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§Chapter 15 - The Digestive System §Irregular tube; open at both ends, called “Alimentary canal” or “Gastrointestinal (GI) Tract” l 29 feet long (adults)

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Presentation on theme: "§Chapter 15 - The Digestive System §Irregular tube; open at both ends, called “Alimentary canal” or “Gastrointestinal (GI) Tract” l 29 feet long (adults)"— Presentation transcript:

1 §Chapter 15 - The Digestive System §Irregular tube; open at both ends, called “Alimentary canal” or “Gastrointestinal (GI) Tract” l 29 feet long (adults) - 9 meters l Food & other substances that enter tube are not really inside body l Passageway of food: broken down (digested) and absorbed thru walls < entering body - cells §Both - Mechanical & Chemical Digestion

2 Break Down of Food §Teeth- first physical breakdown §Stomach-churning of food (physical) §Mouth- first chemical breakdown (salvia) §Digestive enzymes throughout GI tract §Digestion - Process where large food particles reduced to absorbable molecules §Absorption - Process of small molecules passing thru digestive system walls into body

3 Key Organs of the GI Tract §Know Main & Accessory organs, Table 16-2; page 476 §Small Intestine : Duodenum, Jejunum, & Ileum §Large Intestines (elimination > feces): §Cecum, Colon: Ascending, Transverse, Descending, Sigmoid

4 §Wall of Digestive Tract - l Mouth to anus l Four layers of tissue; surrounding the hollow space within the tube “lumen” l May vary in structure in different organs l Mucosa or mucous membrane - tough in esophagus, delicate, for absorption or secretion in rest of tract l Submucosa - connective tissue, blood vessels & nerves

5 l Muscularis - 2 layers, responsible for wavelike, rhythmic contractions (peristalsis), moves contents, assists in mixing & mechanical breakdown l Serosa - outermost covering, composed of visceral peritoneum l Mesentery - double folded peritoneal tissue, anchors loops of digestive tract to posterior wall of abdominal cavity

6 §Mouth - l Oral cavity - hollow chamber (roof, a floor, & walls) l Entrance of food; digestion begins immediately l Mucous membranes > mucus, protects against digestive juices & lubricates food passage l This mucous protects & lubricates l Hard palate - bony structure, front portion l Soft palate - posterior, chiefly muscles l Uvula - cone-shaped process hanging down from soft palate. W/ help of soft pal., prevents food or liquid from entering nasal cavity

7 §Floor of the mouth - §Tongue - skeletal muscular structure, covered w/ mucous membrane l Anchored to bones in skull > hyoid bone §Frenulum- thin membrane; attaches tongue to floor of mouth l Tongue-tied: too short §Papillae: small elevations on surface l Vallate type - largest, inverted V-shaped row of about mushroomlike elevations - tastebuds

8 §Teeth - §Four major types - l Incisors - (sharp/cutting) l Canines - cuspids (pierce/tear) l Premolars - bicuspids & Molars - tricuspids (grinding/crush) §Mastication > chewing of food §Forms a bolus > ready for swallowing §By age 2 - full set 20 teeth (cut 1st - 2 yrs.) §By age 17 to permanent teeth (cut 1st - 6 yrs.)

9 §Typical Tooth - §Three main parts - l Crown - visible, covered w/ enamel (hardest tissue in body) l Neck - narrow portion surrounds by gum tissue (gingiva) l Root - fitted into socket in upper or lower jaw, lined by fibrous, periodontal membrane l Inside Structure - Enamel on outside, Dentin, Pulp cavity (blood vessels & nerves) moving inward

10 §Salivary Glands - §3 Pairs - ducts drain saliva into oral cavity, secretes about 1 liter/day l Parotid - in front of each ear (mumps - tender) l Submandibular - ducts by fernullum l Sublingual - ducts into floor of mouth §Saliva contents - salivary amylase (begins CHO digestion), mucus (moistens food)

11 §Pharynx - l Behind nasal cavity & mouth l Tubelike structure made of muscles, lined w/ mucous membrane l Part of respiratory & digestive systems §Esophagus - l Passage for food to stomach l Tube-like structure, 10 inches long l Mucous lined l GERD - often caused by hiatal hernia

12 §Stomach - l Upper part of abdominal cavity, under diaphragm l Pouch for food, hollow, expands (can push up on diaphragm > discomfort) l Lower esophageal sphincter (LES) or cardiac sphincter - rings of muscle tissue at end of esophagus - keeps food from reentering the esophagus when the stomach contracts

