6b. DIGESTION Flashcards
Name the organs associated with digestion.
Mouth (teeth and salivary gland), oesophagus, stomach, ileum, large intestine, rectum, pancreas, liver, gall bladder
Describe the function of stomach acid
Kills pathogens
Describe what villi are
Folds of the epithelial tissue of the ileum
Describe what microvilli are
Folds of the cell surface membrane of the epithelial cells of the ileum
Describe the function of villi and microvilli
Increase the surface area for absorption of small biological molecules
Define digestion
The breakdown of large biological molecules into smaller biological molecules
Name the two types of digestion
Physical digestion and chemical digestion
What is physical digestion?
The mechanical breakdown of food using physical movement
Give two examples of physical digestion
Chewing (mastication), and muscle contraction causing churning of food in the stomach
Explain the function of physical digestion
To increase the surface area for chemical digestion
What is chemical digestion?
The hydrolysis of bonds by enzymes to break large food molecules into smaller ones.
Name the 6 digestive enzymes
Amylase, maltase, lipase, endopeptidases, exopeptidases, dipeptidases
Why are digestive enzymes specific?
Because their active sites have a specific tertiary shape, which is only complementary to the substrate
Why is it advantageous for digestive enzymes to be embedded in the plasma membranes of the epithelial cells of the ileum, rather than be secreted into the ileum lumen?
Because they are not lost with the gut contents
Where is amylase produced?
The pancreas
Where does amylase act?
The mouth (secreted from the salivary gland) and the plasma membranes of the epithelial cells of the ileum
What is the function of amylase?
To hydrolyse starch to maltose
Where is maltase produced?
The ileum
Where does maltase act?
In the plasma membranes of the epithelial cells of the ileum
What is the function of maltase?
To hydrolyse maltose to glucose
How is glucose transported from the ileum lumen to the blood?
By co-transport
Once monosaccharides are in the bloodstream, what happens to them?
Transported to cells to be used in respiration, or transported to liver and muscle cells to be stored as glycogen
Recall the five stages of lipid digestion and absorption
Emulsification, Hydrolysis, Micelle formation, Chylomicron formation and Chylomicron transport.
Name the chemicals that are used to emulsify lipids
Bile salts
Where are bile salts produced, stored and secreted into?
Produced in the liver, stored in the gall bladder and secreted into the ileum lumen.
Where does emulsification occur?
Ileum lumen
What is emulsification?
Breaking lipids down into many smaller droplets
Explain the function of emulsification
Smaller droplets have a higher SA:Volume, which increases surface area for lipase action, which allows faster hydrolysis of lipids
Where are lipases produced?
Pancreas.
Where do lipases act?
In the plasma membranes of the epithelial cells of the ileum
What is the function of lipases?
To hydrolyse ester bonds in triglycerides, forming a monoglyceride and two fatty acids
What is a monoglyceride?
A molecule containing a glycerol and a fatty acid
Where does micelle formation occur?
In the ileum lumen
What is a micelle?
An association of monoglycerides, fatty acids and bile salts
Describe the function of micelles
To transport monoglycerides and fatty acids across the cell surface membrane of the ileum epithelial cells.
By which type of molecular transport do glycerol and fatty acid molecules cross the cell surface membrane of the epithelial cells of the ileum?
Diffusion
Where does chylomicron formation occur?
In the epithelial cells of the ileum
Which two cell organelles are involved in chylomicron formation?
SER and Golgi apparatus
Describe the role of the SER in chylomicron formation
Here the monoglycerides and fatty acids are reformed into triglycerides
Describe the role of the Golgi apparatus in chylomicron formation
Here triglycerides are combined with proteins and formed into chylomicrons
What are chylomicrons?
Lipoprotein vesicles used to transport lipids from the ileum lumen around the body
How do chylomicrons travel out of the ileum epitheliel cells?
Exocytosis
Where do chylomicrons travel to when they leave the ileum epithelial cells?
Lacteals
What are lacteals?
Lymphatic capillaries
Where are lacteals found in the digestive system?
At the centre of each villus
Where are peptidases (proteases) produced?
Pancreas
Where do peptidases (proteases) act?
Stomach and the plasma membranes of the epithelial cells of the ileum
Why are peptidases (proteases) produced in the pancreas in an inactive form?
So they don’t hydrolyse the pancreas tissue
How is Trypsin transported from the pancreas to the ileum?
Through pancreatic ducts
What is the function of endopeptidases?
They break polypeptides into smaller peptide chains by hydrolysing internal peptide bonds. This increases the surface area for exopeptidases.
What is the function of exopeptidases?
They remove terminal amino acids by hydrolysing the terminal peptide bonds
What is the function of dipeptidases?
Hydrolyse dipeptides into amino acids
How are amino acids transported from the ileum lumen to the blood?
By co-transport
Once amino acids are in the bloodstream, what happens to them?
Transported to cells to be used in protein synthesis.
Which two monosaccharides make up the disaccharide lactose?
Glucose and galactose
Which enzyme hydrolyses lactose to its monosaccharides?
Lactase
Where is lactase found in the digestive system?
In the plasma membranes of the epithelial cells of the ileum
What is ‘lactose intolerance?’
An inability to digest lactose
What is the cause of lactose intolerance?
Lactase deficiency
What are the two advantages of using immobilised lactase in experiments to study lactose intolerance?
No lactase in the milk, and the enzymes can be reused
Which biochemical test could you use to ascertain whether the immobilised lactase has hydrolysed lactose?
Benedict’s solution
If the immobilised lactase hasn’t hydrolysed the lactose, what would the result of the Benedict’s test be?
Blue - negative
If the immobilised lactase has hydrolysed the lactose, what would the result of the Benedict’s test be?
Brick red precipitate - positive
What is the function of an experimental control?
Experimental controls are needed to eliminate alternate explanations of experimental results
