (more) soluble in water;
- Release fatty acids to cell/lining (of the ileum)
- Maintain high(er) concentration of fatty acids to cell/lining (of the ileum)
- Fatty acids (absorbed) by diffusion
what is a chylomicron?
large triglyceride-rich lipoproteins produced in enterocytes from fatty acids and cholesterol
what is a lipoprotein?
molecules composed of lipid and protein that transports cholesterol in the blood.
