DIGESTIVE SYSTEM ORGANS DIGESTIVE SYSTEM BROKEN DOWN INTO

DIGESTIVE SYSTEM

ORGANS

DIGESTIVE SYSTEM BROKEN DOWN INTO 2 PARTS 1. Alimentary Canal – gastrointestinal (GI Tract) – Path that food travels 2. Accessory Organs

GI Tracts Accessory Organs Oral Cavity Ascending Colon Tongue Pancreas Pharynx Transverse Colon Liver Gallbladder Parotid Gland Appendix Esophag us Stomach Duodenu m Jejunum Ileum Descendin g Colon Sigmoid Colon Rectum Anus Sublingual Gland Submandibular Gland Uvula Lingual Frenulum

MOUTH Palate: Hard Soft Uvula Tongue

SALIVARY GLANDS Cleanses Mouth Important for Taste Moistens food Contains Enzymes

MAJOR SALIVARY GLANDS • Parotid gland • Submandibular gland • Sublingual gland The average person produces 1000 -1500 ml a day

TEETH Masticate = to chew Baby teeth (deciduous) Full set = 20 teeth Permanent teeth = 32 teeth Incisors Canines Premolars/molars

PHARYNX Longitudinal & Circular layers of Muscles Peristalsis - is a radially symmetrical contraction and relaxation of muscles that propagates in a wave down a tube

ESOPHAGUS Propels food using muscles (Peristalsis)

STOMACH ØMostly Protein Digestion ØNo Absorption*** ØMechanically & Chemically Digested Into Chyme ØGastric glands produce gastric juice: acidic ØWalls of Stomach lined with mucus so the acid doesn’t “digest itself”

CHYME Substance in the stomach that is formed from food and enzymes

PROBLEMS OF THE STOMACH Ulcers: a hole in the mucus lining of the stomach Heartburn (acid reflux): contents of stomach move into esophagus

SMALL INTESTINE

SM. INTESTINE Chemical digestion of carbohydrates, proteins, nucleic acids, & fats Done with enzymes from pancreas and bile (formed in liver) Pancreatic duct and bile duct empty into duodenum – where enzymes empty into.

LARGE INTESTINE Function: To absorb water Eliminate residue as feces Absorb vitamins produced by bacteria Role of Bacteria: Digest some nutrients Produce vitamins Produce gas

ACTION OF L. INTESTINE Peristalsis Mass Peristalsis: a strong wave that pushes contents towards rectum Problems: Diarrhea Constipation

ACCESSORY ORGANS PANCREAS Releases enzymes into duodenum Has an endocrine function

ACCESSORY ORGANS LIVER Produces bile; leaves through common hepatic duct Bile: part waste produce, part digestive secretion (mechanical digestion of lipids)

OTHER LIVER FUNCTIONS Metabolism of carbs, lipids, and proteins Processing of drugs and hormones Excretion of bilirubin (from hemoglobin of old RBCs)

ACCESSORY ORGANS GALLBLADDER Releases bile in response to fatty food entering duodenum Location: underside of liver Gallstones

STEPS OF DIGESTION

DIGESTION ØMajor functions of the digestive tract are digestion and absorption

ESSENTIAL ACTIVITIES OF THE GI TRACT ØIngestion ØPropulsion ØFood Breakdown – mechanical digestion ØFood Breakdown – chemical digestion ØAbsorption ØDefecation

1. INGESTION • Food must be placed into the mouth before it can be acted on. • Active, voluntary process

2. PROPULSION • In order food to be processed by different organs, they must be propelled from one organ to the next. • Example: • Swallowing – depends on the propulsive process called peristalsis • Peristalsis – involuntary and involves alternating waves of contraction and relaxation of the muscles in the organ walls

3. FOOD BREAKDOWN – MECHANICAL DIGESTION • Mixing of food in the mouth by the tongue • Churning food in stomach • Segmentation – propels foodstuffs through the small intestine • Prepares food for further degradation by enzymes

4. FOOD BREAKDOWN – CHEMICAL DIGESTION • Sequence of steps which large food molecules are broken down to their building blocks by enzymes

5. ABSORPTION • Transport of digested end products from the lumen of the GI tract to the blood or lymph • For absorption to occur, digested foods must first enter the mucosal cells by active or passive transport processes • Small intestine is major site of absorption

6. DEFECATION • Elimination of indigestible residues from the GI tract via the anus to form feces

NEURAL & HORMONAL CONTROL

CEPHALIC PHASE • Occurs before food enters the stomach, especially while it is being eaten • Brain is activated by smell, sight, thought, and taste of food • Neurons to salivary glands and gastric glands/stomach muscles

GASTRIC PHASE STIMULUS: FOOD IN STOMACH • Neural: • Hormonal: • Stretch receptors activated. • Food triggers release of Impulse to neurons in gastrin. Goes in the submucosa blood. • Triggers: • Gastric gland production • Gastric gland juices and causes peristalsis • Sphincter to prevent acidreflux • Stomach muscles • Relaxes lower stomach sphincter

INTESTINAL PHASE STIMULUS: FOOD IN INTESTINE • Neural: • Stretch receptors to medulla oblongata • Sympathetic nerves to stomach cause: • Decreased stomach movement & increase contraction of pyloric – bottom – sphincter (delays stomach emptying) • Hormonal: • Cholecytokinin (CCK): stimulates pancreatic juice/squeezes gallbladder