Chapter 25: The Digestive System

Merged flashcards from Chapter 25, McGraw Hill Anatomy and Physiology Tenth Edition, by Kenneth S. Saladin.

Digestive system

Organ system that processes food, extracts nutrients, and eliminates residue

Broken into ingestion, digestion, absorption, compaction, and defecation

Ingestion

The selective intake of food

Digestion

The mechanical and chemical breakdown of food into a form usable by the body

Absorption

The uptake of nutrients into the digestive tract to the blood and lymph

Compaction

The absorption of water and consolidation of indigestible residue into feces

Defecation

The elimination of feces

Mechanical digestion

The physical breakdown of food into smaller particles; done by the cutting of the teeth, churning of the stomach, and enzymatic action

Chemical digestion

The use of hydrolysis reactions by digestive enzymes to break down food; enzymes are created in salivary glands, stomach, pancreas, and small intestine

Digestive tract (alimentary canal)

The pathway from the mouth to the intestines

Digestive tract pathway

1. Mouth

2. Pharynx

3. Esophagus

4. Stomach

5. Small intestine

6. Large intestine

Gastrointestinal tract (GI tract)

The stomach and intestines

Accessory organs

Organs that aid in digestion, like the teeth, tongue, salivary glands, liver, gallbladder, and pancreas

Digestive tract layers

1. Mucosa (for movement)

2. Submucosa

3. Musclaris externa (muscles)

4. Serosa (bindings)

Mucosa (mucous membrane)

The mucous lining of the digestive tract that aids movement and has mucosa-associated lymphatic tissue for immune responses

Mucosa-associated lymphatic tissue (MALT)

Lymphatic tissue on the mucosa to defend against pathogens in food

Submucosa

The thick layer of loose connective tissue below the mucosa; contains blood vessels, lymphatic vessels, nerve plexus, mucus-secreting glands, and some MALT

Muscularis externa

The layers of muscle in the digestive system that propel and push food and residue through the tract

Serosa

Layer of tissue that has some blood vessels and adventitia (binding fibrous connective tissue)

Adventitia

Binding fibrous connective tissue between the digestive tract and other organs

Enteric plexus

The nervous network within the digestive system that regulates digestive tract motion, secretion, and blood flow — mainly autonomic action

Submucosal plexus

Nerve system part of the enteric plexus within the submucosa; controls mucous and motility

Myenteric plexus

Nerve system part of the enteric plexus within the muscularis externa; controls contractions

Mesentery

The connective tissue sheet that suspends the stomach and intestines from the abdominal wall to allow contractions and freedom of movement; has posterior and anterior sections

Lesser omentum

Ventral mesentery that extends from the lesser curvature of the stomach to the liver

Greater omentum

Mesentery that hangs from the greater curvature of the stomach and covers the small intestine

Short reflexes (myenteric reflexes)

Stretch reflexes in the digestive tract for swallowing

Long reflexes (vagovagal reflexes)

Reflexes part of the parasympathetic stimulation for digestive motility and secretion

Gastrin and secretin

Two hormones secreted into the blood that stimulate distant parts of the digestive tract

Oral cavity (buccal cavity)

The mouth

• functions in ingestion, taste, digestion, swallowing, speech, and respiration

• keratinized in areas subject to food abrasion, like the gums and hard palate

Cheeks and lips

Functions in food retention and oral control, speech, and sucking and blowing actions — closes exposure to outside

Frenulum

A type of tissue that attaches to the parts of the mouth; have superior and inferior labial (lip) types as well as one for the tongue (lingual)

Tongue

A muscular, bulky, but agile and sensitive organ that functions in taste, texture, and speech with non-keratinized squamous epithelium

Lingual papillae

Bumps and projections that are the sites of most taste buds

Body (of the tongue)

The anterior \frac{2}{3} of the tongue that occupies the oral cavity

Root (of the tongue)

The posterior \frac{1}{3} of the tongue that occupies the oropharynx

Lingual tonsils

Tonsils contained in the root of the tongue; inflammation causes pain swallowing

Palate

Section of the mouth that separates the oral cavity from the nasal cavity, allowing breathing while chewing

Hard palate (bony palate)

Anterior portion of the palate supported by the maxillae and palatine bones

Soft palate

Posterior portion of the palate with a more spongy texture; features the skeletal muscle and glandular tissue as well as the uvula

Uvula

Projection visible at the rear of the mouth that helps food retention until ready to swallow

Dentitions

The teeth; they chew food into smaller pieces and expose more surface area for digestive enzyme action — 16 in the maxilla, 16 in the mandible for adults

Alveolus

The tooth socket in the bone where teeth are embedded

Periodontal ligament

Ligament whose collagen fibers penetrate into the bone on one side and into the tooth on the other for firm but slightly loose movement for chewing

Gingiva (gum)

Tissue that covers the alveolar bone for tooth embedding; teeth defined by gingiva portions of crown, root, and neck

Crown

The portion of the tooth above the gum

Root

The portion of the tooth below the gum in the alveolar bone

Neck

Point where the crown, root, and gum meet

Dentin

The hard yellowish tissue that makes up most of the tooth

Enamel

Noncellular secretion that cannot regenerate and covers the crown and neck of the tooth

Cement

Covers the root of the tooth

Root canal

The space in the root of the tooth leading to the pulp cavity in the crown; contains nerves and blood vessels

Eruption

The movement of teeth out of the gums as the develop; seen twice with infants and later permanent tooth replacement

