Structures and functions of the Digestion System
This essay aims to explain the structure and functions of the digestion system, starting from consuming a cooked dinner to chemical and physical changes within the body, to prepare or help absorption of vital nutrients and help disposal of waste.
The structure of the digestive system starts with the gastrointestinal tract, it is a tube that runs from the mouth to the anus and because of this some scientist says it is an external organ; there are also accessory organs for digestion, the salivary glands, teeth, tongue, liver, gall bladder and pancreas. The function of the digestive system is to breakdown food, so nutrients can enter the blood and lymph system.
To start this process, we have to start with the mouth, when food is put in to the mouth you start the process of digestion, the structure of the mouth is made up of the lips, teeth, tongue, salivary glands, soft palate and pharynx. The lips function is to hold food in. The salivary glands, there are three sets of salivary glands, the parotid glands which are in front of the ears one on each side of the face, then the submandibular glands that are below the jaw and the sublingual glands, that are either side the tongue, under the floor of the mouth all these start the chemical process within the mouth by making salvia to help moisten and dissolve food, saliva is made up of water, mucus, a bacterial agent and also has a carbohydrase enzyme called salivary amylase which helps convert starch into maltose. An enzyme, lysozyme destroys harmful bacteria, and saliva has a pH of 6.8; salivary also activates taste buds and lubricates the mouth. Teeth play a large part within the mouth by chewing and crushing food into smaller pieces to be swallowed, there are 4 types of teeth and they play all play a part, incisors are for cutting though food, canines are for tearing and shredding, molars and premolars are for crushing and grinding your food. The tongue’s function is to move food to the back of the mouth to the pharynx which the food is then called a bolus and so far with every function has been voluntary action with the exception of the salivary glands, but as food is guided to the pharynx, there is a soft palate that closes over the nasal passages to prevent food entering the nasal passages and the tongue blocks bolus getting back in to the mouth. When food enters the pharynx it is pushed down to the oesophagus, where a small flap called the epiglottis closes over the trachea (windpipe) to make sure bolus can only go to the oesophagus, peristaltic waves move the chyme down the oesophagus down to the stomach. The stomach can withstand up to 2 litres of food/fluid and is j-shaped bag, it also has the cardiac sphincter at the top that allows food to pass into the stomach and closes to stop food going back into the oesophagus, the stomach has four main sections, the cardia, which is the superior part of the stomach and where the cardia sphincter is, the fundus that normally contains air, but also acts as a holding area for food before going into the body of the stomach, this is also the largest area in the stomach, this is also where most of the churning takes place and the pyloric antrum which leads to the pyloric sphincter, which is a valve that stops chyme from leaving till its ready, this is in the inferior region of the stomach, the stomach has 3 muscle layers where as the rest of the gastrointestinal tract has only 2 layers, the stomach has 3 layers because how much churning it has to do, so it is more effective during mechanical digestion. Within the stomach there are gastric juices, which help speed up digestion, these gastric juices come from the gastric glands, there are 3 types of gastric gland cells, the parietal cells that produces hydrochlorie acid, that breaks down food and kills micro-organisms, then there are chief cells which secrete the enzyme pepsin, which turn protein‘s into polypeptides,...
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