2DigestionThe breaking down of food by both mechanical and chemical meansMechanical Digestion - various movements of the alimentary canal that aid in chemical digestionGrinding of teeth to soften foodChurning of food by smooth muscles to mix with digestive enzymesChemical Digestion - series of catabolic reactions that break down large molecules into smaller molecules
3Types of DigestionChemical digestion is the chemical breakdown of larger nutrient molecules to smaller ones which can be absorbed and used by the body.Mechanical digestion is the physical breakdown of food into smaller pieces.
4Taking food into the body (EATING) IngestionTaking food into the body (EATING)
5Movement (Propulsion) Passage of food along thealimentary canal
6AbsorptionThe passage of digested food from the alimentary canal into the cardiovascular and lymphatic systems for distribution to body cells
7Defecation (Excretion) The elimination of indigestible substances from the alimentary canal
8Digestive Processes Mastication – chewing Maceration – muscular waves in the stomach which mix food with gastric juice to form a liquid paste called chyme.Segmentation – Short, small mixing movements of the alimentary canal.
9Digestive ProcessesPeristalsis – wave-like smooth muscle contractions which help to propel food and wastes along the alimentary canal.Haustral Churning – movement of wastes along the large intestine by the contraction of the pouches or the haustra.
10Gastrointestinal Tract (Alimentary Canal) A continuous tube running through the ventral body cavity extending from the mouth to the anusOrgans of the Alimentary Canalmouth - pharynx - esophagusstomach - S. intestine - L. intestineAccessory Organsteeth - tonguesalivary glands - livergallbladder - pancreas
14Pharynx Also called the throat. Serves as a passageway for food and air.Also helps in the formation of words.
15Esophagus Muscular tube located posterior to the trachea About 10 inches longDoes not participate in digestive processes - simply a transport corridorFood is pushed through the esophagus by peristaltic actionForces food down into the stomachEsophageal hiatus - opening in the diaphragm for the esophagus
17StomachJ-shaped enlargement of the digestive tract located just below the diaphragmSuperior portion - continuation of the esophagusInferior portion empties into the duodenumPosition and size of the stomach varies from individual to individual
18Histology of the Stomach Composed of the same four tissue types as the other structures of the alimentary canalWhen the stomach is empty the mucosa lie in large folds called rugaemucosa contains millions of tiny openings called gastric pits that open into gastric glandsSecretes digestive enzymes and a fluid called gastric juice (2-3 liter per day)
20Features of the Stomach Cardiac Region – where the stomach is connected to the esophagus.Fundus – the rounded, superior area of the stomach that acts as a temporary storage for food.Body – the large, central portion of the stomach below the fundus.
21Features of the Stomach Pylorus – the narrow, inferior region of the stomach.Rugae – the folds in the stomach that allow for stretching of the stomach with the intake of food.Pyloric Sphincter – the one-way valve located between the stomach and the duodenum.
24Secretory Cells of the Gastric Glands Chief CellsDigestive enzymesPepsinogen activated by HCl and converted toPepsinParietal CellsHClIntrinsic Factor (absorption of Vitamin B12)Goblet CellsSecrete mucus to protect the stomach mucosa from the acidic environment
27Mechanical Digestion in the Stomach Several minutes after food enters, the stomach generates mixing waves that churns the food inside - macerationFood mixes with gastric juices and is converted into a thin liquid called chyme
28Chemical Digestion in the Stomach Cephalic Phase - reflexes initiated by sensory receptors in the head- proteases are excretedsight - smell tastethought of foodGastric Phase - sensory receptors in the alimentary canal and stomach initiate nervous and hormonal chemical digestive processesIntestinal Phase - secretion of stomach enzymes that removes nutrients from food
29Absorption in the Stomach Does not participate in the absorption of food molecules into the bloodHowever, can absorb some substances through the stomach wallWaterWeak glucose concentrationsElectrolytesCertain drugs (aspirin)Alcohol
30Small Intestine The next part of the alimentary canal. Divided into three sections – the duodenum, jejunum, and ileum.In the duodenum, chemical digestion is completed.The majority of nutrients are absorbed in the jejunum and ileum.
