digestion and absorption Flashcards
What is the definition of digestion?
The hydrolysis of large biological products to small biological molecules with the use of enzymes
What is the definition of absorption?
The movement of the molecules from the lumen of the ileum, through the ieum lining into the bloodstream
How are carbohydrates digested?
Saliva enters mouth from salivary glands. Salivary amylase produced in the mouth hydrolyse the glycosidic bonds in starch = maltose.
This also contains mineral salts that help to maintain the pH at around neutral (optimal pH for amylase)
enters stomach and the acid denature the amylase and prevents further hydrolysis of the starch
food passed into small intestine, mixes with pancreatic juice, which has pancreatic amylase, continues the hydrolysis of remaining starch to maltose.
Alkaline salts are produced by pancreas and intestinal wall to maintain the pH at around neutral so that amylase can function.
epithelial lining in intestine wall produces membrane- bound disaccharidase (maltase), which hydrolyses the maltose from starch breakdown into alpha glucose
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What are membrane bound disaccharidases?
maltase that are not released into the lumen of the ileum but is part of the cell-surface membrane of the epithelial cells that line the ileum
How are lipids digested?
They begin digestion in the small intestine
bile salts produced in the liver, stored in the gall bladder, are secreted into the small intestine and emulsify lipids into micelles (tiny droplets) to increase SA of lipids= greater access for lipases
lipases produced in the pancreas are secreted into the small intestine. This hydrolyses the ester bond found in triglycerides to form fatty acids and monoglycerides.
Why is emulsification useful?
because it increases the surface area of the lipids so that the action of lipases is speeded up
How are proteins digested?
Begin digestion in the stomach by endopeptides (hydrolyse peptide bonds in the middle of polypeptides) and break down the polypeptides into smaller peptide bonds
HCL in the stomach maintains the optimum pH for these enzymes
In the ileum of the small intestine where exopeptides released from the pancreas (hydrolyse the peptide bonds found at the ends of polypeptides) = many dipeptides
membrane-bound dipeptidases will hydrolyse the peptide bonds within the dipeptides = amino acids
What are the adaptions of the villi?
- very thin-walled = reducing the distance over which diffusion takes place
- Contain muscle and are able to move = maintains diffusion gradient as their movement mixes the content of the ileum = ensures that new material rich in the products of digestion replaces it
- rich blood supply = blood can carry away absorbed molecules and maintain diffusion gradient
- microvilli further increases absorption.
Absorption of triglycerides?
- Micelles (which contains monoglycerides and fatty acids surrounded by bile salts) help to move monoglycerides and fatty acids towards epithelium
- Monoglycerides and fatty acids are transported to ER & combine to form triglycerides
. - Starting in the ER and continuing in the Golgi body, Triglycerides associated with cholesterol and lipoproteins = form chylomicrons (lipid transport structures) and are packaged in vesicles
- Chylomicrons enter lacteal (part of lymphatic system) by exocytosis
- Only drain into bloodstream near heart
What are chylomicrons?
special particles adapted for the transport of lipids.
what do micelles do
Monoglycerides and fatty acids are not very soluble so the micelles aid the transport of these molecules to the surface of the epithelial cells
The micelles break down and add to a pool of fatty acids and monoglycerides that are dissolved in the small intestine solution surrounding the epithelial cells.
what are micelles
The monoglycerides and fatty acids associate with phospholipids and bile salts to form micelles
explain the absorption of monosaccharides
The glucose carrier proteins in the cell-surface membrane of the small intestine work in a similar way to the amino acid carrier proteins
Sodium ions and glucose molecules are co-transported into the epithelial cells via facilitated diffusion
The glucose molecules diffuse across the epithelial cell and enter the capillary at the other end of the cell by facilitated diffusion
The concentration gradient of sodium ions is maintained by actively transporting sodium ions out of the epithelial cells into the blood
explain the absorption of amino acids
Specific amino acid co-transport proteins (carrier molecules) are found within the cell-surface membrane of the epithelial cells in the ileum
They transport amino acids only when there are sodium ions present
For every sodium ion that is transported into the cell, an amino acid is transported in
Amino acids diffuse across the epithelial cell and then pass into the capillaries via facilitated diffusion
The concentration gradient of sodium ions from the lumen of the ileum into the epithelial cell is maintained by the active transport of sodium ions out of the cell and into the blood via a sodium-potassium pump at the other end of the cell
