Digestive System

What are the main functions of the digestive system?

The digestive system is responsible for

• Ingestion

• Mechanical digestion

• Chemical digestion

• Propulsion

• Absorption

• Defecation

What is ingestion?

Ingestion is the process of taking food and liquids into the mouth

What is mechanical digestion?

Mechanical digestion is the physical breakdown of food into smaller pieces through chewing, churning, and segmentation

What is chemical digestion?

Chemical digestion is the enzymatic breakdown of food into smaller nutrients. (absorbable molecules)

What is propulsion?

Propulsion is the movement of food through the gastrointestinal tract by swallowing and peristalsis

What is absorption?

Absorption is the movement of digested nutrients, water, vitamins, and minerals from the GI tract into the blood or lymph

What is defecation?

Defecation is the elimination of indigestible substances from the body as feces

What are the four layers of the GI tract wall from innermost to outermost?

Mucosa, submucosa, muscularis externa, and serosa/adventitia

What are the functions of the mucosa?

The mucosa protects, secretes mucus and digestive enzymes, and absorbs nutrients

What are the three parts of the mucosa?

Epithelium, lamina propria, and muscularis mucosae

What is the function of the submucosa?

The submucosa contains blood vessels, lymphatic vessels, nerves, and connective tissue that support the mucosa

What is the function of the muscularis externa?

The muscularis externa is responsible for segmentation and peristalsis

What are the layers of the muscularis externa?

An inner circular layer and an outer longitudinal layer

What is the serosa?

The serosa is the outer visceral peritoneum that protects and anchors digestive organs

What is the peritoneum?

The peritoneum is a serous membrane lining the abdominal cavity and covering abdominal organs

What is the parietal peritoneum?

The parietal peritoneum lines the abdominal wall

What is the visceral peritoneum?

The visceral peritoneum covers the external surfaces of digestive organs

What is a mesentery?

A mesentery is a double layer of peritoneum that suspends organs and carries blood vessels, lymphatics, and nerves

What structures are found in the oral cavity?

Teeth, tongue, salivary glands, hard palate, soft palate, and uvula

What is mastication?

Mastication is chewing food to mechanically break it down

What is the function of saliva?

Saliva lubricates food, begins carbohydrate digestion, dissolves chemicals for taste, and helps clean the mouth

What enzyme in saliva begins carbohydrate digestion?

Salivary amylase

What is the function of lingual lipase?

Lingual lipase begins the digestion of fats

What are the three major salivary glands?

Parotid, submandibular, and sublingual glands

Which salivary glands produce most saliva?

The submandibular glands

What are the four types of teeth?

Incisors, canines, premolars, and molars

What is the function of incisors?

Incisors cut food

What is the function of canines?

Canines tear food

What is the function of premolars and molars?

Premolars and molars crush and grind food

What is swallowing also called?

Deglutition

What are the three phases of swallowing?

Buccal phase, pharyngeal phase, and esophageal phase

What is peristalsis?

Peristalsis is wave-like muscular contractions that move food through the GI tract

What is the function of the lower esophageal sphincter?

It prevents stomach contents from refluxing into the esophagus

What are the main regions of the stomach?

Cardia, fundus, body, and pylorus

What is the function of the stomach?

The stomach stores food, mechanically mixes food, and begins protein digestion

What is chyme?

Chyme is the semi-liquid mixture of food and gastric juices in the stomach

What are rugae?

Rugae are folds in the stomach wall that allow expansion

What are gastric pits?

Gastric pits are openings in the stomach lining that lead to gastric glands

What do mucous cells secrete?

Mucous cells secrete mucus that protects the stomach lining

What do parietal cells secrete?

Parietal cells secrete hydrochloric acid (HCl) and intrinsic factor

What is the function of hydrochloric acid in the stomach?

HCl activates pepsin, kills microbes, and denatures proteins

What is intrinsic factor?

Intrinsic factor is a substance needed for vitamin B12 absorption

What do chief cells secrete?

Chief cells secrete pepsinogen and gastric lipase

What is pepsinogen?

Pepsinogen is the inactive form of pepsin

What is pepsin?

Pepsin is an enzyme that digests proteins into smaller peptides

What hormone is produced by G cells?

Gastrin

What does gastrin do?

