Chapter 14 Digestive System

Chapter 14: Digestive System
1. System functions:
a. Ingestion – taking in food
b. Digestion – breaking food down both physically and chemically
c. Absorption – movement of nutrients into the blood system
d. Defecation – getting rid of waste
2. Two groups of organs:
a. Alimentary canal (gastrointestinal or GI tract)– continuous coiled hollow tube
b. Accessory digestive organs- “branches” off of alimentary canal
i. Mouth
ii. Pharynx
iii. Esophagus
iv. Stomach
v. Small intestine
vi. Large intestine
vii. Anus
c. Accessory organs –
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 the anterior roof
iv. Soft palate – form the posterior roof
v. Uvula – fleshy projection of the soft palate
vi. Vestibule – space between lips 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 mastication food with saliva
iii. Tongue
1. Initiates of swallowing by the tongue
2. Allows for the sense of taste
a. Function- protects from poisens
4. Pharynx = throat
a. Anatomy
i. Nasopharynx- not part of the digestive system
ii. Oropharynx- posterior to oral cavity
iii. Laryngopharynx- below the oropharynx and connected to the esophagus
b. Physiology
i. Serves as a passageway for air and food
ii. Food is propelled to the esophagus by two muscle layers
1. Circular outer layer
2. Longitudinal inner layer
3. Food movement is by alternating contractions of the muscle layers (peristalsis)
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
ii. Submucosa
iii. Muscularis externa
iv. Serosa
1. Visceral peritoneum
2. Parietal peritoneum
7. Nervous system control
a. Two divisions of the autonomic nervous system
i. Submucosal nerve plexus
ii. Myenteric nerve plexus
8. Stomach
a. Anatomy
i. Located on the left side of the abdominal cavity
ii. Food enters at the cardioesophageal sphincter
iii. Food empties into the small intestine at the pyloric sphincter (valve)
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 medial surface
b. Lesser curvature- concave medial surface
7. Peritoneum attachment
a. Lesser omentum- attaches the liver to the lesser curvature
b. Greater omentum- attached 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. Temporary storage tank for food (1-3 hours)
ii. Site of water and some chemicals absorbed
iii. Water and some chemical absorption
iv. Mechanical digestion- food mixed and churned
v. Chemical breakdown of protein begins
1. Stomach mucosa
vi. Delivers chime (processed food) to the small intestine
c. Stomach mucosa
i. Mucosa structure: 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
i. Villi (villus) – fingerlike structures formed by the mucosa
1. Capillaries & lacteals – for absorption
ii. Microvilli – tiny projections og the plasma membrane (creat a brush border appearance)
iii. Circular folds (plicae circulars) – deep folds of mucosa and submucosa
10. Large intestine
a. Anatomy
i. Large in diameter but shorter in 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
vi. These bands cause the wall to pucker into haustra (pocket-like sacs)
vii. Two common problems:
1. Diarrhea- food moves through too fast
b. Cecum- saclike first part of the large intestine
c. Appendix- no real function (vestigial)
i. Vestigial
ii. Hangs from the cecum
iii. Fatty tissue
iv. Accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis)
d. Colon
i. Ascending- travels up right side if abdomen
ii. Transverse- travels across the abdominal cavity
iii. Descending- travels down the left side
iv. Sigmoid- enters the pelvis
e. Rectum- enters the pelvis
f. Anus- opening of the large intestine
i. External anal sphincter- skeletal muscle (voluntary control)
ii. Internal anal sphincter- forme
Chapter 14: Digestive System & Nutrition: Part B
1. Accessory organs
a. Teeth
b. Salivary glands
c. Pancreas
d. Liver
e. Gall bladder
2. Teeth classification
a. Incisors- cutting
b. Canines- tearing or piercing
c. Premolars- grinding
d. Molars- grinding
3. Salivary glands – three pair of salivary glands empty secretions into the mouth
a. Parotid glands- largest, near ear
b. Submandibular glands- under jaw
c. Sublingual glands- under tongue
d. Saliva
i. Mixture of mucus and serous fluids
ii. Helps to form a food bolus
iii. Contains salivary amylase to begin starch digestion
iv. Dissolves chemicals so they can be tasted
4. Deglutition (swallowing)
a. Buccal phase
i. voluntary
ii. occurs in the mouth
iii. food is formed into a bolus
iv. the bolus is forced into the pharynx by the tongue
b. Pharyngeal-esophageal phase
i. Involuntary transport of the bolus
ii. All passageways except to the stomach are blocked
1. Tongue blocks off the mouth
2. Soft palate (uvula) blocks the nasopharynx
3. Epiglottis blocks the larynx
iii. Peristalsis moves the bolus towards the stomach
iv. Cardio-esophageal sphincter is opened when food presses against it
5. Pancreas
a. found posterior to the parietal peritoneum
b. extends across the abdomen from spleen to duodenum
c. Produces a wide spectrum of digestive enzymes that break down all categories of food
d. Enxzymes are secreted into the duodenum
e. Alkaline (basic) fluid introduced with enzymes neutralizes acidic chime coming from stomach
f. Hormones produced:
i. Insulin- lower blood sugar, sugar into cells
ii. Glucagon- raises blood sugar, liver, glycogen
6. Liver
a. Largest gland in the body
b. Location on the right side of the body under the diaphragm
c. Consists of four lobes suspended from the diaphragm and abdominal wall
d. Connected to the gallbladder via the common hepatic duct
e. Produces bile
i. Salts
ii. Pigments
iii. Function
7. Gall bladder
a. Sac found in hollow fossa of liver
b. When no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder
c. When digestion of fatty foods is occurring, bile is introduced into the duodenum from the gallbladder
d. Gallstones are crystallized cholesterol which can cause blockages
8. Functions to accomplish digestion
a. Ingestion- getting food into the mouth
b. Propulsion- moving foods from one region of the digestive system to another
c. Peristalsis- alternating waves of contraction and relaxation that squeezes food along the GI tract
d. Segmentation- moving materials back and forth to aid with mixing in the small intestine
e. Food breaks down as mechanical digestion
i. Mixing food in the mouth by the tongue
ii. Churning food in the stomach
iii. Segmentation in the small intestine
iv. Mechanical digestion exposes surface are of food for further breakdown by enzymes
f. Chemical digestion
i. Enzymes break down food molecules into their building blocks
1. Carbohydrates are broken down to simple sugars
2. Proteins are broken to amino acids
3. Fats are broken to fatty acids and alcohols
g. Absorption
i. End products of digestion are absorbed in the blood or lymph capillaries (thin walls)
h. Defecation
i. Elimination of indigestible substances from the GI tract in the form of feces
ii. Also: bacteria, bile pigments
9. Nutrition
a. Nutrients (food)- substance used by the body for growth, maintenance and repair
i. Major nutrients
1. Carbohydrates- sugars, starches (energy)
a. Most derived from plants
b. Exceptions: lactose from milk and small amounts of glycogens from meats
2. Lipids- fats, oils, waxes (energy and structure)
a. Saturated fats from animal products
b. Unsaturated fats from nuts, seeds, and vegetable oils
c. Cholesterol from egg yolk, meats, and milk products
3. Proteins- energy, structure, enzymes
a. Complete proteins- contain all essential amino acids
i. Most are from animal products
b. Legumes and beans also have proteins but are incomplete
4. Water- no energy, body solvent
ii. Minor nutrients
1. Vitamins- coenzymes, metabolism
2. Minerals- inorganic, assist physiology, anatomy
b. USDA food guide pyramid