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					Divisions of Digestive System
   GI tract- alimentary canal is a
    continuous tube that extends from the
    mouth to the anus. About 30 feet long
     Mouth-pharynx-esophagus-stomach-small
     intestine-large intestine.
   Accessory structures- aid in digestion
     Teeth, tongue, salivary glands, liver,
      gallbladder, pancreas
     Besides teeth and tongue the other organs
      never come into contact with food but
      produce or store secretions that aid in
      chemical digestion.
                          Parotid gland
    Mouth (oral cavity)   Sublingual gland Salivary
    Tongue                Submandibular
                                           glands
                          gland


  Esophagus                       Pharynx
                                  Stomach
                                  Pancreas
  Liver                           (Spleen)
  Gallbladder
                           Transverse colon
          Duodenum         Descending colon
Small     Jejunum          Ascending colon
intestine Ileum            Cecum              Large
                           Sigmoid colon      intestine
                           Rectum
                           Vermiform appendix
      Anus                 Anal canal
                                                      Figure 23.1
Primary Functions

 Ingestion- taking food into the mouth
  (eating)
 Propulsion- movement of food along tract
 Digestion- The breakdown of food by both
  chemical and mechanical processes.
 Absorption- The passage of digested food
  from the GI tract into the blood and lymph.
 Defecation- The elimination of indigestible
  substances from the GI tract.
Types of Digestion
   Mechanical Digestion- consists of various
    movements of the GI tract.
      Chewing, churning in stomach and small intestine


   Chemical digestion- series of catabolic
    reactions. Enzymes split large
    carbohydrates, lipids, and protein molecules
    that we eat into smaller molecules that can
    be absorbed and used by body cells.
Ingestion
                           Food
Mechanical
digestion                  Pharynx
• Chewing (mouth)          Esophagus
• Churning (stomach)           Propulsion
• Segmentation                 • Swallowing
  (small intestine)              (oropharynx)
Chemical                       • Peristalsis
digestion              Stomach (esophagus,
                                 stomach,
                                 small intestine,
                                 large intestine)
                                Absorption

                                      Lymph
                                      vessel

    Small
    intestine
    Large                             Blood
    intestine                         vessel
                         Mainly H2O
                          Feces

Defecation                 Anus


                                                    Figure 23.2
   From
   mouth




(a) Peristalsis: Adjacent segments of              (b) Segmentation: Nonadjacent segments
    alimentary tract organs alternately contract       of alimentary tract organs alternately
    and relax, which moves food along the tract        contract and relax, moving the food
    distally.                                          forward then backward. Food mixing and
                                                       slow food propulsion occurs.

                                                                                        Figure 23.3
Histology of the Alimentary Canal
   Four basic layers (tunics)
    1. Mucosa- lines lumen, secretes mucus and digestive
      enzymes, absorbs end-products of digestion
       - mucus protects digestive organs from HCl and
      enzymes and eases passage of food.
    2. Submucosa- dense CT, rich in nerves and blood
      vessels
    3. Muscularis externa- responsible for segmentation
      and peristalsis, churning, forms sphincters
    4. Serosa- protective outermost layer. Epithelial and
      CT
                                     Mucosa




                                     Submucosa
                                     Muscularis
                                     externa
                                     • Longitudinal
                                       muscle
                                     • Circular muscle
                                     Serosa
Nerve
Artery                               • Epithelium
Vein                                 • Connective
                                       tissue
                   Gland in mucosa   Lumen
            Lymphatic
Mesentery   vessel

                                                  Figure 23.6
    The Mouth- oral (buccal) cavity
 Cheeks, hard and
  soft palate, tongue,
  teeth, salivary
  glands
 Oral orifice is the
  anterior opening
 Lined with stratified
  squamous
  epithelium
Soft palate
Palatoglossal arch                 Uvula
Hard palate


Oral cavity
Palatine tonsil
Tongue
Oropharynx
Lingual tonsil
Epiglottis
Hyoid bone
Laryngopharynx


