Digestive System Structure and Function Quiz

Overview of the Digestive System

• The digestive system breaks down food to release and absorb nutrients.
• The GI tract is approximately 25 feet long, from the mouth to the anus, and has four layers.

Structures of the Digestive System

• The pharynx, esophagus, stomach, small intestine, and large intestine make up the digestive system.
• Accessory digestive organs include teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

Layers of the Digestive Tract

• Mucosa: a mucous membrane epithelium in contact with food.
• Submucosa: dense connective tissue between mucosa and muscularis, with blood and lymphatic vessels, and a collection of nerves called the submucosal plexus.
• Muscularis: inner circular layer and outer longitudinal layer in the small intestine, responsible for mechanical digestion, exposing food to more chemicals, and peristalsis.
• Serosa: the most superficial layer, only in the region inside the abdominal cavity, made of loose connective tissue holding the canal in place.

Enteric Nervous System

• Runs from the esophagus to the anus and is separated into two plexuses: myenteric for motility and submucosal for regulating digestive secretions.
• Autonomic nervous system: extrinsically innervates the alimentary canal, with sympathetic nerves restricting enteric neurons and parasympathetic nerves increasing GI secretion and motility.

Blood Supply

• Transports protein and carbohydrate to the liver through the hepatic portal system.
• Delivers nutrients and oxygen to organs of the alimentary canal, with 25% of blood being pumped into the arteries serving the intestines while resting and digesting.

Functions of the Mouth

• Ingests, chews, and mixes food.
• Begins chemical breakdown of carbohydrates and lipids.
• Moves food to the pharynx.
• Moistens and tastes food, cleans and lubricates teeth, and has antimicrobial activity.

Functions of the Pharynx

• Propels food to the esophagus.
• Lubricates food and passage.

Functions of the Esophagus

• Propels food to the stomach.
• Lubricates food and passage.

Functions of the Stomach

• Mixes food with gastric juices to form chyme.
• Begins chemical breakdown of proteins.
• Absorbs some fat-soluble substances.
• Stimulates protein-digesting enzymes and secretes intrinsic factor for vitamin B12 absorption in the small intestine.

Functions of the Small Intestine

• Mixes chyme and digestive juices.
• Propels food slowly.
• Absorbs macro and micro nutrients.
• Segmentation optimizes enzymatic activity.

Functions of the Large Intestine

• Further breaks down food residue.
• Absorbs residual water, electrolyte, and vitamins produced by enteric bacteria.
• Propels and eliminates feces.
• Food residue is concentrated and temporarily stored.
• Mucus eases passage of feces through the colon.

Functions of the Liver

• Produces bile salts to emulsify lipids for digestion and absorption.

Functions of the Gallbladder

• Stores, concentrates, and releases bile.

Functions of the Pancreas

• Produces digestive enzymes and bicarbonate.
• Bicarbonate helps to neutralize acidic chyme and provide an optimal environment for enzymatic activity.

Ingestion

• Entry of food into the alimentary canal through the mouth.

Swallowing

• Last voluntary act until defecation, involving propulsion and peristalsis.

Mechanical Digestion

• Physical process that does not change the chemical nature of food, exposes a larger surface area to digestion.

Chemical Digestion

• Breaking down complex food molecules into their building blocks.

Absorption

• Primarily occurs in the small intestine, taking nutrients into the bloodstream or lipids into the lymphatic system.

Defecation

• Undigested materials are removed from the body.

Neural Control

• Sensors for expansion of the stomach, food particles, liquid present, and nutrient type.
• Can activate glands and muscle.
• Two types of reflexes: short reflex (local stimulus and result) and long reflex (ANS and CNS reacting to stimuli outside the digestive tract).

Hormonal Control

• Gastrin stimulates the release of gastric acid.
• Secretin stimulates bicarbonate release from the pancreas.
• CCK stimulates pancreatic secretion of enzymes and bile from the liver and gallbladder.
• Gastric inhibitory peptide inhibits gastric secretion and slows gastric emptying and motility.