Prac 8 - Gastrointestinal Tract Flashcards
The lip displays a mucosal covering typical of the mouth
stratified squamous non-keratizing epithelium
Lip mucosal covering abrupt transformation into skin
stratified squamous keratized epithelium
The epithelial lining sits on a connective tissue layer containing what
(submucosa)
containing collagen and elastic fibres
The deeper layers of the mouth often contain what
glands and skeletal muscle fibres that help to change the shape of the oral cavity.
What lies in the submucosa and what does this do
Many small blood vessels lie in the submucosa and fluid from these helps to keep the epithelium moist.
There is an abrupt transition to what at the margin of the lips
stratified squamous keratinising epithelium
The tongue is covered by a
stratified squamous epithelium that remains non-keratinized on its ventral surface but is often heavily keratinized on its dorsal surface due to constant abrasion of this surface.
What is inside the tongue and where do these insert
Inside, it contains coarse bundles of skeletal muscle that run in different directions.
Some of these insert onto the lower jaw (extrinsic fibres) while others attach only to the fibrous connective tissue underlying the mucosa (intrinsic fibres).
What else is embedded within the tongue
Many mixed sero-mucous salivary glands are embedded within the tongue.
So too are lymph nodules, particularly in the posterior third of the tongue (e.g. lingual tonsils).
The dorsum of the tongue is thrown into complex folds known as
papillae
The most common type of papillae look like what and cover where
Tall, pointed filiform papillae are the most common and cover the whole of the anterior two thirds of the tongue, producing a rasp-like surface.
What kind of papillae are found at the tip and sides of the tongue.
Less numerous mushroom shaped fungiform papillae
Pale-staining taste buds are embedded in the epithelium where
on the lateral sides of these papillae.
How is the anterior two thirds and the posterior third on the tongue’s surface separated
A V-shaped row of dome-shaped circumvallate papillae separate the anterior two thirds and the posterior third on the tongue’s surface. These too bear taste buds.
What do the Parotid Salivary Glands do
These glands produce a watery enzyme-rich secretion (serous secretion) rich in alpha amylase that digests starch.
Where do the parotid salivary glands lie and how do they enter the mouth
They lie anterior to the ear (“para-otid”) on both sides of the face and enter the mouth via ducts adjacent to the first upper molar teeth.
Branches of the facial nerve pass through the gland but do not innervate it. Large lymph nodes are also embedded within the glands. what gland is this
Parotid Salivary Glands
The secretory cells are all of the same type in the parotid salivary glands :
a wholly serous gland
how are the secretory cells arranged in the parotid gland
They are arranged in spherical clumps called acini (singular, acinus) that resemble bunches of grapes, the stalks representing the duct system of the gland
What shape are the secretory cells of the parotid
The secretory cells are pyramidal in shape with a spherical nucleus. They show characteristics typical of protein secreting cells. The basal cytoplasm is filled with rough endoplasmic reticulum and the apex of the cell contains prominent secretion granules.
The acini of the parotid drain into ducts lined by a
simple cuboidal epithelium that may become stratified at its distal end.
Where do the Sublingual Salivary Glands lie and how do they work
These glands lie beneath the tongue and discharge their secretions into the floor of the mouth by a series of ducts either side of the frenulum of the tongue.
what is the Sublingual Salivary Glands purpose
They are branched tubular-acinar glands that produce a sticky mucus-rich secretion that helps to lubricate the mouth and the bolus of food.
How do the secretory cells of the sublingual gland appear
The secretory cells appear swollen and are filled with pale staining mucus granules. The oval nucleus is squashed to the base of the cell.
Secretion from sublingual glands drains into ducts lined by a
simple or stratified cuboidal epithelium whose cells appear pinker than the secretory cells.
Where do the Submandibular Salivary Glands lie
These well-defined globular glands lie subcutaneously, below the mandible, either side of the tongue. Their superficial part can be palpated easily below the lower jaw.
How do the submandibular glands discharge
They discharge by a pair of ducts on to the frenulum of the tongue.
How are the secretory cells of the submandibular gland arranged and what do they produce
The glands are of a branched tubulo-acinar type which are often intersperse by fat. They produce a mixed secretion, part mucus and part an enzyme-rich secretion
How do the submandibular glands appear and why
The glands are of a branched tubulo-acinar type which are often intersperse by fat. They produce a mixed secretion, part mucus and part an enzyme-rich secretion because
They produce a mixed secretion, part mucus and part an enzyme-rich secretion.
