BIO 308 Digestive System

Digestive System

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

Gastroenterology

The study of the digestive tract and the diagnosis and treatment of its disorders.

Mechanical Digestion

The physical breakdown of food into smaller particles.

Mastication

Cutting and grinding action of the teeth.

Chemical Digestion

A series of hydrolysis reactions that breaks dietary macromolecules into their monomers.

Digestive Enzymes

Produced by salivary glands, the stomach, pancreas, and small intestine to aid digestion.

Usable Nutrients

Some nutrients are present in a usable form in ingested food and can be directly absorbed.

Digestive Tract

Alimentary canal that is a 30 ft long muscular tube extending from the mouth to the anus.

Gastrointestinal (GI) Tract

Consists of the stomach and intestines.

Accessory Organs

Teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

Ingestion

Taking food into the mouth.

Deglutition

Swallowing.

Peristalsis

One-way movement through the alimentary tract.

Segmentation

Churning/mixing (not peristalsis).

Exocrine Secretion

Digestive enzymes, acid, and mucus.

Endocrine Secretion

Hormones to regulate digestion.

Absorption

Passing broken-down food into the blood or lymph.

Temporary Storage

Temporary storage and elimination of undigested food.

Defecated Food Residue

Was never in the body; material that cannot be digested never actually 'enters' the body.

Churning Action

Action of the stomach and small intestines that exposes more food surface to digestive enzymes.

Vitamins, Amino Acids, Minerals, Cholesterol, and Water

Nutrients that can be absorbed in their existing form.

Immune barrier

Epithelium of the small intestine are lined with tight junctions that prevents swallowed pathogens from entering the body.

Enteric Nervous System

Nervous network in the esophagus, stomach, and intestines.

Enteric plexus

Regulates digestive tract motility, secretion, and blood flow.

Enteric Nervous System Neurons

Thought to have over 100 million neurons.

Enteric Nervous System Functionality

Can function independently of the CNS.

CNS Influence

CNS usually exerts influence on its action.

Enteric Nervous System Composition

Composed of two networks of neurons.

Submucosal plexus

Controls glandular secretions of the mucosa and movements of the muscularis mucosae.

Myenteric plexus

Parasympathetic ganglia and nerve fibers between the two layers of the muscularis externa.

The Mouth

The mouth is known as the oral, or buccal cavity.

Functions of the Mouth

Ingestion, taste and other sensory responses to food, chewing and chemical digestion, swallowing, speech and respiration.

Cheeks and Lips

Functions include retaining food and pushing it between the teeth, essential for speech.

Labial frenulum

Median fold that attaches each lip to the gum between the anterior incisors.

The Tongue

Muscular, bulky, but remarkably agile and sensitive organ.

Lingual papillae

Bumps and projections that are the sites of most taste buds.

Intrinsic muscles of the tongue

Contained entirely within the tongue.

Extrinsic muscles of the tongue

With attachments outside in the tongue.

The Palate

Separates the oral cavity from the nasal cavity.

Hard palate

Anterior portion that is supported by the maxillae and the palatine bones.

Soft palate

Posterior to the hard palate with more spongy texture.

Uvula

Helps retain food in the mouth until one is ready to swallow.

Dentition

32 adult teeth.

Alveolus

Tooth socket in the bone; gomphosis joint.

Periodontal ligament

Modified periosteum whose collagen fibers penetrate into the bone on one side and into the tooth on the other.

Dentin

Hard yellowish tissue that makes up most of the tooth.

Enamel

Covers the crown and neck; a noncellular secretion that cannot regenerate.

Cementum

Covers the root; living tissue that can regenerate.

Root canal

Space in a root leading to the pulp cavity in the crown.

Tooth and Gum Disease

The human mouth is home to more than 700 species of microorganisms, especially bacteria.

Plaque

Sticky residue on the teeth made up of bacteria and sugars.

Calculus

Calcified plaque.

Saliva

Moistens the mouth, begins starch and fat digestion, cleanses the teeth.

Salivary amylase

Enzyme that begins starch digestion in the mouth.

Pharynx

Muscular funnel connecting the oral cavity to the esophagus and the nasal cavity to the larynx.

Esophagus

Straight muscular tube about 25-30 cm long.

