Digestion and absorption Flashcards

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1
Q
  1. What is digestion?

2. Why is digestion required?

A
  1. During digestion large molecules are broken down into smaller molecules, which can move across cell membranes . This means that they can be easily absorbed from the gut, into the blood to be transported around the body for use by the body cells.
  2. Large biological molecules in food are too big to cross cell membranes
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2
Q

Amylase?

A
  • Catalyses the breakdown of starch
  • Amylase is produced by the salivary glands, which release amylase into the mouth
  • It is also produced by the pancreas, which releases amylase into the small intestine
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3
Q

Digestion of carbohydrates by amylase

A

Amylase works by catalysing hydrolysis reactions that break the glyosidic bonds in starch to produce maltose

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4
Q

What are membrane bound disaccharidases?

A
  • Membrane-bound disaccharidases are enzymes that are attached to the cell membranes of epithelial cells lining the ileum.
  • They help to break down disaccharides into monosaccharides.
    (involves the hydrolysis of glycosidic bonds)
  • The monosaccharides can be transported across the epithelial cell membranes in the ileum via specific carrier proteins
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5
Q

How are carbohydrates digested?

A
  • Breakdown of Large Insoluble Molecules into Small Soluble Molecules (so they can move into the blood and then into the body cells)
  • Starch/Glycogen (Carbohydrates) into Glucose by Amylase (Salivary in mouth, Pancreatic in small intestine)
  • Maltase/Lactase/Sucrase (on lining of small intestine)
    (membrane bound disaccharidases)
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6
Q

Which enzyme breaks down lipids?

A
  • Lipase breaks down lipids into monoglycerides and fatty acids
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7
Q

Where is lipase made?

A
  • Lipase is made mainly in the pancreas, then secreted into the small intestine where they act
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8
Q

Digestion of lipids?

A
  • Lipids into monoglycerides and fatty acids by lipase (hydrolysis of ester bonds)
  • Bile salts are produced by the liver and emulsify lipids
  • cause lipids to form small droplets
  • Several small lipid droplets have a larger surface area than a single large droplet (for the same volume of lipid)
  • Formation of small droplets greatly increases the surface area of lipids that’s available for lipase to work on
  • Once the lipid has been broken down by lipase, the monoglycerides and fatty acids stick together to form micelles
  • Micelles help the product of lipid digestion to be absorbed
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9
Q

Digestion of proteins?

A
  • Endopeptidase (in stomach), hydrolyses peptide bonds within a protein
  • Exopeptidase (in small intestine), hydrolyses peptide bonds at the end of protein molecules
  • Dipeptidase (on lining of small intestine), hydrolyse dipeptides into amino acids (hydrolyse peptide bond between them)
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10
Q

Endopeptidase?

A
  • Endopeptidase (in stomach), hydrolyses peptide bonds within a protein (into smaller chains)
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11
Q

Exopeptidase?

A

-Exopeptidase (in small intestine), hydrolyses peptide bonds at the end of protein molecules

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12
Q

Dipeptidase?

A

-Dipeptidase (on lining of small intestine), hydrolyse dipeptides into amino acids (hydrolyse peptide bond between them)

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13
Q

Absorption of monosaccharides?

A
  • Glucose is absorbed by active transport with sodium ions via co-transporter protein
  • Galactose is absorbed in the same way using the same co-transporter protein
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14
Q

Absorption of monoglycerides and fatty acids?

A
  • Micelles help to move monoglycerides and fatty acids towards the epithelium
  • monoglycerides and fatty acids are lipid-soluble, so can diffuse directly across the epithelial cell membrane
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15
Q

Absorption of amino acids?

A
  • Sodium ions ae actively transported out of the epithelial cells into the ileum
  • They then diffuse back into the cells through sodium-dependent transporter proteins in the epithelial cell membrane, carrying the amino acids with them
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16
Q

What is lactose intolerance?

A
  • Person does not make Lactase Enzyme
  • Lactose remains Undigested
  • Leads to Diarrhoea and Flatulence
  • Undigested Lactose in Lumen of Intestine lowers it’s water potential, so water enters the lumen by osmosis leading to water faeces (Diarrhoea)
  • Undigested Lactose broken down by micro-organisms in Large Intestine, giving off gas (Flatulence)
17
Q

Enzymes of Carbohydrate Digestion?

A
  • Starch/Glycogen (Salivary Amylase in Mouth, Pancreatic Amylase in Small Intestine) into Maltose
  • Maltose (Maltase on lining of Small Intestine) into Glucose
  • Lactose (Lactase on lining of Small Intestine) into Glucose and Galactose
  • Sucrose (Sucrase on lining of Small Intestine) into Glucose and Fructose