A&P II Chapter 24 Digestive System PDF

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Biol 2402 with James Armacost...

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Functions  Digest and absorb food o Food provides chemical energy for metabolism and nutrients for tissue growth and repair o Digestion is necessary before molecule can be used by the body  Absorb water, vitamins, and minerals  Eliminate waste Layers of the Gastrointestinal Tract 1. Mucosa (innermost) o Mucous epithelium o Some blood and lymph vessels, along with smooth muscles o Site of absorption 2. Submucosa o Connective tissue, blood and lymph vessels, and neurons o Site of gas and fluid exchange 3. Muscularis o Muscle and neurons  Inner layer of circular muscles  Outer layer of longitudinal muscles o Site of muscular contractions 4. Serosa (outermost) o Connective tissue and epithelium o Connects GI tract to surrounding tissue Anatomy of Gastrointestinal Tract 1. Mouth o Houses teeth, tongue, and salivary glands o Functions:  Mechanical digestion  Mastication by teeth, aided by tongue  Chemical digestion  Salivary glands secrete saliva, which includes:  Water- lubricates bolus  Salivary amylase- digests starches  Lingual lipase- digests lipids (specifically triglycerides) o Formation of bolus by tongue o Deglutination (movement of bolus from mouth to esophagus) A. Voluntary Stage  Voluntary movement of bolus from mouth to pharynx

B. Pharyngeal Stage  Involuntary movement of bolus from pharynx to esophagus  Epiglottis prevents bolus from entering larynx C. Esophageal Stage  Involuntary movement of bolus through esophagus into stomach  Driven by peristalsis - the progression of coordinated contraction and relaxations of smooth muscle 2. Pharynx 3. Esophagus 4. Stomach  Alkaline mucus o 1-3mm thick o Protects mucosa from acidic gastric juice and from pepsin  Mucosal layer has many gastric glands o In gastric pits o Secrete gastric juice o Cells of gastric glands a. Mucous neck cells  Mucus b. Parietal cells  Secrete H+ and Cl- , where in the stomach they for HCl, denatures proteins c. Chief cells  Pepsin (as pepsinogen) (cleaves peptide bonds between C and H, which hold amino acids together, breaking down proteins) (present a pepsinogen, an inactivated form, which becomes active in aqueous liquid in stomach)  Gastric lipase (continue process of lingual lipase) (splits triglycerides into fatty acids and monoglycerides) d. G cells  Gastrin (a hormone)  Functions: o Secrete gastric juice o Mixes saliva and food with gastric juice  Producing chime o Serves as reservoir as food  Slow release of food into small intestine  Controlled by pyloric sphincter

o Digestion: a. Mechanical  Mixing waves (peristalsis of stomach) b. Chemical  Starch (carbohydrate) o Activity of salivary amylase continues  Protein o HCl denatures proteins o Pepsin cuts peptide bonds  Triglycerides (class of lipids) o Gastric lipase splits triglycerides into fatty acids and monoglycerides 5. Small Intestine  Very large surface area for absorption created by: a. Circular folds o Ridges of mucosa and submucosa b. Villi o Projections of epithelium of mucosa c. Microvilli o Projections of plasma membrane of absorptive cells o Microvilli collectively form brush border  Anatomy o Mucosal cells: i. Absorptive cells  Produce several digestive enzymes  Inserted into plasma membrane of microvilli  Called brush-border enzymes ii. Goblet cells  Secrete mucus iii. Intestinal gland cells  Secrete intestinal juice (water and mucus)  Mechanical digestion o Segmentations  Localized mixing of chime and digestive juices o Migrating motility complex (MMC)  Peristalsis of small intestine (pushing food forward)  Absorption o Main site of absorption

o Mechanisms include: simple diffusion, facilitated diffusion, osmosis, and active transport  Transport: o Most nutrients (monosaccharides, amino acids, electrolytes, and vitamins)  Enter blood or gastrointestinal capillaries  Are transported by hepatic portal system to liver (detoxify substances)  Then are transported to heart and out to body tissue o Lipids are an exception  Absorptive cells of intestine recombine fatty acids and monoglycerides into triglycerides  Triglycerides aggregate into masses called chylomicrons  Too large to enter circulatory capillaries  They enter specialized lymphatic capillaries called lacteals 6. Large Intestine  Regions: o Cecum (Including appendix, which is not well developed), Colon, Rectum, Anal canal  Functions of large intestine: o Final absorption of nutrients  Water, ions, and vitamins o Production of some vitamins  Via symbiotic bacteria, many species (including E. coli)  Functions: i. Digest remaining carbohydrates  Producing H+, CO2, and CH4 (methane) as byproducts ii. Digest remaining proteins iii. Produce some B vitamins and vitamin K o Production and excrement of feces  Absorption of water  85% in small intestine  15% in large (influence water balance in body)  Feces is produced as water is absorbed from chyme in large intestine  Composed of: water, salts, dead cells from mucosa in GI tract, bacteria, products of bacterial

decomposition, unabsorbed nutrients, indigestible part of food (cellulose, etc.) IV.