The serous cells form acini or lie at the closed ends of the tubules where they form characteristic crescent-shaped “demi-lunes” (half moons).
ike the parotid, this gland is a major source of what
epidermal growth factor that promotes the growth of the epithelium of the GI tract.
The epiglottis lies where and forms a barrier between what
The epiglottis lies posterior to the tongue and is directly attached to it. It forms the boundary between the oropharynx and the laryngeal pharynx.
Most of the surface of the epiglottis is covered by
a stratified squamous epithelium, although the lower part of its posterior (lower) surface has a pseudostratified columnar ciliated epithelium (respiratory epithelium).
What does the epiglottis internally contain
Internally it contains a plate of elastic cartilage and its submucosa often contains lymph nodules and salivary glands.
The gastro-intestinal tract has four layers:
- an innermost mucosa
- an underlying submucosa
- an external muscle coat (muscularis propria - sometimes referred to as the muscularis externa)
- a serosa (in some regions)
The mucosa of the GI tract has three components:
a lining epithelium that is often thrown into folds,
a layer of connective tissue (lamina propria) that often contains lymphoid tissue and a ring of smooth muscle (muscularis mucosa).
The submucosa is composed of
loose connective tissue that may contain glands and lymphoid tissue.any of the blood vessels that supply the gut run it this layer.
A rich plexus of nerves that is part of the enteric nervous system (Meissner’s plexus) is also present in this layer.
The muscularis propria normally consists of two layers of smooth muscle whose contractions help to
break up the food and to propel it along the alimentary tract.
Sandwiched between the layers of the muscular propria
are nerves that are also part of the enteric nervous plexus (Auerbach’s plexus).
A serosal layer consisting of a what covers where
simple squamous epithelium covers the outside surface of those parts of the gut tube that face the peritoneal cavity.
The oesophagus is mostly lined by a
stratified squamous non-keratinized epithelium.
What is underneath the stratified squamous non-keratinized epithelium of the oesophagus
Underneath this is a thin lamina propria and a narrow muscularis mucosa of smooth muscle.
Below the thoracic diaphragm the epithelium is often transformed into a
simple columnar type similar to that which lines the cardiac region of the stomach. This region of the oesophagus can become the site of pathological change.
The submucosa contains many sero-mucous glands whose secretions help to
lubricate the oesophagus
At the distal end of the oesophagus the submucosal layer contains many
large, thin-walled veins. These may become the site of oesophageal varicosities.
At the proximal end of the oesophagus the outermost layer of muscle (muscularis externa) is composed mainly of
skeletal muscle but at the distal end it is composed mostly of smooth muscle.
The stomach can be divided into 5 regions:
- the cardia
- the fundus
- the body
- Antrum
- the pyloric
What parts of the stomach show histological similarity
The fundus and body show very similar histological structure particularly with respects to their gastric glands. The cardia and pylorus have a different histological appearance.
Throughout the stomach the mucosa is thrown into visible longitudinal folds known as
rugae.
The stomach is lined by a
simple columnar epithelium punctuated by gastric pits into which the gastric glands drain.
The muscular coat (muscularis propria) is three layers thick. Compared with the rest of the gut tube it has what
an additional oblique layer of fibres closest to the mucosa that helps to churn up the food within the stomach.
The mucosa of the stomach contains many tubular glands within its mucosa. What do these do
These fill the lamina propria and discharge their secretions into gastric pits that communicate with the lumen of the stomach.
There are three main types of cell within the glands of the fundus and body of the stomach,
(i) mucous neck cells that provide a lubricatory, acid-resistant mucus,
(ii) parietal cells that secrete HCl and intrinsic factor and (iii) chief cells that produce digestive enzymes, notably pepsin (which is secreted in an inactive form - pepsinogen).
Full gastric glands are present in the wall of the body and fundus of the stomach. Glands of the cardia and pylorus also have gastric glands but
they are devoid of parietal and chief cells. The remaining mucous neck cells provide protective and lubricatory secretions.
The stomach is lined by
simple columnar epithelium
What do the cells lining stomach do
These tall cells produce a special acid-resistant mucin that protects the lining of the stomach.
The surface epithelium also has deep invaginations called
gastric pits
The surface epithelium also has deep invaginations called gastric pits, (openings shown by green arrows) at the bottoms of which are … what do these do
gastric glands. Several tall straight or branched glands open into each gastric pit. The glands contain different types of secretory cell. These glands fill the lamina propria.
The submucosa consists of
loose connective tissue often with prominent blood vessels.
The muscularis propria consists of thick bands of
smooth muscle often subdivided into three layers.
