The Digestive System rev 11-11

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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

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• 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

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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.

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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.

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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.

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

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• 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.

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• 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

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• 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

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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

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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

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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

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• 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

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• 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

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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

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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)

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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

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• 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

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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)

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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

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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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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