Ch.14: The Digestive System and Body Metabolism Flashcards
What is ingestion?
Taking in food
What is digestion?
Breaking food into nutrient molecules
What is absorption?
Movement of nutrients into the bloodstream
What is defecation?
Excretes to rid the body of indigestible waste
What are the two main groups of organs in the digestive system?
Alimentary canal (gastrointestinal, or G I, tract)—continuous, coiled, hollow tube
• These organs ingest, digest, absorb, defecate
Accessory digestive organs
• Include teeth, tongue, and several large digestive organs
• Assist digestion in various ways
What are the organs of the alimentary canal?
- Mouth
- Pharynx
- Esophagus
- Stomach
- Small intestine
- Large intestine
- Anus
- The alimentary canal is a continuous, coiled, hollow tube that runs through the ventral cavity from stomach to anus
What is the anatomy of the mouth?
• Mouth (oral cavity)—mucous membrane–lined cavity
• Lips (labia)—protect the anterior opening
• Cheeks—form the lateral walls
• Hard palate—forms the anterior roof
• Soft palate—forms the posterior roof
• Uvula—fleshy projection of the soft palate
• Vestibule—space between lips externally and teeth and gums internally
• Oral cavity proper—area contained by the teeth
• Tongue—attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth
• Tonsils
*Palatine—located at posterior end of oral cavity
*Lingual—located at the base of the tongue
What are the functions of the mouth?
- Mastication (chewing) of food
- Tongue mixes masticated food with saliva
- Tongue initiates swallowing
- Taste buds on the tongue allow for taste
Concept Link 1
Recall that papillae containing taste buds, or taste receptors, are found on the tongue surface (see Chapter 8, p. 300). So, besides its food-manipulating function, the tongue allows us to enjoy and appreciate the food we eat.
The _____ serves as a passageway for foods, fluids, and air.
Pharynx
Food passes from the mouth posteriorly into the:
- Oropharynx—posterior to oral cavity
* Laryngopharynx—below the oropharynx and continuous with the esophagus
Food is propelled to the esophagus by what two skeletal muscle layers in the pharynx?
- Longitudinal outer layer
- Circular inner layer
- Alternating contractions of the muscle layers (peristalsis) propel the food
What is the anatomy of the esophagus?
- About 10 inches long
* Runs from pharynx to stomach through the diaphragm
What is the physiology of the esophagus?
- Conducts food by peristalsis (slow rhythmic squeezing) to the stomach
- Passageway for food only (respiratory system branches off after the pharynx)
What are the four layers from innermost to outermost, from esophagus to the large intestine? (Alimentary canal)
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
What is the mucosa? (Alimentary canal)
Innermost, moist membrane consisting of:
• Surface epithelium that is mostly simple columnar epithelium (except for esophagus—stratified squamous epithelium)
• Small amount of connective tissue (lamina propria)
• Scanty smooth muscle layer
Lines the cavity (known as the lumen)
What is the submucosa? (Alimentary canal)
- Just beneath the mucosa
* Soft connective tissue with blood vessels, nerve endings, mucosa-associated lymphoid tissue, and lymphatic vessels
What is the muscularis externa? (Alimentary canal)
- Smooth muscle
- Inner circular layer
- Outer longitudinal layer
What is the serosa? (Alimentary canal)
- Outermost layer of the wall; contains fluid-producing cells
- Visceral peritoneum—innermost layer that is continuous with the outermost layer
- Parietal peritoneum—outermost layer that lines the abdominopelvic cavity by way of the mesentery
Alimentary canal wall contains what two intrinsic nerve plexuses that are part of the autonomic nervous system?
- Submucosal nerve plexus
* Myenteric nerve plexus
Alimentary canal nerve plexuses regulate _____ and _____ activity of the GI tract organs
- Mobility
* Secretory
What is the stomach and where does food enter from and where does food empty into?
- C-shaped organ located on the left side of the abdominal cavity
- Food enters at the cardioesophageal sphincter from the esophagus
- Food empties into the small intestine at the pyloric sphincter (valve)
Concept Link 2
Recall that valves control the flow of fluids, including blood flow in veins and through the heart (see Chapter 11, pp. 361–363). The valves of the digestive system (formed by sphincter muscles) control the flow of food and digestive juices through the GI tract.
