Digestion and Absorption Flashcards
What is digestion?
The process of breaking down large biological molecules (e.g., carbohydrates, proteins, and lipids) into smaller molecules that can be absorbed.
Where does digestion begin?
In the mouth with mechanical digestion (chewing) and chemical digestion by salivary amylase.
What enzyme is in saliva?
Amylase, which breaks down starch into maltose.
What is peristalsis?
Waves of muscular contractions that move food through the digestive tract.
Role of the stomach in digestion?
Secretes hydrochloric acid to kill pathogens and pepsin to break down proteins into peptides.
What enzyme breaks down proteins?
Pepsin in the stomach, trypsin and chymotrypsin in the small intestine.
Why is hydrochloric acid important in the stomach?
Provides an acidic environment (pH 1-2) for pepsin to function and kills bacteria.
What is the role of bile?
Neutralises stomach acid and emulsifies fats to increase the surface area for lipase.
Where is bile produced and stored?
Produced in the liver and stored in the gallbladder.
What is emulsification?
The breakdown of large fat droplets into smaller ones to increase the surface area for enzyme action.
What enzyme breaks down lipids?
Lipase, which breaks triglycerides into monoglycerides and fatty acids.
Where are most enzymes secreted?
The pancreas releases digestive enzymes into the small intestine (duodenum).
What is the role of pancreatic amylase?
Breaks down remaining starch into maltose in the small intestine.
What enzyme breaks down maltose?
Maltase, which hydrolyses maltose into glucose on the epithelial lining of the small intestine.
What is the function of the villi and microvilli?
Increase surface area for absorption in the ileum.
How is glucose absorbed?
By co-transport with sodium ions using a sodium-glucose co-transporter protein.
How are amino acids absorbed?
By co-transport with sodium ions across the epithelial membrane into the blood.
How are lipids absorbed?
Monoglycerides and fatty acids diffuse into epithelial cells and are reassembled into triglycerides. They are packaged into chylomicrons and transported via the lymphatic system.
What is the role of the lacteal?
Absorbs fats and transports them via the lymphatic system.
What is the role of endopeptidases?
Hydrolyse peptide bonds within a protein, creating shorter peptide chains.
What is the role of exopeptidases?
Hydrolyse peptide bonds at the ends of protein chains, releasing amino acids or dipeptides.
What is the role of dipeptidases?
Hydrolyse dipeptides into individual amino acids.
Where are dipeptidases found?
On the membrane of the epithelial cells lining the small intestine.
How are fatty acids and monoglycerides absorbed?
They diffuse across the phospholipid bilayer into the epithelial cells as they are lipid-soluble.
What are chylomicrons?
Lipid-protein complexes formed inside epithelial cells that transport fats into the lymph.
How are monosaccharides absorbed?
Glucose and galactose are absorbed by active transport with sodium ions; fructose is absorbed via facilitated diffusion.
What is the function of the ileum?
The final site of digestion and absorption of nutrients.
What is the role of the large intestine?
Absorbs water and forms faeces.
What happens to undigested material?
It is excreted as faeces through the anus during egestion.
What is the role of the hepatic portal vein?
Transports absorbed nutrients from the small intestine to the liver.
Why is sodium important for glucose absorption?
Sodium ions help facilitate the co-transport of glucose and amino acids into the epithelial cells.
What is co-transport?
A type of active transport where the movement of one substance (e.g., sodium) down its concentration gradient allows the transport of another (e.g., glucose) against its gradient.
What is the role of the epithelial cells in the small intestine?
They contain enzymes in their membranes to complete digestion and facilitate absorption.
How do micelles assist lipid absorption?
They transport monoglycerides and fatty acids to the epithelial membrane for diffusion.
What is the role of trypsin?
A protease secreted by the pancreas that hydrolyses proteins into smaller peptides.
What happens to excess glucose?
It is converted to glycogen and stored in the liver and muscles.
What is lactose intolerance?
A condition where individuals lack lactase, preventing the breakdown of lactose into glucose and galactose, leading to gastrointestinal discomfort.
