Hierarch in Biology The living world is organized in a series of hierarchical levels from less complex to more complex Atom Molecule Organelle Cell Tissue Organ Organ system

Digestive System Cells can perform all the necessary functions of life For nutrition and digestion a single cell acquires nutrients through diffusion, osmosis and active transport Multicellular organisms require a more specialized system for digestion

Role of Digestion The human body requires six types of nutrients in order to function The organs of the digestive system allow you to extract useful nutrients from food, deliver them to your cells and eliminate wastes

Basic Structure The disgestive tract (alimentary canal) is basically a muscular tube open at both ends The inner surface of tube is continuous with outer surface of body Food enters one end, products of digestion are absorbed and waste products are eliminated

Structure of Wall of Digestive Tract Layers of the gastrointestinal wall are basically the same throughout

Types of Mucosa Tissue

Steps in Digestion There are four basic steps in digestion Ingestion Digestion (mechanical and chemical) Absorption Elimination

Ingestion Digestive tract is approx. 6.5 to 9 m long It stores and breaks down organic molecules into simpler components Digestion begins in the mouth where food is taken in, chewed by the teeth and formed into a bolus by the tongue (physical digestion)

Saliva begins the chemical digestion of food Movement through the esophagus is regulated by contractions of smooth muscles called peristalsis

Digestion - Stomach Digestion begins in the stomach Gastric fluids (mucus, HCl, and pepsinogins) aid in digestion Mucus provides the stomach with a protective coating against the effects of HCl and pepsinogins HCl kills harmful substances ingested with food and converts pepsinogin into its active form pepsin Pepsin is a protein digesting enzyme

Digestion – Small Intestines Most digestion occurs in the small intestine (~7 m in length) within the first 25 – 30 cm (the duodenum) Pancreatic fluids are stimulated by the conversion of secretin from prosecretin in the small intestine Pancreatic enzymes begin the chemical digestion of lipids, proteins and carbohydrates

Absorption (stomach and small intestines) The stomach absorbs some water, specific vitamins, some medicines and alcohol Most absorption takes place within the small intestine Long fingerlike tubes (villi) greatly increase the absorptive surface area Cells that make up the lining of each villus have microvilli which further increase the surface area

Each villus contains blood capillaries and lymph vessels called lacteals Some nutrients are absorbed by diffusion while others are actively transported Carbohydrates and amino acids are absorbed into the capillaries Fats are absorbed into the lacteals

Absorption (large intestine) Large intestine (~ 1.5 m long) stores wastes long enough to reabsorb water out of the wastes Large intestine contains bacteria such as E. coli which are essential to life and use waste material to synthesize vitamins B and K

Elimination As wastes build up in the large intestine, receptors in the intestine wall provide information to the central nervous system This results in the prompting of a bowel movement resulting in the removal of potentially toxic wastes from the body Ingestion of indigestible cellulose (fibre) increases the occurrence of bowel movements

Components of Digestion System

Accessory Organs in Digestion Salivary Glands secrete saliva and mucus which: lubricate food contain salivary amylase to begin carbohydrate breakdown Dissolves food particles

Liver Liver synthesizes bile Bile is a mixture of bile salts, bile acids, cholesterol, phospholipids, fatty acids and water Liver also extracts absorbed nutrients or toxins from blood decomposes toxins such as hydrogen peroxide, ammonia and alcohol Converts glucose into glycogen

Gallbladder Muscular sac that stores and concentrates bile from liver When fat enters duodenum endocrine cells in duodenum release hormone cholecystokinin (CCK) CCK causes gallbladder to contract and send bile into duodenum to emulsify fats and aid in absorption of lipids

Pancreas Secretes a number of substances essential to digestion such as: bicarbonate, lipases, carbohydrases and proteases

Homeostatsis Means the maintenance of a steady internal state (such as blood pressure, respiration rate, body temperature and blood sugar levels) Negative feedback relates of homeostasis 1. a variable rises above or below a normal range 2. receptors detect the change and signal other parts to respond 3. Organs receive the signal and respond accordingly to return variable to normal