Digestive System and Human Nutrition

Ingestion = The taking in of food, usually as solids, into the alimentary canal through the mouth Digestion = The process of breaking food into pieces that are small enough to pass through the wall of the intestine Absorption = The process of taking molecules of broken-down food from the alimentary canal into the blood or lymphatic systems, which then transport them to where they will be used or stored

Herbivores = Eat mainly plants and are often called primary consumers Carnivores = Eat mainly meat and are often called secondary consumers Omnivores = Eat both plants and animals

Mechanical Digestion = Using teeth to cut and grind the food in order to increase the surface area Chemical Digestion = Enzymes are used to speed up chemical reactions. The chemical reactions break large, complex molecules into smaller, simpler ones that are small enough to pass through the intestine wall

Mouth = The site of ingestion where food is taken in Stomach = Food is trapped and churned with hydrochloric acid and digestive juices. Food stays in the stomach for two to three hours, at the end it has the consistency of soup and is called chyme Intestine = The site of absorption where broken-down food molecules are taken into the blood or lymphatic systems

Bolus = The food formed into a ball-like shape after being mixed with digestive enzymes and saliva by chewing Peristalsis = A wave of muscular contractions that pushes the bolus down the oesophagus Chyme = The end product of mechanical digestion in the stomach, which has the consistency of soup

Humans = Omnivores that eat both plants and animals Cows = Herbivores that eat mainly plants Foxes = Carnivores that eat mainly meat

Assimilation = Using the materials absorbed to repair damaged tissue or to produce new tissue Egestion = The removal of undigested waste from the body Digestive System = Allows the materials needed to process the food to be localized in a single place and prevents each cell having to contain a full range of all the digestive enzymes Salivary Glands = Produces saliva, which moistens the food, dissolves any of its soluble components, and contains a carbohydrate digesting enzyme called amylase

Incisors = Found at the front of the mouth. They are chisel shaped and have a sharp upper edge, which is used for cutting Canines = Located just beside the four incisors. They are pointed and their job is to puncture skin and flesh to grip and then tear it Premolars = Used for crushing and grinding Molars = Located right at the back of the mouth. Their job is to crush and grind food

Cardiac Sphincter = A strong ring of muscle that relaxes to let food enter the stomach, then shuts tight to keep the food inside Hydrochloric Acid = Kills any bacteria entering the stomach and provides an acid medium to convert the inactive enzyme pepsinogen into the active enzyme pepsin Pyloric Sphincter = Controls the movement of chyme into the duodenum Mucus = Protects the stomach from both the acid and the enzymes it contains

Duodenum = Receives bile from the liver and digestive enzymes from the pancreas Jejunum = The middle part of the small intestine where most of the nutrient absorption takes place Ileum = The final part of the small intestine where remaining nutrients are absorbed Liver = Produces bile, which is stored and concentrated in the gallbladder

Bile = Produced by the liver, stored in the gallbladder, and helps in the digestion and absorption of fats Saliva = Produced by the salivary glands and helps in the initial breakdown of food Hydrochloric Acid = Produced in the stomach and helps in the breakdown of proteins Amylase = Produced in the salivary glands and helps in the breakdown of carbohydrates

Mouth = The starting point of the alimentary canal where mechanical digestion begins Oesophagus = A tube of smooth muscle that moves food from the mouth to the stomach Stomach = An organ that mixes food with hydrochloric acid and produces the enzyme pepsin Anus = The end point of the alimentary canal where undigested waste is eliminated from the body

Amylase = Continues the digestion of carbohydrates started in the mouth and temporarily stopped in the stomach. It turns starch into maltose, which is then turned into glucose by maltase. Protease = Continues the breakdown of proteins started in the stomach. It splits proteins and polypeptides into amino acids that are also absorbed into the blood. Lipase = Digests fats by breaking each fat molecule into a glycerol and three separate fatty acids. Bile emulsifies the fat, increasing the surface area for the lipase to work on. Maltase = An enzyme that breaks maltose into glucose.

Amylase = $pH = 7$ Protease = $pH = 1$ to $pH = 10$ Lipase = $pH = 10$ Bile salts = $pH = 10$

Caecum = Plays a role in the absorption of water and salts Appendix = Stores good bacteria Colon = Absorbs water, salts and some nutrients. Prepares the material called stool or faeces for elimination from the body Rectum = Final part of the intestine where faeces are stored immediately prior to being passed out through the anus by peristalsis

Glucose = Main area of absorption is the ileum Amino acids = Main area of absorption is the ileum Fatty acids = Pass into the lacteals and are carried through the lymph system Water-soluble vitamins = Absorbed by diffusion and active transport into the blood capillaries

Villi and microvilli = Give a large surface area for absorption Thin villi walls = Allows for the rapid movement of substances through them Rich blood capillary network in villi = Carry soluble nutrients to liver Lymphatic capillaries in villi = Carry away fat

Production of vitamins B and K = These vitamins are absorbed through the large intestine wall and used by the human body Prevention of pathogenic bacteria = By outcompeting them in the large intestine

Bread, cereal, rice, and pasta = Should form a large part of the diet Fruit and vegetables = Should be eaten in medium to large portions as they contain carbohydrates, unsaturated fats, minerals, vitamins and roughage Meat and dairy = Only moderate to small amounts should be eaten. These are high-calorie and high-fat foods High in saturated fats and sugars = Should be eaten in very small amounts

Stores excess glucose as glycogen = Glycogen can be converted back into glucose when needed Breaks down excess amino acids into urea = Urea is a waste product that is excreted in urine Breaks down old and damaged red blood cells to produce bile = Bile is used to emulsify fats Stores fat soluble vitamins = These vitamins are absorbed in the small intestine