Essay: Digestive system

A digestive system is a collection of organs working together to transform food into energy and basic nutrients to feed the body. Food moves through a long tube inside the body known as the alimentary canal or the gastrointestinal tract (GI tract) (Inge et al,2008). The alimentary canal is made up of the oral cavity, pharynx, oesophagus, stomach, small intestines and large intestines. In addition to this there are several additional organs that help your body to digest food but food does not pass through them, these are excretion called accessory organs. Accessory organs of the digestive system are the teeth, the tongue, salivary glands, liver, gallbladder, and the pancreas. To provide energy and nutrients to the body, six major roles take place in the digestive system, these are absorption, digestion, ingestion, mixing and movement and secretion.
Most common foods that contain mostly carbohydrates are potatoes, bread, cereals, rice and pasta and should make up about a third of the food you eat (NHS, 2016). Many of these foods contain starch, which can be digested, and fibre, which the body cannot digest. The digestible carbohydrates are broken into simpler molecules by enzymes in the saliva, a fluid produced by the pancreas, and in the lining of the small intestine. Starch is digested in two steps: The first is an enzyme in the saliva and pancreatic fluid breaks the starch into molecules called maltose; The second is when an enzyme in the lining of the small intestine (maltase) splits the maltose into glucose molecules that can be absorbed into the blood. Glucose is carried through the bloodstream to the liver, where it is stored or used to provide energy for the work of the body (Toole and Toole, 2015).
Table sugar is another carbohydrate that must be digested to be useful. An enzyme in the lining of the small intestine digests table sugar into glucose and fructose, each of which can be absorbed from the intestinal cavity into the blood. Milk contains yet another type of sugar, lactose, which is changed into absorbable molecules by an enzyme called lactase, also found in the intestinal lining. However there are some that are lactose intolerant and this happens when they have digested milk or milk based products, their body reacts with symptoms such as bloating, diaoreah and gas. Some people think that being lactose intolerant it is an allergy (Niddk, 2016). This is not the case. There are two further conditions which may
Protein
Further digestion of the protein is completed in the small intestine. Here, several enzymes from the pancreatic fluid and the lining of the intestine carry out the breakdown of large protein molecules into small molecules called amino acid. These small molecules can be absorbed from the hollow of the small intestine into the blood and then be carried to all parts of the body to build the walls and other parts of cells.
Fats
Fat molecules are a rich source of energy for the body. The first step in digestion of a fat such as butter is for the bile acids to combine with the fatty acids and cholesterol and to help these molecules to move into the cells of the mucosa. In these cells the small molecules are formed back into large molecules, most of which pass into vessels (called lymphatics) near the intestine. These small vessels carry the reformed fat to the veins of the chest, and the blood carries the fat to storage depots in different parts of the body.
Vitamins
The large, hollow organs of the digestive system contain muscle that enables their walls to move. The movement of organ walls can force food and liquid and can mix the contents within each organ. Typical movement of the esophagus, stomach, and intestine is called peristalsis. The action of peristalsis looks like an ocean wave moving through the muscle. The muscle of the organ produces a narrowing and then propels the narrowed portion slowly down the length of the organ. These waves of narrowing push the food and fluid in front of them through each hollow organ.
Water and Salt
Food enters the oral cavity. Within the mouth are many organs that help in the digestion of food, tongue, teeth, and salivary glands. Teeth chop food into small pieces, which are moistened by saliva before the tongue and other muscles push the food into the pharynx.
The Digestion System
As the food enters the oral cavity. The teeth are hard organs found along the anterior and lateral edges of the mouth. Teeth are living organs and contain blood vessels and nerves under the dentin in a soft region known as the pulp. Teeth are used for cutting and grinding food into smaller pieces. The tongue is located on the inferior portion of the mouth just posterior. It is a small organ made up of several pairs of muscles covered in a thin, bumpy, skin-like layer. The outside of the tongue contains many rough papillae for gripping food as it is moved by the tongue’s muscles. The taste buds on the surface of the tongue detect taste molecules in food and connect to nerves in the tongue to send taste information to the brain. The tongue also helps to push food toward the posterior part of the mouth for swallowing. Surrounding the mouth are 3 sets of salivary glands. The salivary glands are accessory organs that produce a watery secretion known as saliva. Saliva helps to moisten food and begins the digestion of carbohydrates. The body also uses saliva to lubricate food as it passes through the mouth, pharynx, and esophagus. The pharynx, or throat, is a funnel-shaped tube attached to the posterior end of the mouth. The pharynx is responsible for the passing of masses of chewed food from the mouth to the esophagus. The pharynx also plays an important role in the respiratory system, as air from the nasal cavity passes through the pharynx on its way to the larynx and eventually the lungs. Because the pharynx serves two different functions, it contains a flap of tissue known as the epiglottis that acts as a switch to route food to the esophagus and air to the larynx (Innerbody, 2016). The esophagus is a muscular tube connecting the pharynx to the stomach that is part of the upper gastrointestinal tract. It carries swallowed masses of chewed food along its length. At the inferior end of the esophagus is a muscular ring called the lower esophageal sphincter or cardiac sphincter. The function of this sphincter is to close at the end of the esophagus and trap food in the stomach. The stomach is a muscular sac that is located on the left side of the abdominal cavity, just inferior to the diaphragm. In an average person, the stomach is about the size of their two fists placed next to each other. This major organ acts as a storage tank for food so that the body has time to digest large meals properly. The stomach also contains hydrochloric acid and digestive enzymes that continue the digestion of food that began in the mouth.
