Esophagus Anatomy and Function Quiz

The Esophagus

• Contains both skeletal and smooth muscle
• Upper Esophageal Sphincter: a ring of skeletal muscle surrounding the esophagus at its upper end
• Lower Esophageal Sphincter: a ring of smooth muscle at the lower end of the esophagus, regulating the flow of food from the esophagus to the stomach

The Stomach

• A J-shaped sac beneath the diaphragm that stores food after it is swallowed and releases it into the small intestine
• Gastric Glands: secrete a watery fluid called gastric juice into the lumen
• Chyme: a mixture in the stomach’s wall that pulverizes food into smaller particles and mixes it with gastric juice
• Divided into three anatomical regions: Fundus, Body, and Antrum
• Fundus: extends above the lower esophageal sphincter; the wall is thin and easily expands to accommodate food
• Body: the middle region which accounts for the bulk of the stomach’s volume
• Antrum: the lower region which is narrow and small in volume; has the thickest muscle layer and produces strong contractions responsible for gastric mixing and emptying
• Gastric glands include:
  • Neck Cells: secrete mucus
  • Chief Cells: secrete pepsinogen, the precursor for a proteolytic enzyme called pepsin
  • Parietal Cells: secrete hydrogen ions to acidify the stomach contents and intrinsic factor, necessary for the absorption of vitamin B12
  • G Cells: secrete the hormone gastrin

The Small Intestine

• A coiled tube about 2–3 cm in diameter and 2.5–3 meters long, responsible for digestion of nutrients in food
• Divided into three regions: Duodenum, Jejunum, and Ileum
• Duodenum: the initial short region that begins at the pylorus and extends about 30cm
• Jejunum: the middle portion that extends about 1m
• Ileum: the last, terminal portion that extends approximately 1.5m and joins the colon

The Colon

• Composed of four regions: Ascending Colon, Transverse Colon, Descending Colon, and Sigmoid Colon
• Ascending Colon: runs upward on the right side of the body from the end of the small intestine toward the diaphragm
• Transverse Colon: runs across the abdominal cavity
• Descending Colon: runs downward on the left side
• Sigmoid Colon: an S-shaped segment that leads to the rectum, acts as a storage depot for whatever remains in the lumen after absorption

The Rectum and Anus

• The colons contracts and pushes feces into the rectum
• Movement through the anus is controlled by two sphincters: Internal Anal Sphincter and External Anal Sphincter
• Relaxation of both sphincters allows fecal material to be eliminated from the body, which is called defecation

The Accessory Glands

• The Salivary Glands: secrete saliva
• Three major salivary glands: Parotid Glands, Sublingual Glands, and Submandibular Glands
• Saliva consists of:
  • Bicarbonate that makes the saliva alkaline and neutralizes acid
  • Mucus that lubricates the food and protects the lining of the mouth from abrasion
  • Salivary amylase, a digestive enzyme that breaks down starch and glycogen
  • Lysozyme, an enzyme that destroys certain bacteria and prevents tooth decay

The Pancreas

• Located beneath the stomach and secretes pancreatic juice
• Exocrine organ and endocrine gland
• Gland secretes hormones important to regulation of metabolism
• Pancreatic juice contains:
  • Bicarbonate
  • Several digestive enzymes, including:
    • Pancreatic amylase, which breaks down starch and glycogen
    • Pancreatic lipases, which break down fats
    • Proteases, which break down proteins
    • Nucleases, which break down nucleic acids

The Liver

• The largest organ in the abdominal cavity
• Functions include:
  • Secretion of bile
  • Metabolic processing of nutrients
  • Removal of aged blood cells from the blood
• Liver secretes bile which contains:
  • Bicarbonate
  • Phospholipids
  • Inorganic ions
  • Bile salts