31The Small IntestineDuodenum - the beginning of the small intestine where it attaches to the stomachFirst 6 inchesJejunum - the portion of the small intestine right after the duodenumNormally about 8 ft. longIleum - the final portion of the small intestineAbout 12 ft. longIleocecal valve
35Chemical Digestion of the Small Intestine Complex series of chemical events that results in the breakdown of carbohydrates, fats, and proteinsResult of the collective effort of pancreatic juice, bile, and intestinal juice which contain digestive enzymesResults in absorption - passage of digested nutrients into the blood or lymph
36Mechanisms to Increase Absorption by the Small Intestines Folds in the intestinal walls of the mucosa layer of tissue (Plicae Circulares)Villi arrangement of tissue of mucosa layerLacteals - blood capillaries and lymphatic vessels associated with each villiMicrovilli arrangement of epithelial cells of the mucosa
41Absorption in the Small Intestine 90% of absorption takes place within the small intestineRemaining 10% occurs in the stomach and large intestineAbsorption of nutrients occurs through the villi by means of:diffusion - facilitated diffusionosmosis - active transport
44Additional Components of the Small Intestine Intestinal Juice - slightly alkaline secretion (pH 7.6) secreted by intestinal glandsrapidly absorbed by the villi and provides a mechanism for absorption of substances in chymePeyer’s Patches - lymphatic glands of the small intestineBrunner’s Glands - mucus secreting glands of the small intestine
45Mechanical Digestion of the Small Intestine Segmentation - localized contraction of muscles of the small intestine in areas containing foodRate of about contractions/minuteSloshing of chyme back and forth within the intestinal lumenPeristalsis - rhythmical contraction of muscles of the small intestines that propels chyme through the intestinal tract
46Large Intestine The last part of the alimentary canal. Responsible for the absorption of water, compaction of feces, and the production of Vitamin K.
47The Large Intestine About 1.5 m (5 ft) in length Cecum - beginning of the large intestineVermiform appendixColon - large tube-like portion of large intestineAscending colon Transverse colonDescending colon Sigmoid colonRectumAnal CanalAnus
49Functions of the Large Intestine Completion of absorptionReabsorption of waterManufacture of certain vitaminsFormation of fecesExpulsion of feces from the body
50Histology of the Large Intestine Walls of the large intestine contain no villi or permanent circular folds in the mucosa layerEpithelial tissue layer contain numerous goblet cells (secretes mucus)Lubricates the colonic contents as it passes through the large intestine
51Haustra - series of characteristic pouch like structures that run the entire length of the colon Taenia Coli - bands of smooth muscle that are arranged longitudinally along the length of the colonAnal Columns - parallel ridges of mucosa in the anal canal which reduces friction with feces during defecation
54Mechanical Digestion in the Large Intestine Haustral Churning - the relaxation and contraction of the individual segments of the colonPeristalsis - rhythmical contraction of the colon that moves the contents along through the length of the colonMass Peristalsis - a strong peristaltic wave that begins about the middle of the transverse colon and drives the colonic contents into the rectum
55Chemical Digestion in the Large Intestine Last stage of digestionDue to bacterial action in the large intestineBacteria ferment any remaining carbohydrates and release hydrogen, carbon dioxide, and methane gasAlso converts any remaining proteins into amino acidsAbsorbs any remaining water and electrolytes
56Feces Formation in the Large Intestine By the time chyme has remained in the large intestine for hours it has become a solid or semi-solid and is known as fecesConsists of water, inorganic salts, sloughed off epithelial cells, products from bacterial decomposition, and indigestible parts of food
57Defecation The emptying of the rectum Diarrhea - frequent defecation of liquid fecesConstipation - infrequent or difficult defecation
58Accessory OrgansThe accessory organs include the liver, gallbladder, pancreas, and salivary glands which will be discussed in more detail later on in this unit.
59Salivary GlandsPaired accessory structures that lie outside the oral cavitySecrete their contents (saliva) into ducts that empty into the mouthParotid Glands - underneath the earsSubmandibular Glands - under the mandibleSublingual Glands - under the tongue
61Saliva Fluid secreted by the salivary glands 99.5% water .5% solutes chlorides - bicarbonates - sodiumpotassium - phosphates - ureauric acid - globulin -mucinserum albuminSalivary amylase - digestive enzymebegins carbohydrate digestion in the mouthLysozyme - destroys bacteria in the mouth
62Digestion in the Mouth Mechanical Digestion Chewing (Mastication)Tongue manipulates the foodTeeth grind up the food and mix it with salivaThe result of mechanical digestion is a soft flexible mass of food called a bolusChemical DigestionSalivary amylase initiates the breakdown of carbohydratesOnly chemical digestion in the mouth
63Teeth Accessory structures of the digestive system Deciduous teeth (baby teeth) - 20Permanent teeth - 32Incisors (8) - 4 on top, 4 on bottomchisel shaped - front of mouthCanines (4) - 2 on top, 2 on bottomsharp pointed tearing teethPremolars (8) - 4 on top, 4 on bottomMolars (12) - 6 on top, 6 on bottombroad, flat, crushing teeth
65Portions of the ToothCrown - exposed portion of the tooth above the gum lineNeck - constricted junction line in the tooth between the crown and the rootRoot - one to three projections of the tooth that are embedded in the sockets of the alveolar processes of the mandible and maxillae
