In this essay I will talk about the digestive system and the roles played by certain elements which help the digestion of food, My aims are to discuss the need for digestion for both absorption and the assimilation of nutrients, to discuss, the physical processes involved in digestion and explain their importance, to be able to identify the sites of digestive juices and enzymes and describe their roles in digestion, more importantly to be able to identify the major organs of the digestive tract and their main functions and to be able to identify layers in the gut wall and show how the structures of different parts of the digestive tract relates to the roles in digestion. To start with we will look at the need for digestion.
We all need to digest food to gain energy so we can move, breathe and survive. Without digestion we could not do all these things. To be able to gain extra energy from the things we consume, there has to be a way to absorb the nutrients by way of absorption into the bloodstream. The intestines help us to absorb food into the blood stream, by this the small intestines have a lining of villi, which are a finger like projections which have additional extensions called microvillus, this gives the small intestines a bigger surface area in which to absorb more food into the bloodstream at a faster rate. If this process of absorption is slow, the concentration of nutrients in the blood vessels will be equal and diffusion with not occur. Inside a microvillus/villi cell see fig 1.1 there are capillaries into which the nutrients can diffuse into and into another blood vessel such as the capillaries to be passed around the body to where it is needed. All digested nutrients including sugars and amino acids are absorbed into the capillaries and taken to wherever needed. Assimilation of nutrients can be done chemically. The chemical breakdown of nutrients includes enzymes and acids. The chemical breakdown is very important because we would not be able to break food down for it to be absorbed into our bloodstream, this is where the enzymes and the acids play a part, for example when we eat, we chew which is the physical breakdown, whilst we chew, enzymes from the salivary gland called salivary amylase which takes the starch out of the food and turns into simple sugars such as maltose. The food then passes down the oesophagus into the stomach, which contains an acid in the stomach called hydrochloric acid, which activates more enzymes; pepsin and rennin to further the breakdown of proteins into polypeptides, the nutrients then pass into the duodenum for which then a cocktail of enzymes from the pancreas is added to further the breakdown of nutrients into smaller particles which will allow the assimilation of nutrients into the bloodstream. We will now look at the physical processes involved in digestion and how important it is to digestion.
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The physical processes in digestion is the grinding, tearing up of food, making the food smaller is done in the mouth by the teeth, and by the stomach by the use of enzymes and hydrochloric acid. When we eat something, we chew it using our teeth primarily to fit it in our mouth and then to chew so we donâ€™t choke on it, also when we chew it activates the salivary gland which releases salivary amylase to further the breakdown of anything starchy that we eat to maltose a simple sugar. When the food is small enough to swallow, it is squeezed down the oesophagus and into the stomach, where the next phase of physical breakdown occurs. In the stomach, the walls are made of thick elastic muscles which pressurise the food to actually break down even further this is known as stomach churning see fig 2.2 , this reduces the food to smaller particles ready for the small intestine to digest and absorb into the bloodstream. These physical processes are vital to digestion in the means of getting the energy into the bloodstream, if the physical breakdown does not happen, for a start you cannot swallow the food, or if it reaches the stomach, the food would remain in the stomach until it was small enough to pass into the small intestine, physical processes in digestion is very important. To aid with physical processes there are also chemical processes that aid digestion by way of enzymes and digestive juices.
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Now, we will look at the roles digestive enzymes and juices have an impact on digestion. We will start from the moment we start consuming food. When we chew, the salivary glands in our mouths will secrete salivary amylase, our mouth pH is neutral which the enzymes are comfortable working in, the salivary amylase see fig 3.1 turns complex sugars (starch) into simpler sugars such as maltose.
We then swallow, down the oesophagus, into the stomach, where we meet the hydrochloric acid, this then stimulates the enzymes pepsin and rennin, the pepsin breaks down proteins into peptides which targets and severs particular types of amino acids.
The rennin on the other hand is just used for when we consume milk, this enzyme helps to coagulate or curdle the milk allowing the pepsin to break down the protein into peptides.
