B6 Human Nutrition IGCSE Biology Grade 9 Dr.N.Ayoubirad 2025 Objectives • B6.01 Diet • B6.02 Digestive system • B6.03 Digestion What will we learn? B6.01 Diet Balanced diet The daily intake of food containing all the food stuffs in right proportions according to age ,sex ,work ,and climate Some fatty acids and some amino acids are essential Amino acids • There are 20 different amino acids which are universal to all living organisms • Amino acids can be either essential, non-essential or conditionally non-essential according to dietary requirements • Essential amino acids cannot be produced by the body and must be present in the diet • Non-essential amino acids can be produced by the body and are therefore not required as part of the diet • Conditionally non-essential amino acids can be produced by the body, but at rates lower than certain conditional requirements (e.g. during pregnancy or infancy) – they are essential at certain times only • A shortage of one or more essential amino acids in the diet will prevent the production of specific proteins • This is known as protein deficiency malnutrition and the health effects will vary depending on the amino acid shortage Vitamins • Vitamins are organic molecules with complex chemical structures that are quite diverse and hence categorised by groups Water soluble vitamins need to be constantly consumed as any excess is lost in urine (e.g. vitamins B, C) Fat soluble vitamins can be stored within the body (e.g. vitamins A, D, E, K) • Many vitamins are essential as they cannot be synthesised by the body and their absence may cause a deficiency disease except vitamin D. Vitamin D • Vitamin D (calciferol) is needed to ensure that sufficient calcium is absorbed in the digestive system to build healthy bones • Vitamin D can be naturally synthesised by the body when a chemical precursor is exposed to UV light • Lack of vitamin D can cause ricket – softening in bones and lead to skeletal deformation in children. • Lack of vitamin D can also cause osteomalacia - similar symptoms of ricket in adults. B6.02 Digestive system Structure of the digestive system Anatomy of the Human Digestive System There are two major groups of organs which comprise the human digestive system: 1. The alimentary canal consists of organs forming a ‘tube’ called the alimentary canal which food passes through (esophagus, stomach, small/large intestine) 2. The accessory organs aid in digestion but do not actually transfer food (salivary glands, pancreas, liver, gall bladder) Digestion in the small intestine Movement of Food • Peristalsis: A wave of muscular contractions (both around and down the alimentary canal) that moves food through the digestive tract • 1. Contraction of smooth muscles behind the bolus forces it forward • 2. Waves of muscle contractions move bolus towards the stomach This is important because: • O Food travels in one direction only. This ensures that it only moves forward • O In the intestine it enables the chyme to mix and churn with enzymes. Although it is slow at a few centimeters/contraction it enables • The start of digestion. • Food broken down by teeth (chewing). (mechanical/physical digestion) increases surface area • Saliva added to soften food ready to swallow • Amylase (enzyme) begins chemical digestion of starch (polysaccharide digestion) to maltose • A muscular tube. • Food is pushed down the tube to the stomach after being swallowed by wave of muscles contractions (peristalsis) • Muscular ‘bag’ breaks down food by churning it. Muscular contractions continue mechanical digestion. • Contains acid (HCl) to kill microorganisms. Have thick layers of mucus to stop HCl from breaking down itself • Acid does not digest your food for you! • That’s the job of the enzyme. These are added by the duodenum. • Produces Pepsin that begins digestion of proteins The stomach Food enters the stomach, which is basically a muscular bag, filled with hydrochloric acid (HCl). cross section of stomach Two things happen here: • Chemical breakdown of the food. • Microbes are destroyed. food enters from the gullet muscle tissue digested food leaves •In the small intestine more enzymes are added to finish digestion (break the food up into smaller particles). • The digested food is then absorbed here into the blood stream. • Beginning part of small intestine, In the duodenum, digestive juices from the pancreas are added. •The enzymes help to break the food into smaller particles. • Bile which is made in the liver is also added. Bile is stored in the gall bladder. •The bile helps to neutralize the acid from the stomach and also helps to break the fat into little droplets./ emulsifies fats • In the large intestine the water that is needed is absorbed back into the blood, leaving semi-solid feces. This is stored in the rectum. • Food is now all digested. The large intestine The remains of the food are then passed on to the large intestine (colon). All that is left is waste material and water. The body will want to leave the waste material within the digestive system but the water is valuable and so it is reabsorbed here. The waste material is passed to the rectum where it is stored until it leaves the body through the anus. • The solid waste or faeces is stored in this part of the large intestine or rectum. • The faeces exit the body through the anus. Your Tasks for Next session 1. Be prepared for a small Quiz. 2. Complete Biology Workbook.
