Review Sheet 1 for Test #3        Biology 2213             Dr. James Adams

The Digestive System -- Chapter 23    
    The overall function is to breakdown foodstuffs and absorb materials 
The digestive system organs can be separated into to groups:
     I.  Alimentary Canal/Gastrointestinal (GI) Tract -- digests and absorbs; 
                continuous series
of coiled, muscular, tubular organs. 
            Lumen is technically outside of body (it is a harsh environment)
     II.  Accessory Organs -- aid in process of digestion (teeth, tongue, salivary glands, 
                liver, pancreas, etc.)

Digestive Processes
1.Ingestion (and mastication); 2. Propulsion (peristalsis, segmentation,etc.); 3. Physical
        (Mechanical)/Chemical digestion;
4. Absorption; 5. Defecation 

The Coverings -- The peritoneum (doubled serosae, pathways for vessels/nerves)
Mesenteries (also falciform ligament and greater/lesser omentum, mesocolons
     [pgs. 885, 894, 901, 907909]);  know the terms intra-/retroperitoneal

The Wall
(GI tract organs) --
    Tunics: mucosa, submucosa, muscularis (circular/longitudinal layers), serosa. 
    Nerve plexuses* (submucosal, myenteric [between circular/longitudinal muscles])
now epithelial linings (as always!)
Some of control intrinsic (enteric hormones, local nerve plexuses* [short reflexes]): 
    receptors in GI tract organs respond to:
     1. stretch, 2. osmolarity/pH, 3. digestive end products
The short reflexes initiated in response, along nerve plexuses in organ walls; hormones 
        also released from some organs which also control digestive processes
Some of control also extrinsic:  long reflexes involving vagus nerve and CNS centers
    Parasympathetic stim. increases secretory activity and motility; sympathetic decreases
    Basically, anything that increases secretory activity also increases motility

The Functional Anatomy of the Digestive System
I.  Mouth (Oral, Buccal Cavity) -- Associated Structures:
A. Lips and cheeks (red margin, frenula)
B.  Palate (hard/soft with uvula)
C.  Accessory organs: 
1.  Tongue (frenulum, papillae):  taste, mechanical dig., propulsion (swallowing)
 Salivary glands -- Parotid, Submandibular, Sublingual, Intrinsic
            Secrete saliva: 97% H2O, ions, amylase (hydrolyzes starch into disaccharides), 
             lysozyme and Ab's (disinfection), mucin (mucus); KNOW serous/mucus cells
          Salivation control -- parasympathetic nervous stimulation in response to stimulation 
            of mouth chemo- (esp. acid) and pressoreceptors;  1 to 1.5 liter/day
          Sympathetic stimulation reduces output -- thick saliva
        3.  Teeth: principle organ of mechanical digestion; KNOW different teeth types 
                and adult human dental formula -- I-2, C-1, P-2, M-3
    Digestive processes of mouth -- mastication, initiation of swallowing, amylase (for
        digestion of polysaccharides -- starch [amylose] to maltose)

II.  Pharynx (Oro-, laryngopharynx only) -- mainly propulsive

III. Esophagus -- in mediastinum, 25cm to stomach (through hiatus in diaphragm)
     also mainly propulsive (peristalsis); swallowing involves 22 separate muscle groups; 
        mucosa has mucus-secreting esophageal glands
Wall has numerous distensible folds with fibrous adventitia (no serosa)
Passage of food: 4 - 8 seconds for solids, 1 - 2 seconds for liquids
    Ends at gastroesophageal (cardiac) sphincter

IV.  Stomach -- Storage and secretion; cardiac sphincter controls entry from esophagus
     Rugae make stomach distensible; allow for physical digestion
     Regions: cardia, fundus, body, pylorus; ends at pyloric sphincter.
        Lesser/ greater curvatures, with lesser/greater omenta.
Microscopic Anatomy -- three muscles layers; additional oblique layer (innermost)
     Mucosa: Simple Columnar Epithelium (virtually all goblet cells), with gastric pits
        Pits have secretory cells:
         1. Mucus neck -- thick, protective mucus
         2. Parietal -- HCl and intrinsic factor (only vital function of stomach; why?)
                  Be able to explain HCl production and blood's alkaline tide (leaving stomach)
         3. Chief -- pepsinogen (activated by HCl; digests 15% of proteins), also lipases
            4. Enteroendocrine -- hormones+ (Table 23.1, pg. 888) secreted into capillaries
    Phases of Gastric Secretion -- Cephalic, gastric, intestinal (enteric) (Fig. 23.19, pg. 890)
     +Understand functions of: gastrin, histamine, intestinal gastrin, cholecystokinin (CCK),
                  secretin (all functions of these hormones: Table 23.1), and acetylcholine
        Total volume of gastric juice: 2 - 3 liters/day
     Gastric accommodation and contraction (in response to significant stretch); contrac- 
            tion powerful in pyloric region (any active amylase digested here)
; slow, rhythmic 
            contraction (3/min.) -- the BER (basic electrical rhythm); to a point, the more food
            in the stomach, the more mixing and more rapid the emptying will be
     Gastric emptying (avg. 4 hrs.): liq. rapid, lipids slowest (6 hrs.) WHY?
            Chyme -- lipids on top going into small intestine
Ulcers -- Helicobacter pylori

