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Chapter 17 Digestive System

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Segmentation is a movement of the tube which helps to mix food with the digestive secretions. ... The tube has both sympathetic and parasympathetic innervation. ... – PowerPoint PPT presentation

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Title: Chapter 17 Digestive System


1
Chapter 17 Digestive System
2
Digestive System
  • Digestion is the mechanical and chemical
    breakdown of food into a form that the bodys
    cells can absorb.
  • The digestive system has two sets of organs
  • The Alimentary Canal the organs in this set are
    make up the tube which food uses to pass thru
    the body as it is absorbed.
  • Accessory Organs these structures help to break
    food down as it passes thru the tube.

3
Digestive System
  • The alimentary canal is a muscular tube made up
    of 4 layers
  • The Mucosa is formed from primarily of epithelium
    that is invested with goblet cells. This inner
    lining of this layer has many tiny folds on it in
    order to increase the overall absorptive surface
    area. This is the layer of the tract that
    actually absorbs and secretes (absorbs food,
    secretes digestive enzymes).
  • The Submucosa in made up primarily of loose
    connective tissue, blood vessels, glands, and
    nerves.

4
Digestive System
  • Muscular Layer this layer is made up of 2
    layers of smooth muscle, and provides movement
    for the tube. The inner layer of muscle is
    circular while the outer layer is longitudinal.
  • The Serosa is the outer most layer of the tube
    and is primarily composed of serous epithelium
    and some connective tissue. The serous layer
    secretes serous fluid.

5
Digestive System
  • Segmentation is a movement of the tube which
    helps to mix food with the digestive secretions.
  • Peristalsis is a contraction of the tube which
    causes food to move forward thru the tube. It
    begins when food expands the tube, and as the
    contractions occur the segment ahead of the tube
    relaxes to allow advancement of the food bolus.
  • The tube has both sympathetic and parasympathetic
    innervation. An increase in parasympathetic
    nerve flow is usually responsible for increasing
    peristalsis and digestive secretions.

6
Digestive System
  • Organs of the Digestive System
  • The Mouth is the first item in line in the
    alimentary canal. Mechanical digestion begins
    here with mastication (chewing).
  • The Tongue is an accessory organ of digestion.
    It functions to position food in the mouth. It
    is held to the floor of the mouth by the lingual
    frenulum. The top of it is covered with
    structures called papillae which help to handle
    food and provide the sense of taste. The tongue
    also helps in the formation of speech.

7
Digestive System
  • The Palate forms the roof of the oral cavity. It
    consists of a hard (bony) anterior portion and a
    soft posterior portion. A cone shaped projection
    called the uvula hangs from the posterior most
    aspect of the palate.
  • The Teeth are the hardest structures in the body.
    They aid digestion by way of mastication. There
    are two sets of teeth in humans, deciduous and
    permanent. Children will typically have 20 teeth
    that are gradually replaced by the adult teeth.
    Adults typically have 32 teeth.

8
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9
Digestive System
  • Teeth are arranged in this order
  • Central Incisor
  • Lateral Incisor
  • Cuspid
  • Bicuspid (Pre-molar)
  • Molar
  • Each type of tooth is designed to do a specific
    job. Incisors snip food, Cuspids and Bicuspids
    grip and tear, and Molars grind.
  • Teeth break food into smaller pieces. This
    increases the overall surface area of the food
    allowing the digestive enzymes to act more
    efficiently on the food for the process of
    chemical digestion.

10
Digestive System
  • Each tooth is made of a few different layers.
    Enamel covers the top of the tooth . Below that
    is the dentin. Each tooth has a cavity called
    the pulp cavity or root canal. This cavity is
    home to a connective tissue pulp as well as blood
    vessels and nerves.
  • Below the Gingiva (gums) the tooth is surrounded
    by a substance called cementum and held in place
    by a Peridontal Ligament.

11
Digestive System
  • The Salivary Glands secrete the fluid Saliva
    which helps to moisten food and begin the
    chemical break down of some nutrients. Saliva
    helps to cleanse the mouth and teeth, and helps
    to enhance taste .
  • The pH of saliva is between 6.5 and 7.5. Saliva
    also contains a digestive enzyme called Salivary
    Amylase, which is responsible for beginning the
    break down of starchy foods. The major salivary
    glands are the Submandibular, the Sublingual, and
    the Parotid.

12
Digestive System
  • The Pharynx is divided into 3 separate regions
  • Nasopharynx
  • Oropharynx
  • Laryngopharynx
  • The pharynx is connects the mouth to the
    Esophagus. Neither of these organs digest food,
    but are important passage ways to the Stomach.

