Digestion and absorption Flashcards
What is digestion?
Secretion of enzymes that hydrolyse large, insoluble molecules to smaller, soluble molecules for absorption and transport
What is the stomach?
A muscular sac that secretes enzymes from the inner layer (specifically protease)
What is the ileum?
A long muscular tube that further digests food molecules
What does the large intestine do?
Absorbs water, most of which is from the secretions of many digestive glands
What is egestion?
The removal of faeces from the anus after being stored in the rectum
What enzyme(s) do salivary glands secrete?
Amylase, which hydrolyses starch into maltose
What is the pancreas?
A large gland situated below the stomach, that produces pancreatic juices
What enzymes are within pancreatic juices?
Protease, lipase and amylase
What are the two stages of digestion?
Physical and chemical digestion
What is physical digestion?
Breaking of large food, by structures such as teeth, which provide large surface area for chemical digestion, the churning in the stomach is also physical digestion
What is chemical digestion?
Hydrolysis of large insoluble molecules into smaller soluble ones, carried out by enzymes
What does amylase do?
Hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose
How is maltose hydrolysed?
By the disaccharidase maltase, into alpha glucose molecules, in the ileum lining
What do mineral salts in saliva do?
Maintain the pH at around neutral, which is optimum for amylase
How does pancreatic amylase maintain a neutral pH?
Alkaline salts are produced by both the pancreas and the intestinal wall, so amylase can function
Where are lipases produced and what do they do?
The pancreas, they hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides
What is emulsification?
The production of micelles (droplets of fats and oils) by bile salts
What are three different proteases?
Endopeptidase, exopeptidase and dipeptidase
What does endopeptidase do?
Hydrolyse the peptide bonds between amino acids in the central region of a polypeptide chain, forming a series of peptide molecules
What does exopeptidase do?
Hydrolyse the peptide bonds on the terminal amino acids of of the peptide molecules formed by endopeptidases, they progressively release dipeptides and single amino acids
What does dipeptidase do?
Hydrolyse the bond between the two amino acids of a dipeptide
Where are dipeptidases found?
They are membrane-bound, being part of the cell-surface membrane of epithelial cell lining the ileum
How is the ileum adapted for its function?
1mm long villi and a rich network of blood capillaries
How do the villi increase absorption?
Increase surface area, thin walled, contain muscles which mix contents of ileum and maintain concentration gradient, rich blood supply and microvilli
How are amino acids and monosaccharides absorbed?
Diffusion and co-transport
What’s the average diameter of micelles?
4-7nm
How are micelles broken down?
The come into contact with epithelial cells lining the ileum
How do monoglycerides and fatty acids enter epithelial cells?
As they are non-polar molecules, they easily diffuse across the cell-surface membrane
What happens once monogylcerides and fatty acids enter the epithelial cells?
They are transported to the endoplasmic reticulum, where they are recombined to form triglycerides
What happens after triglycerides are formed by the endoplasmic reticulum?
Continue to the Golgi apparatus, where they associate with cholesterol and lipoproteins to form chylomicrons
What are chylomicrons?
Special particles adapted for the transport of lipids
How do chylomicrons move out of the epithelial cells and where do they go?
Exocytosis, they enter lymphatic capillaries called lacteals
Where are lacteals found?
At the centre of each villus
How do the chylomicrons move into blood vessels and how are they hydrolysed?
They pass via the lymphatic vessels into the blood system, they are hydrolysed by an enzyme in the endothelial cells of blood capillaries, from where they diffuse into cells