Gastrin stimulates gastric secretion and stomach motility

What are the three regions of the small intestine?

Duodenum, jejunum, and ileum

What is the primary site of digestion and absorption?

The small intestine

What is the function of the duodenum?

The duodenum receives chyme, bile, and pancreatic secretions

What are circular folds?

Circular folds are ridges in the small intestine that increase surface area

What are villi?

Villi are fingerlike projections that increase absorptive surface area

What are microvilli?

Microvilli are microscopic projections on epithelial cells that form the brush border

What is the brush border?

The brush border is the microvilli-covered surface of the small intestine where enzymes are located.

What is a lacteal?

A lacteal is a lymphatic capillary inside a villus that absorbs fats.

What does pancreatic amylase digest?

Pancreatic amylase digests carbohydrates.

What does trypsin digest?

Trypsin digests proteins

What does pancreatic lipase digest?

Pancreatic lipase digests triglycerides into fatty acids and monoglycerides

What is secretin?

Secretin is a hormone released by the small intestine that stimulates bicarbonate secretion by the pancreas

What is cholecystokinin (CCK)?

CCK is a hormone that stimulates gallbladder contraction and pancreatic enzyme release

What are the exocrine functions of the pancreas?

The pancreas secretes digestive enzymes and bicarbonate into the small intestine

Why is bicarbonate important?

Bicarbonate neutralizes acidic chyme from the stomach

What are the major functions of the liver?

Produces bile, processes nutrients, detoxifies substances, stores glycogen, and synthesizes plasma proteins

What is bile?

Bile is a digestive secretion that emulsifies fats

What does emulsification mean?

Emulsification is the breakdown of large fat globules into smaller droplets

What is the function of the gallbladder?

The gallbladder stores and concentrates bile

What pigment gives bile and feces their color?

Bilirubin

What are the main parts of the large intestine?

Cecum, colon, rectum, and anal canal

What are the sections of the colon?

Ascending, transverse, descending, and sigmoid colon

What is the main function of the large intestine?

Absorption of water, electrolytes, and vitamins and formation of feces

What are haustra?

Haustra are pouch-like segments of the colon

What are teniae coli?

Teniae coli are three longitudinal bands of smooth muscle on the colon

What is the appendix?

The appendix is a small tube attached to the cecum containing lymphoid tissue

How are carbohydrates absorbed?

Carbohydrates are absorbed as monosaccharides

How are proteins absorbed?

Proteins are absorbed as amino acids

How are fats absorbed?

Fats are absorbed as fatty acids and monoglycerides through lacteals

What are micelles?

Micelles are clusters of bile salts and fat molecules that help transport lipids to intestinal cells

What are chylomicrons?

Chylomicrons are lipoprotein particles that transport absorbed fats through lymph

What are fat-soluble vitamins?

Vitamins A, D, E, and K

What are water-soluble vitamins?

Vitamins B and C

What vitamin requires intrinsic factor for absorption?

Vitamin B12

What deficiency can result from lack of intrinsic factor?

Pernicious anemia

What is GERD?

Gastroesophageal reflux disease is chronic reflux of stomach acid into the esophagus

What is a peptic ulcer?

A peptic ulcer is an erosion of the stomach or duodenal lining

What bacterium is commonly associated with ulcers?

Helicobacter pylori.

What is jaundice?

Jaundice is yellow discoloration of the skin and eyes due to excess bilirubin

What are gallstones?

Gallstones are hardened deposits that form in the gallbladder.

What is diarrhea?

Diarrhea is frequent passage of watery stools

What is constipation?

Constipation is infrequent bowel movements with hard stools

What is appendicitis?

Appendicitis is inflammation of the appendix

Which organ produces bile?

The liver

Which organ stores bile?

The gallbladder

Which organ produces digestive enzymes and bicarbonate?

The pancreas

Which organ absorbs most nutrients?

The small intestine

Which organ absorbs most water?

The large intestine

Which stomach cells produce hydrochloric acid?

Parietal cells

Which stomach cells produce pepsinogen?

Chief cells

Which hormone stimulates gallbladder contraction?

Cholecystokinin (CCK)

Which hormone stimulates bicarbonate release?

Secretin

What is the overall purpose of digestion?

To break food into absorbable nutrients that can be used by the body for energy, growth, and repair