13
Digestive System
  • The swallowing mechanism (Deglutition) is divided
    into a voluntary phase and an involuntary phase.
    The first phase is voluntary and occurs when food
    is chewed and mixed with saliva.
  • The involuntary phase occurs when the tongue
    pushes food to the back of the pharynx and the
    swallowing reflex is triggered. During this time
    the Epiglottis closes the trachea and allows food
    to enter the esophagus.
  • The swallowing reflex momentarily inhibits
    breathing. When food enters the esophagus it is
    moved down the tube toward the stomach by the
    action of Peristalsis.

14
Digestive System
  • The Esophagus is a straight, collapsible tube
    that leads from the pharynx thru the thoracic
    cavity to the stomach. It penetrates the
    diaphragm thru an opening called the Esophageal
    Hiatus.
  • The esophagus terminates at the Cardiac Sphincter
    just above the stomach.

15
Digestive System
  • The Stomach is a curved pouch-like organ that is
    located in the upper left quadrant of the
    abdomen. The inner lining is marked by thick
    folds called rugae. The stomach secretes Gastric
    Juice that has a very low pH and contains an
    enzyme called Pepsinogen that initiates the
    digestion of proteins.
  • Where most of the organs of digestion have two
    layers of smooth muscle to help with peristalsis,
    the stomach has three layers. This helps the
    stomach to churn and mix food in the process of
    mechanical digestion.

16
Digestive System
17
Digestive System
  • There are three types of secretory cells
    associated with gastric glands in the stomach.
  • Mucous cells secrete mucous
  • Chief cells secrete digestive enzymes
  • Parietal cells produce hydrochloric acid
  • Pepsinogen is an inactive form of the enzyme
    pepsin. Pepsinogen is activated into Pepsin by
    HCl secreted by the parietal cells. It begins
    the break down of most dietary protein.
  • Mucous stops the action of the both HCl and
    Pepsin and thus keeps the stomach from
    auto-digesting itself.

18
Digestive System
  • The stomach is divided into 4 regions. The
    cardiac region is located lust inside the cardiac
    sphincter. The fundus is the superior most
    portion located above the cardiac sphincter. The
    body makes up the bulk of the organ in the
    middle. The pyloric region is the inferior most
    area, just above the Pyloric Sphincter.
  • The pyloric sphincter retains food in the stomach
    until it is released into the Small Intestines.

19
Digestive System
20
Digestive System
  • Intrinsic Factor is another component of gastric
    juice. It is critical for the absorption of
    Vitamin B12.
  • Please note that very little food is actually
    absorbed in the stomach. The stomach will absorb
    some water and many electrolytes, but most other
    nutrients are absorbed else where.
  • Vomiting is a reflex where the gears of the
    digestive system work in reverse motion. This
    reflex ultimately results in the emptying of the
    contents of the stomach.

21
Digestive System
  • The Pancreas is located primarily in the upper
    left quadrant of the abdomen, and has both
    endocrine and exocrine functions. In addition to
    insulin and glucagon secretion, it secretes many
    digestive enzymes. These secretions join bile
    secreted by the liver and enter the small
    intestines thru the Ampulla of Vater
    (Hepatopancreatic Ampulla).
  • The pancreas has a head, a body and a tail.

22
Digestive System
23
Digestive System
  • Pancreatic Juice contains enzymes that digest
    carbs, fats, proteins and nucleic acids.
  • Pancreatic Amylase finishes the break down of
    carbohydrates into disaccharides.
  • Pancreatic Lipase breaks down triglyceride
    molecules into fatty acids and monoglycerides.
  • The Proteases are Trypsin, Chymotrypsin, and
    Carboxypeptidase. These enzymes reduce proteins
    to amino acid chains.
  • Nucleases are enzymes that break down nucleic
    acids into nucleotides.
  • Pancreatic juice also contains a high bicarbonate
    concentration. This gives it an alkaline pH
    which is favorable for the actions of the above
    enzymes, as well as neutralizing most of the acid
    in from the stomach.

24
Digestive System
  • The Liver is the largest of all internal organs.
    It is located mostly in the upper right quadrant
    of the abdomen. The liver is enclosed by a
    fibrous capsule and divided into a right and left
    lobe. Two minor lobes also exist. They are the
    caudate lobe and the quadrate lobe.
  • Blood digestive tract, carried in the hepatic
    portal vein brings newly absorbed nutrients into
    the sinusoids of the liver. Here blood is
    cleansed of impurities and microbes by Kupffer
    Cells (phagocytes).

25
Digestive System
26
Digestive System
  • The liver performs several important functions.
    It plays a key role in carbohydrate metabolism by
    helping to maintain blood glucose levels. It
    aids in lipid and protein metabolism. It forms
    urea by deaminating amino acids. It synthesizes
    clotting factors for the blood and helps the
    spleen in breaking down damaged and old RBCs.
    It also synthesizes Bile.