Parietal cells are found where in the stomach
in the gastric glands in the body and fundus of the stomach. They occur mostly in the upper parts of the glands, close to the gastric pits.
Structure and appearance of parietal cells
The cells are globular in shape and stain bright pink with H&E. The surface of these cells is deeply invaginated to form intracellular canaliculi and the cells contain many mitochondria. These often stain darkly and give the cytoplasm a grainy appearance.
What do the parietal cells contain and what do they do
The cells are rich in the enzyme carbonic anhydrase. They secrete hydrochloric acid. They are also believed to be the source of intrinsic factor essential for the absorption of vitamin B12
What is the structure function and appearance of the chief cells
Chief cells are pyramidal in shape and normally occupy the deeper parts of the gastric glands. Part of their cytoplasm stains blue with H&E and the cells can be seen to contain secretion granules.
They synthesise and secrete pepsinogen (pepsin) and lipases.
Like the acid producing cells, these enzyme-secreting chief cells are found only where
only in the glands in the body and fundus of the stomach and not in the glands of the cardiac or pyloric regions.
The gastric glands of the cardiac and pyloric regions of the stomach are shorter than those of the body or fundus and appear how
are coiled rather than straight.
The gastric glands of the cardiac and pyloric regions of the stomach are composed to what
They are composed mainly of mucous neck cells. These are similar to those seen in the glands of the body and fundus where they are confined to a narrow band at the entrance to each gland.
Scattered among the neck cells of the pyloric region are
isolated cells that produce gastrin and a bombesin-like peptide.
, throughout the whole of the gastric mucosa there are scattered pale-staining endocrine cells that produce what
serotonin, somatostatin and vasoactive intestinal peptide (VIP)
What is the purpose of the neck cells and endocrine cells in the gastric mucosa
Together these cells play an important role in regulating the breakdown and delivery of foodstuffs to the duodenum which occurs during the digestion process.
The lining of the intestine is thrown into circular folds that are visible with the naked eye. These are known as
plicae circulares
Where are the plicae circulares most numerous and least numerous
in the jejunum and least numerous in the distal part of the colon.
What is the purpose of the plicae circulares
They increase the surface area of the gut available for absorption.
The surface area is the small intestine is further augmented by what
microscopic leaf-like or finger-like projections of the mucosa known as intestinal villi.
The villi are covered by what
simple columnar epithelium with two main cell types, enterocytes (absorptive cells) and goblet cells (mucus secreting cells). These cells are short lived but are replaced by cells that originate in the crypts.
Each villus contains in its core what, and what do they do
a small arteriole, a thin walled venule and a blind-ended lymphatic (lacteal).
They also contain smooth muscle cells that rhythmically shorten the villus thereby “milking” the blood and lymph from the villus. The venules and lacteals carry absorbed nutrients to the liver.
Between the villi are straight tubular glands known as
crypts of Lieberkuhn.
What is the purpose of the crypts of Lieberkuhn
These contain a stem cell population. Newly formed cells migrate from the crypts on to the surface of the villi and are eventually sloughed off from the tips, the whole process taking about five days.
columnar Enterocytes are what
the major absorptive cell of the small (and large) bowel.
Each cell possesses about 300 short, closely packed processes known as microvilli on its apical surface.
Arising from the outside surface of these microvilli of the enterocytes is what
a well-developed glycocalyx that acts as a filter and as an anchorage for exo-enzymes.
What is absorbed through the enterocytes
Most nutrients are aborbed across this epithelium although water and some glucose is able to be taken up via pathways between the cells.
The presence of high concentrations of hexose sugars within the glycocalyx means that the brush border (like the goblet cell) stains intensely by the what procedure
the Periodic Acid Schiff (PAS) procedure.
How long is the duodenum
12 inches (30 cm long
What is the structure of the lining of the duodenum
It has a relatively smooth lining with few plicae circulares.
The villi are broad leaf-like structures and the epithelium has relatively few goblet cells.
How do scientists histologically determine whether a sample is duodenum or jejunum
(However, it may be worth noting that the shape of the villi is not sufficient information by itself to determine whether the tissue is from the duodenum or jejunum. Histopathologists look for the presence of Brunner’s glands to determine whether this is duodenum or jejunum.)
The submucosa of the duodenum is filled by a mucous secreting what gland ? and what does this help to do
Brunner’s gland. Its alkaline secretion helps to neutralise the chyme emerging from the stomach.
Duodenal crypts, like those of the rest of the intestine contain newly formed enterocytes and goblet cells. In the small intestine these cells migrate on to the villi. In the large intestine where there are no villi, what happens
the cells simply spread out over the flattened surface of the gut.
