Overview of the Digestive Organs - Intro

6 key functions of the digestive system:

• Ingestion of foods and liquids
• Digestion (chemical and mechanical) of foods and liquids
• Propulsion of materials through the body
• Secretion of digestive enzymes and hormones
• Absorption of nutrients and water from foods and liquids
• Elimination of wastes (aka feces)

Anatomical & Functional Divisions

• Gastrointestinal tract (aka, GI tract, alimentary canal, gut)
• Accessory organs

GI tract:

Oral cavity (aka, mouth)

• Initiates digestion of foods and liquids
• Is bound anteriorly by the lips, opens posteriorly to the oropharynx.

Pharynx

• Open to the nasal cavity, the oral cavity, and the larynx because the pharynx is a common passageway for both the digestive and respiratory systems.

Esophagus

• Muscular tube that transports foods and liquids to the stomach.

Stomach

• J-shaped pouch
• Where foods and liquids are stored and also converted to a thick, soup-like substance called chyme

Physiology of Swallowing & Gastric Filling

Small intestine

• Long tube that coils upon itself
• it's the primary site of nutrient absorption
• Its length increases contact with absorptive tissues, which optimizes nutrient absorption.
• Small intestine subdivisions:
  — Duodenum, which is relatively short, and receives chyme from the stomach.
  — Jejunum, which is the longer middle segment.
  — Ileum, which is the terminal segment of the small intestine.

Large intestine

• Primary site of water absorption.
• Large intestine subdivisions:
  — Ascending colon, which ascends the right side of the abdomen.
  — Transverse colon, which passes along the transverse plane of the body.
  — Descending colon, which descends the left side of the abdomen.
  — The sigmoid colon, which is the S-shaped (aka, sigmoid) portion of the colon within the pelvis.
  — Cecum, which is a small, pouch-like structure.
  — Vermiform appendix extends from the cecum; this wormlike (aka, "vermiform") structure houses lymphoid tissue.
  — Rectum is the distal-most portion of the large intestine and receives the sigmoid colon.

Anus

• Terminal end of the GI tract – where wastes exit.

Sphincters

• Muscular rings that regulate the movement of materials through the GI tract.

Accessory organs:

• Teeth, which mash the food
• Tongue, which shapes food into a "bolus"
• Salivary glands, which produce saliva
  — Parotid, the largest, lies in the cheek
  — Sublingual lies under the tongue ("lingual" refers to the tongue)
  — Submandibular lies below the mandible
• Liver produces the bile
• Gallbladder stores and secretes bile
• Pancreas produces enzyme-rich pancreatic juice.
• Ducts connect the liver, gallbladder, and pancreas to the duodenum, which receives bile and pancreatic juices to the duodenum.

Clinical Correlations:

• Gastric reflux occurs when stomach acids move "backwards" through the inferior esophageal sphincter, which manifests symptomatically as "heart burn" (aka, pyrosis).
• The vermiform appendix is susceptible to infection, known as appendicitis, which can spread if it ruptures, an extremely worrisome complication.
• Endoscopy, we examine the upper GI tract (the mouth to the proximal small intestine) – the tube is inserted into the mouth
• Colonoscopy, we examine the lower GI tract (the distal small intestine to the rectum) – the tube is inserted into the anus.