Digestion.docx

**[Human Nutrition]** **Humans are heterotrophs. This means we cannot make our own food, so we must obtain it from other organisms. Heterotrophs are split into three categories:\ - Herbivores: Eat mainly plants and are often called primary consumers e.g., cows, sheep, and rabbits\ - Carnivores: Eat...

**[Human Nutrition]** **Humans are heterotrophs. This means we cannot make our own food, so we must obtain it from other organisms. Heterotrophs are split into three categories:\ - Herbivores: Eat mainly plants and are often called primary consumers e.g., cows, sheep, and rabbits\ - Carnivores: Eat mainly meat and are often called secondary consumers e.g., foxes, pine martens and, orca whales\ - Omnivores: Eat both plants and animals e.g., humans and other primates** **[Stages of Nutrition]** ***Ingestion\ *Ingestion is the taking in of food, usually as solids, into the alimentary canal through the mouth. Before the food is swallowed, smell and taste are used to check its acceptability.** ***Digestion\ *Digestion is the process of breaking food into pieces that are small enough to pass through the wall of the intestine. There are two ways in which food can be broken down;\ - Mechanical: Using teeth to cut and grind the food in order to increase the surface area. At the same time, the food is mixed with digestive enzymes and saliva by chewing. The food is formed into a bolus. Peristalsis, a wave of muscular contractions, pushes the bolus down the oesophagus. Food is trapped in the stomach 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.\ - Chemical: 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.** ***Absorption\ *Absorption is 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.** ***Assimilation\ *Using the materials absorbed to repair damaged tissue or to produce new tissue.** ***Egestion\ *This is the removal of undigested waste from the body. This undigested material is called feces and is stored in the rectum before being passed out through the anus.** **[\ ]** **[The need for a digestive system\ ]Digestion is necessary because the food we eat is too big to pass directly into the bloodstream. Otherwise, our immune system would recognise these structures as being foreign and it would get rid of them.** **A digestive system allows the materials needed to process the food to be localised in a single place e.g., teeth in mouth, acid in stomach. It also prevents each cell having to contain a full range of all the digestive enzymes.** **[Structure and Function of The Digestive System\ ]The alimentary canal (digestive tract) starts at the mouth and ends at the anus.** ***Teeth\ ***A chart of teeth types Description automatically generated***(2)\ *** **Teeth break up food through mechanical actions of grinding, tearing and cutting. Each tooth is covered by a very hard protective layer, called enamel, which is very resistant to wear and chemical attack.\ *Dental Formula*** 2 (I C PM M ) (side view: [top]\ 2 1 2 3 bottom) **Permanent total = 32\ Milk/deciduous/child set= 20, has no molars** **- 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.** ***(3)*** ***Salivary Glands\ *These are located above and below on either side of the mouth. They produce saliva, a colourless liquid that has four main functions:\ - Moistens the food and dissolves any of its soluble components\ - Softens the food compounds, which reduces the chance of damage to the oesophagus and stomach when swallowed\ - Saliva is a good lubricant and it makes the bolus of food formed by the tongue slip down the oesophagus more easily\ - Contains a carbohydrate digesting enzyme called amylase, which begins the chemical digestion of carbohydrates** ***The Oesophagus\ *A tube of smooth muscle that moves food from the mouth to the stomach. A wave of muscular contractions called peristalsis moves the food down the oesophagus to the stomach** ***The stomach\ *The cardiac sphincter, a strong ring of muscle, relaxes to let food enter the stomach, then shuts tight to keep the food inside. Food is mixed with hydrochloric acid produced in hollows in the stomach wall called gastric pits. Hydrochloric acid has two functions:\ - Kills any bacteria entering the stomach\ - Provides an acid medium to convert the inactive enzyme pepsinogen into the active enzyme pepsin. Pepsin breaks down proteins into peptides.\ The stomach produces a lot of mucus, which forms a layer on its inner surface. This mucus protects the stomach from both the acid and the enzymes it contains. If the mucus layer is damaged, the acid and enzymes can attack the cells and a gastric ulcer can result.\ The pyloric sphincter controls the movement of chyme into the duodenum.** ***The Small Intestine\ *The small intestine consists of three parts; the duodenum, the jejunum and the ileum. The small intestine is approximately six metres long.\ The small intestine is folded and fills the centre of the abdominal cavity.\ Two exocrine glands empty their secretions through their ducts into the duodenum. These glands are the liver, which adds bile through the common bile duct, and the pancreas, which empties a cocktails of digestive enzymes through the pancreatic duct.