WEEK 1: UPPER GIT HISTOLOGY Flashcards
State the 4 main layers of the GIT
*Mucosa
*Submucosa
*Muscularis externa
*Adventitia layer
State the 3 layers of mucosa.
*Epithelium
*Lamina propria
*Muscularis mucosae
Describe the basic structures found in the Epithelium.
EPITHELIUM:
It is simple columnar (Absorption/secretion) all over except in the oral cavity, pharynx, Oesophagus and the lower part of Anal canal where it is stratified squamous (protection).
- Numerous folds
- Crypts – At numerous places epithelium dips into the Lamina propria and form crypts (Simple tubular glands).
Villi:
In Small intestine, Mucosa bears numerous finger-like processes that project in the lumen.
Glands:
1. Unicellular secretory cells are scattered among the cells of the lining epithelium.
2. In some parts of GIT, compound tubulo-alveolar glands are present in the submucosa.
Describe the basic structure of lamina propria.
LAMINA PROPRIA:
- Made up of collagen and reticular fibres.
- contain blood capillaries, lymph vessels and nerves
- In SI, the core of villus is attached to the lamina propria.
- Prominent aggregation of lymphatic tissue is seen in Lamina propria (MALT-mucous associated lymphatic tissue)
Describe the basic structure of the muscularis mucosae. What is its function?
MUSCULARIS MUCOSAE
Thin layer of smooth muscle that separates lamina propria from the submucosa.
Usually, outer longitudinal and inner circular or at right angles to the lumen
- - Contraction of Muscularis Mucosa is important for the local mixing of intestinal contents
- It changes the shape of mucosa, that helps in absorption and secretion
Describe the submucosa.
This layer consists of loose areolar tissue that connects mucosa to the muscularis externa.
*Its looseness permits some mobility of mucosa over the muscularis externa.
*Contain numerous blood vessels, lymphatics and nerve fibers and Meissner’s plexus.
Describe the muscularis externa.
Name its 2 layers.
It consists of smooth muscles all over GIT except upper part of oesophagus which contain skeletal muscles.
Arranged in two layers
- Inner layer: Circular
- Outer layer: Longitudinal
(+ Oblique layer – in stomach only)
Between the two layers “Auerbach’s plexus (Myenteric plexus)” is present.
- Inner circular layer acts as sphincter at some parts. Eg: Pyloric sphincter, Internal anal sphincter, Ileo - caecal valve
Describe the serous layer/ adventitia layer.
*It is merely visceral peritoneum composed of connective tissue and simple squamous epithelium.
*The esophagus lies outside the abdominal cavity has a superficial layer called Adventitia which consists of areolar connective tissue
Describe the histology of the oral cavity.
*Epithelium?
*Specialized for what?
*Lamina propria?
*Muscularis mucosae?
*The oral cavity is specialized for taste, chewing, salivary secretion, and immune surveillance (tonsils).
*Oral mucosa varies from site to site
*Epithelium is non-keratinized stratified squamous (lining mucosa)
*Partially keratinized on gums and hard palate and on filiform papillae of tongue (masticatory mucosa)
*Special mucosa on tongue
*Lamina propria is unspecialized.
*A muscularis mucosae is not present.
Deep to the epithelial surface, minor salivary glands are common.
Describe the epithelium present in the following parts of the oral cavity.
*Hard palate
*Soft palate
*Tongue
*Upper epithelium is respiratory
Lower is stratified squamous keratinized (masticatory epithelium)
*The soft palate has a non-keratinized epithelium (lining epithelium), with underlying minor salivary glands and striated muscle. The largest tonsils (the palatine tonsils) are embedded in the sides of the soft palate.
This is the mucosa of the oropharyngeal aspect of the soft palate. It resembles the buccal and labial mucosa; the connective tissue papillae (A) are of moderate height and the stratified squamous epithelium is not keratinized.
*The mucosal surface of the tongue, specialized epithelial variations, including papillae of various shapes.
bulk of tongue has striated muscle fibers arranged in bundles along three mutually perpendicular axes,
Bundles of myelinated nerve fibers also present
Describe the 4 types of lingual papillae.
Which one does not have taste buds?
Which one has more taste buds?
