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.
Twogroups 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, growthfactors, and wasteproducts
Salivary amylase
The most important ingredient in saliva; it initiates the breakdown of carbohydrates.
Bicarbonate and phosphateions in saliva
Functions as chemical buffers, maintaining the saliva at a pH between 6.35 and 6.85.
ImmunoglobulinA
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 25cm (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 buccalphase; 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 convexlateral of the stomach.
Lessercurvature
The concave medial border of the stomach.
Lesseromentum
Holds the stomach in place; extends from the lesser curvature.
Greateromentum
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: ~2.5cm (1 in.). Length: ~3m (10 ft) in a living person, ~6.5m (21 ft) in a cadaver.
Circularfolds or plicaecirculares 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 smallintestine
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 ileocecalsphincter
Largeintestine
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 thebody. It is about 1.5m (5 ft) long and 6.5cm (2.5 in.) in diameter, extends from the ileum to the anus.
Cecum
The first part of the largeintestine; 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.