6.9 & 6.10- Enzymes and digestion & Absorption of the products of digestion

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  • Created by: Megan2413
  • Created on: 02-02-17 17:22
What is the function of the oesphagus?
It carries food from the mouth to the stomach
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Describe the structure of the stomach
It is a muscular sac with an inner layer that produces enzymes from glands
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What is the function of the stomach?
Its role is to store and digest food, especially proteins
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Describe the structure of the ileum
It is a long muscular tube. The walls produce enzymes, and glands pour their seceretion onto the food. The ileum inner walls are folded into villi, which also contain microvilli on the epithelial cells of each villus
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What is the function of the ileum?
It absorbs the products of digestion into the blood stream after further digesting food
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What is the function of the large intestine?
It absorbs water
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Where is most of the absorbed water from in the large intestine?
Secretions of the many digestive glands
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What is the function of the rectum?
It stores faeces before it is removed via the anus
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What is this process called by which faeces is removed from the anus?
Egestion
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Where are the salivary glands?
Situated near the mouth
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How do they pass their secretions into the mouth?
Via a duct into the mouth
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What does the salivary gland secretion contain?
It contains the enzyme amylase
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What does amylase do?
It hydrolyses starch into maltose
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What is the pancreas?
A large gland situated below the stomach
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What does the pancreas produce?
It produces pancreatic juice
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What does pancreatic juice contain?
The enzymes amylase, proteases and lipase
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What is digestion?
The process by which large molecules are hydrolysed by enzymes into smaller molecules, which can be absorbed and assimilated
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What is meant by assimilation?
The absorption and digestion of foods, and creating large molecules again
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What is peristalsis?
A process by which food is actively moved along the digestive system as muscles in the ileum wall contract to push food along it
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What are the two stages of digestion?
Physical digestion and chemical digestion
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Give two examples of physical breakdown in the digestive system
- Chewing food with teeth - Food being churned by muscles in the stomach wall
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Why is physical breakdown essential in the digestive system?
It breaks down the food into smaller pieces so it is possible to ingest the food, and also increases surface area for enzymes to chemically breakdown the food
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What type of reaction occurs with chemical breakdown in the digestive system?
Hydrolysis reaction
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What is a hydrolysis reaction?
The splitting up of molecules by adding water to the chemical bonds that hold them together
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What types of proteins are used in chemical digestion?
Enzymes
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Why is more than one enzyme usually needed to hydrolyse a large molecule?
They are highly specific and may need different ones to break up different bonds
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What are the three main digestive enzymes?
- Carbohydrases - Lipases - Proteases
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What do carbohydrases break carbohydrates down into?
Ultimately monosaccharides
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What do lipases break lipids down into?
Glycerol and fatty acids
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What do proteases break proteins down into?
Ultimately amino acids
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Where does the digestion of starch start?
In the mouth (whilst chewing)
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What enzyme is used in the mouth and where is it secreted from?
It is salivary amylase from the salivary glands
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What does salivary amylase do?
It starts to hydrolyse any starch in the food to maltose (by hydrolysing alternate glycosidic bonds in the starch molecule)
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What type of saccharide is maltose?
A disaccharide
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What does salivary amylase contain to maintain a neutral pH in the mouth?
Mineral salts
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Why is the pH maintained at neutral in the mouth?
It is the optimum pH for salivary amylase to work
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After the digestion in the mouth, food is swallowed and then where does it enter?
The stomach
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The conditions in the stomach are acidic- what happens?
The amylase is denatured by the acidic pH which prevents further hydrolysis of the starch
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After the stomach, where does the digested food go?
Into the small intestine
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What does the digested food mix with in the small intestine?
Pancreatic juice
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What does the pancreatic juice contain and why?
It contains pacreatic amylase which hydrolyses any remaining starch to maltose
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Where are mineral salts produced from the maintain a neutral pH?
Pancreas and intestinal wall
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How is the food pushed further down the small intestine?
Muscles in the intestinal wall contract to actively push down the food
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What enzyme is then produced from the epithelial lining?
Maltase
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What does maltase do?
It hydrolyses maltose into alpha glucose
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As maltase is part of the epithelial cell-surface membrane lining the ileum, what is this referred to?
It is a membrane-bound disaccharidase
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What two other common disaccharides are found in the diet?
Lactose and Sucrose
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Where is sucrose found?
In many natural foods, especially fruits
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What enzyme hydrolyses sucrose?
Sucrase
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What are the products of the hydrolysis of sucrose?
Glucose and Fructose
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What enzyme hydrolyses lactose?
Lactase
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What are the products of the hydrolysis of lactose?
Glucose and Galactose
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What group of enzymes hydrolyse proteins?
Peptidases (or proteases)
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What are the three types of peptidases called?
- Endopeptidases - Exopeptidases - Dipeptidases
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What do endopeptidases hydrolyse?
The peptide bonds between amino acids in the central region of a protein molecule
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What is formed after hydrolysis by endopeptidases?
A series of peptide molecules
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What do exopeptidases hydrolyse?
The peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases
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What is formed after the hydrolysis by exopeptidases?
Dipeptides and single amino acids
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What do dipeptidases hydrolyse?
The bond between two single amino acids of a dipeptide
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What membrane are dipeptidases membrane-bound to?
The cell-surface membrane of epithelial cells lining the ileum
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ABSORPTION OF TRIGLYCERIDES: What emulsifies lipid droplets to form micelles?
Bile
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How are monoglycerides and fatty acids formed fro micelles?
Micelles come into contact with with epithelial cells on the lining of the villi- causing them to break down to release monoglycerides and fatty acids
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Why can monoglycerides and fatty acids diffuse into the epithelial cells?
They are non-polar molecules
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Where are the monoglycerides and fatty acids transported to once inside the epithelial cells?
To the endoplasmic reticulum (ER)
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What happens in the ER?
The monoglycerides and fatty acids recombine to form triglycerides again
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What's formed as triglycerides are moved from the ER to the golgi apparatus?
Chylomicrons
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How are chylomicrons formed?
By combining triglycerides with cholesterol and lipoproteins
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How do chylomicrons exit epithelial cells?
By exocytosis
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What is exocytosis?
The transport of materials out of a cell by means of a sac/vesicle that first engulfs the material and then is extruded through an opening in the cell membrane
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Where do the chylomicrons go from the golgi apparatus?
To the lymphatic capillaries called lacteals
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Where are lacteals found?
In the centre of each villus
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Where do the chylomicrons go from the lacteals?
Into the blood capillaries
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What happens to the triglycerides in the blood capillaries?
They are hydrolysed and then diffuse into the cells
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