The small intestine is a long, thin tube about 1 inch in diameter and about 10 feet long that is part of the lower gastrointestinal tract. It is located just inferior to the stomach and takes up most of the area in the abdominal cavity. The entire small intestine is coiled like a hose and the inside surface is full of many ridges and folds. These folds are used to maximize the digestion of food and absorption of nutrients. By the time food leaves the small intestine, around 90% of all nutrients have been extracted from the food that entered it.
The liver is a roughly triangular accessory organ of the digestive system located to the right of the stomach, just inferior to the diaphragm and superior to the small intestine. The liver weighs about 3 pounds and is the second largest organ in the body. The liver has many different functions in the body, but the main function of the liver in digestion is the production of bile and its secretion into the small intestine. The gallbladder is a small, pear-shaped organ located just posterior to the liver. The gallbladder is used to store and recycle excess bile from the small intestine so that it can be reused for the digestion of subsequent meals. The pancreas is a large gland. it is about 6 inches long and connected to the duodenum pointing to the left wall of the abdominal cavity. The pancreas secretes digestive enzymes into the small intestine to complete the chemical digestion of foods. The large intestine is a long, thick tube about 6.5 cm in diameter and about 1.35m long. It is located just inferior to the stomach and wraps around the superior and lateral border of the small intestine. The large intestine absorbs water and contains many symbiotic bacteria that aid in the breaking down of wastes to extract some small amounts of nutrients. Feces in the large intestine exit the body through the anal canal.
The digestive system is responsible for taking whole foods and turning them into energy and nutrients to allow the body to function, grow, and repair itself. The six primary processes of the digestive system include ingestion of food, secretion of fluids and digestive enzymes, mixing and movement of food and wastes through the body, digestion of food into smaller pieces, absorption of nutrients and excretion of wastes
The first function of the digestive system is ingestion, or the intake of food (Innerbody, 2016). The mouth is responsible for this function, as it is the orifice through which all food enters the body. The mouth and stomach are also responsible for the storage of food as it is waiting to be digested. This storage capacity allows the body to eat only a few times each day and to ingest more food than it can process at one time.
In the course of a day, the digestive system secretes around 7 liters of fluids. These fluids include saliva, mucus, hydrochloric acid, enzymes, and bile. Saliva moistens dry food and contains salivary amylase, a digestive enzyme that begins the digestion of carbohydrates. Mucus serves as a protective barrier and lubricant inside of the GI tract. Hydrochloric acid helps to digest food chemically and protects the body by killing bacteria present in our food. Enzymes are tiny biochemical machines that disassemble large macromolecules like proteins, carbohydrates, and lipids into their smaller components. Finally, bile is used to mix large masses of lipids into tiny globules for easy digestion.
