Histology of the Digestive System Flashcards
What are the components of the digestive tract?
(1) oral cavity
(2) esophagus
(3) stomach
(4) small intestine
(5) large intestine
(6) anus
Associated glands: salivary glands, liver, pancreas
Give the 4 main layers of the GI tract.
Mucosa
Submucosa
Muscularis
Serosa
Give the main histological features of mucosa
Consists of an epithelial lining
An underlying lamina propria of loose connective tissue rich in: blood vessels, lymphatics, lymphocytes, smooth muscle cells, small glands
What is muscularis?
A thin layer of smooth muscle separating mucosa from submucosa
Allows local movements of mucosa
What are the histological features of submucosa?
Denser connective tissue with larger blood and lymph vessels
Submucosal (Meissner) plexus of autonomic nerves
Glands and significant lymphoid tissue
How is the muscularis layer organized?
aka. muscularis externa
Thick
Composed of smooth muscle cells
2 sublayer smooth muscle cellls:
(1) the fiber orientation is circular in the internal sublayer
(2) the fiber orientation is longitudinal in the external sublayer
The connective tissue between the muscle sublayers contains blood and lymph vessels, as well and myenteric (Auerbach) nerve plexus
What are the 2 components of the enteric nervous system?
(1) the myenteric (Auerbach) nerve plexus
(2) the submucosal plexus
Contractions of the muscularis are generated and coordinated by the myenteric plexus that mix and propel the luminal contents forward
What are the key histological features of serosa?
A thin layer of loose CT
Rich in blood vessels, lymphatics, and adipose tissue
Has a simple squamous covering epitheliumm or mesothelium
What are mesenteries?
Thin membranes covered by mesothelium on both sides that support the intestines
The serosa is continuous with mesenteries in the abdominal cavity
What is the difference in general structure between the digestive tract and esophagus?
In the esophagus, the serosa is replaced by a thick adventitia, a connective tissue layer
Adventitia merges with the surrounding tissues and lacks mesothelium
What are the main Histological features of the lip?
One side is covered by typical oral mucosa
The opposite side is covered by:
- skin containing hair follicles
- associated glands
Vermilion Zone - lies between the oral portion of the lips and normal skin
Internally, the lips contain striated muscle and man minor salivary glands
Why is the Vermilion Zone more prone to dryness?
Epidermis is very thin, lightly keratinized, and transparent to blood in the rich microvasculature of the underlying connective tissue
It is prone to excessive dryness and chapping in the cole, dry weather since this region lacks the glands for oil or sweat
What are the features and roles of FILIFORM PAPILLAE?
Pointed
Heavily keratinized epithelium
Provide friction to help move food during chewing
What are the features and roles of FOLIATE PAPILLAE?
Ridge-like
Present on the side of the tongue
Best developed in young children
What are the features of FUNGIFORM PAPILLAE
Mushroom-shaped
Lightly keratinized epithelium
Few taste buds
Compare the features of FILIFORM and FUNGIFORM papillae?
Both are elevations of connective tissue covered by stratified squamous epithelium
Give the location of Vallate Papillae.
8-12 large ones
Present in a V-shaped line near the terminal sulcus
Which papillae have taste buds?
Present on fungiform and foliate papillae
More abundant on VALLATE PAPILLAE
What are the main cell types present in taste buds?
Gustatory (taste) cells
Supporting cells (function not well understood)
Basal stem cells
Microvilli at the ends of the gustatory cells project through an opening in the epithelium, the taste pore
Where do sensory axons enter the taste buds and with what cells do they synapse?
Afferent sensory axons enter the basal end of taste buds
These axons synapse with the gustatory cells
Taste buds form as distinct clusters of cells in the stratified squamous epithelium of the tongue surface
Give the main histological features of Vallate Papillae.
2 Distinctive Features:
(1) many taste buds around the sides
(2) several small salivary glands emptying into the cleft formed by the elevated mucosa surrounding the papillae
These glands continuously flush the cleft, renewing the fluid in contact with the taste buds
How are permanent teeth arranged in humans?
32 adult (permanent) teeth
Arrangement: 2 bilaterally symmetric arches in the maxillary and mandibular bones
Identify the types of teeth in each quadrant
Each quadrant has 8 teeth:
2 incisors
1 canine
2 premolars
3 permanent molars
Identify the teeth with and without precursors
20 of the permanent teeth are preceded by primary teeth (deciduous or milk teeth)
The molars have no deciduous teeth
What are the 3 main regions of teeth?
(1) enamel-covered crown
(2) cementum-covered roots - anchor the tooth to the alveolar bone of the jaw
(3) slightly constricted neck - enamel and cementum coverings meet at the gingiva
Most of the roots and neck consist of dentin
Where do enamel and cementum meet?
slightly constricted neck where enamel and cementum coverings meet at the gingiva
What does pulp cavity contain?
Extends into the neck of a tooth
Filled with well-vascularized, well-innervated mesenchymal connective tissue
