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Download The Digestive System
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HLTAP301A To break down food that we eat Absorb components of food into blood stream Eliminate waste products All cells require nutrients to carry out their specific functions As we ingest food it is too big to enter cells Needs to be broken down into pieces small enough to pass through cell membrane Breakdown process called digestion After digestion particles must be carried to all cells by circulation Transfer of food into circulation called absorption Breakdown of food is both mechanical and chemical Mechanical refers to the physical breakdown of food into smaller pieces Chemical refers to the breakdown of food chemically Digestive tract ◦ ◦ ◦ ◦ ◦ Continuous passage way beginning at mouth Ending at anus Approx 9 metres long Muscular tube extending through body Also called alimentary or gastro intestinal tract Accessory organs ◦ Release substances into digestive tract through ducts ◦ Includes salivary glands liver gall bladder pancreas 1. Mucous membrane or mucosa ◦ Epithelial layer containing cells that secrete mucus, digestive enzymes and hormones ◦ Consists of many layers of squamous or flat cells which help in protection of deeper tissues ◦ Contains blood vessels nerves and glands 2. Smooth muscle ◦ Two layers ◦ Alternate contractions of two layers creates wave like movement ◦ Pushes food through digestive tract ◦ Mixes food with digestive juices ◦ Wave like movement called peristalsis 3. Serous membrane ◦ Outer most layer of organs ◦ In abdomino-pelvic cavity ◦ Thin moist tissue made of simple squamous epithelium and loose connective tissue ◦ Forms part of peritoneum Lines abdomino-pelvic cavity Thin shiny serous membrane Folds back to cover most of the organs within cavity Carries blood vessels lymphatic vessels and nerves Supports organs and binds them to each other Digestive system Mouth Important role in speech as well as digestion Mechanical breakdown of food Saliva secreted by salivary glands, approx 1 litre per day Begins digestion of starch Food mixed with saliva to form pasty, chewed up lump called bolus ◦ Saliva has several functions ◦ ◦ ◦ ◦ ◦ liquefying food protection of teeth and cleaning of mouth fighting bacteria breaking down starch into glucose Tongue ◦ Made of 6 muscles and covered with special mucous membrane ◦ Aids in chewing (masticating) ◦ Swallowing and cleaning of teeth ◦ Contains organs for sense of taste ◦ Involved in producing voice sounds Teeth ◦ Each side of jaw contains 8 teeth ◦ Entire mouth contains 32 teeth ◦ Each side has 2 incisors, 1 canine and 5 premolar and molar teeth ◦ Last molar tooth known as wisdom tooth ◦ Crown covered by enamel extremely resistant can withstand temperature of 2,0000C under enamel is layer called dentine from which crown and root is formed ◦ Deep inside root is red pulp containing blood vessels and nerves Pharynx ◦ Site where food passes from mouth to oesophagus and air from nasal passage to trachea ◦ Contains tonsils and uvula ◦ When swallowing a bolus is pushed by tongue into pharynx ◦ Swallowing occurs rapidly by involuntary reflex action ◦ At same time soft palate and uvula are raised to prevent food and liquid from entering nasal cavity ◦ Tongue is raised to seal back of oral cavity ◦ Entrance of trachea is guarded during swallowing by the epiglottis to prevent choking or aspirating food and fluids Oesophagus ◦ Muscular tube approx. 25cm long ◦ Starts at lower end of pharynx ◦ Passes through chest alongside back of trachea and heart through diaphragm and into abdominal cavity then connects to stomach ◦ Food is lubricated with mucous and moved by peristalsis into stomach ◦ No digestion occurs here Stomach ◦ Muscular bag with capacity for approx. 1.5 – 2.0 litres ◦ Situated upper left abdominal cavity ◦ Most of anterior surface covered by ribs ◦ Food passes from oesophagus into stomach through cardia ◦ At lower end is opening called pylorus where food leaves stomach and enters small intestine ◦ Divided into fundus (top) body (middle) pylorus (bottom) Stomach …cont. ◦ Rugae are big thick folds lining stomach allow for expansion ◦ Special cells in lining secrete gastric juices made of hydrochloric acid and pepsin ◦ Hydrochloric acid softens food and destroys foreign organisms ◦ Pepsin is protein digesting enzyme ◦ Chyme is semi-liquid mixture of gastric juice and food that leaves stomach and enters small intestine ◦ Has 3 main mechanical tasks storage of food and liquid which requires muscles of the fundus to relax and accept mixing of food with digestive juices performed by pylorus, to empty contents slowly into small intestine Small intestine ◦ Approx 5 metres long ◦ Site where chemical breakdown and absorption of food into blood occurs ◦ Divided into Duodenum Jejunum Ileum Small intestine … cont. ◦ Duodenum Towards back of abdominal cavity Encircles head of pancreas Pancreatic and bile duct enter middle of duodenum Digestion of protein and carbohydrates begin here Has tiny projections called villi help to make surface area bigger absorb approx 90% of digested food into capillaries Large intestine ◦ Also