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Chapter 15 - The Digestive System

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1 Chapter 15 - The Digestive System
Irregular tube; open at both ends, called “Alimentary canal” or “Gastrointestinal (GI) Tract” 29 feet long (adults) - 9 meters Food & other substances that enter tube are not really inside body 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 -
Mouth to anus Four layers of tissue; surrounding the hollow space within the tube “lumen” May vary in structure in different organs Mucosa or mucous membrane - tough in esophagus, delicate, for absorption or secretion in rest of tract Submucosa - connective tissue, blood vessels & nerves Mucosa of esophagus- tough and stratified abrasion-resistant epithelium ****Mucosa of reminder of GI tract- delicate layer of simple columnar epithelium (absorption & secretion) *Mucus- coats the lining Submucosa- connective tissue, below the mucosa; contains large amounts of bld. vessels & nerves ***Muscularis- two layers of muscles: wavelike, rhythmic contraction of muscular coat> peristalsis Peristalsis: assists in the mixing of food> further mechanical breakdown of larger food particles Serosa- outermost covering of digestive tract ; composed of the visceral peritoneum * anchored to posterior wall with double fold of peritoneal tissue> mesentary

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

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

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

8 Incisors - (sharp/cutting) Canines - cuspids (pierce/tear)
Teeth - Four major types - Incisors - (sharp/cutting) Canines - cuspids (pierce/tear) 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.) Baby : 2 years old> full set of (20) baby teeth 6 months Deciduous Young adult: age full set of permanent teeth (32) 6 years Parts of the typical tooth: Crown: exposed/visable portion of tooth Hard tissue (enamel & dentin/cementum) Dentin- composed of tooth shell> center: pulp cavity consisting of connective tissue, blood & lymphatic vessels & sensory nerves Cementum- over the neck & root; NECK: surrounded by pink gingiva (gum tissue) ROOT: fits down into socket of upper/lower jaw; lined by the periodontal membrane**** * Orthodonist/Peridontist Clinical Application- Malocclusion page 482

9 Typical Tooth - Three main parts -
Crown - visible, covered w/ enamel (hardest tissue in body) Neck - narrow portion surrounds by gum tissue (gingiva) Root - fitted into socket in upper or lower jaw, lined by fibrous, periodontal membrane 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 Parotid - in front of each ear (mumps - tender) Submandibular - ducts by fernullum Sublingual - ducts into floor of mouth Saliva contents - salivary amylase (begins CHO digestion), mucus (moistens food)

11 Behind nasal cavity & mouth
Pharynx - Behind nasal cavity & mouth Tubelike structure made of muscles, lined w/ mucous membrane Part of respiratory & digestive systems Esophagus - Passage for food to stomach Tube-like structure, 10 inches long Mucous lined GERD - often caused by hiatal hernia Provides active movement of food into the esophagus closing and sealing off the trachea Nasopharynx Oropharynx laryngeal pharynx The motor impulses from the swallowing act conroled by nervous stimulation of trigeminal, glossopharyneal, vagus, and hypoglossal cranial nerves

12 Upper part of abdominal cavity, under diaphragm
Stomach - Upper part of abdominal cavity, under diaphragm Pouch for food, hollow, expands (can push up on diaphragm > discomfort) 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 *Contraction of the muscular walls mixes the food thoroughly with the gastric juice and breaks it down into a semisolid mixture called CHYME. ***Formation of CHYME: continuous of mechanical digestion> beginning in mouth Gastric juices: ***hydrochloric acid and enzymes that function in the digestive process Three layers of smooth muscles in the stomach wall: running lengthwise, around, and obliquely>>> one of the strongest internal organs of body>>able to break up the food into tiny particles > PERISTALSIS Peristalsis- propels food down the digestive tract Mucous membranes line stomach; contains thousands of microscopic gastric glands> HCL and gastric juice Internal folds of stomach : RUGAE *Intrinsic Factor- enables the absorption of Vit B-12; very important for blood cell formation > pernicious anemia

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

15 Ulcer - carterlike wound or sore in membrane of stomach
1 in 10 persons suffer in USA Helicobacter pylori bacterium (H. pylori) Small Intestines - Portion of digestion tract that extends from the pylorus to the ileocecal valve feet in length, coiled, convoluted, and occupies most of the abdominal cavity Intestinal glands - secrete digestive juices Smooth muscle wall - contracts > peristalsis Mucosa- small blood vessels, plasma, nerve cells, and blood cells Submucosa- large blood vessels, connective tissue, nerves, ganglia, and lymphactics VILLA- millions in number; “fingers” or folds projecting into the hallow interior of the intestine> rich with blood capillaries that absorb products of CHO/protein digestion ^ surface area for increased absorption ** Cryts of Lieberkunn- pitlike structures that lie in grooves between the villi & are composed of absorptive cells & mucous-producing goblet cells PH 7.0 ** Peyer’s patches_ lymphoid follicles> important in immune response; antibody synthesis Lacteal (lymph) > absorbs lipids or fatty materials from the chyme passing through the small intestines Approximately 8 liters of water q day is absorbed by the small intestines into the portal blood

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

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

18 C-shaped, exocrine gland that lies behind the stomach & duodenum
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) Control of secretions: vagal control & hormonal control Hormones: beta cells_ secrete insulin- utilization of glucose Alpha cells- secrete glucagon Enymes: trypsin- breaks down proteins Amylase- “”””’’ CHO tosimple sugars Lipase- breaks down trigylercides Pancreatitis- inflammation of pancreas blockage of common bile duct very serious/fata CF- lack of enyzme (too much and too thick pancratic enzymes) Cancer of pancreas- adenocarcinoma; life-span limited to around 5 years after diagnosis

19 Contents - not called chyme Function - reabsorb water & salts
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 Synthesis Vit. K needed for blood clotting, Production of some B-complex vit. Flexures: 1) ***Hepatic: bend at the junction of the ascending and transverse colon; upper right quadrant of abd. 2) ***Splenic: bend at the juction of the transverse and descending colon; located at the left upper quadrant of abd. Vitamin K synthesis: essential (blood clotting) Normal passage of material through colon takes about 3-5 days Anus- inner/outer anal sphincter- straited/voluntary muscle(outer) inner - smooth/involuntary muscle> opens during defecation process Appenditis- inflammation of appendix; rupture > peritonitis: septecemia

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 Bends at hepatic or right colic flexure Transverse colon - extends across front 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 - Peritoneum -
Vermiform appendix - “worm-shaped”, tubular structure, blind tube No important digestive fnc. - digest cellulose Appendicitis - inflammation Peritoneum - Large, moist, slippery sheet of serous membrane Peritoneal space - small space between parietal & visceral layers - surfaces slide freely Retroperitoneal - organs outside peritoneum Extensions of peritoneum-mesentary, greater omentum - both assist in anchoring abd. contents Ascites: abnormal accumulation of fluid in the peritoneal space Osmotic pressure problem (low plasma proteins) Accompanies> abdominal swelling, decreased urinary output CHF, cirrhosis, kidney disease, cancer, malnutrition

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

24 Fats - in small intestine
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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