The food then passes into the duodenum (small intestine) where the pancreatic juices are added; the enzymes it will encounter are trypsin, Chymotrysin, Carboxypeptidase, Pancreatic amylase, Maltase, Sucrase, Lactase, Lipase. Trypsin will target the proteins and polypeptides and sever them into smaller polypeptides
Chymotrypsin only works on proteins and severs them into polypeptides; Trypsin and Chymotrypsin sever the same end of amino acids known as the carboxyl side.
Carboxypeptidase works with the polypeptides and this severs the other end of the amino acid by severing the residue end of the amino acid.
Pancreatic amylase see fig 3.2 is very similar to salivary amylase it works the same way but is made by the pancreas; it breaks starch down to maltose. Maltase breaks down the maltose to glucose.
Any more nutrients that have not been broken down by enzymes yet is probably due to different sugar types such as sucrose which is broken down by the sucrase enzyme, this breaks down sucrose into glucose and fructose.
Another sugar is lactose which is broken down by the enzyme lactase into glucose and galactose.
They may be fats that need to be broken down by enzymes, which are broken down by lipase which breaks up fats and oils into glycerol and fatty acids. All these enzymes are important to allow absorption into the bloodstream via diffusion easily without leaving any nutrients left behind. There are some major organs in the digestive tract that have many important functions to aid us with digestion. (See table of simplified enzymes)
The main organs in the digestive system are the mouth which helps us to physical break down the food to smaller digestible parts. The oesophagus, which helps to squeeze the food down by muscle contractions of latitudinal muscle known as peristalsis into the stomach, the stomach which helps us physically and chemically break the food down with the help of hydrochloric acid activating enzymes such as pepsin and rennin. After the stomach, the liver see fig 4.1 manufactures bile for the gall bladder, the gall bladder adds the bile to the digestive process so it can break down fats into minute droplets of water. Then pancreatic juices see fig 4.2 which contain a hormone called insulin which helps control the blood sugar level and enzymes which to help convert the nutrients to more useful nutrients is added to the digestive process, The small intestine with the help of the peristalsis which has a squeezing motion helps us push the food along the gastrointestinal tract and also as the absorption into the blood by peristalsis. If there is any undigested food at that point, it passes from the small intestine into the large intestine, the blood vessels in the large intestine take back the water that was undigested, the ileocecal value in the large intestine stops the undigested waste from going back into the small intestine, any undigested waste is excreted by the anus. There are many layers in the gut wall that are different from one another, and how it aids digestion.
There are three types of gut wall I will be looking at, the stomach gut wall, the small intestine gut wall and the large intestine gut wall. The stomach gut wall see fig 5.1has different types of epithelial cells in its lining all of which are divided by type, it also has mucous cells which stands between the stomach lining and the acids in the stomach creating a protective layer from the acidic environment inside the stomach. The stomach itself has a highly wrinkled series of folds known as rugal folds, this aids digestion for the stomach fills these rugal folds flatten out which allows the stomach to expand, this allows the stomach to be flexible whilst keeping it strong in structure so it will not rupture. In the small intestine see fig 5.2 it has finger like projections called villi, which is covered in microvillus and mucus, the villi and the microvillus, have a large surface area allowing the absorption of nutrients via diffusion into the blood stream, the surface area secretes mucus, enzymes and water to furthermore absorption into the blood stream. Unlike the small intestine the large intestine see fig 5.3 does not have villi, it is surrounded by blood vessels giving it undigested material and undigested waste back, such as water, electrolytes, the large intestine has a large capacity allowing a lot of waste to be passed down it, it is hollow allowing it to squeeze food down it, eventually allowing it to be excreted by the anus.
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The digestive system is amazing it helps us to mechanically break down food physically and chemically with the use of enzymes, acids etc. the digestive system is the biggest system in our body hence it is a passage from the mouth to the anus.