Human Nutrition Chpt. 29

Nutrition The way an organism obtains and uses its food.

General Definitions Autotrophic: Autotrophic: means an organism can make its own food. Heterotrophic: Heterotrophic: means an organism cannot make its own food, but must obtain its food from the environment.

General Definitions Heterotrophic: - parasite – is an organism which gets its food from a live source. - saprophyte – is an organism which gets its food from a dead host. Heterotrophs can be divided into three groups: 1.Herbivores 2.Carnivores 3.Omnivores

General Definitions Herbivores: Herbivores: are animals that feed on plants only. Carnivores: Carnivores: are animals that feed on other animals.

General Definitions Omnivores: Omnivores: are animals that feed on plants and animals.

Digestion The physical and chemical breakdown of food into soluble particles small enough to pass into body cells. Need for Digestion: - to break down food into a form suitable for absorption. - to rid the body of unabsorbed food.

Need For a Digestive System Food can be digested in a single location. Individual cells do not have to contain a full range of digestive enzymes.

Digestive System in Humans Consists of the ailmentary canal. Ailmentary Canal: - starts at mouth and ends at the anus. - salivary glands, liver and pancreas are glands attached to ailmentary canal.

Human Digestive System

Stages in Human Nutrition Ingestion: food is taken into the ailmentary canal. Digestion: the physical and chemical breakdown of food into smaller soluble pieces. Absorption: when small molecules of food pass from the ailmentary canal into the blood system. Egestion: removal of unabsorbed food as faeces.

Mechanical breakdown of Food Mechanical breakdown of food is the breaking down of large molecules into smaller ones. Occurs in three parts of the body: 1. Mouth 2.Oesophagus 3.Stomach

Mechanical Breakdown of Food Mouth Mechanical digestion carried out by the chewing action of the teeth. Human Teeth IncisorsCutting CaninesTearing Crushing and Grinding Molars Pre molars

Human Dental Formula 32 teeth in a full set of human permanent teeth The number of each type of tooth in the upper jaw one side of the mouth. Incisors Canines Premolars Molars

Human Dental Formula ic pmm Letters – 4 types of teeth. Top no. – no. of each type of tooth in upper jaw on one side of mouth. Lower no. – no. of each type of tooth in lower jaw on same side of mouth.

Mouth Once food has undergone physical and chemical digestion food is formed into a ball – Bolus and pushed backwards into pharynx. Epiglottis (flap) closes over trachea and ensures bolus passes down the oesophagus.

Oesophagus A muscular tube about 25 cm long. Connects pharynx to the stomach. Food (bolus) moves down the oesophagus by a wave of muscular contraction – Peristalsis

Stomach J shaped muscular bag which stores and digests food. Stores food for about four hours. Persistalsis in stomach: - helps to break down food mechanically. - it also churns and mixes food with gastric juice forming chyme.

Stomach Note: Small Intestine: peristalsis pushes food forwards and backwards – helps absorption. Large Intestine: strong waves of peristalsis force waste into rectum.

Chemical Breakdown of Food Chemical breakdown of food: is the breaking down of insoluble substances by ENZYMES into a form that can be absorbed by the body. Mouth chemical digestion occurs due to the action of the enzyme amylase. Amylase – found in saliva which is secreted from salivary glands located: - under tongue - back of jaws - in the cheeks

Mouth saliva helps to soften and dissolve food. saliva consists of: - water - salts - mucous - amylase - lysozyme Note: - lysozyme – helps destroy micro-organisms. - amylase – digests starch into maltose i.e. Starch Maltose Enzymes Amylase

Stomach Chemical Digestion - using Gastric Juice containing: 1. Mucous 2.HCl 3.Pepsinogen

Stomach Functions of gastric juice: 1.Mucous lines and protects the stomach wall i.e. prevents self digestion and formation of gastric ulcers. 2. HCl - kills bacteria - maintains pH 2 - loosens fibrous and cellular foods - activates pepsinogen - denatures salivary amylase

Stomach Functions of gastric juice: 2. HCl Note: - overproduction of acid in the stomach - HEARTBURN - control by neutralising the acid with an alkali – RENNIES 3. Pepsinogen - converted to the active enzyme Pepsin by HCl - Pepsin digests proteins into smaller peptides i.e. Proteins Peptides Pepsin

Stomach Preventing gastric juice from digesting stomach wall: mucous lines the stomach. mucous is alkaline thus reducing acidity near stomach wall. pepsin released as inactive pepsinogen. cells lining the stomach are tightly packed and can be replaced very rapidly. Failure of the above results in an ulcer – ‘Peptic Ulcer’

Stomach Sphincter Muscles Cardiac Sphincter: Circular muscle which controls food entering the stomach from the oesophagus. Pyloric Sphincter Muscle Circular muscle which contracts to close the entry to duodenum from the stomach. ( Open when relaxed )

Small Intestine Muscular tube 5 – 6 m long Functions: - Digestion - Absorption Made up of three parts: 1.Duodenum (Digestion) 2.Jejunum 3.Ileum Absorption

Small Intestine Duodenum 25 cm long tube products of pancreas and liver enter duodenum. Function: most digestion takes place in the duodenum. - cells lining duodenum produce a range of digestive enzymes. - inner lining contains many infoldings called villi which increase the surface area for digestion.