What are the regions of the stomach?
• Cardial (cardia)—near the heart and surrounds the cardioesophageal sphincter
• Fundus—expanded portion lateral to the cardiac region
• Body—midportion
*Greater curvature is the convex lateral surface
*Lesser curvature is the concave medial surface
• Pylorus—funnel-shaped terminal end
The stomach can stretch and hold __ L (__ gallon) of food when full
- 4
* 1
What is the rugae?
Internal folds of the mucosa present when the stomach is empty
What is the lesser omentum?
- Double layer of the peritoneum
* Extends from liver to the lesser curvature of stomach
What is the greater omentum?
- Another extension of the peritoneum
- Covers the abdominal organs
- Fat insulates, cushions, and protects abdominal organs
What is the structure of the stomach mucosa?
• Simple columnar epithelium composed almost entirely of mucous cells
• Mucous cells produce bicarbonate-rich alkaline mucus
• Dotted by gastric pits leading to gastric glands that secrete gastric juice, including:
*Intrinsic factor, which is needed for vitamin B12 absorption in the small intestine
• Chief cells—produce protein-digesting enzymes (pepsinogens)
• Parietal cells—produce hydrochloric acid that activates enzymes
• Mucous neck cells—produce thin acidic mucus (different from the mucus produced by mucous cells of the mucosa)
• Enteroendocrine cells—produce local hormones such as gastrin
What are the functions of the stomach?
- Temporary storage tank for food
- Site of food breakdown
- Chemical breakdown of protein begins
- Delivers chyme (processed food) to the small intestine
What is the small intestine and what is its function and structure?
- The body’s major digestive organ
- Longest portion of the alimentary tube (2–4 meters, or 7–13 feet, in a living person)
- Site of nutrient absorption into the blood
- Muscular tube extending from the pyloric sphincter to the ileocecal valve
- Suspended from the posterior abdominal wall by the mesentery
What are the subdivisions of the small intestine?
- Duodenum
- Jejunum
- Ileum
How does chemical digestion begin in the small intestine?
- Enzymes produced by intestinal cells and pancreas are carried to the duodenum by pancreatic ducts
- Bile, formed by the liver, enters the duodenum via the bile duct
- Hepatopancreatic ampulla is the location where the main pancreatic duct and bile ducts join
What are structural modifications in the small intestine?
• Increase surface area for food absorption
• Decrease in number toward the end of the small intestine
1. Villi—fingerlike projections formed by the mucosa
*House a capillary bed and lacteal
2. Microvilli—tiny projections of the plasma membrane (brush border enzymes)
3. Circular folds (plicae circulares)—deep folds of mucosa and submucosa
What are Peyer’s patches and where are they located?
- Collections of lymphatic tissue
- Located in submucosa
- Increase in number toward the end of the small intestine
- More are needed there because remaining food residue contains much bacteria
What is the large intestine?
- Larger in diameter, but shorter in length at 1.5 meters, than the small intestine
- Extends from the ileocecal valve to the anus
What are the subdivisions of the large intestine?
- Cecum
- Appendix
- Colon
- Rectum
- Anal canal
What is the cecum?
Saclike first part of the large intestine
What is the appendix?
- Hangs from the cecum
* Accumulation of lymphoid tissue that sometimes becomes inflamed (appendicitis)
What is the colon?
- Ascending—travels up right side of abdomen and makes a turn at the right colic (hepatic) flexure
- Transverse—travels across the abdominal cavity and turns at the left colic (splenic) flexure
- Descending—travels down the left side
- Sigmoid—S-shaped region; enters the pelvis
Sigmoid colon, rectum, and anal canal are located in the:
Pelvis
What is the anus?
- Opening of the large intestine
- External anal sphincter—formed by skeletal muscle and is voluntary
- Internal anal sphincter—formed by smooth muscle and is involuntary
- These sphincters are normally closed except during defecation
The large intestine delivers _____ to the _____.
- Indigestible food residues
* Body’s exterior
Goblet cells produce _____ to lubricate the passage of feces.