Esophagus

Trachea
(a) Sagittal section of the oral cavity and pharynx
                                                      Figure 23.7a
Lips and Cheeks
 Contain orbicularis oris and buccinator
  muscles
 Vestibule: recess internal to lips and
  cheeks, external to teeth and gums
 Oral cavity proper lies within the teeth
  and gums
 Labial frenulum: median attachment of
  each lip to the gum
                    Upper lip
Gingivae (gums)
                    Superior labial
Palatine raphe      frenulum
                    Palatoglossal arch
Hard palate
Soft palate         Palatopharyngeal
                    arch
Uvula
                    Posterior wall
Palatine tonsil
                    of oropharynx
                    Tongue
Sublingual fold
                    Lingual frenulum
with openings of
sublingual ducts    Opening of
                    submandibular duct
                    Gingivae (gums)
Vestibule
Lower lip           Inferior labial
                    frenulum
(b) Anterior view
                                      Figure 23.7b
Palate
 Hard palate: palatine bones and palatine
  processes of the maxillae
 Soft palate: fold formed mostly of
  skeletal muscle
     Closes off the nasopharynx during
      swallowing
     Uvula projects downward from its free edge
    Brain Freeze
   "Brain freeze" is the pain sometimes inflicted by
    devouring something cold like ice cream or a cold
    beverage, often very quickly.
    The reaction is (obviously) triggered by the cold ice
    cream or beverage; coming into contact with the roof of
    the mouth. It triggers nerves that give the brain the
    impression of a very cold environment. To heat up the
    brain again, blood vessels start to swell, which causes
    the headache-like pain for approximately 30 seconds.
    The temperature change in the roof of the mouth has to
    be rather drastic; this is why brain freeze often occurs on
    warm days.
    The pain can be relieved by putting the tongue to the
    roof of the mouth, which logically will heat it up.
Bifid Uvula- occurs in 2% of newborns
Cleft Palate
    Tongue
   Functions include
     Repositioning and mixing food
      during chewing
     Formation of the bolus
     Initiation of swallowing, speech,
      and taste
   Lingual frenulum: attachment to
    the floor of the mouth
   Contains papillae which provide
    roughness/friction and house
    taste buds.
Salivary Glands: Parotid, Submandibular, and Sublingual


Tongue
Teeth
                                       Parotid
Ducts of
                                       gland
sublingual
gland                            Parotid duct
                                Masseter muscle
                                Body of
Sublingual                      mandible (cut)
gland


                                Submandibular
                Submandibular   duct
                gland                                   Mucous   Serous cells
(a)                                                     cells    forming
                                                  (b)            demilunes




                                                                       Figure 23.9
Composition of Saliva
   97–99.5% water, slightly acidic solution
    containing
     Electrolytes—Na+, K+, Cl–
     Salivary amylase and lingual lipase
       - Amylase is an enzyme that initiates
      the breakdown of starch
       - Lingual lipase is secreted by
      salivary glands at the base of the
      tongue, but becomes active in the
      stomach where it begins the digestion
      of fats.
     Metabolic wastes—urea and uric acid
     Lysozymes protect against
      microorganisms


                                      PLAY   Animation: Rotatable head
Functions of Saliva
1. Lubrication and binding: the
   mucus in saliva is extremely
   effective in binding masticated
   food into a slippery bolus that
   (usually) slides easily through the
   esophagus without inflicting
   damage to the mucosa.
2. Solubilizes dry food: in order to be
   tasted, the molecules in food must
   be solubilized (dissolved).
3. Oral hygiene: The oral cavity is
   almost constantly flushed with
   saliva, which floats away food
   debris and keeps the mouth
   relatively clean. Flow of saliva
   diminishes considerably during
   sleep, allow populations of
   bacteria to build up in the mouth --
   the result is dragon breath in the
   morning. Saliva also contains
   lysozyme, an enzyme that lyses
   many bacteria and prevents
   overgrowth of oral microbial
   populations.
    PHARYNX- Oropharynx and laryngopharynx
      Allow passage of food, fluids, and air




