Chapter 23: The Digestive System Overview

Gastrointestinal Tract

Includes mouth, pharynx, esophagus, stomach, intestines.

Accessory Digestive Organs

Organs aiding digestion: salivary glands, liver, pancreas.

Ingestion

Intake of food into the digestive system.

Mechanical Digestion

Physical breakdown of food into smaller pieces.

Chemical Digestion

Enzymatic breakdown of food into molecules.

Absorption

Nutrients taken into blood or lymph from intestines.

Defecation

Elimination of indigestible substances as feces.

Mucosa

Innermost layer of the gastrointestinal tract.

Submucosa

Layer containing blood vessels and nerve plexus.

Muscularis

Layer responsible for peristalsis and food movement.

Serosa

Outer layer covering abdominal organs.

Peristalsis

Involuntary muscle contractions moving food through GIT.

Salivary Glands

Produce saliva to aid digestion and lubrication.

Parotid Gland

Largest salivary gland, secretes saliva into mouth.

Sublingual Gland

Salivary gland located under the tongue.

Submandibular Gland

Salivary gland located beneath the jaw.

Tongue

Muscular organ aiding in taste and food manipulation.

Palate

Roof of the mouth, separates oral cavity from nasal.

Uvula

Projection from soft palate, aids in swallowing.

Pharynx

Muscular tube connecting mouth to esophagus.

Esophagus

Tube transporting food from pharynx to stomach.

Stomach

Organ for food storage and initial digestion.

Small Intestine

Site for most digestion and nutrient absorption.

Large Intestine

Absorbs water and forms feces from indigestible waste.

Teeth

Mechanical breakdown of food into smaller pieces.

Crown

Top part of the tooth above the gum line.

Root

Part of the tooth embedded in the jawbone.

Neck

Region between the crown and root of a tooth.

Enamel

Hardest substance in the body covering the crown.

Maxillary Teeth

Upper set of teeth in the mouth.

Mandibular Teeth

Lower set of teeth in the mouth.

Deciduous Teeth

Temporary teeth, 20 total in children.

Permanent Teeth

Adult teeth, 32 total in adults.

Incisors

8 teeth adapted for cutting food.

Canines

4 teeth adapted for tearing food.

Premolars

8 teeth adapted for grinding food.

Molars

12 teeth adapted for grinding food.

Saliva

Fluid that lubricates and begins digestion.

Salivary Amylase

Enzyme in saliva that digests carbohydrates.

Lingual Lipase

Enzyme that begins fat digestion in the mouth.

Upper Esophageal Sphincter

Regulates food entry into the esophagus.

Lower Esophageal Sphincter

Regulates food movement into the stomach.

Swallowing Phases

Two phases: voluntary and involuntary.

Bolus

Mass of food swallowed into the esophagus.

Gastroesophageal sphincter

Muscle controlling food entry into the stomach.

Cardia

Upper region of the stomach near the esophagus.

Fundus

Dome-shaped upper region of the stomach.

Body of stomach

Main central region of the stomach.

Pylorus

Canal-like lower part of the stomach.

Rugae

Folds in the stomach lining when empty.

Greater curvature

Left border of the stomach.

Lesser curvature

Right border of the stomach.

Chyme

Semi-liquid mixture of gastric juice and food.

Mucous neck cells

Cells secreting mucus in the stomach lining.

Parietal cells

Cells secreting HCl and intrinsic factor.

Chief cells

Cells secreting pepsinogen and gastric lipase.

G cells

Endocrine cells secreting gastrin hormone.

Acid reflux

Backflow of stomach acid into the esophagus.

Gastric juice

Digestive fluid containing HCl and enzymes.

Intrinsic factor

Essential for vitamin B12 absorption.

Pepsinogen

Inactive enzyme converted to pepsin in stomach.

Gastric lipase

Enzyme that digests fats in the stomach.

Cephalic phase

Initial response to food sight, smell, or taste.

Gastric phase

Hormonal response to food in the stomach.

Intestinal phase

Inhibition of gastric activity by duodenal hormones.

Ileocecal valve

Valve between ileum and cecum.

Bile duct

Duct delivering bile to the duodenum.

Pancreatic duct

Duct delivering pancreatic juice to the duodenum.

Villi

Finger-like projections enhancing absorption surface area.

Microvilli

Epithelial cell extensions increasing absorption capacity.

Lacteals

Lymphatic capillaries absorbing large fat molecules.

Absorptive cells

Cells with microvilli secreting digestive enzymes.

Goblet cells

Secrete mucus for lubrication and protection.

Paneth cells

Immune cells secreting antimicrobial lysozymes.

Enteroendocrine cells

Secrete hormones regulating digestive processes.

Gastric inhibitory peptide (GIP)

Inhibits stomach, stimulates insulin secretion.

Secretin

Stimulates bicarbonate and bile secretion; inhibits stomach.

Cholecystokinin (CCK)

Stimulates pancreatic enzymes and bile release.

Brush border enzymes

Digestive enzymes secreted by absorptive cells.

Enterokinase

Activates trypsinogen into trypsin for protein digestion.

Amylase

Enzyme that digests starch into sugars.

Trypsinogen

Inactive form activated to digest proteins.

Chymotrypsinogen

Inactive form activated to digest proteins.

Carboxypeptidase

Enzyme that digests proteins into amino acids.

Lipase

Enzyme that digests lipids into fatty acids.

Bicarbonate ion

Neutralizes gastric acidity in small intestine.

Monosaccharides

Simple sugars absorbed into blood capillaries.

Fat-soluble vitamins

Vitamins A, D, E, K absorbed with fats.

Cecum

Blind pouch receiving ileum and appendix.

Ascending Colon

Vertical section on right side of abdomen.

Right Colic Flexure

Bend between ascending and transverse colon.

Transverse Colon

Horizontal section connecting right and left colic flexures.

Left Colic Flexure

Bend between transverse and descending colon.

Descending Colon

Vertical section on left side of abdomen.

Sigmoid Colon

S-shaped segment entering the pelvis.

Rectum

Final section of large intestine before anus.

Anal Canal

Passage leading to the anus, guarded by sphincter.

External Anal Sphincter

Skeletal muscle controlling voluntary defecation.

Functions of Large Intestine

Absorbs water and salts, forms feces.

Fermentation

Metabolic process converting sugars into acids or gases.