Human Biology Digestive system Senior Lecturer Talib F. Abbas Collage of Pharmacy University of Muthana

INTRODUCTION Body cells require simple sugars, amino acids, fatty acids, vitamins and minerals and water in order to function properly. Vitamins, minerals and water are in the form of small molecules and are able to pass through the differentially permeable membrane surrounding each cell. Carbohydrates, proteins and fats are larger molecules which need to be broken down into smaller particles which can be absorbed by the cell. Digestion is the process where large carbohydrate, protein and fat molecules are broken down into smaller particles by physical and chemical means in order to be absorbed by the blood and into the cells.

Digestive system basic activities The organs of the digestive system are structured to carry out six basic activities: 1. Ingestion of food and water 2. Mechanical digestion of food 3. Chemical digestion of food 4. Movement of food along the alimentary canal 5. Absorption of digested food and water into the blood and lymph 6. Elimination of material that is not absorbed.

Mechanical digestion Breakdown into smaller particles. e.g.: • Teeth: Physical process; breaking & grinding food. • Stomach: Churning and mixing • Muscle: Peristalsis (a series of wave-like muscle contractions that moves food (bolus) down the oesophagus and through the intestines.) • Bile: Increases surface area; emulsifies fats

Chemical digestion Breakdown of food molecules into smaller, simple molecules by the action of enzymes. • Mouth (saliva) ^Salivary amylase- breaks down starch molecules into smaller units. • Stomach (gastric protease = protein broken down into polypeptides (amino acids) • Small intestine: Intestinal amylase, protease, lipase

The Mouth Saliva The intake of food is known as ingestion. It occurs at the mouth. • The action of the jaw and teeth begins mechanical digestion where the food is broken up into small pieces. • As the food is chewed it is mixed with saliva. A fluid which is secreted by three pairs of salivary glands. It contains mucus and a digestive enzyme, salivary amylase which begins chemical digestion of starch. *Mucus: - lubricates food • Holds food in lumps • Dissolves food-taste receptors are stimulated.

Teeth • 4 incisors: Chisel shaped teeth for cutting and biting. • 2 canines: On each side of the incisors. Conical teeth used for tearing. • 4 pre-molars: On each side of the jaw, for grinding and crushing. • 6 molars: Grinding and crushing, three on each side of the jaw. After chewing, the food is formed by the tongue into a lump (bolus). It is then swallowed as the tongue moves backwards and upwards, pushing the food into the back of the mouth, the pharynx. The pharynx leads into the oesophagus (23-25 cm long) that connects the pharynx to the stomach.

The Alimentary canal • Has 4 layers: 1. Mucose: Mucus membrane lining the entire alimentary canal. 2. Submucose: Consists of glands and connective tissues, through which blood vessels, lymph vessels and nerves run. 3. Muscular: Circular muscle; muscle fibres arranged in circles around the canal. Longitude muscle. Fibres arranged along the length of the canal. 4. Serose: Outer layer of connective tissue.

Alimentary canal