13 l Chyme - semi-solid mixture, produced by contraction of stomach muscles that mixes food w/ gastric juices §Stomach contractions - §Created by 3 layers of muscles, run lengthwise, around, obliquely §Makes stomach one of strongest organs > peristalsis §Breaks food into tiny particles

14 l Mucous membranes line stomach - contains gastric glands > secrete gastric juice & hydrochloric acid l When empty, wrinkled folds - rugae §Three divisions of stomach - l Fundus, body, pylorus §Pyloric sphincter - holds food in stomach, empties contents slowly into small intestine

15 l Ulcer - carterlike wound or sore in membrane of stomach 1 in 10 persons suffer in USA Helicobacter pylori bacterium (H. pylori) §Small Intestines - l Portion of digestion tract that extends from the pylorus to the ileocecal valve l feet in length, coiled, convoluted, and occupies most of the abdominal cavity l Intestinal glands - secrete digestive juices l Smooth muscle wall - contracts > peristalsis

16 l Plicea - circular folds covered w/ villi, increases surface area > absorption l In or on the villi - l Blood capillaries - absorb CHO & protein end products (glucose & amino acids) l Lacteal - lymphatic vessel - absorb lipids l Microvilli - brushlike border, > surface more l Chemical digestion - most occurs in 1st subdivision of duodenum l Minor & major duodenal papillae - ducts where pancreatic enzymes & bile enter small intestine

17 §Liver - l Large organ, fills R upper abdominal cavity l Exocrine gland - secretes bile into ducts l Hepatic - means liver l Bile - essential for breaking up or emulsification of fats l CCK (cholecystokinin) - hormone secretion triggered by lipids in chyme > makes gallbladder contract & release bile l Drains from common bile duct into duodenum §Gallbladder - concentrates & stores bile

18 §Pancreas - §C-shaped, exocrine gland that lies behind the stomach & duodenum §Pancreatic juice - most important digestive juice - contains enzymes for all 3 food groups §Sodium bicarbonate (alkaline substance) - neutralizes hydrochloric acid §Enters small intestine thru same duct as bile §Islets of Langerhans - hormones produced §Pancreatitis - inflammation (blockage, CF)

19 §Large Intestine - §Begins with the ending of the ileum at the ileocecal valve - called the cecum §Approximately 5 feet in length, much larger in diameter than small intestine §Contents - not called chyme §Function - reabsorb water & salts §Material acted on by bacteria > more nutrients from cellulose & other fibers l Synthesis Vit. K needed for blood clotting, l Production of some B-complex vit.

20 §Not as well suited for absorption as small intestine - no villi §Normal passage of material thru large intestine - 3 to 5 days §Subdivisions - flow in GI Tract one-way §Cecum - pouchlike area §Ascending colon - right side of body l Bends at hepatic or right colic flexure §Transverse colon - extends across front l Bends at splenic or left colic flexure §Descending colon - left side abdomen

21 §Sigmond colon - S-shaped segment, terminates in rectum §Anal canal - terminal end of rectum, ends at external opening - anus §Inner anal sphincter - involuntary, smooth muscle, keeps anus closed except during defecation §Outer anal sphincter - striated, voluntary muscle

22 §Appendix - l Vermiform appendix - “worm-shaped”, tubular structure, blind tube l No important digestive fnc. - digest cellulose l Appendicitis - inflammation §Peritoneum - l Large, moist, slippery sheet of serous membrane l Peritoneal space - small space between parietal & visceral layers - surfaces slide freely l Retroperitoneal - organs outside peritoneum l Extensions of peritoneum-mesentary, greater omentum - both assist in anchoring abd. contents

23 §Digestion -Chemical & mechanical breakdown §CHO - amylase in mouth, slight effect §amylase from pancreas - into small intestine l Absorption of simple sugars (glucose) §Proteins - stomach (HCL/pepsinogen> pepsin) l Finished in small intestine by pancreatic (trypsin) & peptidases in intestinal juice l Amino acids - basic protein units

24 §Fats - in small intestine l Bile emulsification of fats > pancreatic lipase > fatty acids & glycerol §Key digestive juices & enzymes §* page 410 Table 15-2 §Absorption - taking food, breaking it down in form for utilization of body §Just as important as digestion


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