Digestive System: Overview and Organs

• Nutrients from the environment sustain living organisms, providing raw materials for synthesizing essential compounds (anabolism) and energy for cell function (catabolism).
• The digestive system interacts with the cardiovascular and lymphatic systems to deliver organic molecules like carbohydrates, fats, and proteins.
• The digestive system fuels body cell function and supplies the building blocks for cell growth and repair.
• The digestive system, or alimentary system, consists of a muscular tube known as the digestive tract (gastrointestinal (GI) tract or alimentary canal), and accessory organs
• The digestive tract starts at the oral cavity (mouth), continues through the pharynx (throat), esophagus, stomach, small intestine, large intestine; and ends with the anus.
• Accessory digestive organs include the teeth, tongue, salivary glands, liver, pancreas, and gallbladder (the latter has only a secretory function).

Major Organs of the Digestive Tract

• Oral Cavity (Mouth):
  • Main functions include ingestion, mechanical digestion (with teeth and tongue), moistening, and mixing with salivary secretions.
• Pharynx:
  • Propels materials into the esophagus via muscular contractions.
• Esophagus:
  • Transports materials to the stomach.
• Stomach:
  • Facilitates chemical digestion via acid and enzymes, and mechanical digestion via muscular contractions.
• Small Intestine:
  • Responsible for enzymatic digestion and absorption of water, organic substrates, vitamins, and ions.
• Large Intestine: -Dehydrates and compacts indigestible materials for elimination.

Accessory Organs of the Digestive System

• Teeth:
  • Accomplishes mechanical digestion by chewing (mastication).
• Tongue:
  • Aids mechanical digestion with teeth, performs sensory analysis
• Salivary Glands:
  • Secretes lubricating fluid containing enzymes that break down carbohydrates.
• Liver: -Secretes bile (for lipid digestion), stores nutrients, and performs other vital functions.
• Gallbladder:
  • Stores and concentrates bile.
• Pancreas:
  • Exocrine cells secrete buffers and digestive enzymes with endocrine cells secreting hormones.

Processes of the Digestive System

• Ingestion occurs as food enters the oral cavity, and involves choices and decision making.
• Mechanical Digestion and Propulsion: The crushing/shearing of food + propelling it along GI tract.
• Chemical Digestion: Breakdown of food into small organic/inorganic molecules absorbable by the digestive epithelium,.
• Secretion: The release of water, acids, enzymes, buffers, and salts by the epithelium, glandular organs, and gallbladder; these products are secreted into ducts.
• Absorption involves movement of organic molecules, electrolytes, vitamins, minerals and water across the digestive epithelium and into interstitial fluid for body distribution.
• Defecation: Eliminates waste products from the body; the digestive tract and related organs discharge wastes mixed with indigestible food, which is then dehydrated/compacted into feces and eliminated via the anus.

Oral cavity

• It contains the:
  • Sensory analysis of food
  • Mechanical digestion via teeth, tongue, and palatal surfaces.
  • Lubrication from mixing with mucus and saliva.
  • Limited chemical digestion of carbohydrates and lipids.

Stomach

• Expandable, tube-like organ in the upper left quadrant of the peritoneal cavity.
• The functions are to: -Temporarily store that is ingested from the esophagus. -Mechanically digest food through muscular contractions. -Chemically digest food via acids and enzymes.
• Ingested substances plus stomach gland secretions create a viscous, acidic mixture (chyme).

Pancreas

• Posterior to the stomach and extends laterally from the duodenum toward the spleen.
• Primarily an exocrine organ that produces digestive enzymes and buffers.
• An elongate, pinkish-gray organ that is 15 cm (6 in.) long, weighs about 80 g (3 oz).
• The broad head lies within the duodenal loop with the body extending to the short, blunt tail near the spleen.
• Functionally retroperitoneal and bound to the posterior abdominal wall.
• The surface has a lumpy, lobular texture covered by a thin, transparent connective tissue capsule.
• The anterior capsule and peritoneal layer make pancreatic lobules, blood vessels, and excretory ducts visible.
• It is supplied by the splenic, superior mesenteric, and, common hepatic arteries.
• The large pancreatic duct delivers secretions to the duodenum.
• Endocrine cells of pancreatic islets secrete insulin and glucagon into the bloodstream to control blood sugar
• The pancreas is exocrine (acinar and epithelial cells lining the duct system).
• Exocrine cells secrete pancreatic juice (alkaline mix of digestive enzymes, water, ions) into the small intestine, where acinar cells secrete pancreatic enzymes that primarily work there.
• Pancreatic enzymes break down ingested materials into smaller molecules, enabling absorption.
• Water and ions help dilute & neutralize acid in chyme, secreted by cells lining the pancreatic ducts

Liver

• The largest visceral organ, weighing about 1.5 kg (3.3 lb).
• Primarily in the right hypochondriac and epigastric regions.
• Performs essential metabolic/synthetic functions.
• It is mostly wrapped in a tough fibrous capsule covered by a layer of visceral peritoneum.
• It carries out over 200 functions in three main catagories:
  • Metabolic regulation: The liver is the primary organ involved in regulating circulating blood composition.
  • Hematological regulation: It receives 25% of cardiac output and largest blood reservoir in the body.
  • Bile production: Synthesizes and secretes bile into the duodenal lumen regulated by hormonal/neural mechanisms.
    • Bile is mostly water, and consists of small amounts of ions, bilirubin (from hemoglobin), cholesterol, and bile salts (lipids).

An overview of the digestive system, its interaction with other systems, and its crucial role in providing nutrients for energy and growth. Key components include the digestive tract (oral cavity to anus) and accessory organs (teeth, tongue, liver, pancreas, and gallbladder). The system facilitates the breakdown and absorption of essential organic molecules.