67Composition of TeethEnamel - outermost portion of the tooth, protects the tooth from wear and tearthe hardest substance in the bodyDentin - calcified connective tissue that gives the tooth its basic shape and rigidityPulp Cavity - large cavity enclosed by the dentin that is filled with pulpCementum - a bone-like substance that covers the dentin of the root
68Periodontal LigamentAn area of dense fibrous connective tissue attached to the socket walls and the cemental surface of the roots of the teethAnchors teeth in positionServes as a shock absorber when chewing
69Swallowing (Deglutition) Moving food from the mouth to the stomachVoluntary Stage - bolus is moved through the mouth into the oropharynxPharyngeal Stage - involuntary passage of the bolus through the pharynx and into the esophagusEsophageal Stage - involuntary passage of the bolus through the esophagus and into the stomach
72PancreasOblong gland that lies posterior to the greater curvature of the stomachConnected by ducts to the duodenumComposed of clusters of glandular epithelial cellsTwo main types of Pancreatic Cells:Pancreatic Islets-Islets of Langerhans (1%)Hormones: insulin, glucagon, somatostatinAcini Cells (99%)Digestive pancreatic enzymes
74Pancreatic JuiceAlkaline mixture of fluid and digestive enzymes from the acini cellsPancreatic digestive enzymes:Pancreatic amylase - carbohydrate digestionPancreatic lipase - fat digestionChymotrypsin-Trypsin-Carboxypeptidase - protein digestionNucleases - nucleic acid digestionRegulated by the intestinal hormones secretin and cholecystokinin
75Liver Located just under the diaphragm on the right side of the body Largest organ of the abdominal-pelvic cavityWeighs about 1.4 kgs (3 lbs)Called the chemical factory of the bodyCompletely covered by the peritoneum and a dense layer of connective tissue beneath the peritoneum
76Anatomy of the Liver Right Lobe - largest lobe of the liver Located on the lateral-right side of the bodyCaudate Lobe - posterior portion of right lobeQuadrate Lobe - inferior portion of right lobeLeft Lobe - smaller, medial lobe of the liverFalciform Ligament - separates the right and left lobes of the liver and anchors it to the diaphragm and anterior abdominal wall
78Lobules of the Liver Smaller functional units of the liver Hepatocytes in the lobules produce and secrete a yellowish, brownish, or olive green liquid called bile (1 quart daily)Composed of bile salts and pigments, lecithin, and several ionspH ofExcretory product and digestive secretionAssists in the breakdown of fat molecules (emulsification)Principle bile pigment is bilirubin
79Functions of the Liver Metabolism of carbohydrates, fats, and proteins Removal of drugs and hormonesExcretion of bileSynthesis of bile saltsStorage of vitamins, minerals, and food moleculesPhagocytosis of old worn out red and white blood cellsActivation of Vitamin D
80The Gallbladder A pear shaped sac about 7 - 10 cm long Located on the inferior surface of the liverStores and concentrates bile until it is needed by the small intestine for the emulsification of fat
83Digestive System Diseases and Homeostatic Imbalances
84Appendicitis Inflammation of the vermiform appendix Can be caused by an obstruction of the lumen of the appendix by fecal material, a foreign body, stenosis, kinking of the organ, or carcinoma
85Cirrhosis of the LiverDistorted or scarred liver tissue due to chronic inflammationCommonly caused by hepatitis, chemical exposure, parasites, and alcoholismSymptoms include: jaundice, bleeding, edema, and increased sensitivity to drugs and chemicals
86Tumors of the Digestive System Can occur in all areas of the digestive systemCan be malignant or benignColorectal Cancer3rd most common cause of cancer for both males and femalesOverall mortality rate is over 60%Factors contributing to colorectal cancer include genetic predisposition, diet high in fat, protein, insufficient dietary fiber, and low calcium and selenium in the diet
87Gall Stones Crystallization of bile in the gallbladder Can block the bile duct causing intense painUsually treated with gall stone dissolving drugs, lithotripsy, or surgery
88Hepatitis Inflammation of the liver Can be caused by viruses, drugs, and certain chemicals including steroids and alcoholMany different types of Hepatitis including:Hepatitis A (Infectious Hepatitis)Hepatitis B (Serum Hepatitis)
89Hepatitis A Infectious hepatitis Caused by Hepatitis A virus Spread by fecal contamination of food, clothing, toys, eating utensils, etc.Generally a mild disease of children and young adultsCharacterized by anorexia, malaise, jaundice, nausea, diarrhea, fever, and chills
90Hepatitis B Serum hepatitis Caused by the Hepatitis B virus Transmitted by sexual contact, contaminated syringes, transfusion equipment, saliva, tears, and puncture wounds in the skinCan produce cirrhosis and possibly cancer of the liver
91Obesity Clinically classified as obese if: > 30% of projected body weight as determined height and frame sizedoesn’t factor in Body CompositionCurrently over 50% of U.S. population is clinically classified as obese14% of all male cancers linked to obesity20% of all female cancers linked to obesity
92A serious risk factor for: U.S. surgeon general has said Obesity is the second most serious threat to the health of AmericansA serious risk factor for:Heart Disease - DiabetesHypertension - CancersRespiratory DisordersEndocrine DisordersGastrointestinal DisordersUrinary and Reproductive System Disorders
93Peptic UlcersCrater like lesions that develop in the gastrointestinal tractGastric Ulcers ---> StomachDuodenal Ulcers ---> DuodenumCommonly caused by hypersecretion of gastric juices and acidsContributing factors include: stress, cigarette smoking, certain foods, some medications, and bacterial infections