5Digestive Tract muscular tube approximately 9 M long open at both ends Wall has 4 layers with some variation due to specific function.
6Layers of Digestive Tract innermost: mucosaepithelial cells which line cavityattached to connective tissuesurrounded by thin muscular layerprotects tissues of canalcarries out secretion and absorption
7Layers of Digestive Tract next: submucosathick layer of loose connective tissue housing blood vessels, lymph vessels, and nervesnourishes surrounding layers of tract
8Layers of Digestive Tract next: muscular layerinner: circular smooth muscleouter: longitudinal smooth musclepropels food through digestive tractcontains lots of nerves to control movement and secretion
9Layers of Digestive Tract outermost: serosavisceral peritoneumprotects underlying tissuesecretes serous fluid to keep tract from sticking to other tissues of abdominal cavity
11Mouth (Oral Cavity) Anatomy teeth – 32 total in adultsincisors, premolars, molars, wisdom teethtongue – thick, muscular organfunctions in digestion, taste and speechattaches to posterior part of mouth and by frenulumcovered by mucous membranehouses taste buds within papillaesalty, sweet, sour, bitter
12Mouth (Oral Cavity) Anatomy tonsilslingual and palatinepalate – roof of oral cavityhard = bonesoft = muscle and connective tissueseparates oral and nasal cavitiesuvula – fleshy projection of the soft palate
13Salivary Glands produce saliva – mixture of mucous and serous fluids keeps mouth moistcontains enzymes that aid in chemical digestion3 pairs in oral cavityparotid – located anterior to earssecrete serous and mucous fluidssubmandibular – base of jawducts open below tonguesecrete more serous than mucous fluidssublingual – smallest, below tongueduct opens into floor of oral cavitysecretes thick, stringy mucous fluid
15Saliva produce 1 liter a day serous fluid: parotid and submandibular glandscontains amylase, enzyme to break down starcheslysozyme: reduces bacterial growth in mouthmucous: contains mucin for lubricationregulated by parasympathetic stimulation (involuntary nervous system)increase in secretions with sight, smell, thought of food
16Processes of the Mouth mechanical digestion mastication (chewing) of foodmixing of food with saliva by tonguechemical digestionsalivary amylase breaks down starchesallow for the sense of tasteNO food absorption occurs in mouth.
17Swallowing tongue, soft palate, pharynx and esophagus phase 1: voluntary (mouth)Bolus (food mass) is forced into pharynx by tongue.phase 2: involuntary (pharynx)Pharynx connects mouth and esophagus.Receptors in pharynx sense food which triggers swallowing reflexes.Epiglottis covers larynx.phase 3: involuntary (esophagus)Esophagus connects pharynx to stomach.Peristalsis moves food from esophagus to stomach.Lower esophageal sphincter helps prevent regurgitation of food.
23Muscles of the stomach different than rest of digestive tract 3 layers outer longitudinal layermiddle circular layerinner oblique layerproduce churning action – mechanical digestion
24Specialized Mucosa of the Stomach gastric glands – secrete gastric juice3 types of cellsmucus cells – produce a sticky alkaline mucus which protects stomach liningchief cells – secrete protein-digesting enzymes (pepsinogen which becomes pepsin)parietal cells – secrete hydrochloric acidrugae – internal folds of the mucosaallows stomach to stretch when full
25Other Stomach Secretions gastrin – hormone that increases stomach secretionsintrinsic factor – aids in absorption of vitamin B12cholecystokinin – hormone that stimulates gastric secretionsProduction of gastric juices is regulated by hormones and the nervous system.Humans produce about 2 L per day.
26How Stomach Digests Food As food enters digestive tract, gastrin is produced which causes production of gastric juices.Food mixes with gastric juices and forms chyme which passes to pyloric region.As food empties, secretions from stomach wall are inhibited by nervous system.
27Stomach Movement2 types resulting from stomach wall muscle contractionsmixing – from weak contractionsmix ingested food with stomach secretions to form chymeperistalsis – from stronger contractionsforce chyme toward and through pyloric sphincter
29Small Intestine absorbs products of digestion receives secretions from pancreas and livertransports remaining residue to large intestine6 meters longileocecal junction – joins ileum and large intestineIleocecal sphincter and ileocecal valve keep materials moving in right direction.
32Chemical Digestion in the Small Intestine 3 modifications to increase surface area up to 600 timescircular folds – run perpendicular to long axis of tractvilli – tiny finger-like projections formed by mucosamicrovilli – extensions of villi found in absorptive cells
36Absorption in the Small Intestine major function of small intestinemost in duodenum and jejunummonosaccharides – absorbed through active transport or facilitated diffusion by villiamino acids – absorbed through active transport by villi and carried away in bloodfatty acids – dissolve into cell membranes of villi and carried away by lymphatic vesselswater – absorbed through osmosis into villielectrolytes – absorbed by active transport by villi
37Movement in the Small Intestine mixing and propulsion – mechanical breakdownperistaltic contraction – causes chyme to move along tract; occur along entire digestive tractsegmental contraction – short movements to mix contents
38Large Intestinelarger in diameter, but shorter than the small intestine1.5 metersextends from ileocecal valve to anusmajor functions:absorption of water, electrolytes, vitamins K and Belimination of indigestible food (feces)production of mucus for lubricationNo digestion of food occurs here.Bacteria produce vitamin K and B.
39Divisions of the Large Intestine cecum – saclike first part of the large intestineappendixaccumulation of lymphatic tissuehangs from the cecumcolonascendingtransversedescendingS-shaped sigmoid (in pelvis)rectumanusexternal body openingcontains 2 sphincters
41Structures of the Large Intestine 3 bands of longitudinal musclearranged in teniae colicreate haustra (pocket like sacs in wall)large numbers of goblet cells
42Absorption in the Large Intestine no digestive enzymesabsorption of water and electrolytes and vitamins K and B
43Propulsion in the Large Intestine mass movementsslow, powerful contractionsmove contents toward anusoccur two to three times per daycover more distance than peristaltic contractionsPresence of feces in the rectum causes a defecation reflex.Internal anal sphincter is relaxed.Defecation occurs with relaxation of the voluntary (external) anal sphincter.
44Pancreas located behind the stomach produces digestive enzymes that break down all categories of foodtrypsin – protein digestionpancreatic amylase – starch digestionlipidase – fat digestionsecreted into the duodenumAlkaline fluid introduced with enzymes neutralizes acidic chyme.
46Liver located on the right side of the body under the diaphragm consists of four lobescapable of regenerationconnected to the gall bladder via the common hepatic ductmetabolizes carbohydrates, lipids, proteinsstores glycogen, vitamins A,D and B12, iron and bloodfilters blood, removes toxins and damaged blood cellssecretes bile
48Bile yellowish, green liquid includes water, bile salts, bile pigments, cholesterol and electrolytesBile saltsemulsify fats.aid in absorption of fatty acids, cholesterol and some vitamins
49Gall Bladder sac found beneath liver stores bile from the liver releases bile into the duodenum in the presence of fatty foodrelease controlled by sphincter musclesCrystallized bile causes gallstones.