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The Digestive System Chapter 23 OVERVIEW • https://www.youtube.com/watch?v=nM5kMSjBrmw INTRODUCTION Digestion is the mechanical and chemical breakdown of food into forms that cells can absorb. • Mechanical Digestion – breaks down food into smaller pieces Chemical Digestion – decomposes food into smaller molecules • Add these terms to vocabulary list… The digestive system consists of: • The alimentary canal – extends from mouth to anus • Accessory glands –secrete chemicals into the alimentary canal. HUMAN DIGESTIVE SYSTEM THE ALIMENTARY CANAL If stretched out, the alimentary canal is about 8 meters long. That’s 26 feet! STRUCTURE OF THE WALL Mucosa – mucous membrane • Epithelial tissues on a bed of connective tissue • This layer absorb nutrients, secrete chemicals, and protect the underlying layers. Submucosa – Beneath the mucosa • Loose connective tissue • Blood vessels, nerves, and lymphatic vessels • This layer nourishes the surrounding tissues, and carries away nutrients. Muscular – • Decrease and increase the diameter of the A.C. to push food through Serosa – serous membrane • Secretes serous fluid, which lubricates the A.C. MOVEMENTS OF THE ALIMENTARY CANAL Muscles of the A.C. provide two basic movements: Segmentation – mixing movement • Smooth muscles contract and relax, mixing foods with digestive juices Peristalsis – propelling movement • Smooth muscles contract in a wave-like motion pushing food through the alimentary canal THE MOUTH (ORAL CAVITY) • The mouth: • Receives food • Mechanically breaks up solid particles using TEETH & TONGUE • Chemically digest food using saliva. • This action is called mastication • Makes a BOLUS (wet ball of food) • The mouth also functions as an organ of speech, and sensory reception. SALIVARY GLANDS • Secrete saliva Saliva moistens the food, and begins the digestion of carbohydrates Three pairs of major salivary glands, include: • Parotid glands • Submandibular • Sublingual SALIVARY GLANDS SALIVA = water + mucus + amylase Parotid glands • Secrete clear watery fluid • Rich in salivary amylase – begins the chemical digestion of carbohydrates Submandibular glands • Secretes a mixed saliva with both watery fluid and mucus Sublingual glands • Secrete primarily mucus THE PALATE AND UVULA • The palate forms the roof of the oral cavity Hard Palate - bony roof of the mouth • Formed by the palatine bones and portions of the maxilla Soft Palate - Muscular arch Uvula – cone-shaped projection During swallowing, muscles draw the soft palate and the uvula upward preventing food from entering the nasal cavity. THE TEETH Teeth are the hardest structures in the body •primary (deciduous) teeth numbering 20 •Usually erupt through the gums from age of 6 months to 2 years •secondary (permanent) teeth numbering 32 •Usually begin to erupt at 6 years • 3rd molars = wisdom teeth, which may erupt between 17-25 years of age TYPES OF TEETH Incisorsblade shaped teeth that bite or cut off large pieces of food Adult – 8 Child – 8 Caninescone shaped teeth that grasp and tear food Adult – 4 Child – 4 Premolars – flattened surface for grinding food Adult – 8 Child – 0 Molars – flattened surface for grinding food Adult – 12 Child – 8 THE TONGUE • Thick, muscular organ • Manipulate foods and aids in swallowing Mucous Membrane Frenulum Root • Anchored to the hyoid bone. • Covered with lingual tonsils Papillae – projections on the surface of the tongue. • Some provide friction, others house taste buds. PHARYNX • The back of the throat. • Deglutition (swallowing) • 3 parts SWALLOWING • Epiglottis • flap of cartilage • closes trachea (windpipe) when swallowing • food travels down esophagus ESOPHAGUS • Peristalsis • involuntary muscle contractions to move food along • Esophageal Hiatus – opening in the diaphragm, passage for esophagus • Hiatal hernia – part of the stomach protrudes through the hiatus. STOMACH • 2 sphincters (valves) • 3 layers of muscle • Secretes gastric juices (enzymes + HCl) • Mechanically and chemically breaks down food STOMACH • Fundus = top portion • Pyloris = funnelshaped lower portion • Rugae – gastric folds line the stomach GASTRIC JUICE • Acidic (pH 1.5-2.5) (HCl) • Pepsin- an enzyme that breaks down large proteins into amino acids. • HCl activates pepsin • BOLUS + GASTRIC JUICE = chyme. ACCESSORY ORGANS •Pancreas •Gall Bladder •Liver PANCREAS • An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine) • Pancreatic juice digests all major nutrient types. • “ENZYME COCKTAIL” includes enzymes top break down all compounds: proteins, lipids and carbohydrates • Alkaline (base) neutralizes acidic chyme coming from stomach. PANCREAS