Deciduous teeth

Early teeth that erupt from 6 to 30 months

Permanent teeth

Teeth that replace deciduous teeth between the ages of 6 and 25

Third molars (wisdom teeth)

Teeth that may erupt from 17 to 25 years, if at all — may be impacted or crowded so they cannot erupt

Plaque

A sticky residue on teeth made of bacteria and sugars due to the high count of microorganisms in the mouth — can dissolve enamel and dentin to form cavities

Root canal therapy

Treatment for cavities to remove the tooth to prevent further bacterial invasion

Mastication (chewing)

Process that breaks food down into smaller pieces to be swallowed and exposes more surface to digestive enzymes — starts with teeth and saliva

Saliva

Functions to moisten the mouth, begin some digestion, cleanse the teeth, inhibit bacterial growth, and dissolves food to stimulate taste buds

Salivary glands

Glands that secrete saliva at a constant rate

Pharynx

Muscular funnel that connects the oral cavity to the esophagus and nasal cavity to the larynx

Esophagus

The straight muscular tube 25 to 30 cm long between the pharynx and stomach to move food with some mucus

Lower esophageal sphincter (LES)

Sphincter at the inferior end of the esophagus to prevent stomach acid regurgitation that can damage the esophageal mucosa

Heartburn

Burning sensation produced by acid reflux into the esophagus

Deglutition (swallowing)

A complex action involving over 22 muscles in the mouth, pharynx, and esophagus to move food

Swallowing center

A pair of nuclei in the medulla oblongata that controls swallowing

Swallowing phases

1. Oral phase (voluntary to collect food)

2. Pharyngeal phase (involuntary to prevent choking)

3. Esophageal phase (involuntary to move food down)

Oral phase

Voluntary swallowing phase; collects food with tongue to push it posteriorly as it accumulates

Pharyngeal phase

Involuntary swallowing phase; prevents food and drink from entering the mouth or nasal cavity and breathing is suspended as the airway is closed

Esophageal phase

Involuntary swallowing phase with involuntary contractions (peristalsis) to move food through esophagus regardless of gravitational orientation

Peristalsis

Involuntary contractions that move food down the esophagus; is controlled by the swallowing center and leads the lower esophageal sphincter to relax

Stomach

A J-shaped, muscular sac in the upper left abdominal cavity that functions as a food storage organ for mechanical and chemical digestion

Chyme

The acidic, soupy mixture of semidigested food that passes on to the small intestine

Cardiac part

A small area within about 3 cm of the cardiac orifice; connects esophagus to stomach

Fundic region (fundus)

Dome superior to the esophageal attachment

Body

The greatest part of the stomach distal to the cardiac orifice

Pylorus

The narrow passage from the stomach to the duodenum

Pyloric sphincter

A ring of smooth muscle around the pylorus that regulates the passage of chyme into the duodenum

Greater curvature

40 cm curvature from which the greater omentum hangs

Lesser curvature

10 cm curvature from which the lesser omentum hangs

Gastric rugae

Longitudinal wrinkles that allow for expansion when full and contraction when empty

Gastric pits

Depressions in the gastric mucosa with two or three tubular glands at the bottom; secretes substances

Mucous cells

Cells that secrete mucus in the cardiac and pyloric glands (called mucous neck cells in gastric glands due to their position)

Regenerative cells (stem cells)

Cells found in the base of the gastric pit and neck of the glands; divides rapidly and produces a continual supply of new cells for replenishment

Parietal cells

Cells found mostly in the upper half of the glands; secretes hydrochloric acid, intrinsic factor, and a hunger hormone called ghrelin

Chief cells

The most numerous cell type in the stomach; secretes gastric lipase and pepsinogen in the gastric glands to dissolve lipids and proteins

Enteroendocrine cells

Cells concentrated in the lower end of the glands that secrete hormones and messengers to regulate digestion

Gastric juice

The 2 to 3 liters of juice produced by the gastric glands per day; mainly a mixture of water, hydrochloric acid, and pepsin

Hydrochloric acid (HCl)

Acid that breaks up connective tissues and plant cell walls for liquification and chyme formation; also destroys pathogens

Pepsinogen

Enzyme that is secreted by chief cells to digest proteins

Gastric lipase

Enzyme that digests about 10 to 15% of dietary fats in the stomach (the rest is digested in the small intestine)

Intrinsic factor

Helps absorb vitamin B₁₂ in the small intestine to later synthesize hemoglobin — secretion of this is the only indispensable function of the stomach

Swallowing center

Part of the medulla oblongata that signals the stomach to relax during swallowing; controls chyme flow to 3 mL for digestion and neutralization

4 to 6 hours

The typical time needed for the stomach to empty after a meal (higher fat contents extend time)

Vomiting

The forceful ejection of stomach and intestinal contents (chyme) from the mouth; can be caused by overstretching the stomach, alcohol or other irritants, trauma, or pain or sensory stimuli

Retching

Spasms of the chest and abdomen that dilate the esophagus before vomiting, often accompanied by tachycardia, salivation, and sweating, with chyme sometimes moving into the esophagus

Projectile vomiting

Sudden vomiting with no prior nausea or retching; common in feeding infants

Bulimia

An eating disorder with sometimes chronic, intentional vomiting; hydrochloric acid in vomit can cause tooth enamel erosion and respiratory tract destruction

Digestion

The chemical and mechanical breakdown of food; partially done by salivary and gastric enzymes but primarily done in the small intestine

Absorption

Obtaining nutrients or substances from food; not done by the stomach (except for some drugs like aspirin) and can be affected by capacity (as is with alcohol being more intoxicating with food)