7. Anus Accessory Digestive Organs A. Teeth o Top to bottom A. Crown B. Neck C. Root o Inside to Outside A. Pulp cavity and root canals  Blood and lymph vessels and neurons B. Dentin  Calcified connective tissue C. Enamel  Calcium carbonate and calcium phosphate  Hardest substance in the body o 4 types of Adult Dentition (32 teeth) 1. Incisors  Chisel-shaped for nipping and cutting 2. Canines  Pointed for piercings and tearing 3. Premolars  Broad, flat crown for crushing and grinding  One or two roots 4. Molars  Broad, flat crown for crushing and grinding  Two or three roots B. Tongue C. Three Pairs of Salivary Glands (and some minor glands) o Functions  Secrete saliva into oral cavity via salivary glands  Saliva contains water and some solutes  Mucous, buffers, and digestive enzymes 1. Parotid Glands 2. Submandibular Glands 3. Sublingual Glands D. Pancreas  Anatomy: o Composed of clusters of cells

a. Pancreatic islets  1% of cell clusters  Endocrine function  Produce insulin and glucagon b. Acini  99% of cell clusters  Exocrine function (secrete product in a duct/tube) 

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Functions: o Exocrine glands secrete pancreatic juice  Into small intestine  Via pancreatic and accessory ducts o Pancreatic juice  Water, salts, sodium bicarbonate (neutralizes acidity), and digestive enzymes (for small intestine) Pancreatic enzymes a. Pancreatic amylase o Digest starch (carbohydrate) b. Trypsin (digest protein) c. Chymotrypsin (digest protein) d. Carboxypeptidase (digest protein) e. Elastase (digest protein) f. Triglycerides (class of lipids) a. Digested by pancreatic lipase g. Ribonuclease a. Digest nucleic acids h. Deoxyribonuclease a. Digest nucleic acids

E. Liver  Anatomy: o Two lobes, composed of many lobules o Each lobule contains many hepatocytes o Hepatocytes secrete bile  Bile: o Composition: water, bile salts (digestion), bile pigments (excretory product), etc. o It is classified as both an excretory product and digestive secretion o Functions as an emulsifier – emulsification is where bile salts break up drops of fat or oil (lipid) into smaller droplets F. Gallbladder  Receives bile from liver

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Stores and concentrates bile Secretes bile into small intestine

Peritoneum  Anatomy: o Folds weave between digestive organs A. Parietal peritoneum  Lines abdominal cavity B. Peritoneal cavity  Cavity between the two layers filled with serous fluid C. Visceral peritoneum  Surrounds most digestive organs  Functions: o Attaches and anchors digestive organs to rest of body o Provides for movement and expansion and contraction of digestive tract o Supplies digestive organs with blood and lymph vessels and neurons Stages of Digestion 1. Ingestion 2. Secretion 3. Mixing and propulsion 4. Digestion i. Mechanical ii. Chemical 5. Absorption 6. Defecation

Enzyme Salivary Amylase Lingual Lipase Pepsin

Gastric Lipase

Gastrin

Pancreatic Amylase Pancreatic lipase Ribonuclease Deoxyribonuclease Bile salts Trypsin Chymotrypsin Carboxypeptidase Elastase

Full list of digestive enzymes Produced in Activated Effect Salivary glands Mouth Digests starches Serous acini in Mouth Digest lipids (triglycerides) tongue By HCl in Breaks down peptide bonds Activated as pepsinogen by stomach HCl in stomach Chief cells in Stomach Continues lingual lipase process (splits stomach triglycerides into fatty acids and monoglycerides) Stomach Regulate secretion of digestive acid G cells of duodenum and stomach Serous acini in Pancreas Digest starch (carbohydrate) pancreas Serous acini in Pancreas Digest triglycerides (lipids) pancreas Serous acini in Pancreas Digest nucleic acids pancreas Serous acini in Pancreas Digest nucleic acids pancreas Hepatocytes in Liver Break up drops of fat or oil (lipid) into liver smaller droplets Digest proteins Serous acini in Pancreas pancreas...