Digestion and Absorption Flashcards
To understand how the body digests molecules and substances and how they are absorbed
What are the stages of carbohydrate digestion?
Food enters the mouth and is broken up by teeth (mechanical digestion), then mixed with saliva.
Salivary amylase starts to hydrolyse glycosidic bonds in the starch producing maltose (chemical digestion).
In the stomach this salivary amylase is denatured due to acidic pH.
In the small intestine, pancreatic amylase continues to hydrolyse the starch to maltose.
Maltose is then hydrolysed to glucose by maltase ( a membrane bound dissaccharidase) enzymes in the membrane of the epithelial cells. The glucose can then be absorbed.
Where is the enzyme amylase produced and what is the product of the reaction catalysed by the enzyme?
Produced in the salivary glands and pancreas
And it produces starch to maltose
Where is the enzyme maltose produced and what is the product of the reaction catalysed by the enzyme?
In epithelium cell membrane of small Intestines
And it produces maltose to glucose
Why can only monosaccharides be absorbed?
This is because monosaccharisedes are small enough to move across the epithelial cell membrane.
Monosaccharides (glucose, fructose, and galactose) are absorbed by facilitated diffusion and active transport using SPECIFIC carrier proteins
What is the process of co transport?
Sodium ions actively transported out of epithelial cell into the blood (by sodium potassium pump);
This creates a concentration gradient of sodium ions (between lumen of the ilium and the epithelial cell)
Sodium ion and glucose enter by facilitated diffusion
Sodium ions moves into the cell down its concentration gradient
Glucose moves into the cell against its concentration gradient / down an electrochemical gradient
Glucose moves into the blood by facilitated diffusion
How are proteins digested?
Proteins are digested by enzymes called proteases. This process begins in the stomach, an endopeptidases hydrolyse the peptide bonds within the protein. This produces many smaller polypeptide chains and increases the surface area for the next enzyme. This makes digestion faster and more efficient.
In the small intestine, the pancreatic juice neutralises the acid and contains more endopeptidases and exopeptidases. Exopeptidases hydrolyses the peptide bonds at the end of the protein.
The dipeptidases - enzymes embedded in the cell surface membrane of the epithelial cells. These hydrolyse dipeptides into amino acids which can then be absorbed by facilitated diffusion and active transport (co-transport).
What are endopeptidases?
An enzyme that hydrolyses the peptide bonds within the protein.
What are exopeptidases?
An enzyme that hydrolyses the peptide bonds at the end of the protein.
What are dipeptidases?
Enzymes embedded in the cell surface membrane of the epithelial cells. These hydrolyse dipeptides into amino acids which can then be absorbed by facilitated diffusion and active transport
Is ATP used to move amino acids into the cell?
No because amino acids move against their concentration gradient, so it’s not active transport
How is the ileum adapted to its function?
High surface area provided with many villi each with millions of microvilli so that diffusion is increased
They have thin walls so that the distance for diffusion is reduced
They contain muscle allowing the contents to be mixed so that diffusion gradients are maintained when the products of digestion are absorbed and are replaced by new material
They have a good blood supply so that a diffusion gradient is maintained
Where are lipids digested?
Lipids are ONLY digested within the lumen of the small intestine
Where in the body are the lipids churned into fat droplets?
In the stomach
Where is bile produced, stored and released to?
Bile is produced in the liver and stored in the gall bladder .
It is released into the small intestine with the food.
What do bile salts do?
Bile salts emulsify fat droplets.
