Histology of the Digestive System

Question 1

What are the components of the digestive tract?

Answer 1

(1) oral cavity
(2) esophagus
(3) stomach
(4) small intestine
(5) large intestine
(6) anus

Associated glands: salivary glands, liver, pancreas

Question 2

Give the 4 main layers of the GI tract.

Answer 2

Mucosa

Submucosa

Muscularis

Serosa

Question 3

Give the main histological features of mucosa

Answer 3

Consists of an epithelial lining

An underlying lamina propria of loose connective tissue rich in: blood vessels, lymphatics, lymphocytes, smooth muscle cells, small glands

Question 4

What is muscularis?

Answer 4

A thin layer of smooth muscle separating mucosa from submucosa

Allows local movements of mucosa

Question 5

What are the histological features of submucosa?

Answer 5

Denser connective tissue with larger blood and lymph vessels

Submucosal (Meissner) plexus of autonomic nerves

Glands and significant lymphoid tissue

Question 6

How is the muscularis layer organized?

aka. muscularis externa

Answer 6

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

Question 7

What are the 2 components of the enteric nervous system?

Answer 7

(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

Question 8

What are the key histological features of serosa?

Answer 8

A thin layer of loose CT

Rich in blood vessels, lymphatics, and adipose tissue

Has a simple squamous covering epitheliumm or mesothelium

Question 9

What are mesenteries?

Answer 9

Thin membranes covered by mesothelium on both sides that support the intestines

The serosa is continuous with mesenteries in the abdominal cavity

Question 10

What is the difference in general structure between the digestive tract and esophagus?

Answer 10

In the esophagus, the serosa is replaced by a thick adventitia, a connective tissue layer

Adventitia merges with the surrounding tissues and lacks mesothelium

Question 11

What are the main Histological features of the lip?

Answer 11

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

Question 12

Why is the Vermilion Zone more prone to dryness?

Answer 12

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

Question 13

What are the features and roles of FILIFORM PAPILLAE?

Answer 13

Pointed

Heavily keratinized epithelium

Provide friction to help move food during chewing

Question 14

What are the features and roles of FOLIATE PAPILLAE?

Answer 14

Ridge-like

Present on the side of the tongue

Best developed in young children

Question 15

What are the features of FUNGIFORM PAPILLAE

Answer 15

Mushroom-shaped

Lightly keratinized epithelium

Few taste buds

Question 16

Compare the features of FILIFORM and FUNGIFORM papillae?

Answer 16

Both are elevations of connective tissue covered by stratified squamous epithelium

Question 17

Give the location of Vallate Papillae.

Answer 17

8-12 large ones

Present in a V-shaped line near the terminal sulcus

Question 18

Which papillae have taste buds?

Answer 18

Present on fungiform and foliate papillae

More abundant on VALLATE PAPILLAE

Question 19

What are the main cell types present in taste buds?

Answer 19

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

Question 20

Where do sensory axons enter the taste buds and with what cells do they synapse?

Answer 20

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

Question 21

Give the main histological features of Vallate Papillae.

Answer 21

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

Question 22

How are permanent teeth arranged in humans?

Answer 22

32 adult (permanent) teeth

Arrangement: 2 bilaterally symmetric arches in the maxillary and mandibular bones

Question 23

Identify the types of teeth in each quadrant

Answer 23

Each quadrant has 8 teeth:

2 incisors

1 canine

2 premolars

3 permanent molars

Question 24

Identify the teeth with and without precursors

Answer 24

20 of the permanent teeth are preceded by primary teeth (deciduous or milk teeth)

The molars have no deciduous teeth

Question 25

What are the 3 main regions of teeth?

Answer 25

(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

Question 26

Where do enamel and cementum meet?

Answer 26

slightly constricted neck where enamel and cementum coverings meet at the gingiva

Question 27

What does pulp cavity contain?

Answer 27

Extends into the neck of a tooth

Filled with well-vascularized, well-innervated mesenchymal connective tissue