Accessory Organs of Small Intestine:
    1.  Liver and Gallbladder -- Accessory organs; main digestive function -- bile secretion
Liver 4-lobed; supported by falciform ligament, ligamentum teres
Microscopic Anatomy: hepatocytes
        Hexagonal liver lobules:
(at corners) with branches of hepatic artery/portal vein/hepatic bile duct
            bile canaliculi
            central vein leading into hepatic vein to inferior vena cava
     Sinusoidal capillaries with Kupffer cells (macrophages)
Gallbladder mainly storage organ for bile, though can concentrate bile (gall stones)
     Ducts: cystic, hepatic, common bile.     Total bile production: 0.5 - 1 liter/day
Know bile composition; main function is emulsification of lipid droplets (mechanical
     digestion using salts and phospholipids); secretion controlled mainly by CCK release

  2.  Pancreas Accessory digestive and endocrine organ
     Principal digestive enzyme producing organ (see enzyme handout); enzymes released
            into small intestine
Head, tail, duct cells, acini (secretory units: enzymes [zymogen granules, alkaline 
        NaHCO3], pancreatic duct, hepatopancreatic duct
    Secretion mainly controlled by hormones:
secretin --> bicarbonate-rich, CCK--> 
        enzyme-rich pancreatic juice; 1.2 to 1.5 liters/day

V.  Small Intestine -- 6 meters; duodenum, jejunum, ileum; lined with enterocytes
     Know hepatopancreatic duct/sphincter (see pancreas/liver, gall bladder)
Modifications of wall: plicae circulares, villi , microvilli (with brush border enzymes)
    Absorptive simple columnar epithetlium (tight junctions); turnover: 5 - 6 days
    Goblet cells (increase along length of S.I.), crypts (decrease along length; 
        secrete watery mucus/lysozyme, a few enzymes); 1 - 2 liters/day
    Specialized duodenal (Brunner's) glands (alkaline secretions)
Enteroendocrine cells
Lacteals (and don't forget Peyer's Patches)

Digestive processes occurring in small intestine:  *chemical (see Enzyme handout)
Most chemical digestion and absorption takes place in small intestine
Motility of Small Intestine -- segmentation; peristaltic contractions weak, until after 
        most absorption. Gastroileal reflex; enhanced by gastrin.

VI. Large Intestine -- cecum (w/ appendix), ascending/transverse/descending/sigmoid 
        colon (ascending and descending retroperitoneal), rectum (with valves), anal canal,
        internal/external anal sphincters, teniae coli, haustra
Bacterial flora (make B/K vitamins, which are absorbed in L.I.; also methane [flattus])
        Keeping pathogenic bacteria in check (see page 909)
Haustral contractions/mass movements/defecation reflex (remember Valsalva Maneuver)
Some absorption of water, but most water absorbed in small intestine

Chemical Digestion -- See handout/text; understand names (eg., lipase); brush border enzymes

Absorption -- Up to 10 liters of food, drink, GI secretions per day, only 0.5 - 1 liter 
        reaches L.I., of which only approximately 150 ml becomes feces.
Most nutrients absorbed by active transport across S.I. mucosa.
     Carbohydrates: most monosaccharides co-transported with Na+; fructose by
         factilitated diffusion
     Proteins: several dif. carriers for amino acids, co-transported with Na+ also.
         Some active carriers for di- and tripeptides.

     Lipids: bile salts important for absorption as well; lipases digest neutral lipids to
         two fatty acids and monoglycerides; these and cholesterol form micelles, which
         passively cross mucosa. Triglycerides resynthesized in epith. sER. Chylomicrons 
            released to lacteals. Redigested at tissue cap. endothelium.
     Nucleic Acids: Active transport of pentose sugars, PO43, nitrogenous bases.
     Vitamins: Most (both fat/water soluble) diffuse; vitamin B12 requires intrinsic fac.
     Electrolytes: Na+ actively pumped (many anions [Cl, HCO3] and water follow
         passively), however, Cl & HCO3 exchanged in ileum (double-pump); K+
         diffuses; Fe and Ca have special mechanisms -- KNOW (ferretin, vitamin D, PTH)

NUTRITION  -- Chapter 24

Nutrient -- a substance in food used for any bodily function; building blocks and energy.
        Major nutrients -- carbohydrates, lipids, proteins, and water
        (Micro) nutrients -- vitamins and minerals; needed, but in small amounts
    Most foods offer combinations of these; energy measure -- Calories
    Note: recommended daily allowances (RDA's); see Table 24.1, pg. 930

Essential nutrients -- nutrients the body cannot manufacture; MUST be obtained in the diet
    Some 45 to 50+ of the nutrients you take in are essential; the rest you need can be
    made from the essentials (as long as the essentials are provided)

The essential nutrients include:
    (1.  A certain minimal amount of carbohydrates)
    2.  Two fatty acids: linoleic and linolenic acids (two of the most abundant, so no big deal)
    3.  Eight (ten in infants) of the amino acids
    4.  Most vitamins (but not D & K)
    5.  All minerals
    (6.  A certain amount of water)

    Technically, the carbohydrates and water are not actually essential, as we can manufacture
some of both carbohydrates and water, but we cannot live without some intake of both.

For each major nutrient, know dietary sources and basic uses in the body
    Although not responsible for the precise amounts of each, you should understand the
    concept of "recommended daily allowances/requirements"

For the vitamins, know importance in the body of all fat soluble vitamins (A, D, E, K),
    and know the importance of the following water soluble vitamins --
        C, B2, nicotinamide (niacin), B5, B12, and folic acid
        (see Table 24.2, pgs. 932)

For the minerals, know the importance in the body of all seven major minerals (Ca, Cl, S,
    K, Na, Mg, and P), and for the following trace minerals (F, I, Fe, Zn)
        (see Table 24.3, pgs. 933)