DIGESTIVE SYSTEM

• Digestive system


  Breaks down food into forms that can be absorbed and used by body cells. Allows for absorption of water, vitamins, and minerals. Eliminates wastes from the body. Digestion is the process of breaking down food into molecules.
• Gastroenterology


  A medical specialty that deals with the structure, function, diagnosis, and treatment of diseases of the stomach and intestine.
• Proctology


  A medical specialty concerned with the treatment and diagnosis of the rectum and anus.
• Two groups of organs that compose the digestive system


  • Gastrointestinal (GI) tract or alimentary canal
  • Accessory digestive organs
• Gastrointestinal (GI) tract or alimentary canal


  Composed of the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Length: ~ 5 – 7 meters or 16.5 – 23 ft in a living person, ~ 7 – 9 meters or 23 – 29.5 ft in a cadaver.
• Accessory digestive organs


  Include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
• Functions of the digestive system

  • Ingestion – taking of food into the mouth
  • Secretion – the release of water, acid, buffers, and enzymes into the lumen of the GI tract
  • Mixing and propulsion - churning and propulsion of food through the GI tract
  • Digestion – the mechanical and chemical breakdown of food
  • Absorption – passage of digested products from the GI tract into the blood and lymph
  • Defecation – the elimination of feces from the GI tract
• Salivary glands


  Glands that release a secretion called saliva into the oral cavity. Lubricates, dissolves, and begins the chemical breakdown of food.
• Major salivary glands


  • Submandibular glands
  • Sublingual glands
  • Parotid glands
• Submandibular glands


  Located in the floor of the mouth, secrete saliva into the mouth through the submandibular ducts. Contains salivary amylase and mucus-secreting cells.
• Sublingual glands


  Lie below the tongue, use the lesser sublingual ducts to secrete saliva into the oral cavity. Contains mucous cells.
• Parotid glands


  Lie between the skin and the masseter muscle, near the ears; secrete saliva into the mouth through the parotid duct, which is located near the second upper molar tooth. Contains salivary amylase.
• Composition of saliva


  • 95.5 % water
  • 4.5 % a complex mixture of ions, glycoproteins, enzymes, growth factors, and waste products
• Salivary amylase


  The most important ingredient in saliva; it initiates the breakdown of carbohydrates.
• Bicarbonate and phosphate ions in saliva


  Functions as chemical buffers, maintaining the saliva at a pH between 6.35 and 6.85.
• Immunoglobulin A

  Prevents microbes from penetrating the epithelium.
• Lysozyme

  The component of saliva that makes it antimicrobial.
• Mumps


  The enlargement and inflammation of the parotid glands, causing a characteristic swelling between the ears and the jaw. Symptoms include fever and throat pain, which can be severe when swallowing acidic substances such as orange juice.
• Pharynx


  The pharynx (throat), is a funnel-shaped tube that extends from the internal nares to the esophagus posteriorly and to the larynx anteriorly. It is composed of skeletal muscle and lined by mucous membrane, and is divided into three parts: the nasopharynx, the oropharynx, and the laryngopharynx.
• Nasopharynx


  Functions only in breathing and speech.
• Oropharynx and laryngopharynx


  Used for both breathing and digestion. Swallowed food passes from the mouth into the oropharynx and laryngopharynx; the muscular contractions of these areas help propel food into the esophagus and then into the stomach.
• Esophagus


  A collapsible muscular tube, about 25 cm (10 in.) long that lies posterior to the trachea. It begins at the inferior end of the laryngopharynx and passes through the mediastinum anterior to the vertebral column. Then it pierces the diaphragm through an opening called the esophageal hiatus, and ends in the superior portion of the stomach. It secretes mucus and transports food into the stomach. It does not produce digestive enzymes, and it does not carry on absorption.
• Deglutition or swallowing


  A mechanism that moves food from the mouth into the stomach.
• Phases of deglutition


  • Voluntary phase – also known as the oral or buccal phase; in this phase, chewing has been completed and swallowing is set in motion
  • Pharyngeal phase – stimulation of receptors in the oropharynx sends impulses to the deglutition center in the medulla oblongata
  • Esophageal phase – marked by the entry of food in the esophagus; initiation of peristalsis
• Hiatal hernia


  A condition where part of the stomach protrudes above the diaphragm through the esophageal hiatus.
• Stomach


  Links the esophagus to the first part of the small intestine (the duodenum). The empty stomach is only about the size of your fist, but can stretch to hold as much as 4 liters of food and fluid, or more than 75 times its empty volume, and then return to its resting size when empty. It holds food and parses only small amounts into the small intestine at a time as it serves as only temporary holding chamber for the food ingested.
• Regions of the stomach

  • Cardia (or cardiac region) - the point where the esophagus connects to the stomach and through which food passes into the stomach
  • Fundus – a dome shaped structure located inferior to the diaphragm, above and to the left of the cardia
  • Body – the main part of the stomach located below the fundus
  • Pylorus – funnel-shaped structure that connects the stomach to the duodenum
• Parts of the pylorus

  • Pyloric antrum – the wider end of the funnel connecting the pylorus to the body of the stomach
  • Pyloric canal – the narrower end of the pylorus which connects to the duodenum
  • Pyloric sphincter – located at the latter point of connection and controls stomach emptying
• Greater curvature


  The convex lateral of the stomach.
• Lesser curvature


  The concave medial border of the stomach.
• Lesser omentum


  Holds the stomach in place; extends from the lesser curvature.
• Greater omentum


  Runs from the greater curvature and to the posterior abdominal wall.
• Small intestine


  The primary digestive organ in the body. The site where most of the digestion and absorption of nutrients occur. The longest part of the alimentary canal. Begins at the pyloric sphincter of the stomach. Diameter: ~2.5 cm (1 in.). Length: ~3 m (10 ft) in a living person, ~6.5 m (21 ft) in a cadaver.
• Circular folds or plicae circulares in the small intestine


  The folds of the mucosa and submucosa; enhances absorption by increasing surface area and causing the chyme to spiral, rather than move in a straight line.
• Functions of the small intestine

  • Segmentations mix chyme with digestive juices and bring food into contact with the mucosa for absorption; peristalsis propels chyme through the small intestine
  • Completes the digestion of carbohydrates, proteins, and lipids; begins and completes the digestion of nucleic acids
  • Absorbs about 90% of nutrients and water that pass through the digestive system
• Regions of the small intestine


  • Duodenum - the shortest region and is retroperitoneal, starts at the pyloric sphincter and extends about 25 cm (10 in.) until it merges with the jejunum
  • Jejunum - is about 1 m (3 ft) long and extends to the ileum
  • Ileum - the final and longest region of the small intestine, measures about 2 m (6 ft) and joins the large intestine at a smooth muscle sphincter called the ileocecal sphincter
• Large intestine


  The terminal portion of the GI tract. The overall functions are the completion of absorption, the production of certain vitamins, the formation of feces, and the expulsion of feces from the body. It is about 1.5 m (5 ft) long and 6.5 cm (2.5 in.) in diameter, extends from the ileum to the anus.
• Cecum


  The first part of the large intestine; a small pouch about 6 cm (2.4 in.) long, hanging inferior to the ileocecal valve.
• Vermiform appendix


  A twisted, coiled tube attached to the cecum; ~8 cm (3 in.) in length.
• Mesoappendix


  The mesentery of the appendix.