27
Digestive System
  • Bile is a yellow-green liquid that is
    continuously secreted by the liver. It is then
    stored in the Gall Bladder until needed.
  • The Gall Bladder is found on the inferior side of
    the liver and stores bile until it is called for
    by the body. It concentrates the bile by
    dehydration and keeps it in this form until
    release. Under certain conditions this liquid
    can form a crystal and an accumulation of these
    crystals is referred to as a gall stone. This
    process is referred to as Choleolithiasis.
    Choleolithiasis can lead to Choleocystitis, which
    can lead to a medical emergency.

28
Digestive System
  • Bile salts aid digestive enzymes by the
    emulsification of fats. In this process fat
    droplets are sequestered from each other,
    increasing the overall surface area and
    maximizing enzymatic action of the lipases.

29
Digestive System
  • The Small Intestine is a tubular organ that
    extends from the pyloric sphincter to the Large
    Intestines. This organ is divided into three
    parts
  • The Duodenum is the proximal most portion and
    receives secretions from both the pancreas and
    the liver.
  • The Jejunum is usually larger in diameter than
    the ileum and more vascular
  • The Ileum is the distal portion of this organ and
    is usually less active than the jejunum.
  • The Mesentery are a double fold of peritoneum
    that suspend most of the small intestine within
    the abdominal cavity. The mesentery supports
    blood vessels and nerves that supply the
    intestinal wall.

30
Digestive System
  • The interior lining of the intestinal wall are
    covered by numerous Villi. These structures
    project into the lumen of the intestine and
    greatly absorb the absorptive capacity of this
    organ.
  • Each villus is made up of a layer of epithelium
    and a core of connective tissue containing blood
    capillaries, nerve fibers, and a lymphatic
    Lacteal. At their free surface the epithelial
    cells have many fine extensions called Microvilli
    that form what is known as the Brush Boarder
    that further enhances absorption. The
    capillaries and lacteals carry absorbed nutrients
    into general circulation.

31
Digestive System
  • The small intestines also have an exocrine
    function. Mucous is secreted in varying amounts.
    Also, the following enzymes are secreted
  • Peptidases which break down protein.
  • Sucrase, maltase, and lactase which split
    disaccharides into monosaccharides.
  • Intestinal lipase which breaks down fats.

32
Digestive System
  • The small intestine is the main organ of
    absorption. It is incredibly efficient in this
    process. Carbs, once broken down into
    monosaccharides, are absorbed into a villus and
    enter the blood capillaries.
  • Proteins are broken down into smaller amino acid
    chains and absorbed by a villus into the blood
    capillaries.
  • Most fats are absorbed by lymphatic lacteals and
    ultimately make their way to the cysterni chyli,
    then on to general circulation.
  • Electrolytes are moved by active transport, and
    water is generally moved by osmosis.

33
Digestive System
  • Generally, very little in the way of actual
    nutrients reaches the end of the digestive tract.
  • If the small intestine begins to push chyme thru
    too fast, nutrients will not be as well absorbed.
    This includes water, and the result is a watery
    stool called Diarrhea. Prolonged diarrhea can
    cause dehydration and electrolyte imbalance.
  • The small intestine ends where it joins the large
    intestine at the Ileocecal Valve (another
    sphincter muscle).

34
Digestive System
  • The Large Intestine is so named because of its
    diameter. This organ absorbs water,
    electrolytes, and remnants of the digestive
    secretions remaining in the left over waste
    product that was once food. It also forms and
    stores Feces.
  • The colon has a few parts
  • Ascending portion
  • The Cecum is the pouch like end of the ascending
    portion
  • The Veriform Appendix is the terminal portion of
    the cecum
  • Transverse portion
  • Descending portion
  • The Sigmoid Colon is the final portion of the
    descending portion

35
Digestive System
  • The Anal Canal is made up two sets of sphincter
    muscles. The internal anal sphincter is made of
    smooth muscle and is under voluntary control.
    The external anal sphincter is made up of
    skeletal muscle and is under voluntary control.
  • The large intestine has little or no digestive
    function, other than to eliminate an unneeded
    waste product. Its epithelial lining has many
    goblet cells in it and thus mucus is the only
    significant secretion of this organ.

36
Digestive System
  • Many bacteria inhibit the large intestine and
    make up the Intestinal Flora. Many of these
    bacteria synthesize vitamins such as K and B12
    which are then absorbed by the mucosa.
  • Movement thru the large intestine are caused by
    peristalsis, but these movements are usually less
    prevalent here than in the small intestine.
  • Feces are composed of materials that were not
    digested (such as cellulose), or not absorbed,
    some water and electrolytes, mucus, and bacteria.
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