Digestive
System
Objectives
• List in sequence each of the component
parts of the GI tract.
• Identify accessory organs of digestion.
• List and compare the layers of the
alimentary canal.
• Discuss the basics of protein, fat, and
carbohydrate digestion.
Objectives
• Define and contrast mechanical and
chemical digestion.
• Define digestive related term.
• Discuss pathology related to the digestive
system.
• Define medical and surgical treatment of
digestive diseases or disorders.
Functions
• Intake and digestion of food.
• Absorption of nutrients from digested
food to be metabolized.
• Elimination of solid waste products.
Digestive System
• Long, hollow, irregular tube open at both
ends.
• Called the alimentary canal or
gastrointestinal (GI) tract.
– Upper GI Tract
– Lower GI Tract
• Consists of primary and accessory organs
to digest, absorb, and eliminate food
products.
Walls of Digestive Tract
• Digestive tube consists of four layers
surrounding a lumen.
•
•
•
•
Mucosa or Mucous membrane
Submucosa
Muscularis
Serosa
Mucosa
• Innermost layer of the digestive system.
• Structure varies in different areas:
– Esophagus
• Tough stratified abrasion-resistant
epithelium.
– Other digestive structures
• Layer of simple columnar
epithelium.
• Secretes mucus.
Submucosa
• Connective tissue beneath the mucosa.
• Contains nerve and blood vessels.
Muscularis
• Smooth muscle tissue.
• Permits rhythmic wavelike contractions
called peristalsis.
• Assists in moving and mixing of food.
• Provides mechanical breakdown of larger
food particles.
Serosa
• Outermost covering
• Known as the visceral peritoneum in the
abdominal cavity.
• Anchored to the abdominal wall by tissue
shaped like a giant pleated fan called
mesentery.
Walls of Digestive Tract
Mouth
• Hollow chamber where the process
of digestion begins.
• Structures:
– Hard palate
• Bony anterior portion
– Soft palate
• Soft muscular posterior
portion
– Uvula
Mouth
• Structures:
– Tongue
• Papillae
–Taste buds – salty, sour, sweet,
bitter.
• Frenulum
–Thin membrane attaching the
tongue to the floor of the mouth.
Pathology of the Mouth
• Herpes labialis
– Known as cold sores or fever blisters.
– Caused by Herpes Simplex Virus I.
– Reactivated periodically.
• Thrush – fungal infection
• Cleft lip/Cleft palate
– Fissure of the upper lip, hard and/or
soft palate.
– Difficulties with speech and eating
Teeth
• 32 mature teeth assist with mastication or
chewing of food and forming a “bolus” to
be swallowed.
• Four types:
– Incisors
– Canines
– Premolars
– Molars
Teeth
• Incisors
– Cutting edge
• Canine (Cuspids)
– Pierce or tear
• Premolars (Bicuspids)/Molars
(Tricuspids)
– 2-3 cusps for grinding or crushing.
Teeth
• Crown
– Exposed visible portion of a tooth.
– Covered by enamel.
• Neck
– Narrow portion of the tooth
surrounded by gingiva or gum tissue.
Teeth
• Root
– Holds the tooth securely into a socket
in the upper or lower jaw.
– Protected by cementum.
– Socket is lined with periodontal
membrane.
• Dentin
– Comprises the bulk of the tooth.
Teeth
Pathology of the Teeth
• Dental caries (Cavity)
– Infectious disease of the enamel/dentin.
• Periodontitis
– Inflammation of the tissues that
surround the teeth.
• Gingivitis
– Inflammation of the gums.
– Trench mouth
Salivary Glands
• Accessory organ to digestion.
• Three pairs:
– Parotids
• Largest
– Submandibulars
– Sublinguals
• Produces enzyme salivary amylase
which begins chemical digestion.
Pharynx (Throat)
• Tube like passageway for food and air.
• Functions as part of the respiratory and
digestive systems.
• Epiglottis directs food and air and closes
over the trachea when swallowing.
Esophagus
• 10 inch muscular lined
tube connecting the
pharynx with the
stomach.
• Ring like muscle controls
the flow of food into the
stomach called the
Cardiac sphincter
Gastroesophageal Reflux
Disease (GERD)
• Upward flow of stomach acid into the
esophagus.
– Often caused by a hiatal hernia.
• Protrusion of stomach thru the
cardiac sphincter.
– Causes a burning sensation. “Heartburn”
– Treated with antacid medication or surgery.
Stomach
• Expandable pouch like organ in the
upper abdominal cavity.
– Lies under the diaphragm.
• Contraction of the stomach mixes the
food with gastric juices creating chyme.
– Mechanical process
Stomach
• Three divisions:
– Fundus
• Enlarged portion to the left
of the esophageal opening.
– Body
• Central portion
– Pylorus
• Lower narrow portion
joining the small intestine.
