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The Digestive System rev 11-11

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Title: The Digestive System rev 11-11


1
The Digestive System rev 11-11
  • Digestion is a process of breaking down large
    molecules contained in food into basic building
    blocks which our body can then use to build
    nutrients.
  • The digestive system includes
  • mouth --small intestine
  • pharynx --large intestine
  • esophagus --rectum
  • stomach --anus

2
  • These organs are collectively called the
    Gastrointestinal System or Tract. It is actually
    a hollow tube extending from the mouth to the
    anus.
  • The space within the tube is called the lumen.
  • The system also includes 4 accessory organs
  • Salivary glands --gallbladder
  • Liver --pancreas

3
Gastrointestinal (GI) Tract Layers
  • Structure of the system
  • Mucosa innermost layer is composed of simple
    columnar epithelial tissue
  • Lymphatic capillaries in the digestive tract are
    called lacteals.
  • Submucosa- is made of connective tissue which
    contains blood, lymphatic vessels, and nerves.
  • This layer also has a lot of elastic fibers.

4
Gastrointestinal (GI) Tract Layers
  • Muscularis the thickest part of the wall is
    responsible for motility
  • composed of 2 layers of smooth muscle.
  • this layer is responsible for peristalsis (the
    wavelike propulsion of material through the
    digestive tract) and segmentation (the back and
    forth mixing of food which occurs primarily in
    the small intestine).
  • Serosa the outermost layer, is made up of
    connective tissue covered with an epithelial
    membrane
  • Sphincter thick ring of circular smooth muscle.

5
Digestive System Processes
  • Five processes accomplish digestion
  • Mechanical Digestion by chewing we break down
    large food particles into smaller ones and we
    mix the food.
  • Secretion fluid, digestive enzymes and hormones,
    bile, acid, alkali, mucus are secreted into the
    GIT.
  • Digestion breaking down food to smallest
    absorbable units.

6
  • Absorption nutrient molecules pass through
    mucosa, into blood or lymph vessels
  • Elimination undigested material eliminated

7
  • The smooth muscle in the GIT produces 2 kinds of
    movement Peristalsis and Segmentation
  • Peristalsis propels food forward.
  • The bolus stretches a portion of the tract and
    causes the muscle in front of it to relax and the
    muscle behind it to contract.
  • Segmentation mixes food.
  • The sections of smooth muscle relax and contract
    in a random manner causing a back and forth
    mixing and presses food against the mucosa so the
    body can absorb the nutrients.

8
  • Mouth begins digestion with chewing
  • Teeth
  • Break down food into small pieces
  • Mouth contain bacteria that live off the food
    that remains on our teeth
  • Tongue skeletal muscle, moves food in mouth,
    contributes to sense of taste and necessary for
    speech

9
  • Saliva
  • Source parotid, submandibular, sublingual
    salivary glands
  • Connect to the mouth via ducts
  • Moistens food
  • Mucin holds food particles together to make
    swallowing easier
  • Amylase begins digesting carbohydrates
  • Bicarbonate maintains the pH between 6.5-7.5
  • Lysozyme inhibits bacterial growth

10
Swallowing Delivers Food to Stomach
  • Swallowing is coordinated with a temporary
    breathing stoppage.
  • Voluntary movement of the tongue and jaws push
    bolus of food into pharynx
  • Involuntary phase swallowing reflex receptors
    in pharynx stimulated by presence of food
  • Soft palate rises
  • Larynx rises slightly
  • Epiglottis closes opening to trachea
  • Tongue pushes food further
  • Food enters esophagus

11
Pharynx and Esophagus
  • Pharynx
  • Common passageway for air and food
  • Participates in swallowing
  • Esophagus muscular tube which connects pharynx
    to stomach
  • Structure mix of skeletal and smooth muscle
  • Mucus-secreting cells assist passage of food
  • Food motility gravity and peristalsis

12
Stomach Function
  • Is a muscular, stretchable sac
  • Functions
  • Stores food until it can be digested
  • Digestion chemical digestion of proteins due to
    acids and enzymes
  • Muscular contractions mix secretions with food
    and mechanically break apart food
  • Regulation of delivery of food into small
    intestine

13
  • Gastric juices
  • The mucosa contains gastric pits (small openings)
    that lead to gastric glands.
  • Glandular cells secrete gastric juices
  • Hydrochloric acid produces a pH of about 2,
  • Intrinsic factor used to help absorb vitamin B12
  • Mucus protects stomach lining from acid
  • Pepsinogen when combined with acid from stomach
    produces pepsin which begins protein breakdown

14
  • Chyme is the name of the watery mixture of
    partially digested food and gastric juices
  • Pyloric sphincter regulates rate of movement of
    chyme into the small intestine

15
Small Intestine
  • Functions
  • Digestion neutralize acid from stomach , add
    digestive enzymes and bile, digest proteins,
    carbohydrates, and lipids to absorbable
    materials, pancreas also adds enzymes (lipase,
    amylase, and protease)
  • Absorption 95 of food absorbed here

