Overview of the Human Digestive System

What is the primary function of the digestive system?

To provide the body with nutrients, water, and electrolytes essential for health.

What are the two major groups of organs in the digestive system?

The alimentary canal (GI tract) and accessory digestive organs.

What organs make up the alimentary canal?

The mouth, pharynx, esophagus, stomach, small intestine, and large intestine.

What are the accessory digestive organs?

Teeth, salivary glands, gallbladder, liver, and pancreas.

What is the process called that breaks down ingested food into smaller molecules?

Digestion.

What is absorption in the context of the digestive system?

The process by which digested end products pass through epithelial cells into the blood for distribution to body cells.

What is the role of the teeth in digestion?

To physically break down foods.

What is the function of the salivary glands?

To secrete saliva into the alimentary canal.

What is the hard palate?

The anterior portion of the palate supported by bone.

What is the soft palate?

The posterior portion of the palate that is a fibromuscular structure unsupported by bone.

What is the uvula?

A fingerlike projection of the soft palate that extends inferiorly.

What supports the muscular tongue in the oral cavity?

The mylohyoid muscle.

What is the lingual frenulum?

A membrane that secures the inferior midline of the tongue to the floor of the mouth.

What are the palatine tonsils?

Masses of lymphoid tissue located at the posterior end of the mouth.

What is the function of the tonsils in the digestive system?

They are part of the body's defense system.

What condition occurs when the palatine tonsils become inflamed and enlarged?

Tonsillitis.

What is the oral vestibule?

The space between the teeth and cheeks (or lips).

What is the oral cavity proper?

The area that lies within the teeth and gums.

What are the boundaries of the palatine tonsils?

Bounded anteriorly by the palatoglossal arch and posteriorly by the palatopharyngeal arch.

What is the primary role of the digestive system's accessory organs?

To secrete products into the alimentary canal to aid in digestion.

What is the significance of the digestive system in nutrient absorption?

It allows digested nutrients to enter the bloodstream for distribution to body cells.

What happens to the food after it is digested in the digestive system?

It is absorbed into the blood or eliminated as feces.

What are the three pairs of salivary glands responsible for?

They duct their secretion, saliva, into the oral cavity.

What enzyme in saliva begins the digestion of starchy foods?

Salivary amylase.

What is the role of the tongue during mastication?

It manipulates food and initiates swallowing.

What are the three anatomical subdivisions of the pharynx?

Nasopharynx, oropharynx, and laryngopharynx.

What type of muscle primarily composes the walls of the pharynx?

Skeletal muscle, consisting of an inner layer of longitudinal muscle and an outer layer of circular constrictor muscles.

What is the function of the pharynx in the digestive system?

It serves as a common passageway for food, fluid, and air.

How does food move from the pharynx to the esophagus?

Through wavelike contractions initiated by the muscle layers of the pharynx.

What is the length of the human esophagus?

Approximately 25 cm.

What is the primary function of the esophagus?

To conduct food to the stomach in a wavelike peristaltic motion.

What type of muscle is found in the upper end of the esophagus?

Skeletal muscle.

What controls the passage of food into the stomach?

The gastroesophageal sphincter.

Where is the stomach primarily located?

In the upper left quadrant of the abdominopelvic cavity.

What are the two types of mesenteries associated with the stomach?

Greater omentum and lesser omentum.

What is the function of the greater omentum?

It extends from the greater curvature of the stomach and covers most of the abdominal organs.

What is the stomach's role in digestion?

It serves as a temporary storage region for food and is a site for mechanical and chemical breakdown.

What additional layer of muscle does the stomach have in its muscularis externa?

An innermost obliquely oriented layer of smooth muscle.

What do gastric glands in the stomach secrete?

Hydrochloric acid (HCl) and hydrolytic enzymes.

What protects the stomach lining from being digested by its own enzymes?

A viscous mucus secreted by the mucosal glands.

Where does most digestive activity occur in the stomach?

In the pyloric part of the stomach.

What is chyme?

A creamy mass that food resembles after being processed in the stomach.

How long is the small intestine in a living person?

About 2 meters (6 feet) long.

What are the three subdivisions of the small intestine?

Duodenum, jejunum, and ileum.

What is the function of the pyloric sphincter?

It allows chyme to enter the small intestine from the stomach.

How long is the duodenum?

About 25 cm (10 inches) long.

Where is the majority of the jejunum located?

In the umbilical region of the abdominal cavity.

What is the length of the ileum?

About 3.6 meters (12 feet) long.

Where does the ileum join the large intestine?

At the ileocecal valve.

What are the two sources of enzymes that complete digestion in the small intestine?

Brush border enzymes and enzymes produced by the pancreas.

How does bile enter the duodenum?

Via the bile duct.

What is the hepatopancreatic ampulla?

The bulblike structure where the pancreatic duct and bile duct join before emptying into the duodenum.

What is the role of the hepatopancreatic sphincter?

It controls the orifice through which digestive products enter the duodenal lumen.

What structural modifications increase the absorptive surface of the small intestine?

Microvilli, villi, and circular folds.

How long is the large intestine?