called colon ◦ Main task is absorption of water and salt ◦ Waste product is faeces ◦ Divided into Caecum sac like enlargement where blind ended tube called appendix is attached Ascending colon Transverse colon Sigmoid colon Rectum Anus Large intestine The anus is made of two sphincter muscles that remain closed except during defaecation Bacterial action occurs in large intestine which is important in the synthesis of vitamins Digestion of food residue generates gas that is eliminated as flatus Defaecation occurs when rectum is full. Wall of rectum stretches and sends a message to the nerves in the sacral spine that causes the rectal walls to contract Accessory organs ◦ Salivary glands ◦ Liver ◦ Gall bladder ◦ Pancreas Liver ◦ Large vascular organ in upper right abdominal cavity, largest gland in the body ◦ Below diaphragm ◦ Mostly covered by ribs ◦ Has two main lobes ◦ Makes bile ◦ Hepatic artery supplies arterial blood ◦ Hepatic vein drains venous blood ◦ Portal vein brings venous blood to liver ◦ Common bile duct transports bile to gall bladder Functions of liver ◦ Production of proteins clotting factors and albumin ◦ ◦ ◦ ◦ Detoxifies toxins found in food and medications Breaks down old red blood cells which produces bilirubin Which in high levels is poisonous to the body Regulates nutrients in blood during fasting produces glucose to maintain normal blood sugar levels ◦ Manufactures RBC in emergency ◦ Production and excretion of bile which counteracts acidity of food digests fats Gall bladder ◦ Hollow organ with muscular wall ◦ Reservoir for bile ◦ Lies under liver ◦ Connected to liver via cystic duct ◦ Between meals fills with bile from liver and stores about 1.2 litres per day ◦ When food reaches duodenum gall bladder retracts and pours bile into duodenum Does this via the common bile duct Pancreas ◦ In posterior abdominal cavity extending from duodenum to spleen ◦ Tissue consists of endocrine and exocrine glands ◦ Secretes approx. 2 litres of digestive juices daily ◦ One part alkaline and neutralises acidity of food ◦ Other part are digestive enzymes Amylase – breaks down starch to glucose Lipase – breaks down fats to fatty acid Carboxpeptidase – breaks down protein to amino acids Digestive system Enzymes ◦ Enzymes are substances that speed up rate of chemical reactions ◦ Required for digestion ◦ All enzymes are proteins and highly specific to their function Water ◦ ◦ ◦ ◦ Needed in large amounts Helps to produce digestive juices and dilute food Aids in movement through tract Used in chemical process of digestion Stomach ◦ Where food is acted on by hydrochloric acid and enzymes ◦ Breaks down protein ◦ Chyme is made Small intestine ◦ Where chyme is mixed with bile ◦ Splits fats into smaller particles and mixes with pancreatic juice ◦ Fat digestion, starch to sugar and proteins to amino acids Absorption ◦ Digestive nutrients reach blood ◦ Occurs through villi which have own blood vessels ◦ Fats reach blood through lymphatic capillaries ◦ Vitamins and minerals absorbed directly into blood Control ◦ Nervous ◦ Hormones Hunger and appetite ◦ Regulated by hypothalamus responding to levels of nutrients in blood ◦ Hunger is strong mildly painful contraction of empty stomach ◦ Appetite usually has no relation to need for food usually emotion, habit and memory 1. 2. Digestion – means by which food is taken into the body ( ingested ) and broken down into minute particles which are capable of passing through the cell membrane to be used by the cell in fulfilling its function Peristalsis – the wave like movement caused by the continual contraction and relaxation of the muscular fibres in the walls of the oesophagus and intestines which propels the contents along the alimentary canal 3. Enzymes – are produced by the body to initiate or accelerate chemical reactions 4. Villi – hair-like projections which provide a large surface area for the absorption of food. They are found the length of the small intestine 5. Absorption – movement of tiny particles of digested food from the alimentary tract into the blood stream mainly from the small intestine and a little from the stomach and large intestine 6. Portal system – the transport system of connecting blood vessels which form the portal vein and transports the absorbed nutrients to the liver for further processing Nutrition includes food selection, eating, digestion and metabolism Nutrients are components of food needed for energy, growth, repair and maintenance Activity 9.2 Protein, carbohydrates, fats and water are needed in large amounts Vitamins and minerals are required in small amounts 55-60% of daily calories from carbohydrates are recommended daily from bread, potatoes, legumes, rice, spaghetti, fruits and vegs Categories of vitamins are water soluble and fat soluble Water soluble are vit C and B which dissolve in water and body fluids Fat soluble are A, D, E and K and are absorbed with fat Minerals are inorganic substances found in nearly all body tissues and fluids The sum of all the chemical changes in the body Occurs in the cells When energy intake is equal to the amount of energy used, weight remains stable More energy intake than expenditure results in weight gain
