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 

Anatomy
   
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
    Physical (Mechanical)/Chemical digestion
   
Ingestion (and mastication)
   
Propulsion (peristalsis, segmentation,etc.)
   
Absorption
    Defecation 

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 Coverings -- The peritoneum (doubled serosae, pathways for vessels/nerves)
   
Mesenteries (also falciform ligament and greater/lesser omentum, mesocolons
   
     [pgs. 852, 866, 875, 878, 887889]);  know the terms intra-/retroperitoneal
   
Adventitia
   
Splanchnic/hepatic portal circulation

The Wall (GI tract organs) --
    Tunics: mucosa, submucosa, muscularis (circular/longitudinal layers), serosa. 
    Nerve plexuses (submucosal, myenteric [between circular/longitudinal muscles])
    K
now epithelial linings (as always!)

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)

   
     2.  Teeth: principle organ of mechanical digestion; KNOW different teeth types 
                and adult human dental formula
        3. 
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

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)
            4. Enteroendocrine -- hormones (Table 23.1, pg. 868) secreted into capillaries

    Phases of Gastric Secretion -- Cephalic, gastric, intestinal (enteric) (Fig. 23.17, pg. 871)
   
     Understand functions of: gastrin, acetylcholine, histamine, intestinal gastrin,
   
         cholecystokinin (CCK) & secretin (all functions)
        Total volume of gastric juice: 2 - 3 liters/day
   
     Gastric plasticity and contraction (in response to significant stretch); contraction 
            powerful in pyloric region (any active amylase digested here)
; slow, rhythmic 
            contraction (3/min.); retropulsion against pyloric sphincter
   
     Gastric emptying (avg. 4 hrs.): liq. rapid, lipids slowest (6 hrs.) WHY?
            Chyme
       
Ulcers -- Helicobacter pylori

V.  Small Intestine -- 6 meters; duodenum, jejunum, ileum
   
     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
    Peyer's Patches

  A.  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:
            triad
(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

  B.  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

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, appendix, ascending/transverse/descending/sigmoid colon, 
        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])
   
Haustral contractions/mass movements/defecation reflex (Valsalva Man.)
   
Some absorption of water, but most water absorbed in small intestine

Chemical Digestion -- See handout and text; understand names* (eg., lipase)

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.
        Major nutrients -- carbohydrates, lipids, proteins, and water
        (Micro) nutrients -- vitamins and minerals; needed, but in minute amounts
    Most foods offer combinations of these

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 (nine 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. 912)

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. 915)