About 1.5 meters (5 feet) long.

What are the subdivisions of the large intestine?

Cecum, appendix, colon, rectum, and anal canal.

What is appendicitis?

Inflammation of the appendix, often due to bacterial accumulation.

Which part of the colon travels up the right side of the abdominal cavity?

The ascending colon.

What is the right colic (hepatic) flexure?

The right-angle turn where the ascending colon turns to become the transverse colon.

What is the primary function of the small intestine?

Nearly all nutrient absorption occurs here.

What is the mesentery?

A double layer of peritoneum that suspends the small intestine from the posterior abdominal wall.

What is the retroperitoneal position of the duodenum?

Most of the duodenum lies behind the peritoneum.

What is the significance of the circular folds in the small intestine?

They increase the surface area for digestion and absorption.

What is the course of the colon after the left colic (splenic) flexure?

It continues down the left side of the abdominal cavity as the descending colon, then takes an S-shaped course as the sigmoid colon.

Where are the sigmoid colon, rectum, and anal canal located?

They lie in the pelvis anterior to the sacrum and are not considered abdominal cavity structures.

Which parts of the colon are retroperitoneal?

Except for the transverse and sigmoid colons, the colon is retroperitoneal.

What are the two sphincters of the anal canal and their muscle types?

The external anal sphincter is voluntary and composed of skeletal muscle, while the internal anal sphincter is involuntary and composed of smooth muscle.

What happens to the sphincters of the anal canal during defecation?

The sphincters are normally closed except during defecation, when they open to eliminate feces.

What are the teniae coli?

They are three longitudinal muscle bands that reduce the longitudinal muscle layer of the muscularis externa in the large intestine.

What structures are formed due to the shorter teniae coli in the large intestine?

They cause the wall of the large intestine to pucker into small pocketlike sacs called haustra.

What are epiploic appendages?

They are fat-filled pouches of visceral peritoneum that hang from the colon's surface.

What are the major functions of the large intestine?

To consolidate and propel unusable fecal matter toward the anus and eliminate it from the body, while also manufacturing vitamins B and K and reclaiming water from undigested food.

What causes diarrhea in relation to the large intestine?

Diarrhea results from conditions that rush undigested food residue through the large intestine before sufficient water absorption occurs.

What causes constipation in relation to the large intestine?

Constipation occurs when food residue remains in the large intestine for extended periods, leading to excessive water absorption and hard stool.

What is the initial set of teeth called and when do they typically appear?

The initial set is called deciduous (or milk) teeth, which normally appears between 6 months and 2½ years.

What is the sequence of shedding deciduous teeth?

Children begin to shed deciduous teeth around the age of 6, gradually replaced by permanent teeth.

What are the classifications of teeth?

Teeth are classified as incisors, canines, premolars, and molars.

What is the function of incisors?

Incisors are chisel-shaped and exert a shearing action used in biting.

What is the function of canines?

Canines are cone-shaped teeth used for tearing food.

What is the function of premolars and molars?

Premolars have two cusps for grinding, while molars have broad crowns with rounded cusps specialized for fine grinding of food.

What is a dental formula?

A dental formula designates the numbers, types, and position of the teeth in one side of the jaw.

What is the complete dental formula for deciduous teeth?

Upper teeth: 2 incisors, 1 canine, 0 premolars, 2 molars; Lower teeth: 2 incisors, 1 canine, 0 premolars, 2 molars, abbreviated as 2,1,0,2 for each side.

What is the dental formula for permanent teeth?

The dental formula for permanent teeth is 2,1,2,3 for each side, totaling 32 permanent teeth.

What is a common variation in the development of permanent teeth?

Not everyone develops a full set of 32 permanent teeth; many people do not have third molars (wisdom teeth) that erupt.

What are the four types of teeth?

Incisors, canines, premolars, and molars.

What are the two major regions of a tooth?

The crown and the root.

Where do the crown and root of a tooth meet?

At the neck near the gum line.

What covers the surface of the crown of a tooth?

Enamel.

What is the composition of enamel?

95% to 97% inorganic calcium salts.

What is the gingival sulcus?

The crevice between the end of the crown and the upper margin of the gingiva.

What is the function of cement in a tooth?

It attaches the tooth to the periodontal ligament.

What is dentin?

The bonelike material interior to the enamel and cement that composes the bulk of the tooth.

What is found in the pulp cavity of a tooth?

Pulp, which is composed of connective tissue, blood vessels, nerves, and lymphatics.

What are odontoblasts?

Specialized cells that produce and maintain dentin.

What is the root canal?

The extension of the pulp cavity into the distal portions of the root.

What is the apical foramen?

An opening at the root apex that allows entry for blood vessels and nerves into the tooth.

What are the three pairs of major salivary glands?

Parotid glands, submandibular glands, and sublingual glands.

Where are the parotid glands located?

Anterior to the ear, ducting into the mouth over the second upper molar.

Where are the submandibular glands located?

Along the medial aspect of the mandibular body in the floor of the mouth.

Where are the sublingual glands located?

Most anteriorly in the floor of the mouth, emptying under the tongue.