                                                TONGUE
       PHARYNX



      EPIGLOTTIS




ESOPHAGUS                         TRACHEA
Esophagus
               Muscular, collapsible tube that
                lies behind trachea.
               Made up of stratified
                squamous tissue and smooth
                muscle.
               Produces mucous, does not
                produce digestive enzymes, no
                absorption.
               Contains an upper and lower
                esophageal sphincter that
                regulates the movement of
                food into the esophagus and
                stomach, respectively.
               Involuntary muscles of the
                esophagus propel food in a
                wave-like movement called
                peristalsis.
Digestive Processes: Mouth
 Ingestion
 Mechanical digestion
     Mastication is partly voluntary, partly
      reflexive
 Chemical digestion (salivary amylase
  and lingual lipase)
 Propulsion
     Deglutition (swallowing)
Deglutition
 Involves the tongue, soft palate,
  pharynx, esophagus, and 22 muscle
  groups
 Buccal phase
     Voluntary contraction of the tongue
   Pharyngeal-esophageal phase
     Involuntary
     Control center in the medulla and lower
     pons
      Bolus of food

      Tongue

      Pharynx
      Epiglottis
      Glottis

      Trachea



 1 Upper esophageal sphincter is contracted. During
the buccal phase, the tongue presses against the hard
palate, forcing the food bolus into the oropharynx
where the involuntary phase begins.
                                                Figure 23.13, step 1
                                  Uvula
                                  Bolus

                                  Epiglottis




      Esophagus
 2 The uvula and larynx rise to prevent food from
entering respiratory passageways. The tongue blocks
off the mouth. The upper esophageal sphincter
relaxes, allowing food to enter the esophagus.
                                               Figure 23.13, step 2
                                       Bolus


 3 The constrictor muscles of the pharynx contract,
forcing food into the esophagus inferiorly. The upper
esophageal sphincter contracts (closes) after entry.
                                                Figure 23.13, step 3
Relaxed muscles             4 Food is moved through
Circular muscles            the esophagus to the
contract                    stomach by peristalsis.

Bolus of food

Longitudinal muscles
contract




Gastroesophageal
sphincter closed


                       Stomach




                                              Figure 23.13, step 4
Relaxed   5 The gastroesophageal
muscles   sphincter opens, and food
          enters the stomach.




           Gastroesophageal
           sphincter opens




                            Figure 23.13, step 5
FYI
 Heartburn- when the
  lower esophageal
  sphincter fails to close
  completely, HCl from the
  stomach can enter the
  esophagus and cause
  the burning sensation
  associated with acid
  reflux. NOT a heart
  condition!
 We can eat and drink
  upside down because of
  peristalsis!
The Stomach to
Superior portion connected
esophagus, inferior portion
empties into the duodenum,
first part of small intestine.
When empty the stomach is
about the size of a large
sausage.
The lining of the stomach
(mucosa) lies in large folds
called rugae.                    An alkaline mucous layer
                                 1-3 mm thick lines and
The mucosa contains various      protects the stomach
types of cells that produce      against HCl.
mucous, HCl, digestive
enzymes.
    Hiatal Hernia
   Any time an internal body
    part pushes into an area
    where it doesn't belong, it's
    called a hernia.
   The hiatus is an opening in
    the diaphragm -- the
    muscular wall separating
    the chest cavity from the
    abdomen. Normally, the
    esophagus (food pipe) goes
    through the hiatus and
    attaches to the stomach. In
    a hiatal hernia (also called
    hiatus hernia) the stomach
    bulges up into the chest
    through that opening.
   What Causes a Hiatal Hernia?
   Most of the time, the cause is not known.
    Some people develop a hiatal hernia after
    sustaining an injury to that area of the body;
    others are born with a weakness or an
    especially large hiatus. Some experts
    suspect that increased pressure in the
    abdomen from coughing, straining during
    bowel movements, pregnancy and delivery,
    or substantial weight gain may contribute to
    the development of a hiatal hernia.
   What Is an Ulcer?
An ulcer is a sore, which
   means it's an open,
   painful wound.
   Peptic ulcers are
   ulcers that form in
   the stomach or the
   upper part of the
   small intestine.
 Peptic ulcers are
   very common.
   Doctors say that in
   the United States,       What Causes an Ulcer?
   almost 1 in every 10     For almost 100 years, doctors believed that
   people will get an       stress, spicy foods, and alcohol caused most
   ulcer at some time       ulcers. Now we know that most peptic ulcers are
   during their lives.      caused by a particular bacterial infection
                            (Helicobacter Pylori) in the stomach and upper
                            intestine, by certain medications, or by smoking.
 Today doctors know that
  most peptic ulcers are
  caused by an infection
  from H. pylori.
Lots of people have H. pylori
  infections. Almost 2 out of
  every 10 people younger
  than 40 have this bacteria
  in their digestive systems,
  but not all result in ulcers

