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Upper gastrointestinal tract (Stomach (Screen Shot 2018-04-01 at 10.35.33…
Upper gastrointestinal tract
Upper GIT:
Mouth & Pharynx: chewing, initial digestion and swallowing.
Eosophagus: simply a passage.
Stomach: main functions are mixing and churning.
Mouth & tongue:
a) They are different from the rest of the gut tube since they have voluntary skeletal muscle.
b) Also, they
stratified squamous epithelium
as they are in a place where wear and tear are common.
c) Normally, oral epithelium is not keratinized. When it becomes so, it is called Leukoplakia and appears as white patches to naked eyes.
The lips:
a) They are also covered by non-keratinized stratified squamous epithelium, and having underlying striated muscle.
b) They appears red since they are highly vascular.
Tongue
a) It is covered by 3 types of
lingual papillae
: circumvallate, filiform and fungiform.
b) It is composed mainly of striated muscles.
Filiform:
a) Can be found over the entire tongue
b) The most numerous papillae.
c) They are tall, narrow and pointed.
d) No taste buds contained.
Fungiform:
a) Anteriorly, they detect
sweetness
behind the tip of the tongue.
b) Laterally, they detect
saltness
.
c) Fungiform are mushroom-shaped and scattered on the surface.
Circumvallate:
a) Found in the posterior portion of the tongue.
b) In the ditch (grooves) around the circumvallate, there are numerous taste buds lie laterally and into which the small salivary glands open.
c) The taste buds here detect
bitter substances
.
d) Circumvallate are large and visible to the naked eyes.
Taste buds:
a) At the apex of the taste buds, there are pores, through which the tastes can be sensed.
b) Several cell types are found in the taste buds, and the most important one is the
neuroepithelial cell
.
c) Neuroepithelial cells are responsible for
transducing chemical stimuli into neural impulses
. The neural impulses then sent to the cranial nerves VII, IX, and X.
Oral cavity
Lymphoid tissue
b)
Waldeyer's ring
: formed by tonsils and adenoids--> see FUN1 (lymphoid & immune organs)
a)
Lingual tonsils
: found at the posterior third of the tongue, guarding the oropharyngeal isthmus.
Salivary glands
a) They are arranged in
typical exocrine acinar structure
(see histology note4).
b) Contractile cells are found in all the salivary glands.
c) Myoepithelial cells are innervated by parasympathetic nervous system.
d) Functions: digestion (water, amylase, glycoproteins, electrolytes, especially K+), protection (alkaline & buffer & antibacterial substances), dental repair (Ca2+ & P) and defence (IgA).
a)
Sublingual gland
They appear pale in H&E preparation.
They produce
mucous
. Mucus-secreting cells do not take up routine histological stains strongly.
They are found
under the front of the tongue.
Open into submandibular gland & oral cavity.
b)
Submandibular gland
- It is a
mixture of mucous and serous cells.
Serous cells take up stains and appear purple; whereas, the mucous cells appear pale.
An individual acinus can be entirely serous, mucous or mixed.
If mucous cells exceed serous cells--> serous cells being pushed to the edge--> crescentic
serous demilunes
(right-hand side pic) formed.
c)
Parotid gland
- It is the largest salivary gland.
It's secretion is
serous
, thus stained darkly.
It has a thick outer connective tissue capsule, which sends trabeculae into the parotid gland to divide the gland
into lobules.
And the secretory acini are tightly packed within these lobules.
Salivary glands are arranged in typical acinar structure.
Contractile cells are found in all the salivary glands, are responsible for squeezing secretary acini. They are innervated by parasympathetic nervous system.
Salivary ducts
(The three salivary glands have similar duct arrangement)
b.
Interlobular duct/ Striated duct
Intercalated ducts combine and form interlobular duct.
a.
Intercalated duct
Secretory acini open into intercalated duct.
It has
columnar epithelium.
c.
Main duct
Finally, these interlobular ducts fuse and form the main duct.
Clinical notes:
Stone
formed in the salivary gland
a) Submandibular secrete mucous and thus it's secretion is fairly sticky. This increases their opportunity to congeal and form stones or calculi that block the duct. It is painful.
b) Parotid gland secrete serous, and thus it's secretion is watery. It never form stones.
Oesophagus
a) It is a single tube that conveys food from pharynx to stomach.
b) The external muscle coat is voluntary striated at the top and gradually becomes involuntary smooth muscle at the bottom.
c) Due to the striated muscles on the top, we can swallow while standing on the head.
d) When eosophagus is empty, the mucosa folds.
e) It is capable of being stretched.
f) Since it is friction resistance,
eosophageal epithelium is stratified squamous.
g) At the
bottom of the oesophagus
is the
squamocolomnar junction
.
Stomach
a) The gastric epithelium is
simple columnar
. Also, stomach has a powerful muscular wall for mixing and churning stomach contents.
b) When these muscles contract, numerous
rugae
formed, which are the longitudinal folds. They formed in the
mucosa and submucosa.
c) Rugae disappear when the stomach filled and stretched.
d) The deeply in-folded parts called the
gastric glands
; whereas, the deepest part of them (closer to lumen) are called
crypts or pits
.
e) Gastric glands open into gastric pits, indentation into the stomach, and lined with simple columnar epithelium.
f) Gastric glands consist of many different cell types.
Different cell types in the gastric glands:
.
a) Mucus
-produced by
mucous cells
-present in all areas of the stomach
b) Hydrochloric acid and intrinsic factor
-produced by
oxyntic (parietal) cell
-confined to fundus & the body
c) Enzymes
-produced by
zymogenic chief (peptic) cell
-then, secretion of HCl helps converting pepsinogen to pepsin
d) Hormones
-produced by
enteroendocrine cells.
-endocrine cells that produce gastrin are confined to the pyloric antrum.
*Only mucous cells are identifiable since it is pale
Different anatomical areas of the stomach
:
Cardia
: mucus & enteroendocrine cells
Fundus & Body
: all cell types
Atrium & Pylorus
: mucus + gastrin-producing enteroendocrine
Summary:
A) Mouth & Pharynx:
Stratified squamous epithelium
Skeletal muscles in wall.
B) Salivary glands:
Sublingual gland: mucus gland
Submendibular gland: mixed gland
Parotid gland: serous gland
C) Gastric epithelium:
Mucus cells: all areas.
Oxyntic (parietal) cells: fundus & body
Zymogenic (chief/ peptic) cells: secrete enzymes
Enteroendocrine: gastrin-secreting cells confined to pyloric antrum.
