Advanced Biology The Digestive System

Overview of Digestive System Alimentary canal (gastrointestinal – GI – Tract) is the continuous, muscular digestive tube that winds through the body Digest = dissolve Absorbs digested fragments through its lining into the blood

Digestive Process 1. Ingestion – taking in food through mouth 2. Propulsion – swallowing or the process of moving food through the Alimentary canal Peristalsis – alternate waves of contraction and relaxation of muscles in the organ walls 3. Mechanical digestion – physically prepares food for chemical digestion by enzymes Segmentation – rhythmic local constrictions of the intestine

Digestive Process 4. Chemical Digestion – a series of catabolic steps in which complex food molecules are broken down to their monomers 5. Absorption – the passage of digested end products from the lumen of the GI tract to the blood 6. Defecation – elimination of indigestible substances from the body

Alimentary Canal Mouth Pharynx Ingestion of food Propulsion Mechanical digestion – chewing (mastication) Chemical digestion - starches Pharynx

Alimentary Canal Esophagus Stomach Propulsion Mechanical digestion and propulsion Chemical digestion (proteins begun by pepsin); gastric juices Absorption – fat-soluble substances (aspirin, alcohol, some drugs)

Stomach

Alimentary Canal Small intestine Mechanical digestion and propulsion Continually mixes contents with gastric juices Chemical digestion – digestive enzymes from pancreas Border enzymes attached to villi – digestion of all foods Absorption – breakdown of carbohydrate, protein, fat, nucleic acid, vitamins, electrolytes, and water

Small Intestine Four layers of small intestine: The mucosa Submucosa Muscularis externa serosa

Small Intestine

Alimentary Canal Large intestine (leads to the terminal opening – anus) “the water-wringer” Chemical digestion – remaining food residues are digested by bacteria (produce vitamin K and some B vitamins) Absorption – absorbs almost all remaining water, electrolytes (especially NaCl) and vitamins produced by bacteria Propulsion – propels feces toward rectum Defecation

Alimentary Canal Human cadaver GI tract is about 30ft (9m) long Shorter in living humans because of muscle contraction Food is outside of the body because the canal is open to the environment

Accessory Digestive Organs Teeth – grinding, tearing, etc. Tongue – taste, swallowing, movement, etc. Gallbladder – store bile (digestive enzyme) from liver Digestive glands: Salivary glands – produce saliva (digests starches) Liver – produce bile Pancreas – produce and secrete other digestive enzymes

Functional Concepts 1. Digestive activity is provoked by a range of mechanical and chemical stimuli 2. Controls of digestive activity are both extrinsic (CNS) and intrinsic (“In- house”)