 When H. pylori bacteria do cause ulcers, here's how doctors think these
 ulcers develop:
 Bacteria weaken the protective coating of the stomach and upper small
 intestine.
 Acid in the stomach then gets through to the sensitive tissues lining the
 digestive system underneath.
 Acid and bacteria directly irritate this lining resulting in sores, or
 ulcers.
    Gastric Bypass Procedures
   People who are at least 100
    pounds over weight and have
    exhausted all other options may
    be candidates.
   May involve stapling a portion of
    the stomach to reduce its volume
    to about 1 cup instead of 1 qt.
   May also bypass the duodenum
    and jejunum and attach ileum
    directly to stomach to reduce
    about of food absorbed.
   Costs about $20,000. Patients
    lose about 10 pounds per month.
    Stabilize after 18 months.
    Endoscopy procedure
   An endoscope is an illuminated
    usually fiber-optic flexible or
    rigid tubular instrument for
    visualizing the interior of a
    hollow organ or part (as the
    bladder or esophagus) for
    diagnostic or therapeutic
    purposes that typically has one
    or more channels to enable
    passage of instruments (as
    forceps or scissors)
    Chemical Digestion of Stomach
 HCl- destroys bacteria in food and partially
  denatures proteins, stimulates secretion of
  hormones that promote the flow of bile and
  pancreatic juices.
 Proteins are digested by the enzyme pepsin which
  is secreted by the stomach.
 Lipase from saliva digests fats.
  Mechanical Digestion of Stomach
Several minutes after food enters
  the stomach, peristaltic          Esophagus
  movements called mixing
  waves pass over the stomach           Pyloric
  every 15-25 seconds.                  Sphincter

 The waves macerate food, mix
  it with gastric secretions and
  reduce it to a thin liquid called
  chyme.
                                      Duodenum
 As chyme reaches the pylorus a
  few milliliters is squeezed
  through the pyloric sphincter
  into the duodenum. The rest is
  subject to further mixing.
Response of the Stomach to
Filling
   Stretches to accommodate incoming
    food
     Gastric accommodation
      ○ Plasticity (stress-relaxation response) of
        smooth muscle
Gastric Contractile Activity
 Peristaltic waves move toward the
  pylorus at the rate of 3 per minute
 Distension increases force of contraction
 Most vigorous near the pylorus
 Chyme is either
     Delivered in ~ 3 ml spurts to the duodenum,
      or
     Forced backward into the stomach
Pyloric                     Pyloric                    Pyloric
valve                       valve                      valve
closed                      closed                     slightly
                                                       opened




1 Propulsion: Peristaltic   2 Grinding: The most       3 Retropulsion: The pyloric
waves move from the         vigorous peristalsis and   end of the stomach acts as a
fundus toward the           mixing action occur        pump that delivers small
pylorus.                    close to the pylorus.      amounts of chyme into the
                                                       duodenum, simultaneously
                                                       forcing most of its contained
                                                       material backward into the
                                                       stomach.