16
Small Intestine
  • Structure
  • 3 different sections duodenum, jejunum, ileum
  • Mucosa has folds covered with projections called
    villi and each villi has smaller projections
    called microvilli. At the center of each villus
    are capillaries and a lymph vessel called a
    lacteal.
  • Named small intestine because its diameter is
    smaller than the large intestine (1inch vs 2
    inches)

17
Accessory Organs Aid Digestion and Absorption
  • Pancreas exocrine functions
  • Secretes, into the duodenum, digestive enzymes
    for proteins, carbohydrates and fats and sodium
    bicarbonate
  • Liver
  • Produces bile to break down lipids (fats). Bile
    emulsifies lipids in the small intestine
  • Hepatic portal system drains blood from
    digestive tract directly to liver before going to
    general circulatory system

18
  • Metabolic functions
  • Storage of fat soluble vitamins and of glucose
  • synthesis and chemical processing of nutrients
  • Inactivates many chemicals including alcohol,
    hormones, drugs and poisons
  • Destroys worn out RBC
  • Cirrhosis destruction of liver cells resulting
    in impaired liver function
  • Gallbladder stores and concentrates bile after
    meals, secretes bile into the small intestine via
    the bile duct

19
Large Intestine Structure and Function
  • Most nutrients have been absorbed by the time the
    digestive contents reach the large intestine
    contents are more solid than liquid
  • Functions absorbs nutrients and water and stores
    waste until it can be eliminated
  • Feces contain about 30 bacteria many of these
    can eat the leftover material in the colon some
    produce vitamin K, others produce gas
  • Structure
  • Cecum (first area to receive chyme), appendix
  • Colon ascending, transverse, descending, sigmoid
  • Rectum, anus (internal and external sphincters)

20
Endocrine and Nervous Systems Regulation of
Digestion
  • Regulation dependent on volume and content of
    food
  • Nervous system stretch receptors in stomach
  • Hormones
  • Gastrin stimulates stomach to release gastric
    juice
  • Secretin released by small intestine stimulates
    pancreas to secrete a watery bicarbonate-rich
    pancreatic juice to neutralize chyme and liver
    cells to release bile
  • Cholecystokinin (CCK) intestinal hormone
    released when fatty chyme enters the duodenum
    causes gallbladder to contract

21
Disorders of the Digestive System
  • Inflammatory Bowel DiseaseIBD
  • Crohns Disease
  • Can affect any area of the GI tract, but most
    commonly affects the ileum
  • All layers of intestine may be involved and
    healthy bowel may be found between sections of
    diseased bowel
  • Cause unknown, possibly heredity, autoimmune,
    environment

22
  • Symptoms similar to other intestinal disorders ?
    irritable bowel syndrome and ulcerative colitis
    (inflammation and ulcers only in the submucosa
    layer of the intestine)
  • Abdominal pain, diarrhea, rectal bleeding,
    intestinal ulcers, weight loss, arthritis, skin
    problems, fever, eye inflammation, fatigue
  • Treatment may include medication, nutritional
    supplements, surgery There is no cure
  • Drugs can include anti-inflammatory medications,
    steroids, immune system suppressors, antibiotics
    (if secondary infection present), anti-diarrheal
    and fluid replacement, pain relievers

23
  • Surgery-bowel diversion surgery
  • Diet no special diet has proven effective for
    preventing or treating Crohns
  • Stress no evidence showing that stress causes
    this, but many people say that stress causes
    flare-ups

24
  • Diverticulosis weakness of the intestinal wall
    so that there are small sacs produced when the
    mucosa protrudes through the other layers of the
    intestinal wall diverticula can become infected.
  • Colon polyps non-cancerous growth that projects
    from a mucus membrane
  • Esophageal varices enlargement of veins at lower
    end of esophagus
  • caused by portal hypertension, which can be
    caused by cirrhosis and chronic hepatitis

25
  • Cirrhosis destruction of liver cells resulting
    in impaired liver function
  • Hepatitis inflammation of the liver generally
    viral Hepatitis A, B, and C
  • Hepatitis A is transmitted by contaminated food
    or water causes a brief illness before complete
    recovery
  • Hepatitis B travels in blood or body fluids
    usually passed via contaminated needles, blood
    transfusions or sexual contact.
  • If not treated?liver failure
  • Vaccine available

26
  • Hepatitis C transmitted in infected blood also
    blood banks now test blood so the risk of getting
    this type of hepatitis is decreased.
  • Can remain dormant but still damages liver
  • Gallstones excessive cholesterol in the bile may
    precipitate out of solution forming gallstones.
    If they obstruct bile flow, cause tremendous pain
  • Treatment drugs to try to dissolve them,
    treatments to try to break them, surgery to
    remove gallbladder

27
  • Eating disorders
  • Anorexia nervosa a person diets excessively or
    stops eating completely
  • Can cause death
  • Bulimia binge and purge condition in which the
    person eats and then forces themselves to vomit
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