LIVER LIVER FUNCTIONS • The liver carries on many important metabolic activities, including: • Glycogenesis: producing glycogen from glucose • Glycolysis: breakdown of glycogen into glucose • Gluconeogenesis: converts non-carbohydrates to glucose • Oxidizes fatty acids • Synthesizes phospholipids and cholesterol • Forms urea • Synthesizes plasma proteins •Stores glycogen, iron, and vitamins A, D, and B12 • Phagocytosis of worn out RBCs and foreign substances • Removes toxins such as alcohol and certain drugs from the blood LIVER • Function: produces bile • BILE breaks up fats GALL BLADDER • It stores bile between meals • It concentrates bile by reabsorbing water • The gall bladder itself does not produce bile • Bile duct – • a long tube that carries BILE • Connects the liver, pancreas, and gall bladder to the duodenum (small intestine) GALLSTONES • GALLSTONES – an accumulation of hardened cholesterol and/or calcium deposits in the gallbladder • Can either be “passed” (OUCH!!) or surgically removed SMALL INTESTINE • Function • chemical digestion • major organ of digestion & absorption • absorption through lining • over 6 meters! • small intestine has huge surface area = 300m2 (~size of tennis court) • Structure • 3 sections • duodenum = most digestion • jejunum = absorption of nutrients & water • ileum = absorption of nutrients & water DUODENUM • 1st section of small intestines • acid food from stomach • mixes with digestive juices from: pancreas liver gall bladder ABSORPTION IN THE SI • Much absorption is thought to occur directly through the wall without the need for special adaptations • Almost 90% of our daily fluid intake is absorbed in the small intestine. • Villi - increase the surface area of the small intestines, thus providing better absorption of materials Villi increase surface area. More surface area = More absorption APPENDIX Vestigial organ APPENDICITIS • inflammation of the appendix due to infection • Common treatment is removal of the appendix via surgery THE LARGE INTESTINE The large intestine is named because of its diameter It has four parts: 1. Cecum – blind pouch • Ileocecal sphincter • The appendix projects from the cecum. 2. Colon (ascending, transverse, descending, sigmoid) 3. Rectum straight 4. Anal canal • The anus – is guarded by two sphincter muscles • external anal sphincter – composed of skeletal muscle • internal anal sphincter – composed of smooth muscle LARGE INTESTINES (COLON) • Function • re-absorb water • use ~9 liters of water every day in digestive juices • > 90% of water reabsorbed LARGE INTESTINE • Solid materials pass through the large intestine. • These are undigestible solids (fibers). • Water is absorbed. • Vitamins K and B are reabsorbed with the water. • Rectum- solid wastes exit the body. FECES • Poop, excrement, solid waste, etc… • Feces is composed of materials not digested or absorbed, and include: Water, Electrolytes, Mucus, Bacteria, and Bile pigments • Approximately 1/3 of the dry weight of feces is bacteria. . • The color of feces is provided by bile pigments altered by bacteria DIARRHEA • a gastrointestinal disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine. • This results in increased, multiple, watery feces. • This condition may result in severe dehydration, especially in infants CONSTIPATION • a condition in which the large intestine is emptied with difficulty. • Too much water is reabsorbed • Solid waste hardens BACTERIAL FLORA • Living in the large intestine is a community of helpful bacteria • Escherichia coli (E. coli) • produce vitamins • vitamin K; B vitamins • generate gases • by-product of bacterial metabolism • methane, hydrogen sulfide RECTUM • Last section of colon (large intestines) • eliminate feces • undigested materials • extracellular waste • mainly cellulose from plants • roughage or fiber • masses of bacteria ANAL CANAL / ANUS… LAST STOP • Exit or opening for solid wastes • Regulated by anal sphincter (valve) • Anal sphincter surrounded by muscles • Elimination aided by abdominal muscles HEMORRHOIDS •Very common, especially during pregnancy and after childbirth. •Result from increased pressure in the veins of the anus. The pressure causes the veins to bulge and expand, making them painful, particularly when you are sitting.. Symptoms Pain during bowel • Anal itching movements • Anal ache or pain, One or more hard tender lumps near the especially while sitting anus • Bright red blood on toilet tissue, stool, or in the toilet bowl EPISIOTOMY This… NOTEBOOKS Due Monday, April 14 Must include: • RESPIRATORY SYSTEM • DIGESTIVE SYSTEM • URINARY SYSTEM See website for DIGESTIVE SYSTEM powerpoint to help finish notes on chart.