Small Intestine Jejunum and Ileum Function: absorb nutrients. Lining contains many infoldings called villi which increase the surface area for absorption. Adaptions for absorption: - Long Tube – gives time for absorption. - Has a lot of villi and microvilli. - Walls of villi are very thin.

Small Intestine Jejunum and Ileum Adaptions for absorption: - rich blood supply to carry away water – soluble products. - each villius has a lymph supply (lacteal) to carry away the fats.

Small Intestine Villi Infolding in the lining of the small intestine

Small Intestine A single villus Inside each villus: rich blood supply. capillaries absorb water and soluble nutrients. Capillaries: carry nutrients to hepatic portal vein which takes them to liver. Liver: stores some nutrients. releases others for use throughout the body. Deamination: breaking down of amino acids to form urea.

Small Intestine A Single Villus Fatty acids and glycerol are absorbed into the villus lining. Reformed fats are coated with protein and pass into lymph in lacteal. Lymph transports fats to bloodstream: - Protein coat – dissolved in blood. - fats absorbed into cells.

Large Intestine Colon Anus Caecum Appendix Rectum

Large Intestine 1.5 m long stores from 10 hours up to a few days

Large Intestine Functions (Colon) 1.Reabsorb water:- converting liquid waste that enters large intestine to semi solid waste – faeces. 2.Produce B Group Vitamins 3.Digest cellulose Note: Functions 2 and 3 are carried out by symbiotic bacteria

Large Intestine (Colon) 1.Diarrhoea and Constipation: Diarrhoea – occurs when unabsorbed material moves too rapidly through the colon – less water absorbed therefore faeces contains more liquid. Constipation – occurs when unabsorbed material moves too slowly through the colon – too much water absorbed.

Large Intestine (Colon) 2 & 3. Symbiotic Bacteria: - bacteria which obtain food from humans and provide useful vitamins/nutrients in return. - Example 1: bacteria in colon feed on the waste and produce some B group vitamins and vitamin K. - Example 2: bacteria in the digestive system break down food (especially cellulose).

Large Intestine Caecum Vestigial Organ Function unknown in humans Appendix Vestigial Organ Function unknown in humans Rectum Stores faeces

Pancreas Secretes Pancreatic Juice Pancreatic Juice consists of: - sodium bicarbonate which neutralises chyme. - pancreatic amylase converts starch to maltose. - pancreatic lipase converts lipids to fatty acids and glycerol. Pancreatic lipase and amylase enter duodenum via pancreatic duct. Optimum pH for pancreatic lipase and amylase = pH7 – pH8

Liver Role of the liver in digestion Functions: making bile. detoxifying the body. breaks down excess amino acid urea. converts glucose to glycogen for storage. stores fat soluble vitamins and minerals. converts excess carbohydrates to fats. making plasma proteins - fibrinogen. making cholesterol. producing heat – to warm the blood and body.

Liver Role of the liver in digestion Bile Bile is produced by the liver. Bile is a yellow-green liquid. Bile is stored in the gall bladder Bile enters the duodenum via the bile duct.

Liver Role of the liver in digestion Bile consists of: 1.Water2. Bile Salts3. Bile Pigments Functions of Bile: 1.Emulsifies Fat:- this increases the surface area for enzyme digestion. 2.Neutralises (using sodium hydrogen carbonate) the acidic chyme from the stomach. 3.Excretes the pigments biliverdin and bilirubin.

Role of Dietary Fibre Dietary Fibre (roughage): consists of cellulose. Humans cannot digest cellulose. Fibre absorbs and stores water causing unabsorbed waste to expand. Large size of this waste stimulates muscles of intestine to work – Peristalsis. Sources of Fibre: Wholemeal bread Cereals Vegetables Fruit

Three Enzymes Involved with Digestion Enzymes are biological catalysts 1. Amylase 2. Pepsin 3. Lipase

Salivary Amylase: Role Production site Where it acts pH in mouth Digestion product Digest starch Salivary glands Mouth Alkaline, pH Maltose

Pepsin: Role Production site Where it acts Digestion product pH stomach Digest protein Gastric glands in stomach wall Stomach Peptides Acid, pH 2

Lipase: RoleDigest fat Production site Pancreas Where it acts Duodenum Digestion product Fatty acids + Glycerol pH in DuodenumAlkaline, pH 7 - 8

Balanced Human Diet Handouts given out on this section!!!