The document summarizes the structure and function of the human digestive system. It describes the organs that make up the alimentary canal including the mouth, esophagus, stomach, small intestine, large intestine and accessory organs like the liver, pancreas and gallbladder. It provides details on the layers of the digestive tract, how food is broken down and absorbed, and common digestive disorders like GERD, ulcers, IBS and inflammatory bowel diseases.

1. Department of Health & Biomedical Sciences

3.  Ingest food
 Break down food into
nutrient molecules
 Absorb molecules into
bloodstream
 Rid the body of
indigestible remains

4.  Alimentary canal
 Continuous, muscular digestive
tube winding throughout the
body
 Digests and absorbs food
particles
 Comprised of the following:
 Mouth, pharynx, esophagus,
stomach, small and large
intestines
 Accessory Digestive Organs
 Contains the following:
 Teeth, tongue, gallbladder,
salivary glands, liver, and
pancreas

7.  From esophagus to anus, the walls of the
alimentary canal have the same 4 layers
(inner/deep - to - outer/superficial):
1) Mucosa (secretes hormones and mucus, absorbs end
products of digestion, and protects against infection
2) Submucosa (contains lymphoid follicles and elastic tissue)
3) Muscularis externa (segmentation and peristalsis,
contains inner circular layer and outer longitudinal layer,
area where valves are found)
4) Serosa (same as visceral peritoneum, made of areolar
connective tissue)

9.  Mouth processes:
 Ingestion
 Mechanical digestion (e.g. salivary amylase)
 Initiation of Propulsion
 Mastication: chewing
 Pharyngeal processes:
 Deglutition = swallowing
 Voluntary Buccal phase
 Involuntary Pharyngeal-Esophageal Phase
 Esophageal processes:
 Peristalsis (rhythmic contractions, involuntary)

10.  Buccal/oral cavity
 Contains stratified squamous epithelium
 Vestibule: area bounded by lips and cheeks externally and teeth
and gums internally
 Palate: forms roof of the mouth, soft and hard palate, uvula

11.  Assists with:
 grind food into a bolus which contains partially digested food and saliva
 form words and is a sensory organ for taste
 Three surface features:
 Filiform papillae (roughness and grip)
 Fungiform papillae (contains taste buds)
 Circumvallate papillae (contains taste buds)

12.  Main functions:
 Produces and secretes saliva
 Cleanses the mouth
 Dissolves food chemicals so
it can be tasted
 Moistens food, compacting
it into a bolus
 Begins the chemical
breakdown of food
 Salivary amylase: starch
 3 types of salivary glands:
 Parotid Gland, Submandibular Glands, Sublingual Glands
 Saliva secreted travels to oral orifice via ducts from all three glands

13.  Break food into smaller parts,
increasing surface area for
digestion
 Types of Teeth
 Deciduous Teeth (“baby” teeth)
 Permanent Teeth
 Incisors- cutting and shredding
 Canines- piercing and tearing
 Molars- grinding
 Premolars- grinding and crushing

14.  Deglutition = swallowing
 Pharynx (throat)
 Muscular tube from base of skull to C6
 Connects nasal cavity and mouth to larynx
and esophagus
 3 regions: Nasopharynx, Oropharynx and
Laryngopharynx
 contains stratified squamous
epithelium (friction-resistant)

15.  Muscular tube that propels food to stomach; bolus enters stomach
through esophageal hiatus
 Skeletal muscle (upper third) for swallowing and
Smooth muscle (lower third) for peristalsis
 Esophageal glands – produce mucus to lubricate bolus
 Esophageal sphincter – prevents backflow into oral cavity
 Cardiac sphincter- prevents backflow into esophagus

17.  By muscular layers of the digestive tract
 Consist of visceral smooth muscle
 Along digestive tract:
 Has rhythmic cycles of activities (peristalsis)
 Controlled by pacesetter cells

19.  Temporary storage area for food and allows it to mix with
gastric juice to produce chyme
 Regions: cardiac, fundus, body, and pyloric
 Greater and Lesser Curvatures: connected to greater
and lesser omentums
 Rugae folds: longitudinal folds in stomach wall; mucous
b/w folds
 Muscle layers arranged circularly, longitudinally, AND
obliquely (aids in digestion)

21.  Peristaltic waves approach stomach and become stronger near
pyloric region
 Pyloric sphincter allows ~ 3 mL of chyme to pass to duodenum
and the rest to return to stomach for further mixing

22.  Simple columnar epithelium – contains gastric pits that secrete
gastric juices
 Goblet cells – secrete mucus that coats stomach and prevents
it from being digested itself
 Parietal cells – secrete hydrochloric acid (converts pepsinogen
into pepsin) and intrinsic factor (necessary for absorption of
vitamin B12)
 Chief cells – secrete pepsinogen which is converted to pepsin
to aid in protein digestion
 Enteroendocrine cells – release hormones such as:
 Histamine, Serotonin, Gastrin, Endorphins, and Somatostatin

24.  Receives chyme from stomach; performs majority
of digestion and absorption of nutrients
 Regions of the small intestine:
 Duodenum (upper region receiving chyme from stomach
and digestive enzymes from pancreas and bile from liver
and gallbladder)
 Jejunum/Ileum (middle and lower regions where
absorption occurs)
*Plicae circulares (permanent folds in mucosa and
submucosa that slow movement of chyme)

26.  Secretin: released by enteroendocrine cells when acidic
chyme enters SI; causes release of bicarbonate-rich
pancreatic juices
 Somatostatin: slows gastric motility and emptying and
inhibits production of gastric secretions
 Cholecystokinin (CCK): released when fatty, protein-rich
chyme enters SI; causes release of enzyme-rich pancreatic
juices and bile
 Brush border enzymes: process long peptides, nucleic acids,
and sugars into smaller ones