1.*Filiform – most common – on dorsum of tongue – all over the tongue, elongated; keratinized no taste buds
*Fungiform – fewer, larger, rounded mushroom like, red dots – on dorsum of the tongue, have taste buds
*Foliate papillae – vertical ridges on the posterior lateral side of the tongue, have taste buds
*Circumvallate papillae – located just in front of sulcus terminalis; have taste buds (Von Edner’s glands, producing serous saliva situated at base of CV clefts)
2.Filiform papillae
3.Cicumvallate papillae
What are taste buds?
Describe the 3 cell layers found in the
What are taste cells called?
*A pore
Each gourd-shaped taste bud consists of three major cell types:
*Supporting cells – insulate the receptor
*Basal cells – dynamic stem cells
*Gustatory cells – taste cells
Describe the epithelium of the esophagus.
*Epithelium?
*muscularis mucosae?
*Submucosa
*Muscularis externa
*Esophagus has few functional specializations:
-Lined by non-keratinized stratified squamous epithelium.
muscularis mucosae is thicker than that in the stomach and intestine, and includes only longitudinal muscle fibers.
Distinct basic layers
lamina propria is less cellular (fewer lymphocytes) than that in the stomach and intestine.
Describe the muscularis externa of esophagus.
Describe the types of muscles on the upper, middle and lower 1/3 of the esophagus.
Arranged in two layers:
- Inner layer: Circular
- Outer layer: Longitudinal
* Between the two layers – Myenteric plexus of nerve fiber and ganglion cells are present. It controls peristaltic movement.
TYPES OF MUSCLES:
Upper 1/3rd – Skeletal muscle
Middle 1/3rd – Both skeletal and smooth muscle
Lower 1/3rd – purely smooth muscle
Describe the serous layer of the esophagus.
It consists of loose areolar connective tissue, which merges with the connective tissue of surrounding structures.
What is the cardio-esophageal junction?
What is the other its other name?
Epithelial change?
Clinical correlation?
*It is the part where the esophagus meets the stomach.
*Or gastro-esophageal junction
*Epithelial lining at the cardio-esophageal junction changes from stratified sq. to simple columnar epithelium
Clinical Correlation:
-Esophageal epithelium may be transformed to a simple columnar form in the condition called Barrett’s esophagus.
-GASTRO- ESOPHAGEAL REFLUX DISORDER: A condition which is characterized by the compromised state of the lower esophageal sphincter, which leads to reflux of food and acid into esophagus.
State the 3 histological regions of the stomach.
*Cardia
*Fundus and body
*Pylorus
State the features of stomach mucosa.
Cells present.
*Rugae: increase surface area to allow more food.
- The surface is indented into numerous short gastric pits which open freely to the lumen.
*Thick glandular mucosa, packed with gastric glands which secrete digestive enzymes and acid.
*The entire surface consists uniformly of surface mucous cells, which protect the stomach from self-digestion.
*The surface of the stomach is lined by surface mucous cells which comprise a simple columnar epithelium.
CELLS in the gastric glands:
*Chief cells predominate in the deep band.
*Parietal cells predominate in the middle band
*Surface mucous cells line gastric pits in the outer band.
*Mucous neck cells are most common in the necks of the glands.
Describe the muscularis externa of the stomach.
*The muscularis externa of the stomach is thicker than elsewhere along the tract.
*The smooth muscle fibers of the muscularis may form an oblique layer in addition to the inner circular and outer longitudinal.
- An especially thick region forms the pyloric sphincter
Describe the cardiac region of the stomach.
*Mucosa:
-Epithelial lining at the cardio-esophageal junction changes from stratified sq. to simple columnar epithelium
-Presence of Mucous surface cells and cardiac glands
*Submucosa:
-Consists of Meissner’s plexus and blood vessels
*Muscularis externa:
Inner – Oblique
Middle – circular
Outer – longitudinal
Myenteric plexus between muscle layers
*Serosa – Simple squamous epithelium resting on a thin layer of connective tissue
Describe the FUNDUS of the stomach.
Mucosa:
- Lining Epithelium – Simple columnar epithelium that invaginates to various extents into the lamina propria, forming gastric pits.
- These cells are involved in mucus secretion. The mucus protects the epithelial lining from damage due to the presence of acid in the stomach.
