digestion and absorption

• what occurs in the mouth during digestion?

  food enters the mouth and there a lots of salivary glands that produce enzymes to start the digestive process. The food then travels down the oesophagus.
• what organ is at the end of the oesophagus?

  the stomach.
• what occurs in the stomach?

  adds further enzymes and digestive acid to continue the digestive process. Stomach is surrounded by muscle tissue allowing it to churn and mix the digestive mixture.
• what is the step after the stomach?

  the small intestine or ileum. An incredibly long tube that has cells along its entire length that produce further enzymes and also villi (specialised cells) that are covered with hair-like projections called microvilli. This gives the ileum a large surface area to maximise the absorption of digestive products.
• what is the step after the ileum?

  the large intestine or colon. Main role is to absorb water. Most of the water absorbed comes from the salivary and other glandular secretions along the tract so far.
• what is the final part of the intestines?

  the rectum. Where solid waste matter or faeces is temporarily stored. The rectum terminates in a type of value called the anus where the faeces is removed.
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• what are the 2 categories that digestion can be categorised into?

  mechanical and chemical.
• what is mechanical digestion?

  the physical breakdown of foods through chewing by the teeth and the churning created by the stomach muscles. The idea behind this is to break the food into smaller pieces that are easier to digest chemically bc of the increased surface area this creates.
• what is chemical digestion?

  secretions like enzymes and acids are introduced to the food along the gastrointestinal tract. This starts at the mouth and further enzymes are added by the stomach, pancreas and the small intestine. These digestive enzymes usually have a single molecule as their target and all of them work by hydrolysing these larger molecules into smaller molecules that can be more easily absorbed when they reach the ileum.
• what are the 3 most important groups of digestive enzymes?

  carbohydrates, lipases and proteases.
• what are carbohydrates hydrolysed into?

  monosaccarides.
• what is an example of a carbohydrate being hydrolysed?

  amylase breaks down starch into maltose and glucose.
• what are lipases hydrolysed into?

  glycerol and fatty acids.
• what is an example of a lipase being hydrolysed?

  HPL breaks down dietary oils into monoglycerides and fatty acids.
• what are proteases hydrolysed into?

  amino acids.
• what is an example of protease being hydrolysed?

  pepsin breaks down various proteins into constituent peptides.
• what is the breakdown of a complex carbohydrate like?

  a multi step process with different enzymes involved each taking it in turns to remove the next monosaccharide or the next smaller piece from the molecule.
• what is the breaking down of starch like?

  starch is a long chain of alpha glucose molecules so the breaking down occurs in a particular sequence, which is crucial in the chemical digestion of other biological molecules.
• what is step 1 of the digestion of starch?

  the 1st enzyme to work on starch is salivary amylase, secreted by the salivary glands in the mouth. Salivary amylase begins to breakdown the starch molecule into smaller maltose molecules (a disaccharide).
• what is step 2 of the digestion of starch?

  on entering the stomach, the acidity of the digestive acids denatured the amylase and stops hydrolysis of the starch.
• what is step 3 of the digestion of starch?

  when the food reaches the small intestine, secretions coming from the pancreas (called pancreatic juice) are mixed with the food. Within the pancreatic juice is opancreatic amylase (another carbohydrase enzyme). This restarts the hydrolysis of starch into maltose.
• what is step 4 of the digestion of starch?

  the muscles of the intestine continue to push the food mixture through the ileum. Another enzyme is produced at the epithelial cells of the ileum called maltase. Maltase is never released into the lumen of the ileum but remains part of its absorption surface. The role of the maltase, is to breakdown the maltose formed by the amylase earlier.
• what sugar is in standard table sugar?

  sucrose.
• what food is lactose found?

  dairy products bc its a fundamental part of the milk used to make them.
• where are both maltose and sucrose hydrolysed?

  within the ileum surface by membrane bound disaccharides.
• what hydrolyses sucrose?


  sucrase.
• what hydrolyses lactose?


  lactase.
• what is another biological macromolecule that needs to be broken down into its component parts to pass through the membranes in the ileum and to be used around the body?

  lipids.
• what is the group of enzymes responsible for the breakdown of lipids?

  lipases. The pancreas produces lipases. Their role is to break the ester bond holding lipids together leaving us with a monoglyercide (one of the fatty acid chains remain attached to the glycerol) and individual fatty acids.
• what must happen before lipids can be treated by the lipases?

  bile salts from the liver separate the lipids into micelles (small distributed droplets). This process, emulsification, and the creating of tiny droplets creates a large surface area and lets more lipase work at the same time so spending up hydrolysis.
• what is the responsibility of the peptidases?

  to break down proteins, which can be quite complicated structured made of many amino acids.
• within peptidases, what are the 3 subgroups called?

  endopeptidases, exopeptidases and dipeptidases.
• what does endopeptidase do? eg?

  hydrolyses peptide bonds inside the protein molecule. eg: pepsin.
• what does exopeptidase do?

  hydrolyses the peptide bonds of amino acids on the ends of protein molecules. eg: angiotensin-converting enzyme (ACE)
• what does dipeptidase do? eg?

  hydrolyses the peptide bond in a dipeptide, forming 2 peptides. eg: beta-lactamase.
• what give the ileum a large surface area to increase the rate of absorption?

  villi and microvilli.
• what reduces the diffusion pathway in the ileum?

  the walls of the villi and microvilli cells are incredibly thin.
• what are the villi powered by and why?

  powdered by muscle to create a sweeping action that moves food along the ileum, constantly replacing the food it has drawn the nutrients from with new nutrient rich food. The contact with the blood supply is very important here and the villi are surrounded by lots of blood vessels to constantly remove the absorbed nutrients maintaining a conc gradient.
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