• Pyloric sphincter
Pathology of the Stomach
• Gastritis/Gastroenteritis
– Inflammation of the stomach or
intestinal lining often caused by
Helicobacter Pylori.
– May cause ulcers
• Perforating, gastric, duodenal.
Eating Disorders
• Anorexia nervosa
– False perception of body appearance.
– Fear of gaining weight.
– Compulsive dieting and excessive exercising.
• Bulimia nervosa
– False perception of body appearance.
– Frequent episodes of binge eating followed by
induced vomiting and misuse of laxatives or
diuretics.
Small Intestine
• Hollow, tube approx 20 foot long
digestive organ responsible for
absorption of food and water.
• 3 subdivisions
– Duodenum
– Jejunum
– Ileum
Small Intestine
• Inner lining is arranged in multiple circular
folds called plicae.
• Folds are covered with tiny fingers called villi.
• Villi are covered with brush like structures
called microvilli.
– All of these structures help to increase
surface area for greater absorption of
nutrients. (Page 401)
Small Intestine
• Duodenum
– First portion of the small intestine.
– Responsible for most of the chemical
digestion.
• Receives digestive enzymes from the
pancreas and liver.
– Frequent area of ulcers
Small Intestine
• Jejunum
– Middle portion of the small intestine.
– Extends from the duodenum to the
ileum.
– Secretes large amounts of digestive
enzymes.
• Peptidase, Sucrase, Lactase,
Maltase.
Small Intestine
• Ileum
– Last and longest portion of the small
intestine.
– Extends from the jejunum to the
cecum of the large intestine.
• Ileocecal sphincter (Valve)
Liver and Gallbladder
• Accessory organs of digestion.
• Located in the right upper quadrant of
the abdominal cavity.
• Liver stores glycogen and produces bile
needed for fat emulsification.
– Mechanical breakdown of fats.
• Bile is stored in the gall bladder until
needed.
Liver and Gallbladder
• Biliary tree
– Bile travels from the liver via the
hepatic duct.
– Stored bile travels from the gall
bladder via the cystic duct.
– These two ducts meet to form the
common bile duct, then joining the
pancreatic duct and emptying into the
duodenum.
Liver and Gallbladder
Pathology of the Liver
• Blockage of bile by a gallstone in the
hepatic duct may result in a condition
called Jaundice.
– Excessive amounts of bile (bilirubin)
absorbed by the blood.
– Causes a yellow discoloration of the
skin and eyes.
Pathology of the Liver
• Hepatitis
– Inflammation of the liver caused by a
virus.
– A, B, C, D, E
• Cirrhosis
– Progressive disease of the liver where
scar tissue replaces normal tissue.
– Blood flow is decreased causing body
shutdown.
Pathology of the Liver
Pathology of the Gallbladder
• Cholecystitis
– Inflammation of the gall bladder
usually associated with gallstones
blocking the flow of bile.
• Cholelithiasis
– Presence of gallstones or calculi.
Pathology of the Gallbladder
Pancreas
• Accessory organ of digestion.
• Secretes most important digestive juice.
– Pancreatic juice
– Contains enzymes to digest proteins,
fats, and carbs.
– Contains sodium bicarbonate to
neutralize the hydrochloric acid of the
stomach.
Large Intestine
• Larger diameter hollow tube approx 5
feet in length.
• Responsible for excretion of undigested
or unabsorbed waste products.
• Water and salts are reabsorbed from
chyme changing it into a semisolid called
feces.
Large Intestine
• Normal passage takes approx 3-5 days.
– Faster = diarrhea
– Slower = constipation
• Bacteria present in the large intestine:
– Break down of remaining food products.
– Production of some B-complex vitamins.
– Synthesis of vitamin K
Large Intestine
• Major divisions:
– Cecum
• Veriform Appendix
– Colon
• Ascending
• Transverse
• Descending
• Sigmoid
– Rectum
– Anus
Large Intestine
• Cecum
– Pouch like beginning of colon.
– Located on the right side.
– Veriform appendix hangs from the
lower portion.
• Lymphatic tissue that may become
inflamed.
–Appendicitis
Large Intestine
• Colon
– Ascending colon (Right side)
– Hepatic flexure
– Transverse colon (across)
– Splenic flexure
– Descending colon (Left side)
– Sigmoid
• S shaped segment terminating at the
rectum.
Large Intestine
• Rectum
– Last division of the large intestine.
• Anal canal/Anus
– Terminal end of the rectum.
– Flow of waste is controlled by two anal
sphincters.
• Inner – smooth muscle/involuntary
• Outer – striated muscle/voluntary
Large Intestine
Pathology of the Intestines
• Enteritis
– Inflammation of the small bowel
caused by pathogens.
– Dysentery, cholera, salmonella,
typhoid.
