Human Nutrition Lesson objectives By the end of

Human Nutrition

Lesson objectives • • By the end of this lesson you be able to: Distinguish between autotrophic and heterotrophic nutrition Discuss the 4 steps involved in human nutrition Distinguish between physical and chemical digestion Draw and label the parts of the digestive system and the accessory organs

Types of nutrition • “Nutrition is the way in which an organism gets and uses it food” 2 types: Autotrophic Heterotrophic

Events in human nutrition

The digestive system

Digestion Can you distinguish between chemical and physical digestion?

What have you learned? • • Can you. . . Distinguish between autotrophic and heterotrophic nutrition? Discuss the 4 steps involved in human nutrition? Distinguish between physical and chemical digestion? Draw and label the parts of the digestive system and the accessory organs?

Lesson objectives • • By the end of this lesson you be able to: Discuss peristalsis with respect to the alimentary canal Discuss in detail the 4 stages of digestion and the role of all organs in the digestive system and the accessory organs Name at least 3 enzymes, their substrates and products formed in the human digestive system Discuss the role of a balanced diet, dietary fibre and the food pyramid

Mouth Cavity

Chemical Digestion in the Mouth • Salivary glands secrete a digestive juice containing amylase. • Amylase converts starch to maltose. • Amylase optimum p. H is 8 and optimum temperature 37ºC. • Saliva moistens the food making it easier to chew and swallow.

Oesophagus • Muscles in the wall of the oesophagus propel the swallowed material to the stomach by peristalsis.

High resolution image: A normal oesophagus

High resolution image: The distal part of the oesophagus and cardia

Stomach • • • Physical digestion Chemical digestion Gastric glands and gastric juice • Gastric juice consists of: 1. Mucous (goblet cells) 2. Pepsinogen (zymogen cells) 3. HCl (oxyntic cells) • What causes heartburn? • Why does gastric juice not digest the stomach wall? • What are ulcers?

Stomach Ulcers caused by a Helicobacter pylori infection

Small Intestine • Duodenum, jejenum and ileum • Duodenum 25 cm • Remainder 5. 5 m • Food remains here for 1 – 6 hrs

Duodenum • Digestion! • Cells lining duodenum produce a wide range of enzymes • Products of pancreas and liver enter here • The inner lining contains many infoldings called villi • 600 microvilli per villus • Intestinal glands located between villi

Pancreas • Insulin and digestive enzymes • Pacreatic juice consists mainly of the salt sodium hydrogen carbonate, amylase and lipase • Enters duodenum through the pancreatic duct • p. H of duodenum 7 - 8

The liver • The liver is the only organ to get its blood supply from 2 major blood vessels: the hepatic artery and the hepatic portal vein • Blood leaves the liver in the hepatic vein

Functions of the liver • Breaking down old red blood cells • Forming bile • Detoxifying poisons • Deamination of amino acids to form urea • Converting glucose to glycogen • Converting excess carbohydrate to fat • Storing vitamins and minerals • Forming plasma proteins such as clotting proteins • Forming cholesterol (used to make hormones) • Producing heat to warm blood

• Bile is a yellow-green liquid formed from the breakdown of RBC’s • It is composed of water, bile salts and bile pigments • Made in the liver • Stored in the gall bladder • Released into the duodenum through the bile duct Functions of bile • Emulsify fats • Neutralise acid coming from the stomach • Eliminate bile pigments from the body Bile

Jejunum/Ileum • This is the second part of the small intestine • The function of the jejunum and illeum is absorption • The ileum has numerous infoldings called villi (singular villus) – these increase the surface area for absorption • The villi have numerous micro-villi • The lining of the villi is only 1 cell thick

Adaptations of the small intestine • It is made of muscle (allows peristalsis, moves food along) • The duodenum produces many enzymes (improves digestion) • It is very long (improves absorption) • It contains villi and micro-villi (improve absorption • The villi have thin walls (improve absorption) • The villi are covered by many blood vessels (to transport the absorbed food) • Each villus contains a lacteal (to allow lipids to be absorbed)

Summary of enzymes Enzyme Made in p. H Substrate Product Amylase Salivary glands and pancreas Pepsin Stomach lining 7 -8 starch maltose 2 peptides Lipase 7 -8 fat pancreas protein Fatty acids and glycerol

Final products of digestion Food Digested to Carbohydrates glucose Proteins Amino acids Fatty acids and glycerol

Large Intestine • The large intestine is large in diameter (about 6 cm) but is only 1. 5 m long • The function of the large intestine is to re-absorb water – this happens mainly in the colon • The functions of the caecum and appendix are not fully understood • Semi – solid waste (called faeces) is stored in the rectum and egested through the anus

Symbiotic bacteria in the intestines • The large intestine contains a huge number of bacterial cells • These bacteria are beneficial in 2 ways: 1. Some of them produce B group vitamins and vitamin K 2. Other types of bacteria break down small amounts of cellulose • Both of these types of bacteria are symbiotic or mutualistic

Benefits of Dietary Fibre • Stimulates peristalsis. • Reduces the risk of colon cancer, heart disease and middle age diabetes. • Role in the formation of soft faeces so reduced risk of constipation.

A balanced diet • A balanced diet contains the correct proportions of the following 7 components: • Carbohydrates, proteins and fats • Vitamins and minerals • Fibre and water • The total amount of food eaten depends on age, activity levels, gender and health

What have you learned? • • Can you. . Discuss peristalsis with respect to the alimentary canal? Discuss in detail the 4 stages of digestion and the role of all organs in the digestive system and the accessory organs? Name at least 3 enzymes, their substrates and products formed in the human digestive system? Discuss the role of a balanced diet, dietary fibre and the food pyramid?