Download Organs of the Digestive System

Chapter14-Digestive System
The Digestive System Functions
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Ingestion—taking in food
Digestion—breaking food into nutrient molecules
Absorption—movement of nutrients into the bloodstream
Defecation—elimination of indigestible waste
Organs of the Digestive System
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Two main groups of organs
o Alimentary canal (gastrointestinal or GI tract)—continuous, coiled,
hollow tube
 These organs ingest, digest, absorb, defecate
o Accessory digestive organs
 Includes teeth, tongue, and other large digestive organs
Organs of the Alimentary Canal
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The alimentary canal is a continuous, coiled, hollow tube that runs through
the ventral cavity from stomach to anus:
o Mouth
o Pharynx
o Esophagus
o Stomach
o Small intestine
o Large intestine
o Anus
Mouth (Oral Cavity)
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Anatomy of the mouth
o The mouth (oral cavity)—mucous membrane–lined cavity
o Lips (labia)—protect the anterior opening
o Cheeks—form the lateral walls
o Hard palate—forms the anterior roof
o Soft palate—forms the posterior roof
o Uvula—fleshy projection of the soft palate
Mouth (Oral Cavity)
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Anatomy of the mouth (continued)
o Vestibule—space between lips externally and teeth and gums
internally
o Oral cavity proper—area contained by the teeth
o Tongue—attached at hyoid bone and styloid processes of the skull,
and by the lingual frenulum to the floor of the mouth
Mouth (Oral Cavity)
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Anatomy of the mouth (continued)
o Tonsils
 Palatine—located at posterior end of oral cavity
 Lingual—located at the base of the tongue
Mouth
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Functions of the mouth
o Mastication (chewing) of food
o Tongue mixes masticated food with saliva
o Tongue initiates swallowing
o Taste buds on the tongue allow for taste
Pharynx
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Food passes from the mouth posteriorly into the:
o Oropharynx—posterior to oral cavity
o Laryngopharynx—below the oropharynx and continuous with the
esophagus
The pharynx serves as a passageway for food, fluids, and air
Esophagus (Gullet)
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Anatomy
o About 10 inches long
o Runs from pharynx to stomach through the diaphragm
Physiology
o Conducts food by peristalsis (slow rhythmic squeezing) to the stomach
o Passageway for food only (respiratory system branches off after the
pharynx)
Stomach
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The stomach is a C-shaped organ located on the left side of the abdominal
cavity
Food enters at the cardioesophageal sphincter from the esophagus
Food empties into the small intestine at the pyloric sphincter (valve)
Stomach
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Regions of the stomach
o Cardial part (cardia)—near the heart
o Fundus—expanded portion lateral to the cardiac region
o Body—midportion
o Pylorus—funnel-shaped terminal end
Stomach
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Stomach can stretch and hold 4 L (1 gallon) of food when full
o Rugae—internal folds of the mucosa present when the stomach is
empty
External regions
o Lesser curvature—concave medial surface
o Greater curvature—convex lateral surface
Stomach
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Functions of the stomach
o Temporary storage tank for food
o Site of food breakdown
o Chemical breakdown of protein begins
o Delivers chyme (processed food) to the small intestine
Small Intestine
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The body’s major digestive organ
Longest portion of the alimentary tube (2–4 m or 7–13 feet in a living person)
Site of nutrient absorption into the blood
Muscular tube extending from the pyloric sphincter to the ileocecal valve
Suspended from the posterior abdominal wall by the mesentery
Small Intestine
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Subdivisions
o Duodenum
 Attached to the stomach
 Curves around the head of the pancreas
o Jejunum
 Attaches anteriorly to the duodenum
o Ileum
 Extends from jejunum to large intestine
 Meets the large intestine at the ileocecal valve
Large Intestine
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Larger in diameter, but shorter in length at 1.5 m, than the small intestine
Extends from the ileocecal valve to the anus
Subdivisions:
o Cecum
o Appendix
o Colon
o Rectum
o Anal canal
Large Intestine Anatomy
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Cecum—saclike first part of the large intestine
Appendix
o Accumulation of lymphoid tissue that sometimes becomes inflamed
(appendicitis)
o Hangs from the cecum
Large Intestine Anatomy
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Colon
o Ascending—travels up right side of abdomen
o Transverse—travels across the abdominal cavity
o Descending—travels down the left side
o Sigmoid—S-shaped region; enters the pelvis
Sigmoid colon, rectum, and anal canal are located in the pelvis
Large Intestine Anatomy
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Anal canal ends at the anus
Anus—opening of the large intestine
The large intestine delivers undigestible food residues to the body’s exterior
Accessory Digestive Organs
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Teeth
Salivary glands
Pancreas
Liver
Gallbladder
Teeth
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Teeth masticate (chew) food into smaller fragments
Humans have two sets of teeth during a lifetime:
1. Deciduous (baby or “milk”) teeth
 A baby has 20 teeth by age 2
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First teeth to appear are the lower central incisors
Teeth
2. Permanent teeth
o Replace deciduous teeth between the ages of 6 and 12
o A full set is 32 teeth, but some people do not have wisdom teeth (third
molars)
o If they do emerge, the wisdom teeth appear between ages of 17 and
25
Classification of Teeth
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Incisors—cutting
Canines (eyeteeth)—tearing or piercing
Premolars (bicuspids)—grinding
Molars—grinding
Regions of a Tooth
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Two major regions of a tooth
1. Crown
2. Root
Regions of a Tooth
1. Crown—exposed part of tooth above the gingiva (gum)
Regions of a Tooth
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Note: The neck is a connector between the crown and root.
o Region in contact with the gum
o Connects crown to root
Salivary Glands
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Three pairs of salivary glands empty secretions into the mouth
1. Parotid glands
 Found anterior to the ears
2. Submandibular glands
3. Sublingual glands
 Both submandibular and sublingual glands empty saliva into the
floor of the mouth through small ducts
Salivary Glands
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Saliva
o Mixture of mucus and serous fluids
o Helps to moisten and bind food together into a mass called a bolus
Pancreas
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Produces a wide spectrum of digestive enzymes that break down all
categories of food
Secretes enzymes into the duodenum
Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from
stomach
Hormones produced by the pancreas
o Insulin
o Glucagon
Liver
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Largest gland in the body
Located on the right side of the body under the diaphragm
Consists of four lobes suspended from the diaphragm and abdominal wall by
the falciform ligament
Connected to the gallbladder via the common hepatic duct
Liver
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Bile is produced by cells in the liver
Bile leaves the liver through the common hepatic duct and enters duodenum
through the bile duct
Gallbladder
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Sac found in shallow fossa of liver
When no digestion is occurring, bile backs up the cystic duct for storage in the
gallbladder
During digestion of fatty food, bile is introduced into the duodenum from the
gallbladder
Gallstones are crystallized cholesterol, which can cause blockages