** ***The Liver\ *The main function of the liver is to produce clear, greenish-yellow liquid called bile. Bile contains cholesterol, bile salts and bilirubin. Bilirubin is a breakdown product of worn-out red blood cells. It contains bicarbonate ions. Bile is stored and concentrated in the gallbladder and has two main functions:\ - The bicarbonate ions neutralise the acid chyme, changing its pH from 1 to around 10. This is the pH the digestive enzymes produced by the pancreas need to function at their optimum level\ - Bile emulsifies the fats in food, greatly increasing their surface area, and thus increasing the rate of reaction with the enzyme lipase, which breaks fats into fatty acids and glycerol\ *Liver Functions\ *- Stores excess glucose as glycogen\ - Breaks down excess amino acids into urea\ - Breaks down old and damaged red blood cells to produce bile\ - Stores fat soluble vitamins\ - Breaks down toxins** ***The Pancreas\ *Produces a cocktail of digestive enzymes;\ - 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** **[Digestive Enzymes]** +-----------+-----------+-----------+-----------+-----------+-----------+ | **Enzyme* | **Acts | **Made | **Action | **pH** | **Product | | * | on** | in** | site** | | ** | +===========+===========+===========+===========+===========+===========+ | **Amylase | **Starch* | **Salivar | **Mouth/ | **7** | **Maltose | | ** | * | y | Small | | ** | | | | Glands/ | Intestine | **10** | | | | | Pancreas* | ** | | **Glucose | | | | * | | | ** | +-----------+-----------+-----------+-----------+-----------+-----------+ | **Proteas | **Protein | **Stomach | **Stomach | **1** | **Polypep | | e** | s** | wall/ | / | | tides** | | | | Pancreas* | Small | **10** | | | | | * | Intestine | | **Amino | | | | | ** | | acids** | +-----------+-----------+-----------+-----------+-----------+-----------+ | **Bile | **Emulsif | **Liver** | **Duodenu | **10** | **Fat | | salts** | ies | | m** | | Droplets* | | | fats** | | | | * | +-----------+-----------+-----------+-----------+-----------+-----------+ | **Lipase* | **Fat** | **Pancrea | **Small | **10** | **Fatty | | * | | s** | Intestine | | acids and | | | | | ** | | glycerol* | | | | | | | * | +-----------+-----------+-----------+-----------+-----------+-----------+ ***The ileum\ *Main area of absorption of digested foodstuffs i.e.,\ - Glucose, amino acids, water-soluble vitamins, and minerals are absorbed by diffusion and active transport into the blood capillaries. These capillaries unite to form the hepatic portal vein, which carries food to the liver.\ - Fatty acids, glycerol, cholesterol and fat-soluble vitamins pass into the lacteals and are carried through the lymph system, which eventually enters the circulatory system via the subclavian vein\ [Adaptations of the ileum for absorption\ ]Very long tube with villi and microvilli which give a large surface area for absorption.\ - Villi walls are thin, this allows for the rapid movement of substances through them\ - Rich blood capillary network in villi to carry soluble nutrients to liver\ - Lymphatic capillaries in villi carry away fat** ***The Large Intestine\ *The large intestine consists of five main sections;\ - 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\ - Anus: A sphincter muscle that remains tightly closed, preventing leakage, but is relaxed when defecation occurs** **[Function of symbiotic bacteria in the intestine\ ]- They produce vitamins B and K, which are absorbed through the large intestine wall and used by the human body\ - They prevent pathogenic bacteria from becoming established in the large intestine by outcompeting them** **[Role of Fibre in the diet\ ]Fibre is an indigestible material found mainly in plants. It can be either soluble or insoluble. A high-fibre diet prevents constipation by retaining sufficient water in the large intestine to keep the faeces soft and pliable enough to easily be moved along by peristalsis. Fibre helps to prevent bowel cancer by carrying toxins through the large intestine more rapidly, giving them less time to do damage.** **[Balanced Human Diet]** **A balanced diet is one that contains the correct amounts of all the food groups. Nutrients should be obtained from a variety of foods.\ **A food pyramid with different foods Description automatically generated**(4)** **- 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\ - Only moderate to small amounts of meat and dairy should be eaten. These are high-calorie and high-fat foods\ - Those at the top of the pyramid are high in saturated fats and sugars and should be eaten in very small amounts** **Daily calorie intake is dependant on age, gender and activity levels. A person who is doing a lot of strenuous exercise will need more calories than a person is a sedentary occupation who takes only a little exercise.** **Age** **Gender** **Sedentary** **Moderate** **Very Active** ------------- ------------ ------------------ ------------------ ------------------ **14 - 18** **Male** **2000 -- 2400** **2400 -- 2800** **2800 -- 3200** **Female** **1800** **2000** **2400** **19 - 30** **Male** **2000 -- 2400** **2400 -- 2800** **3000** **Female** **1800 - 2000** **2000 - 2200** **2400** **[\ ]**