Human Nutrition PDF

Chapter 4: Human nutrition So why must food be digested?  DIGESTION PROBLEM Most food molecules are too large or insoluble...

Chapter 4: Human nutrition So why must food be digested?  DIGESTION PROBLEM Most food molecules are too large or insoluble It cannot be absorbed directly into EFFECT OF PROBLEM the blood stream and into the cells that need the nutrients Digestion is needed to break up SOLUTION the larger food particles  DIGESTION Digestion is the process where large, insoluble food molecules are broken down into smaller, soluble molecules in the body DIGESTION Glucose Amino Acids (Maltose) (Polypeptides) Starch Proteins The smaller molecules can then be absorbed into cells where they are used for growth, repair and for respiration to provide energy. Lipids Fatty Acids Glycerol  2 TYPES OF DIGESTION Carbohydrase DIGESTIVE ENZYMES Carbohydrase (Maltose) (amylase, maltase) (pepsin, trypsin) Process of obtaining nutrients** Digestive system Alimentary canal https://youtu.be/bFczvJp0bpU Definition Digestive system/ Alimentary canal Human digestive system is a coiled, muscular tube (alimentary canal) extending from the mouth to the anus  MOUTH – BUCCALCAVITY(INGESTION) Teeth chewing breaks down the food into smaller pieces to increase the surface area for enzymes to act on and makes swallowing easier (mechanical) Mouth Only starch is digested to maltose by amylase (chemical) https://biology-igcse.weebly.com/human-teeth-and-dental-decay.html Teeth Teeth Cut, tear, grind food so food particles are reduced for swallowing and have a larger surface area for digestive enzymes to work on. Bite Hold Rip Tear cut Chew Chew Crush Chew MOUTH – BUCCAL CAVITY (INGESTION) Saliva moistens food, contains amylase, which is an enzyme that breaks down starch into maltose (chemical) Tongue rolls the partly digested food into a bolus (ball) for it to be swallowed into the oesophagus (gullet) OESOPHAGUS Narrow muscular tube Muscles repeatedly contract and relax, producing a wave-like pattern called peristalsis to push the food to the stomach **No digestive enzymes produced here, but amylase in the saliva can still digest the starch** PERISTALSIS Circular muscles behind the food bolus contracts and pushes the bolus forward Longitudinal muscles around the food bolus relaxes to accommodate the food bolus https://www.youtube.com/watch?v=rJS-Kh5wCQU Think of food moving like a tube of toothpaste. STOMACH continual contractions and relaxations of the stomach muscles cause a churning action which mixes and breaks down the food particles into smaller pieces Chemical Secretes gastric juice which contains hydrochloric acid and pepsin digestion (enzyme) 1) Pepsin breaks down proteins into polypeptides (shorter chains) 2) Hydrochloric acid kills bacteria and germs and provides an acidic pH for pepsin to work well (optimum pH is 2) Mixture of food and gastric juice is known as chyme Think of food churning like washing machine.  SMALL INTESTINE 1) Most of the digestion occurs here 2) Absorption of digested food into the blood stream SMALL INTESTINE (Duodenum) Chemical Pancreatic juices secreted by the pancreas contain enzymes to break down the different food molecules: digestion 1) Amylase digests starch to maltose 2) Maltase digests maltose to glucose 3) Trypsin digests polypeptide to amino acids 4) Lipase digests lipids to fatty acids and glycerol Exam tip: You are required to know the enzymes, substrates and products of final digestion in the duodenum.  ACCESSORY ORGANS** Not part of the alimentary canal, but helper organs Pancreas secretes pancreatic juice into small intestine through the pancreatic duct Liver produces bile, stores it in gall bladder and slowly releases it into the small intestine through the bile duct Bileemulsification Bile emulsification *Bile does not digest fat. Lipase digests fats. Bile emulsification → Bile - emulsifies fats o Physically breaks apart large fat droplet to smaller fat droplets. Done by bile salts. → These smaller fat droplets still have glycerol combined with fatty acid. It is still triglyceride. Has not been digested by lipase yet!!! → Objective: increase surface area to volume ratio to speed up chemical digestion later in the duodenum. ADAPTATIONS OF SMALL INTESTINE (il Structure of small intestine: - walls of the small intestine have villi - each cell has microvilli to increase the surface area for faster absorption Digested food molecules diffuses through the cells of the small intestine walls into the blood stream  Celiac disease 1) Loss of healthy villi 2) Loss of surface area to absorb nutrients effectively  Assimilation Assimilation is the movement of digested food molecules into the cells of the body where they are used. For example: glucose is used in respiration to provide energy Liver has many functions. Can amino acids are used to build new proteins you name all? The liver is important in assimilation. For example, it converts glucose into glycogen (a complex carbohydrate used for storage) and amino acids into proteins. The liver also breaks down alcohol, drugs and toxins. S U M M A R Y (1) LARGE INTESTINE Undigested food, such as Fibre leaves the water, mineral salts, body undigested Most of the water and fibre and bacteria are mineral salts / ions passed on here diffuse into the blood stream through the walls of ** water is absorbed from the remaining the large intestine material in the colon to form faeces RECTUM For the process of egestion: removal of excess and unused food from the body Temporarily stores faeces which contains mainly fibre until it is passed out through the anus Summary video: https://youtu.be/08VyJOEcDos S U M M A R Y (2)