• Irritable Bowel Syndrome (IBS)
– Intermittent cramping, pain,
bloating, constipation or diarrhea.
– Aggravated by stress.
Pathology of the Intestines
• Ulcerative colitis
– Chronic unknown condition causing
repeated episodes of ulcers and
inflammation to the colon.
• Crohn’s Disease
– Autoimmune disorder of the ileum and
colon.
– Causes scarring and thickening of the
walls of the intestines.
Pathology of the Intestines
• Intestinal blockage
– Partial or complete blocking of the
large or small bowel.
– Adhesions
– Volulus
– Inguinal hernia
• Strangulated
Pathology of the Rectum
• Hemorrhoids
– Painful dilated veins near the anal
opening.
– May become inflamed or bleed.
Peritoneum
• Large, moist, slippery sheet of serous
membrane that lines and covers the
abdominal wall and organs.
– Parietal peritoneum
– Visceral peritoneum
**Organs outside of the peritoneum are
said to be Retroperitoneal.
Peritoneal Extensions
• Mesentery
– Anchors the intestines to the abdominal wall.
– Shaped like a giant pleated fan.
• Greater Omentum
– Pouch like extension of visceral peritoneum
protects and cushions the organs.
– Fatty deposits give lacy appearance. (Lace
Apron)
Peritoneal Extensions
Digestion
• Complex process consisting of physical and
chemical changes that prepare food for
absorption.
• Mechanical Digestion
– Breaks food into tiny particles, mixes them
with digestive juices, moves them along the
GI tract, and eliminates them.
• Mastication, deglutition, peristalsis,
defecation.
Digestion
• Chemical Digestion
– Breaking down large nonabsorbable
food molecules into absorbable ones.
– Chemical reactions by enzymes.
• Saliva, gastric, pancreatic, and
intestinal juices.
Enzymes
• Amylase
– Digests carbohydrates
– Monosaccharides end products
• Protease
– Digests proteins
– Amino acids end products
• Lipase
– Digests fats
– Fatty acid and glycerol end products
Metabolism
• All the processes involved with the use of
nutrients.
• Anabolism
– Building up of substances from
nutrients.
• Catabolism
– Breaking down of substances from
nutrients for energy.
Medical Specialties
• Dentist
– DDS or DMD specializes in the diseases
or disorders of the teeth and tissues of
the oral cavity.
– Periodontist
• Orthodontist
– Dental specialist who prevents or
corrects malocclusion of the teeth.
Medical Specialties
• Gastroenterologist
– Specializes in diseases and disorders of
the stomach and intestines.
• Proctologist
– Specializes in disorders of the colon,
rectum, and anus.
Diagnostic Procedures
• Abdominal X-rays/CT/Ultrasound
– Upper and lower GI series
– Uses barium as a contrast media
• Endoscopy
– Colonoscopy
– Sigmoidoscopy
– Esophagogastroduodenoscopy
Medications
• Acid blockers
– Taken before eating to block signals to
the stomach to produce acid.
• Antacids
– Relieves indigestion and neutralizes
acid.
• Emetic
– Produces vomiting – syrup of ipecac
– Antiemetic
• Laxatives
Surgery of the Oral Cavity
• Maxillofacial surgery
– Specialized surgery of the face and jaw
to correct deformities, diseases, and
repair injuries.
• Palatoplasty
– Surgical repair of cleft palate.
Surgery of the Oral Cavity
Surgery of the Oral Cavity
Surgery of the Stomach
• Gastrectomy
– Surgical removal of all or part of the
stomach.
• Gastric bypass (Stapling)
– Surgical procedure to reduce the size of
the stomach.
– Used to treat morbid obesity
Surgery of the Stomach
Surgery of the Intestines
• Colectomy
– Surgical removal of all or part of the
colon.
• Ileectomy
– Surgical removal of the ileum.
• Gastroduodenostomy
– Removal of the pylorus and anastomosis
of the stomach and duodenum.
Surgery of the Intestines
Surgery of the Intestines
• Gastrostomy
– Creation of an artificial opening into the
stomach for placement of permanent
feeding tube.
• Colostomy
– Creation of an artificial opening between
the colon and the body surface.
– Fecal matter flows into a disposable bag.
Surgery of the Intestines
Surgery of the
Rectum and Anus
• Hemorrhoidectomy
– Surgical removal of hemorrhoids
– Surgical banding
• Proctopexy
– Surgical fixation of a prolapsed rectum.
Surgery of the
Rectum and Anus
Surgery of the Liver
• Liver Transplant
– Option for patients whose liver has failed.
– Because liver tissue regenerates, a partial
transplant may be indicated.
– Blood typing must match.
Surgery of the Gallbladder
• Laparoscopic Cholecystectomy
– Surgical removal of the gallbladder using
a laparoscope through small abdominal
incisions.
Any Questions?