Digestive Tract Flashcards
Gastrointestinal tract (digestive organs)
Oral cavity, pharynx, esophagus, stomach, large intestine, small intestine
Digestive System Process
Ingestion of nutrients into the oral cavity.
Mastication of food into smaller pieces.
Movement (motility) of food through digestive tract.
Secretion of several fluids: mucus, enzymes, acids,
bases, and bile.
Hormone release for control of motility and
secretion of glands.
Chemical and enzymatic breakdown of large
macromolecules into smaller ones.
Absorption of small molecules and water.
Elimination of indigestible components.
Layers of the GI Tract
The GI tract is a hollow tube with a lumen of variable
diameter and a wall made up of four main layers:
Mucosa (Internal lining of GI tract)
Submucosa
Muscularis
Serosa (External lining of GI tract)
Mucosa
Consists of:
Epithelial lining
Lamina propria: underlying loose connective tissue with blood vessels, lymphatics,
lymphocytes, smooth muscle cells, and often small glands.
Muscularis mucosae: A thin layer of smooth muscle allowing local movements of the mucosa.
Submucosa
Contains denser connective tissue with larger blood and lymph vessels and the submucosal plexus of autonomic nerves. It also contains glands and lymphoid tissue.
Muscularis
Composed of smooth muscle cells organized
in an inner circular layer and outer longitudinal layer.
The connective tissue between the muscle layers contains blood and lymph vessels, as well as the myenteric nerve plexus
of many autonomic neurons.
Serosa
A thin layer of loose connective tissue, rich in blood vessels, lymphatics,
and adipose tissue.
It has a simple squamous covering epithelium or mesothelium. In the abdominal cavity the serosa is continuous with mesenteries, which are thin double membranes of mesothelium that support the intestines.
Enteric nervous system
The connective tissue between the muscle layers of the muscularis contains blood and lymph vessels, as well as the myenteric nerve plexus of many autonomic neurons.
This and the submucosal plexus together comprise the
enteric nervous system of the digestive tract.
Mucosa-associated immune defense system
(MALT)
Provides an essential backup to the thin
physical barrier of the epithelial lining.
Lamina propria
Located just below the epithelium, is rich with macrophages and lymphocytes, many for production of IgA (immunoglobulin A) antibodies.
This IgA complex resists
proteolysis by digestive enzymes and protects
against specific viral and bacterial pathogens.
Oral Cavity (Mouth)
Lined with stratified squamous epithelium, which may be keratinized, partially
keratinized, or nonkeratinized depending on the location.
Taste buds
Detect five categories: Salty, sour, sweet, bitter, and umami
The four types of lingual papillae are elevations of the tongue’s mucous membrane that assume various forms and functions.
Filiform papillae
Fungiform papillae
Foliate papillae
Vallate (or circumvallate) papillae
Filiform papillae
Very numerous, have an elongated conical shape, and are heavily keratinized, which gives their surface a gray or whitish appearance. They provide a rough surface that facilitates movement of food during chewing. These have no taste buds.
Fungiform papillae
Much less numerous, lightly keratinized, and interspersed among the filiform papillae. They are mushroom-shaped with well-vascularized and
innervated cores of lamina propria. A few taste buds are present.
Foliate papillae
Consist of several parallel ridges on each side of the tongue. Some taste buds are present.
Vallate (or circumvallate) papillae
The largest papillae, with diameters of 1-3 mm.
Ducts of several small, serous salivary glands empty near each vallate papilla. This provides a flow of fluid over the numerous taste buds, clearing food particles so that the taste buds can receive and process new stimuli.
Dentin
A calcified tissue harder than bone, consisting of 70% hydroxyapatite.
Enamel
The hardest component of the human body, consisting of 96% calcium hydroxyapatite and only 2%-3% organic material including very few proteins and no collagen.
Periodontium
Comprises the structures
responsible for maintaining the teeth in their sockets, and includes the cementum, the periodontal ligament, and the alveolar bone with the associated gingiva (gums).
Cementum
Covers the dentin of the root and resembles bone, but it is avascular.
