The Digestive System and the Role of Enzymes in the Breakdown and Release of Nutrients.

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The Digestive System is the name given to the sequential process that our bodies perform when ingesting food, and the breaking down of macromolecules into micromolecules so that the body can absorb it’s nutrients into the bloodstream and it’s cellular system to obtain energy for cellular respiration, and the excretion all indigestible waste products. This happens within the digestive tract, which starts at the Mouth or Oral cavity and ends at the Anus. (Reference Appended image 1,’ The Human digestive system and associated organs). The molecules of food that we eat are generally Polymers, i.e., large, complex Molecules that are composed of long chains of Monomers. Polymers are insoluble and therefore cannot be absorbed into our bloodstream and need to be assimilated into different absorptive products. Polymers have to be hydrolysed into smaller, soluble molecules. This process happens during the process of digestion. Food is broken down by mechanical or chemical means (Hydrolysis) and this process is aided by Enzymes. Enzymes are biological, process catalysing Proteins which massively speed up the breaking down of compound molecules into micromolecules to allow nutritional absorption. All digestive Enzymes are Hydrolytic, i.e., a water molecule is added to allow compound molecular breakdown and separation. All Enzymes have a unique shape to their ‘active site’ allowing only the target substrate to bond for biological processing. Enzymes have optimum operating requirements and can denature if the temperature becomes too warm or the environment too acidic or alkaline. Digestive Enzyme secretion is regulated by both the nervous and the hormonal systems. Hormones are a chemical substance signalling system that communicates from one set of cells to another set, the target cells, which will then trigger enzyme secretion. Upon ingesting food into the mouth, salivary glands secrete saliva which contains the digestive enzyme ‘Salivary Amylase’. This has a neutral pH and starts the breakdown of starch into Maltose. The mechanical actions of the teeth and the tongue break the food down into a swallowable Bolus. When ready, the bolus is swallowed through the Pharynx and travels down the Oesophagus by Peristalsis - the rhythmic, mechanical processing action achieved by the longitudinal and circular muscles of the Oesophagus lining. The bolus travels through the Gastroesophageal sphincter into the Stomach where digestion begins. The stomach is acidic, pH2, so as to kill off any food borne bacteria travelling with the warm, moist bolus. The stomach recognises the presence of food and releases gastric juices from the gastric glands within the stomach walls. These contain the enzyme Pepsin (for the breakdown of proteins and creation of Peptides), Hydrochloric acid and Mucus. Mucus protects the stomach wall from it’s acidic contents and is reproduced by Goblet cells within the stomach lining. The food is churned by mechanical processing by the contractions of the muscular, stomach wall. The processed food becomes a liquid called Chyme and is released through the Pyloric Sphincter into the first part of the Small Intestine – the Duodenum. Duodenum intestinal wall lining is made up of thousands of Villi, which protrude like columns increasing the Duodenum’s surface area(Ref Appendix image 2. “Villus – a detailed view”). Each Villus contains blood capillaries, a thin lymphatic capillary, and has an outer wall of thousands of epithelial cells able to absorb nutritional, micro molecules. Most enzyme digestion occurs in the Duodenum. As Chyme travels through the Lumen of the small intestine, Bile, (produced by the Liver but stored in the Gall Bladder) is secreted via the Bile Duct and Pancreatic juices from the Pancreas are added. Bile, made from Bile salts and mineral salts, emulsifies the fats into fat droplets making it water soluble, whilst the pancreatic juices contain Sodium Bicarbonate which neutralises the acidic content of the Chyme...
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