Nutrition in mammals involves:
1. Ingestion of food into body
2. Digestion of food into smaller molecules that can be absorbed into cells
3. Absorption and uptake of nutrients into cells
4. Assimilation: Use of nutrients for energy or making protoplasm
5. Egestion: Removal of undigested and unabsorbed material from the body
This involves the action of the digestive system, which consists of the gut (tube stretching from mouth to anus) and the other glands such as the liver and pancreas.
Gut structure:
1. Outer layer: Serosa (serous coat), secretes oily fluid to reduce friction due to rubbing of the exterior of the organs against each other.
2. Muscle layer: 2 layers of muscle (stomach has 3 layers) arranged in rings (circular muscle), and lengthwise (longitudinal muscle). These contract and relax to bring about peristalsis to push food along the gut.
3. Submucosa (submucous coat): Layer with blood vessels. Blood vessels are required to bring oxygen to gut cells, and to bring digested food to other parts of body. [Sub just means "under", hence the submucosa is just the layer below the mucosa.]
4. Mucosa (Mucous coat): As the name suggests, the layer contains the glands, which produce mucus (for lubrication of food), as well as digestive enzymes and other substances like acid. This is the layer nearest to the lumen of the gut.
Digestion
Can be classified as:
1. Physical: Mechanical breakdown of food into smaller particles, without the use of enzymes. Eg. Mastication in buccal cavity, churning in stomach, emulsification of fats in small intestine.
2. Chemical: Breakdown of food, involving the breaking of chemical bonds, which hence requires the action of enzymes. Eg. Digestion of amylase into maltose by maltase.
Important note: When describing chemical digestion processes, you must include in your answer:
1. Name of enzyme
2. Source of enzyme (where is enzyme made?)
3. Substrate that enzyme acts on
4. Product formed from reaction
Additional Notes
1. All proteases (enzymes that act on proteins/peptones) usually end with "-in" (pepsin, rennin, trypsin, erepsin).
2. Proteases that act on proteins must be produced in the inactive form inside cells, or the protease will cause the destruction of the cell as it will digest the proteins in the cell. Activation of the proteases depends on the type of protease: Those in the stomach are activated by acid, those in the small intestine (trypsin) is activated by another enzyme, enterokinase (from intestinal glands). This ensures protease is only activated in the lumen of the gut.
3. Bile salts allow for emulsification of fats into fat globules, which increases the surface area available for lipase to act on, hence increasing rate of lipase action.
4. Bile pigments DO NOT play a digestive function. They are just excretory products, formed from the breakdown of haemoglobin during the destruction of old red blood cells. Of course, since they are pigments, they give faeces their brown colour (but that's not a function!), and are removed out along with the faeces.
5. Coagulation is the change in state for a mixture from a liquid to a gel (ie semi-solid) state. This occurs in liquid foods which contain proteins because the shape of the proteins change when the liquid is heated/exposed to extreme pH. The proteins denature (recall that heat energy breaks the H-bonds, and acid breaks both H-bonds and ionic bonds, which are the bonds that cause the folding of the polypeptide chain) and unfolds. Other bonds then form and the protein forms a network of molecules. At this stage the food has semi-solid characteristics, and we say it has coagulated.
Note: Caseinogen (soluble milk proteins) has a slightly different structure, and does not coagulate with heating (when you boil milk, it does not clump and form curds). However, the presence of rennin in the mammalian stomach helps to coagulate caseinogen into insoluble casein.
1. Ingestion of food into body
2. Digestion of food into smaller molecules that can be absorbed into cells
3. Absorption and uptake of nutrients into cells
4. Assimilation: Use of nutrients for energy or making protoplasm
5. Egestion: Removal of undigested and unabsorbed material from the body
This involves the action of the digestive system, which consists of the gut (tube stretching from mouth to anus) and the other glands such as the liver and pancreas.
Gut structure:
1. Outer layer: Serosa (serous coat), secretes oily fluid to reduce friction due to rubbing of the exterior of the organs against each other.
2. Muscle layer: 2 layers of muscle (stomach has 3 layers) arranged in rings (circular muscle), and lengthwise (longitudinal muscle). These contract and relax to bring about peristalsis to push food along the gut.
3. Submucosa (submucous coat): Layer with blood vessels. Blood vessels are required to bring oxygen to gut cells, and to bring digested food to other parts of body. [Sub just means "under", hence the submucosa is just the layer below the mucosa.]
4. Mucosa (Mucous coat): As the name suggests, the layer contains the glands, which produce mucus (for lubrication of food), as well as digestive enzymes and other substances like acid. This is the layer nearest to the lumen of the gut.
Digestion
Can be classified as:
1. Physical: Mechanical breakdown of food into smaller particles, without the use of enzymes. Eg. Mastication in buccal cavity, churning in stomach, emulsification of fats in small intestine.
2. Chemical: Breakdown of food, involving the breaking of chemical bonds, which hence requires the action of enzymes. Eg. Digestion of amylase into maltose by maltase.
Important note: When describing chemical digestion processes, you must include in your answer:
1. Name of enzyme
2. Source of enzyme (where is enzyme made?)
3. Substrate that enzyme acts on
4. Product formed from reaction
Additional Notes
1. All proteases (enzymes that act on proteins/peptones) usually end with "-in" (pepsin, rennin, trypsin, erepsin).
2. Proteases that act on proteins must be produced in the inactive form inside cells, or the protease will cause the destruction of the cell as it will digest the proteins in the cell. Activation of the proteases depends on the type of protease: Those in the stomach are activated by acid, those in the small intestine (trypsin) is activated by another enzyme, enterokinase (from intestinal glands). This ensures protease is only activated in the lumen of the gut.
3. Bile salts allow for emulsification of fats into fat globules, which increases the surface area available for lipase to act on, hence increasing rate of lipase action.
4. Bile pigments DO NOT play a digestive function. They are just excretory products, formed from the breakdown of haemoglobin during the destruction of old red blood cells. Of course, since they are pigments, they give faeces their brown colour (but that's not a function!), and are removed out along with the faeces.
5. Coagulation is the change in state for a mixture from a liquid to a gel (ie semi-solid) state. This occurs in liquid foods which contain proteins because the shape of the proteins change when the liquid is heated/exposed to extreme pH. The proteins denature (recall that heat energy breaks the H-bonds, and acid breaks both H-bonds and ionic bonds, which are the bonds that cause the folding of the polypeptide chain) and unfolds. Other bonds then form and the protein forms a network of molecules. At this stage the food has semi-solid characteristics, and we say it has coagulated.
Note: Caseinogen (soluble milk proteins) has a slightly different structure, and does not coagulate with heating (when you boil milk, it does not clump and form curds). However, the presence of rennin in the mammalian stomach helps to coagulate caseinogen into insoluble casein.
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