Digestion

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What is the role of the oesophagus?
Carries food from the mouth to the stomach
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What id the role of the stomach?
To store and digest food. Glands produce enzymes (pepsin) that digest protein
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What occurs in the ileum?
Food is digested further by enzymes that are produced in its walls and by glands that pour secretions on to the food
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How is the small intestine adapted to its function?
The inner walls are folded into villi which incease its SA. The SA is then further increased by microvilli on the epithelial cells of the villus. Adapts the ileum to its function of absorbing digestion products into the bloodstream
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What is the function of the large intestine?
Absorbing water
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What is the role of the rectum?
Where the faeces are stored before they are removed by egestion
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What enzyme does the salivary glands produce?
Amylase which hydrolyses starch into maltose
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Define digestion
The process in which large molecules are hydrolysed by enzymes into smaller molecules which can be absorbed and assimilated
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What are the stages of physical breakdown of food?
Mastication is breaking down food by the teeth into smaller pieces so the SA is increased for chemical digestion. Food is churned by the muscles in the stomach wall and this physically breaks up food
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Why is more than one enzyme needed to hydrolyse a molecule in chemical digestion?
Usually one enzyme hydrolyses a large molecule into sections which are then hydrolysed by other molecules
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What is the role of carbohydrases?
Hydrolyse carbohydrates into monosaccharides
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What is the role of lipases?
Hydrolyse lipids into fatty acids and glycerol
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What is the role of proteases?
Hydrolyse proteins into amino acids
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Describe the process of carbohydrate digestion in the mouth
Saliva enters from the salivary glands and is mixed with the food while chewing. Contains salivary amylase which hydrolyses the alternate glycosidic bonds in starch to produce maltose. Mineral salts maintain the pH as neutral (optimum for amylase)
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Describe the process of carbohydrate digestion in the stomach
Starch is not hydrolysed in the stomach due to the stomach being acidic which denatures amylase
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Describe the process of carbohydrate digestion in the intestines
Food in the small intestine mixes with pancreatic juice which contains pancreatic amylase which continues to hydrolyse starch into maltose. Alkaline salts are produced by the pancreas and intestinal wall to maintain the pH at neutral. cont
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the epithelial wall of the intestine produces membrane bound dissacharidase maltase. Hydrolyses maltose into alpha glucose
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How is sucrose hydrolysed?
Sucrase os a membrane-bound disaccharidase which hydrolyses the single glycosidic bond in the sucrose molecule. Produces glucose and fructose
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Describe lactose hydrolysis
Lactase hydrolyses the single glycosidic bond in the lactose molecule. Produces glucose and galactose
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Where is lipase produced?
The pancreas
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How does lipase breakdown lipids?
Hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides
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Define monoglyceride
A glycerol molecule with a single fatty acid molecule attached
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Describe the process of emulsification
Lipids are split up into small droplets called micelles by bile salts which are produced in the liver. This is done to increase the SA of the lipid so the action of the lipases is sped up
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What do endopeptidases do?
Hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules
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What is the role of exopeptidases?
Hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. Release dipeptidases and single amino acids
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What is the function of dipeptidases?
Hydrolyse the bond between the two amino acids of a dipeptide. Dipeptidases are membrane-bound and are part of the epithelial cells lining the ileum
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Why does lactase production diminish as you get older?
Milk is not as significant in the adult diet
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What is lactose intolerance?
Humans that produce no lactase cannot hydrolyse the lactose they consume. The undigested lactose reaches the large intestine where it is hydrolysed by microorganisms. This produces small soluble molecules and a large volume of gas. cont
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Can result in diarrhoea bc the soluble molecules lower the water potential of the material in the colon. This is called lactose intolerance
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How do villi increase the efficiency of absorption?
Increase SA for diffusion so increases the rate, thin walled so short diffusion pathway, able to move which maintains the diffusion gradients bc their movement mixes the contents of the ileum, well supplied with blood vessels so that blood can cont
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cont carry away absorbed molecules and maintain a diffusion gradient, microvilli further increase the SA available for absorption
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Describe the absorption of fatty acids
Bile salts play a role. One end of the bile salt is lipophilic but hydrophobic and the other end is hydrophilic but lipophobic. The bile salt molecules arrange themselves with their lipophilic ends in the fat droplets leaving the lipophobic ends cont
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sticking out. This prevents fat droplets from sticking together to form large droplets leaving only micelles. In this form they reach the epithelial cells of the ileum where they break down releasing the fatty acid for absorption
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Define diffusion
The net movement of molecules or ions from a region of higher concentration to a region of lower concentration
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Why is there a greater conc of glucose and amino acids in the ileum than in the blood?
Carbohydrates are continuously being digested in the ileum
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What helps maintain this diffusion gradient?
Blood is constantly being circulated by the heart so the glucose absorbed in it is continuously being removed by the cells as they use it in respiration
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What is the problem with using diffusion in absorption?
Only results in concs on either side of the intestinal epithelium being equal so not all available glucose+ amino acids can be absorbed that way
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What can be used to ensure all glucose and amino acids are absorbed into the blood?
Active Transport
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Describe the process of the sodium potassium pump
Sodium ions are actively transported out of epithelial cells into the blood by the s-p pump using a protein carrier molecule. This maintains a higher conc of sodium ions in the lumen of the intestine than inside the epithelial cells. Sodium ions cont
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diffuse into the epithelial cells down this conc gradient through another protein carrier. Carries an amino acid or glucose molecule into the cell with them. The glucose/amino acid pass into the blood plasma by facilitated diffusion
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Why is this an indirect form of active transport?
The sodium ions move down their conc gradient but the glucose/amino acids move against theirs. Its the sodium conc gradient rather than ATP directly that powers the movement of amino acids/glucose into the cell
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Other cards in this set

Card 2

Front

What id the role of the stomach?

Back

To store and digest food. Glands produce enzymes (pepsin) that digest protein

Card 3

Front

What occurs in the ileum?

Back

Preview of the front of card 3

Card 4

Front

How is the small intestine adapted to its function?

Back

Preview of the front of card 4

Card 5

Front

What is the function of the large intestine?

Back

Preview of the front of card 5
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