Alkaline mucus
Muscularis externa layer is reduced to three bands of muscle, called:
Teniae coli
The bands of teniae coli cause the wall to pucker into:
Haustra (pocketlike sacs)
What are the accessory digestive organs?
- Teeth
- Salivary glands
- Pancreas
- Liver
- Gallbladder
Humans have what two sets of teeth during a lifetime?
Deciduous (baby or milk) teeth
• A baby has 20 teeth by age 2
• First teeth to appear are the lower central incisors
Permanent teeth
• Replace deciduous teeth between ages 6 and 12
• A full set is 32 teeth (with the wisdom teeth)
Teeth are classified according to _____ and _____.
- Shape
- Function
- Incisors—cutting
- Canines (eyeteeth)—tearing or piercing
- Premolars (bicuspids)—grinding
- Molars—grinding
What are the two major regions of a tooth?
- Crown
* Root
What is the crown of a tooth?
- Exposed part of tooth above the gingiva (gum)
- Enamel—covers the crown
- Dentin—found deep to the enamel and forms the bulk of the tooth, surrounds the pulp cavity
- Pulp cavity—contains connective tissue, blood vessels, and nerve fibers (pulp)
- Root canal—where the pulp cavity extends into the root
What is the root of a tooth?
- Cement—covers outer surface and attaches the tooth to the periodontal membrane (ligament)
- Periodontal membrane holds tooth in place in the bony jaw
- Note: The neck is a connector between the crown and root
- Region in contact with the gum
What are the three pairs of salivary glands that empty secretions into the mouth?
1. Parotid glands • Found anterior to the ears • Mumps affect these salivary glands 2. Submandibular glands 3. Sublingual glands • Both submandibular and sublingual glands empty saliva into the floor of the mouth through small ducts
What is saliva?
• Mixture of mucus and serous fluids
• Helps to moisten and bind food together into a mass called a bolus
• Contains:
*Salivary amylase—begins starch digestion
*Lysozymes and antibodies—inhibit bacteria
• Dissolves chemicals so they can be tasted
What is the pancreas?
• Soft, pink triangular gland
• Found posterior to the parietal peritoneum
*Mostly retroperitoneal
• Extends across the abdomen from spleen to duodenum
• Produces a wide spectrum of digestive enzymes that break down all categories of food
• Secretes enzymes into the duodenum
• Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from stomach
• Hormones produced by the pancreas
*Insulin
*Glucagon
What is the liver?
- Largest gland in the body
- Located on the right side of the body under the diaphragm
- Consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament
The digestive role of the liver is to produce:
• Bile
• Bile leaves the liver through the common hepatic duct and enters duodenum through the bile duct
• Bile is yellow-green, watery solution containing:
*Bile salts and bile pigments (mostly bilirubin from the breakdown of hemoglobin)
*Cholesterol, phospholipids, and electrolytes
• Bile emulsifies (breaks down) fats
What is the gallbladder?
Green sac found in a shallow fossa in the inferior surface of the liver
• When no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder
• While in the gallbladder, bile is concentrated by the removal of water
• When fatty food enters the duodenum, the gallbladder spurts out stored bile
What are the two gastrointestinal processes and controls?
- Digestion
* Absorption
What are essential processes of the GI tract?
- Ingestion
- Propulsion
• Peristalsis
• Segmentation - Food breakdown: mechanical breakdown
- Food breakdown: digestion
- Absorption
- Defecation
What is propulsion?
- Swallowing and peristalsis
* Movement of foods from one region of the digestive system to another
What is peristalsis?
Alternating waves of contraction and relaxation that squeeze food along the GI tract
What is segmentation?
Movement of materials back and forth to foster mixing in the small intestine
What are examples of mechanical breakdown?
- Mixing of food in the mouth by the tongue
- Churning of food in the stomach
- Segmentation in the small intestine
- Mechanical digestion prepares food for further degradation by enzymes
Digestion occurs when _____ chemically break down large molecules into their building blocks.
Enzymes
Each major food group uses different:
- Enzymes
- Carbohydrates are broken down to monosaccharides (simple sugars)
- Proteins are broken down to amino acids
- Fats are broken down to fatty acids and glycerol