Chapter 14, Digestive System, Part A

Chapter 14: Digestive System
1. System functions:
a. Ingestion – taking in food
b. Digestion – breaking down food both physically and chemically
c. Absorption – movement of nutrients into the bloodstream
d. Defecation – rids the body of indigestible waste
2. Two groups of organs:
a. Alimentary canal – (gastrointestinal or GI tract): continuous coiled hollow tube
i. Mouth
ii. Pharynx (throat)
iii. Esophagus (long tube)
iv. Stomach
v. Small intestine (small in width)
vi. Large intestine (large in diameter)
vii. Anus
b. Accessory organs – branches off of alimentary canal
i. Salivary glands
ii. Pancreas
iii. Liver
iv. Gall bladder
3. Mouth – oral cavity
a. Anatomy
i. Lips (labia) – protect the anterior opening
ii. Cheeks – form the lateral walls
iii. Hard palate – forms anterior roof
iv. Soft palate – forms posterior roof
v. Uvula – fleshy projection of the soft palate
vi. Vestibule – space between lips and externally and teeth and gums internally
vii. Oral cavity proper – area contained by the teeth
viii. Tongue – attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth
ix. Tonsils – bacteria filters
1. Palatine – on palate
2. Lingual – base of tongue
b. Physiology
i. Mastication – (chewing) of food
ii. Mixing masticated food with liquid
iii. Tongue
1. Initiation of swallowing by the tongue
2. Allows for the sense of taste- function?
4. Pharynx = throat
a. Where food is propelled to
b. Anatomy
i. Nasopharynx – not part of the digestive system
ii. Oropharynx – posterior to oral cavity
iii. Laryngopharynx- below the oropharynx and connected to esophagus
c. Physiology
i. Mixed passageway: serves as a passageway for air and food
ii. Food movement is propelled to the esophagus by two muscle layers
1. Circular layer (outer layer)
2. Longitudinal inner layer
3. Peristalsis: food movement is by alternating contractions of the muscle layers
5. Esophagus
a. Anatomy
i. Length
ii. Runs from
b. Physiology
i. Peristalsis
ii. Food only
6. Common structure of alimentary canal organs
a. Four layers
i. Mucosa (innermost layer)
- Moist membrane consisting of
1. Surface epithelium- for absorption or secretion
2. Small amounts of connective tissue
3. Small smooth muscle layer
ii. Submucosa
- Just beneath the mucosa
- Soft connective tissue with blood vessels, nerve endings, glands, and lymphatics
iii. Muscularis externa- smooth muscle
- Inner circular layer
- Outer longitudinal layer
iv. Serosa- outermost layer of the wall contains fluid-producing cells:
1. Visceral peritoneum- outermost layer that is continuous with the innermost layer
2. Parietal peritoneum- innermost layer that lines the abdominopelvic cavity
7. Nervous system control
a. Two divisions of the autonomic nervous system serves the alimentary canal (autonomic nervous system)
- Function is to regulate mobility and secretory activity of the GI tract organs in coordinated way
i. Submucosal nerve plexus
ii. Myenteric nerve plexus
8. Stomach
a. Anatomy
i. Located on the left side of the abdominal cavity
ii. Cardioesophageal sphincter (where food enters)
iii. Pyloric sphincter (where food empties into the small intestine)
iv. Regions
1. Cardiac – near the heart
2. Fundus – expanded portion lateral to the cardiac region
3. Body - midportion
4. Pylorus – funnel-shaped terminal end
5. Rugae – internal folds of the mucosa
6. External
a. Greater curvature – convex lateral surface
b. Lesser curvature – concave medial surface
7. Peritoneum attachment: layers of peritoneum attached to the stomach:
a. Lesser omentum – attaches the liver to the lesser curvature
b. Greater omentum – attaches the greater curvature to the posterior body wall:
i. Contains fat to insulate, cushion, and protect abdominal organs
ii. Has lymph nodules containing macrophages
b. Physiology
i. Food & water storage
1. Temporary storage tank for food (1-3 hours)
ii. Site of Water and some chemical absorption
iii. Mechanical digestion – food mixed and churned
iv. Chemical digestion – breakdown of protein begins
1. Stomach mucosa
v. Delivers Chyme (processed food) to the small intestine
c. Stomach mucosa
i. Mucosa structure: is simple columnar epithelium
ii. Mucous neck cells – produce a sticky alkaline mucus
iii. Gastric glands – situated in gastric pits and secrete gastric juice
1. Chief cells – produce protein-digesting enzymes (pepsinogen  pepsin)
2. Parietal cells – produce hydrochloric acid
3. Enteroendocrine cells – produce (hormone) gastrin
9. Small intestine
a. Overview
i. Body’s main organ for
ii. Site of
iii. Muscular tube
iv. Suspended from posterior abdominal wall
b. Subdivisions
i. Duodenum
ii. Jejunum
iii. Ileum
c. Chemical digestion – enzymes from:
i. Intestinal glands
ii. Pancreas
iii. Liver/gall bladder
d. Surface area increase mainly for absorption
e. Three structural modifications that increase surface area:
i. Villi (villus) – fingerlike structures formed by the mucosa
1. Capillaries & lacteals – for absorption (absorb food)
ii. Microvilli – tiny projections of the plasma membrane (create a brush borer appearance
iii. Plicae circulares (circular folds) – deep folds of mucosa and submucosa
10. Large intestine
a. Anatomy
i. Large = in diameter, but shorter min length, than the small intestine
ii. Frames the internal abdomen
iii. No villi present – absorb water through walls
iv. Goblet cells produce alkaline mucus which lubricates the passage of feces
v. Muscularis externa = teniae coli (three bands of muscle)
1. These bands cause the wall to pucker into haustra (pocket-like sacs)
vi. Two common problems
1. Diarrhea – food moves through too fast
2. Constipation – food moves through too slowly
b. Cecum – saclike first part of the large intestine
c. Appendix – no real function (vestigial):
i. Hangs from the cecum
ii. Accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis)
iii. Vestigial
iv. Location
v. Fatty tissue
d. Colon
i. Ascending – travels up the right side of the abdomen
ii. Transverse – travels across the abdominal cavity
iii. Descending – travels down the left side
iv. Sigmoid – enters the pelvis
e. Rectum – where feces is stored
f. Anus – opening of the large intestine:
i. External anal sphincter – skeletal muscle (voluntary control)
ii. Internal anal sphincter – formed by smooth muscle (involuntary)
iii. These sphincters are normally closed except during defecation