27.  Villi: fingerlike projections that increase the surface area of
the small intestine
 Microvilli: tiny projections on the plasma membranes of
columnar cells that appear fuzzy (i.e. brush border cells)
 Crypts of Lieberkuhn: secrete intestinal juice and special
lysozymes that protect against bacteria
 Peyer’s Patches: aggregated lymphoid tissues containing
lymphocytes

29.  Largest solid, internal organ in the human body
 Functions:
 Filters and processes nutrient-rich blood of
carbohydrates, proteins, and lipids from intestine
 Production and regulation of cholesterol
 Production of bile which emulsifies fats
 Removes drugs and hormones from circulation
 Storage of vitamins and minerals

31.  Liver Lobules: structural unit of liver
 Hepatocytes: liver cells contained within the lobules
 Hepatic portal vein & Hepatic Artery: the circulation of
the liver, they bring blood into the liver where it is
filtered through the liver sinusoidal capillaries
 Kupffer cells: remove debris
 Filtered blood drains into the central vein, then to the
hepatic vein, and eventually to the inferior vena cava
 Bile (produced by hepatocytes) drains into the bile duct
after passing through portal triad. Bile then shipped to
gallbladder for storage

33.  Bile ducts are present at every portal triad
 Bile flows down bile canaliculi (tiny canals)
between adjacent hepatocytes towards bile
duct branches at every portal triad
 Bile enters the bile ducts which drain into the
common hepatic duct
 Bile emulsifies fats, separating them into
smaller parts
 Bilirubin: the chief bile pigment, a waste
product of the heme of hemoglobin formed
during the breakdown of worn-out erythrocytes

34.  Bile exits cystic duct upon
stimulation
 CCK released when acidic,
fatty chyme enters
intestines
 Causes:
 Gallbladder Contraction
 Pancreatic Juice Secretion
 Relaxation of
hepatopancreatic sphincter

35.  Pancreatic Juice secreted by acinar cells
 Islets of Langerhans release insulin and
glucagon (important in glucose metabolism)
 Pancreatic Juice contains:
 Sodium Bicarbonate (buffers HCl in stomach)
 Proteases (break down polypeptides)
 Pancreatic amylase (digests oligosaccarides and
disaccharides into monosaccharides)
 Pancreatic lipases (break down lipids into fatty acids
and glycerol)
 Pancreatic nucleases (break down nucleic acids)

37.  Functions:
 Reabsorption of remaining water and electrolytes
 Production and absorption of Vitamins B and K
 Elimination of feces
 Diameter is only 7 cm but is larger than that of the small intestine
 Regions of the large intestine:
 Ascending, Descending, Transverse, and Sigmoid Colon
 Landmarks and Structures of the large intestine:
 Cecum: sac-like connection between the small and large intestines
 Appendix: small structure containing lymphoid tissue; small
immune function
 Teniae Coli: bands of smooth muscle that create pocket-like sacs
(haustra)
 Splenic and hepatic flexure
 Rectum: storage area; Anus: regulates defecation with two sphincter
muscles; internal and external

39.  Simple columnar epithelium for absorption except in the
anal canal where there is stratified squamous
 No villi, no digestive-secreting cells
 Goblet cells produce mucus for lubrication of feces
 Bacterial flora synthesize vitamin B and most of the vitamin K
needed for blood clotting

43.  Most common outpatient GI
dx in the U.S.
 Reflux of gastric juices
produces mucosal injury
 Most common in >40 years
of age
 Symptoms:
 Heartburn
 Dysphagia
 Sour-tasting regurgitation

44.  A hernia is the protrusion of part
of an organ through a muscular
wall or body opening. A hiatal
hernia is the protrusion of part of
the stomach through the
diaphragm at the point where the
esophagus joins the stomach.
 Symptoms include
 Indigestion and heartburn after eating
and possibly shortness of breath
 Avoidance of irritants such as spicy
foods and caffeine and frequent small
meals may be adequate treatment. If
the person is obese, weight loss is
recommended.
 Surgery may be required to
correct the defect.

45.  Extremely common office
visit/hospitalization in the U.S.
 Most often associated with
Helicobacter pylori or chronic
NSAID use
 May occur at any part of the GI
tract exposed to gastric juices
 Common in 1st part of duodunem
 Classic symptom:
 Epigastric pain occurs 1-3 hours
after meals
 Complications:
 Life-threatening hemorrhage
 Perforation

46.  Ulcerative colitis
 Diffuse mucosal inflammation
limited to the colon
 Symptoms:
 Blood diarrhea
 Colicky pain
 Urgency
 Crohn’s disease
 Patchy inflammation
 May affect any part of the GI tract
 Symptoms:
 Abdominal pain
 Diarrhea
 Weight loss
 Intestinal obstruction
 Increase risk of colorectal cancer
 Common disorder that affects the large intestine. IBS
commonly causes cramping, abdominal pain, bloating, gas,
diarrhea, constipation. Long-term manageable condition

47.  Removing stress
 Avoidance of foods found to aggravate
the disease
 Corticosteroids are sometimes
administered to control autoimmunity
 Surgery may be necessary, occasionally
requiring a colostomy.
 A colostomy is an artificial opening in
the abdominal wall with a segment of
the large intestine attached. Evacuation
of the feces is through this opening. A
colostomy may be temporary or
permanent, depending on the nature of
the colon surgery.