The digestive system uses three main processes to move and mix food, Swallowing is the process of using smooth and skeletal muscles in the mouth, tongue, and pharynx to push food out of the mouth, through the pharynx, and into the esophagus (Innerbody, 2016). Peristalsis is a muscular wave that travels the length of the GI tract, moving partially digested food a short distance down the tract. It takes many waves of peristalsis for food to travel from the esophagus, through the stomach and intestines, and reach the end of the GI tract. Segmentation occurs only in the small intestine as short segments of an intestine contract like hands squeezing a toothpaste tube. Segmentation helps to increase the absorption of nutrients by mixing food and increasing its contact with the walls of the intestine. Digestion is the process of turning large pieces of food into its component chemicals. Mechanical digestion is the physical breakdown of large pieces of food into smaller pieces. This mode of digestion begins with the chewing of food by the teeth and is continued through the muscular mixing of food by the stomach and intestines. Bile produced by the liver is also used to mechanically break fats into smaller globules. While food is being mechanically digested it is also being chemically digested as larger and more complex molecules are being broken down into smaller molecules that are easier to absorb. Chemical digestion begins in the mouth with salivary amylase in saliva splitting complex carbohydrates into simple carbohydrates. The enzymes and acid in the stomach continue chemical digestion, but the bulk of chemical digestion takes place in the small intestine thanks to the action of the pancreas. The pancreas secretes an incredibly strong digestive cocktail known as pancreatic juice, which is capable of digesting lipids, carbohydrates, proteins and nucleic acids. By the time food has left the duodenum, it has been reduced to its chemical building blocks—fatty acids, amino acids, monosaccharides, and nucleotides. Once food has been reduced to its building blocks, it is ready for the body to absorb. Absorption begins in the stomach with simple molecules like water and alcohol being absorbed directly into the bloodstream. Most absorption takes place in the walls of the small intestine, which are densely folded to maximize the surface area in contact with digested food. Small blood and lymphatic vessels in the intestinal wall pick up the molecules and carry them to the rest of the body. The large intestine is also involved in the absorption of water and vitamins B and K before feces leave the body. The final function of the digestive system is the excretion of waste in a process known as defecation. Defecation removes indigestible substances from the body so that they do not accumulate inside the gut. The timing of defecation is controlled voluntarily by the conscious part of the brain, but must be accomplished on a regular basis to prevent a backup of indigestible materials.
Figure 1 Diagram of the digestion system
When food enters the duodenum, the pancreas releases enzymes to help break down fat, protein and carbohydrate (Enzymeesentials, 2016). The gall bladder releases bile, which has been produced by the liver, to help further break fats down into a form that can be absorbed by the intestines.
The small intestine is lined with villi, which provide a large surface area enabling the absorption of nutrients, including carbohydrates, proteins, and fats, into the bloodstream (Pickering, 2002).
The small intestine also plays a key role in regulating blood glucose levels. The small intestine contains a number of receptive cells which detect the presence of macronutrients and secrete hormones which instructs the pancreas on how much insulin and glucagon to release.
Gluten sensitivity or intolerance is a condition that causes a person to respond after ingesting gluten, a protein found in wheat, barley, and rye. The symptoms can vary and can include gastrointestinal problems, joint pain, fatigue, and depression. These can also be very similar to the condition celiac disease. A further test can be carried out to identify which is the correct diagnosis (Gluten-free living, 2016).
Figure 1: Role of Nutrients of the Body
Carbohydrates
Examples Diagram of structure with name Description of structure Role in the body
Examples
Starch
Glucose
Cellulose
Figure 2 Carbohydrates
Glucose Monosaccharide:
Known as Simple sugar
Disaccharide:
Are also called double sugar, any substance that is composed of two molecules of simple sugars linked to each other. Disaccharides are crystalline water-soluble compounds.
Starch: A starch molecule is a polysaccharide assembled from the simple sugar glucose; it can contain large amounts varying from five hundred to several hundred thousand glucose molecules joined by covalent bonds into a single structure.
Carbohydrates are a source of energy for the body. They can be converted more readily into glucose, the form of sugar that’s transported and used by the body. Cooking starch-containing items result in the hydration of starch molecules and the swelling of starch granules, increasing the rate and enhancing the enzymatic breakdown of starch. Amylases also convert starch to glucose.
Proteins
Examples
Enzymes
Antibodies
Hormones
Collagen
Keratin
Cell Receptors Figure 3 Proteins (Analitik, 2016)
Amino Acid, R Group Amino-acid: Always contain Carbon, hydrogen and oxygen and can also carry sulphur. These are used in protein synthesis.
Primary structure:
Secondary structure:
Tertiary structure:
Quaternary structure:
Lipids
Examples Figure 4 Lipids (Info-please, 2016)
Lipid Lipid:
Phospholipid: There are two classes of phospholipids. The first are the glycerophospholipids, which are themselves subdivided into two groups. Phosphatides are molecules composed of glycerol substituted with two fatty acid esters. Three alcohols that form phosphatides are choline, ethanolamine, and serine. The second are sphingolipids (Mandal. 2014). Sphingolipids have a long-chain or sphingoid base, such as sphingosine, to which a fatty acid is connected by an amide bond. Sphingomyelin is one of the most copious sphingolipids in animal tissues. Sphingomyelin is a significant building block of membranes
Steroid:
Bibliography