B. Accessory Structures
    1. assist in digestion
    2. includes teeth, salivary glands, liver, gall bladder, pancreas

 C. Four Major Layers of GI Tract
    1. mucosa - innermost lining of GI organs
       a. epithelium
       b. lamina propria – areolar CT, MALT, blood vessels, lymph vessels
       c. thin muscularis layer
    2. submucosa
       a. areolar CT
       b. blood vessels
       c. autonomic nerves
    3. muscularis
       a. smooth & skeletal muscles
    4 serosa - outermost lining of GI organs
       a. CT + simple squamous epithelium (mesothelium)
       b. peritoneum
          i. visceral – mesothelium on organ surface
          ii. parietal – mesothelium on abdominal wall
          iii. major periotoneal folds – extensions of peritoneum layers
             aa. mesentary – attaches SI to posterior wall
             bb. mesocolon – attaches LI to posterior wall
             cc. falciform ligament – attaches liver to anterior wall
             dd. lesser omentum – attaches stomach & duodenum to liver
             ee. greater omentum – attaches transv. colon & SI to stomach & duodenum

 D. Oral Cavity Structures
    1. deciduous teeth (20)
    2. permanent teeth (32)
    3. tongue
       a. skeletal muscles
       b. moves food mass “bolus”
       c. appropriate use of “lingual” terminology
    4. salivary glands (3 pair)
       a. parotid
       b. submandibular
       c. sublingual
       d. parasympathetic innervation (activation)
    5. saliva
       a. amylase - begins starch digestion (not very significant amount)
       b. lysozyme - protective, digests bacterial cell walls
       c. lingual lipase - begins lipid digestion (not very significant amount)
    6. appropriate use of “buccal” terminology

 E. Pharynx
    1. oropharynx
    2. esophagus - connects pharynx to stomach
    3. peristalsis - rhythmic smooth muscle contractions propel material inside

II. Major Organs of Digestion and Absorption
 A. Stomach
    1. general anatomic regions
       a. cardia
       b. fundus
       c. body
       d. pyloric region
    2. stomach is important in the process of physical digestion
    3. rugae are undulations in stomach wall to help grind
    4. gastric pits contain four major secretory cells:
       a. chief cells
          i. pepsinogen
             aa. activation of pepsinogen by low pH to form pepsin
             bb. pepsin is a protease for protein digestion
       b. parietal cells
          i. HCl
             aa. secretion enhanced by histamine via H2 receptors
             bb. Tagamet blocks H2 histamine receptors to inhibit HCl secretion
          ii. intrinsic factor
             aa. binds to and allows B12 absorption in intestines
       c. G-cell
            i. secretes gastrin hormone
            aa. gastrin activates gastric juice secretion & gastric smooth muscle “churning”
            bb. gastrin activates gastroileal reflex which moves chyme from ileum to colon
       d. mucus cell
            i. protective role of mucus against acids and digestive enzymes
     5. pyloric sphincter regulates entry into the duodenum
     6. chyme is liquified digested material

 B. Gastric Activity
    1. major action in the stomace are secretion of gastric juice & contraction of smooth muscle
    2. three major  mechanisms of gastric regulation
       a. cephalic phase
          i. initiated by parasympathetic activation (vagal innervation)
          ii. cortical (smell, thoughts, etc.) activation of medulla
          iii. medulla activates gastric juice secretion
          iv. medulla activates gastrin secretion
          v. medulla activates smooth muscle “churning”
       b. gastric phase
          i. food mass and chemicals trigger parasympathetic reflex
          ii. enhance parasympathetic activation of stomach
          iii. activate & enhance emptying of chyme into duodenum
       c. intestinal phase – will cover later in outline

 C. Small Intestine
    1. major site of chemical digestion & absorption
    2. approx. 21 ft long/ 1inch diameter
    3. three major segments
       a. duodenum  ~10 inches
       b. jejunum  ~8 ft
       c. ileum  ~ 12 ft
    4. histology
       a. mucosa has intestinal glands (cavities) for secretion of intestinal juice
       b. mucosa also has circular folds, villi & microvilli for increased surface area
       c. “brush border” has many enzymes embedded in plasma membranes
          i. several carbohydrate-digesting enzymes
          ii. peptidases
          iii. nucleosidases
          iv. enterokinase is released by epithelial cell “shedding”
             aa. important enzyme activator – see later

