Download Digestive System (Human): Introduction

Digestive System (Human): Introduction
The digestive system comprises organs that break down and digest food, and remove unabsorbed
wastes from the body. Its main feature is the alimentary canal, which measures about 30 ft (9 m) from
mouth to anus and includes the esophagus, stomach, small and large intestines, and rectum. Also
contributing to the digestive process are various accessory digestive organs: the teeth, tongue, salivary
glands, liver, gallbladder, and pancreas.
Mouth cavity Here the teeth, tongue, salivary
glands, and other structures process food for
swallowing.
Esophagus This is the alimentary canal between the
lower pharynx (throat) and the stomach. Swallowed
food is moved through it by rhythmic muscular
contractions known as peristalsis.
Stomach This enlarged section of the alimentary
canal churns, disinfects, and starts digesting food,
producing chyme, a semifluid mixture.
Sphincters These are rings of smooth muscle that
contract to close an orifice. They include the pyloric
sphincter (between the stomach and duodenum) and
two anal sphincters.
Digestive juices Saliva and juices secreted in the
stomach, small intestine, and pancreas contain
enzymes for digesting specific food substances.
Small intestine This convoluted tube, about 21 ft
(6.5 m) long, connects the stomach and the large
intestine. It is subdivided into the duodenum,
jejunum, and ileum. The small intestine is the part of
the alimentary canal where most digestion occurs.
Large intestine Also called the colon, this is a broad
tube about 5 ft (1.5 m) long, extending from the ileum
to the rectum. It is subdivided into the cecum (from
which the appendix projects), and the ascending,
transverse, descending, and sigmoid colons.
Rectum This tube extends from the sigmoid colon
and ends at a narrow orifice, the anus.
Liver The body’s largest solid organ, the liver lies in
the upper right part of the abdomen. Its complex
chemical activities include secreting the emulsifying
substance bile, and storing vitamins and glycogen (a
carbohydrate produced from glucose).
Gallbladder This sac stores bile, releasing it via the
cystic duct and common bile duct into the duodenum.
Pancreas This endocrine gland secretes insulin and
pancreatic juice into the duodenum.
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