Digestion and Absorption Flashcards
Digestive system, Starch digestion, Carbohydrate absorption, Co-transport of glucose, Protein digestion, Amino acid digestion, Co-transport of amino acids, Lipid digestion, Lipid absorption
What is a digestive system?
A tube which extends from the mouth, to the anus. Each section of this tube has a specialised role in the breakdown and absorption of food molecules and water.
What are proteins hydrolysed by?
Amino acids and proteases
What are carbohydrates hydrolysed by?
Carbohydrases
What are fats hydrolysed by?
Lipases
What are proteins hydrolysed into?
Amino acids
What are carbohydrates hydrolysed into?
Simple sugars
What are fats hydrolysed into?
Glycerol, fatty acids and monoglycerides
Salivary glands -
Secrete saliva containing amylase which hydrolyses starch to maltose
Stomach -
Food is mixed with gastric juice which kills microorganisms and contains endopeptidases and exopeptidases which breaks down proteins
Pancreas -
Secretes pancreatic juice containing amylase (and other carbohydrases), protease and lipase
Small intestine -
Adapted to provide a larger SA for absorption. Maltase enzymes are embedded
What is the first stage in starch digestion?
Salivary amylase starts to hydrolyse glycosidic bonds in the starch producing maltose
What is the second stage in starch digestion?
In the stomach the amylase is denatured due to the acidic pH
What is the third stage in starch digestion?
In the small intestine, pancreatic amylase continues to hydrolyse the starch to maltose
What is the fourth stage in starch digestion?
Maltose is then hydrolysed to glucose by maltase enzymes in the membrane of the epithelial cells. The glucose can then be absorbed
Describe the first step of the co-transport of glucose
Sodium ions are actively transported out of the epithelial cell into the blood by a sodium potassium pump (Na+/K+)
Describe the second step of the co-transport of glucose
This creates a concentration gradient of the sodium ions between the lumen and of the ilium and the epithelial cell
Describe the third step of the co-transport of glucose
Sodium ions and glucose enter by facilitated diffusion
Describe the fourth step of the co-transport of glucose
Sodium ions move into the cell down their concentration gradient
Describe the fifth step of the co-transport of glucose
Glucose moves into the cell against its concentration gradient
Describe the sixth step of the co-transport of glucose
Glucose moves into the blood by facilitated diffusion
What is the first step in protein digestion?
It begins in the stomach with endopeptidases hydrolysing the peptide bonds within the protein. This increases the SA for the next enzyme, making digestion faster and more efficient.
What is the second step in protein digestion?
In the small intestine endopeptidases continue to hydrolyse the peptide bonds within the protein while exopeptidaes hydrolyse the peptide bonds at the end of the protein. This breaks down the polypeptide chains into amino acids and dipeptides
What is the third step of protein digestion?
The dipeptidaes are broken down into amino acids by enzymes embedded into the cell surface membrane of the epithelial cell. Once broken down the amino acids can be absorbed by facilitated diffusion and active transport in co-transport
Describe the first step in how amino acids are absorbed through co-transport
Sodium ions are actively transported out of the epithelial cell into the blood by a sodium potassium pump
Describe the second step in how amino acids are absorbed through co-transport
This creates a concentration gradient of sodium ions between lumen and the ilium and the epithelial cell
Describe the third step in how amino acids are absorbed through co-transport
Sodium ions and amino acids enter by facilitated diffusion
Describe the fourth step in how amino acids are absorbed through co-transport
Sodium ions move into the cell down its concentration gradient
Describe the fifth step in how amino acids are absorbed through co-transport
Amino acids move into the cell against their concentration gradient
Describe the sixth step in how amino acids are absorbed through co-transport
Amino acids move into the blood by facilitated diffusion
What happens to lipids before digestion?
In the stomach the lipids are churned into fat droplets. In the lumen of the small intestine the lipids are digested. Bile salts, that are produced in the liver and stored in the gall bladder, are released into the small intestine with the food and emulsify the fat droplets. This increases the SA of the lipids for the action of enzymes to make digestion faster and more efficient. Lipases hydrolyse lipids into glycerol, fatty acids and monoglycerides
What is the first step in lipid absorption?
Lipid droplets are mixed with bile salts and make smaller droplets which increase the SA for faster absorption
What is the second step in lipid absorption?
Triglycerides are broken down into glycerol and fatty acids which form micelles
What is the third step in lipid absorption?
Micelles are small enough to enter the cell by simple diffusion
What is the fourth step in lipid absorption?
At the SER fatty acids and glycerol are recombined to tryglycerides
What is the fifth step in lipid absorption?
At the golgi apparatus tryglycerides are modified by proteins being added to make lipoproteins (chylomicrons) and packaged into vesicles
What is the sixth step in lipid absorption?
Chlomicrons are transported into a lymph vessel by exocytosis, they then enter the blood
What is a trigyliceride modified with proteins called?
Chylomicrons/Lipoproteins