 D. Intestinal Phase of Regulating Digestion
    1. chyme enters duodenum
    2. three hormones secreted from SI mucosa
       a. gastric inhibitory peptide (GIP)
          i. fatty acids in chyme induce GIP secretion
          ii. GIP inhibits gastric secretion
          iii. GIP inhibits gastric “churning”
          iv. GIP activates insulin secretion
       b. secretin
          i. secretin inhibits gastric secretion
       c. cholecystokinin (CCK)
          i. CCK fatty acids in chyme induce CCK secretion
          ii. CCK slows gastric emptying
    3. receptors in SI mucosa sense food/chemical presence in duodenum
    4. neuronal activation of sympathetic NS/ inhibiton of parasympathetic NS

 E. Role Of The Pancreas In Digestion
    1. approx 1.5L/day pancreatic secretions produced
    2. secretions enter duodenum via two pancreatic ducts
    3. many different components in these secretions
       a. NaHCO3 – buffers pH of chyme
       b. pancreatic amylase
       c. trypsinogen, chymotrypsinogen, carboxypeptidase
          i. trypsinogen activated by enterokinase to become trypsin
          ii. trypsin acts on other proteases to activate them
       d. lipases
       e. ribonucleases

 G. Regulation Of Pancreatic Secretions
    1. neuronal regulation
       a. initiated by parasympathetic activation (vagal innervation)
       b. same stimuli as with cephalic and gastric phases
    2. hormonal regulation
       a. CCK stimulates pancreatic enzyme secretions
       b. secretin stimulates bicarbonate secretions

 H. Role Of The Liver
    1. liver is largest gland in body
    2. overall function to “filter” and process nutrient-rich blood delivered to it
    3. receives nutrient-rich blood from SI via the hepatic portal vein
    4. many functions to liver besides aiding in digestion
    5. regulates carbohydrate metabolism
       a. glucose secretion into blood/absorption from blood into glycogen storage
       b. regulated by insulin & glucagon (endocrine review)
    6. regulates many aspects of lipid metabolism
       a. chemical digestion of fatty acids (B-oxidation) for entry into Krebs cycle
          i. release of ketones as metabolic waste product of fatty acid metabolism
       b. cholesterol synthesis
    7. detoxifies blood
       a. ETOH detoxification
       b. other dietary toxins neutralized by liver
    8. bile synthesis (approx 1L/day)
       a. bile salts (cholesterol derivatives) function to emulsify fats to aid enzymatic digestion
          i. bile salts are recycled (are not excreted) from colon back into liver for reuse
       b. main bile pigment is bilirubin – derived from RBC heme
          i. bilirubin and other neutral fats in bile do not aid in digestion; they are excreted
       e. bile is synthesized in liver, stored in gall bladder
       f. release of bile from gall bladder stimulated by CCK and vagus nerve
          i. CCK also causes hepatopancreatic sphincter to relax – allows bile to enter duodenum
          ii. secretin also stimulates bile synthesis
          iii. bile salts also act as positive feedback activator to enhance more bile synthesis
       g. “gallstones” are concentrated precipitates of cholesterol
          i. gallstones form when bile is too rich in cholesterol or lacking bile salts

 I. Large Intestine
    1. major function to absorb water and eliminate indigestable matter
    2. major structures
       a. cecum with vermiform appendix
       b. ascending, transverse, descending colon
       c. sigmoid colon, rectum
       d. haustra are pouches in wall of large intestine
          i. haustral churning is sequential movement of contents from one haustra to the next
          ii. gastrocolic reflex is rapid peristalsis in LI triggered by food in stomach
    3. normal bacterial flora colonize colon
       a. vitamin K synthesis by E. coli bacterium
    4. vermiform appendix
       a. lymphatic structure attached to cecum

 J. Nutrient Absorption
    1. carbohydrates
       a. enzymatically digested to form monosaccharides (glucose, fructose, galactose)
       b. absorbed in SI by active transport or facilitated diffusion
       c. enter blood capillary in villi, then directed to hepatic portal vein
    2. proteins
       a. enzymatically digested to amino acids or di- and tri-peptides
       b. absorbed in SI by active transport or facilitated diffusion
       c. enter blood capillary in villi, then directed to hepatic portal vein
    3. lipids
       a. enzymatically digested to short or long chain fatty acids
       b. suspended in SI in form of micelles with bile salts
       c. micelle formation aids lipid diffusion into SI epithelial lining
       d. inside epithelial cells, lipids bound into chylomicrons for transport
       e. chylomicrons transported to lacteal villi;  then into lymphatics and then to venous blood