                                                                               Figure 23.19
Regulation of Gastric Emptying
    As chyme enters the duodenum
      Receptors respond to stretch and chemical
      signals
  Carbohydrate-rich chyme moves quickly
   through the duodenum
  Fatty chyme remains in the duodenum
   6 hours or more
Pancreas
   Oblong gland connected
    to the duodenum.
   Each day the pancreas
    produces about 1.5 qts of
    pancreatic juice. Contains
    enzymes:
      Pancreatic amylase- digests
       carbohydrates
      Trypsin- digests proteins
      Pancreatic lipase- digests
       fats
 Liver
 Heaviest gland in
  body (3 lbs).
 Produces bile which is
  stored in the
  gallbladder. After
  eating, stimuli cause
  contraction of the
  gallbladder, which
  releases bile into
  duodenum. Bile
  emulsifies fat into
  droplets that can be
  absorbed into
  bloodstream.
 Liver also stores
  nutrients and stores or
  detoxifies poisons.   Emulsify means combining two liquids
                            together which normally don't mix
                            easily. i.e lipids (fats) and water (blood).
Liver: Microscopic Anatomy
   Hepatocyte functions
     Process bloodborne nutrients
     Store fat-soluble vitamins
     Perform detoxification
     Produce ~900 ml bile per day
    What is Bile?
 Bile, formed in the liver, is principally composed of
  cholesterol, bile acids, lecithin, pigments, and
  salts. Most of the salts in this liquid are
  reabsorbed back into the body, and are necessary
  electrolytes. When people get severe stomach flus
  for instance, they may begin to vomit a yellow
  substance once their stomachs are empty that is
  principally made up of this fluid.
 In some ways you can compare bile to a
  detergent, since it has emulsification properties.
  Emulsification binds two substances together. For
  instance, when you wash dishes, the soap you
  use binds to fats and grease, helping you to
  remove both soap and the grease.
    Gallstones
 Occasionally bile can work against the body instead of for it. For
  instance, the high cholesterol content may form gallstones in the gall
  bladder, a painful condition that sometimes necessitates gallbladder
  removal. When people do need to have their gallbladder removed
  they may have trouble synthesizing and digesting fats thereafter,
  because the pathways of bile ducts from liver to gallbladder are
  essentially useless.
 Cholesterol or bilirubin in bile harden to form stones
 Grain of sand to golf ball size
    Small Intestine
   Made up of three
    segments- duodenum (10
    inches), jejunum (8 ft), and
    ileum (12 ft).
   Major events of digestion
    and absorption occur here.
   Most water is absorbed
    here
   Chyme remains in the
    small intestine for 3-5
    hours.
   Contains villi which are
    folds of the intestinal lining
    that contain microvilli that
    increase surface area for
    absorption and digestion.
                                             Right and left
                                             hepatic ducts
                                             of liver
                                         Cystic duct
                                   Common hepatic duct
                                   Bile duct and sphincter
                                   Accessory pancreatic duct



Mucosa
with folds                                   Tail of pancreas
Gallbladder                              Pancreas
Major duodenal                           Jejunum
papilla                            Main pancreatic duct
Hepatopancreatic                   and sphincter
ampulla and sphincter   Duodenum   Head of pancreas
                                                          Figure 23.21
    Large Intestine
   5 ft long tube that extends from
    the ileum to the anus.
   An area called the cecum
    connects the ileum to the
    ascending colon. Also contains
    transverse, and descending
    colon. The rectum is the last 8
    inches of L.I. that opens to the
    anus. The anus contains an
    internal involuntary sphincter
    and an external voluntary
    sphincter.
    Major function is to absorb       Feces is made up of water,
    remaining water and form and       salts, sloughed off epithelial
    eliminate feces. Bacteria that     cells from mucosa of GI tract,
    live in colon ferment remaining    bacteria, products of bacterial
    carbohydrates which releases       decomposition, and undigested
    methane gas.                       parts of food.
Functions of the Large
Intestine
 Vitamins, water, and electrolytes are
  reclaimed
 Major function is propulsion of feces
  toward the anus
 Colon is not essential for life

				
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