Surface Mucus Cells
Their nuclei are less-compressed basally and their apical mucus droplet (m) shows some affinity for standard stains. These differences presumably reflect the fact that the mucus secreted by these cells must have a special composition to resist attack by digestive acid and enzymes.
Stomach, gastric pit
The mucosal surface is invaginated into numerous gastric pits, each of which opens freely onto the mucosal surface. Several gastric glands (not included in this image) open inconspicuously into the deep end of each pit.
Lamina propria:
- Small tubular fundic/gastric glands are present.
- Types of cells: Mucous neck cells, parietal/oxyntic cells, chief cells and enteroendocrine glands.
MUSCULARIS MUCOSAE:
- It consists of two thin layer of smooth muscles.
i.e., Outer longitudinal and inner circular
SUBMUCOSA:
- Consists of blood vessels, lymphatic vessels and Meissner’s plexus.
MUSCULARIS EXTERNA:
Inner: Oblique
Middle: circular
Outer: Longitudinal
SEROSA:
Outermost layers of the stomach which consists of loose connective tissue covered by mesothelium.
What are the functions of the mucous neck cells
) Mucous neck cells – Located just below gastric pit.
- Columnar in shape
- Contain mucinogen granules in apical cytoplasm, while nuclei are basally situated basally.
- Produces soluble mucus
What are the functions of the parietal cells.
What is the other name used for parietal cells?
Parietal or oxyntic cells:
- They are large, ovoid or polyhedral cells with a large central nucleus.
- More numerous in the upper half of the gland than in the lower half
- Secretes HCL and intrinsic factor.
- Intrinsic factor combines with vitamin B12 to form a complex necessary for erythrocytes formation.
Describe the Chief cells.
What is the function of chief cells?
Chief or zymogenic cells:
- Located in the lower 1/3rd of gastric glands.
- Contain rough endoplasmic reticulum near the base, secretory granules near their apex and a small Golgi apparatus.
- Secrete pepsinogen which is converted into pepsin in an acid environment.
What are the functions of the enteroendocrine glands in the fundus?
Enteroendocrine and APUD cells:
- Located in the basal portion of gastric glands
- Secretes serotonin, histamine and gastrin. These are endocrine cells which release their products into the blood vessels.
Describe the pyloric region of the stomach.
MUCOSA:
- Epithelium: Simple columnar as in fundic part
- Pyloric glands occupy the lamina propria
- Gastric pits are deeper
- Glands are short, tortuous and branched
- Produce mucus and gastrin
- Muscularis mucosa and Submucosa are similar to fundic
part.
PYLORIC GLANDS:
*Secrete alkaline mucus. These mucous glands remain within the mucosa in the stomach but expand across the muscularis mucosae to fill the submucosa of the duodenum.
Both cardiac and pyloric glands are predominantly mucous (i.e., few parietal or chief cells). This mucus can help protect the adjacent regions of the tract from damage by stomach acid and digestive enzymes. Surface mucous cells protect the stomach lining, but the esophagus and duodenum lack any such protection.
MUSCULARIS EXTERNA:
Inner: Oblique – absent in pylorus
Middle: circular
Outer: Longitudinal
Similar to Fundic part, but the circular fibers are much thickened to form pyloric sphincter.
The pyloric stomach is also characterized by a considerable thickening of the muscularis externa, forming the pyloric sphincter
Describe the stomach/ duodenum junction.
The junction marked not only by the pyloric sphincter as well as an abrupt change in mucosal tissue.
*The gastric epithelium of surface mucous cells (lining gastric pits) ends at the beginning of intestinal epithelium of absorptive cells (covering villi).
*The pyloric mucosal glands expand into the submucosa of the duodenum.
Describe the difference between the cardia, fundus and body, pylorus in terms of:
*Gland present
*Gastric pit
*Parietal cells
CARDIA
*Has cardiac glands
*Less deep gastric pit than pylorus
*No parietal cells
FUNDUS AND BODY
*Has gastric glands
*Gastric pits less deep than the pylorus
*Many parietal cells
PYLORUS
*Has pyloric glands
*Deeper gastric pit compared to the cardia and fundus and body regions
*Few parietal cells