Lower esophageal sphincter

Prevents stomach contents from regurgitating into the esophagus.

Swallowing

Complex action involving over 22 muscles in the mouth, pharynx, and esophagus.

Stomach Functions

Stores food, churns food to mix with gastric secretions, begins protein digestion.

Mucous neck cells

Secrete mucus, lines the internal surface of the stomach and the gastric pits.

Parietal cells

Secretes HCl and intrinsic factor.

Chief cells

Secretes pepsinogen.

G-cell

Secretes gastrin into the blood.

Functions of HCl

Activates enzymes, breaks up connective tissues, helps liquefy food and form chyme.

Nonspecific disease resistance

Contributes to nonspecific disease resistance by destroying most ingested pathogens

Pepsin

An enzyme that begins the digestion of proteins in the stomach

Digestion in the stomach

Salivary and gastric enzymes partially digest protein and some starch and fat

Stomach absorption

The stomach does not absorb any significant amount of nutrients but does absorb aspirin and some lipid-soluble drugs

Alcohol absorption

Alcohol is absorbed mainly by the small intestine, so its intoxicating effect depends partly on how rapidly the stomach is emptied

Stomach defenses

Defenses that help prevent acid from eating the stomach lining include an adherent layer of mucus with bicarbonate, tight junctions between epithelial cells, and rapid epithelial mitosis

Peptic ulcers

Erosions of the mucosa of the stomach or duodenum, often caused by acid-resistant bacteria

Helicobacter pylori

Bacterium that reduces mucosal barriers to acid, spicy food, and stress, leading to ulcers

Treatment for ulcers

Combines K+/H+ pump inhibitors (Prilosec) and antibiotics

Gastric ulcers

The mucosal lining of the stomach is damaged by acidic gastric juices

Liver

Reddish brown gland located immediately inferior to the diaphragm; the body's largest gland

Functions of the liver

Secretes bile, detoxifies harmful agents, and processes absorbed nutrients

Hepatocytes

Liver cells that absorb nutrients after a meal and release glucose between meals

Bile canaliculi

Narrow channels into which the liver secretes bile

Gallbladder

Pearl-shaped sac on the underside of the liver that stores and concentrates bile

Bile

Yellow-green fluid containing minerals, cholesterol, neutral fats, phospholipids, bile pigments, and bile acids

Functions of bile

Neutralizes acidic chyme, emulsifies lipids, and eliminates bilirubin

Gallstones

Hard masses in the gallbladder or bile ducts that may form if bile becomes excessively concentrated with wastes

Cholelithiasis

Presence of gallstones, most common in obese women over 40

Lithotripsy

Use of ultrasonic vibration to pulverize stones without surgery

Pancreas

Spongy retroperitoneal gland that is both an endocrine and exocrine gland

Pancreatic juice

Secreted by the exocrine portion of the pancreas, about 1,200 to 1,500 mL per day

Small intestine

The longest part of the digestive tract where nearly all chemical digestion and nutrient absorption occurs

Duodenum

First 25 cm of the small intestine where stomach contents, pancreatic juice, and bile are received

Jejunum

First 40% of the small intestine beyond the duodenum, where most digestion and nutrient absorption occurs

Ileum

Last 60% of the postduodenal small intestine, ending at the ileocecal junction

Small intestine structure

Mucosa and submucosa are folded into plicae circulares, with further folds into villi and microvilli to increase surface area

Intestinal contractions

Serve to mix chyme with intestinal juice, bile, and pancreatic juice, and to bring it in contact with the mucosa

Starch

Most digestible dietary carbohydrate, ultimately digested to the disaccharide maltose.

Maltose

Disaccharide that is finally digested to glucose, which is absorbed by the small intestine.

Lipases

Fat-digesting enzymes involved in lipid digestion.

Lingual lipase

Enzyme secreted by the intrinsic salivary glands of the tongue.

Gastric lipase

Enzyme secreted in the stomach that works with lingual lipase.

Chylomicrons

Triglycerides coated with phospholipids and protein, formed within intestinal cells.

Fat hydrolysis

Process of breaking down fats into free fatty acids and monoglycerides.

Fat-soluble vitamins

Vitamins A, D, E, and K that are absorbed with other lipids.