Dividing cells in the crypts can be recognised how
their compact very dark staining nuclei or by sets of chromosomes if the nuclear membrane has broken down.
At the bottom of the crypts are a population of differeniated Paneth cells. These secrete what? what does this do? How are they recognised?
These secrete lysozyme, an enzyme important for the breakdown of bacterial cell walls.
They play an important part in regulatiing the bacterial flora of the gut.
The cells can be recognised by their bright pink-staining cytoplasmic granules.
How does the epithelium of the jejunum appear
It has close-packed plicae circulares, the villi are long and narrow and the crypts are relatively short. Many goblet cells are present within the epithelium.
How does the submucosa of the jejunum appear
The submucosa is variable in thickness but is generally very loose so that the mucosa is almost detached from the muscularis externa outside it.
Unlike the duodenum, the jejunum does not have what in its submucosa
Brunner’s gland in its submucosa nor does it have the large lymph nodules (Peyer’s patches) characteristic of the ileum
What helps to distinuish the jejunum from the duodenum and the ileum
he jejunum does not have Brunner’s gland in its submucosa nor does it have the large lymph nodules (Peyer’s patches) characteristic of the ileum
Where are lymph nodules present in the jejunum
Lymph nodules are present in the lamina propria but they do not normally penetrate into the submucosa
what do the Lymph nodules are present in the lamina propria but they do not normally penetrate into the submucosa look like in the ileum
Here the plicae circulares are not as closely packed as in the jejunum and the villi are not as tall. Goblet cells increase in number towards its distal end.
Large patches of lymphoid tissue (Peyer’s patches) are present where in the ileum
Large patches of lymphoid tissue (Peyer’s patches) are present in the submucosa and in places these can be seen to erupt through the muscularis mucosa into the lamina propria.
Explain the muscularis mucosa of the ileum
There is no muscularis mucosa but the muscularis externa shows two layers of smooth muscle similar to the rest of the intestine. The taenea coli originate at the base of the appendix and run the whole length of the large intestine
The colon has four segments:
ascending, transverse, descending and sigmoid colon
These segments together with the caecum at its proximal end and the rectum that follows it all have a similar histological appearance.
There are no intestinal villi in the large intestine. Instead, the mucosa consists of
consists of close packed intestinal crypts that mainly contain enterocytes and abundant goblet cells. The lamina propria is restricted in volume due to the packed nature of the crypts but a prominent muscularis mucosa separates the mucosa from underlying tissues.
Why is The lamina propria is restricted in volume in the large intestine
due to the packed nature of the crypts but a prominent muscularis mucosa separates the mucosa from underlying tissues.
What do the The mucosa and submucosa of the colon and rectum look like
The mucosa and submucosa frequently have lymph nodules embedded within them, part of the GALT system of immunologic defense.
The muscularis externa consists of what in the colon
The muscularis externa consists of a thickened inner circular layer of smooth muscle and an outer layer that is drawn up into three longitudinal bands (ribbons) known as taeniae coli. These brands are clearly visible in a fresh gross specimen.
The rectum has a similar histological appearance to the colon, being lined by
a simple columnar epithelium.
The anal canal, on the other hand, is lined mainly by a
stratified squamous epithelium that becomes keratinized at its distal end.
The submucosa of the anus contains what
The submucosa contains fat and a prominent (internal) plexus of veins that may give rise to anal varicosities.
Describe the structure of the muscularis externa
The smooth muscle of the mucularis externa is thickened to form the internal anal sphincter and is surrounded by striated muscle of the external anal sphincter (derived from the pelvic bowl).
what does the peri anal skin contains what
The peri-anal skin contains hair follicles and modified sebaceous glands.
Where are the circumvalate papillae?
The circumvallate papillae form a V-shaped line between the anterior two-thirds and posterior third of the tongue.
Which statement concerning filiform papillae is true?
They contain taste buds for bitter taste They contain taste buds for salty taste The contain taste buds for sweet taste They contain taste buds for umami They roughen the surface of the tongue
They roughen the surface of the tongue
Filiform papillae are the most numerous of the papillae on the tongue, but they do not contain taste buds. Instead, they roughen the dorsal surface of the tongue, which possibly aids in mastication.
It is worth noting that although the textbook describes different tastes being localised to different parts of the tongue, this is not true.
The submandibular gland is
mixed mucous/serous
mucous glands have clear cytoplasm)
The sublingual gland, buccal and lingual glands are mostly
mucous glands.
The parotid glands are
serous salivary gland
How Oesophageal mucosa recognised
Oesophageal mucosa is recognised by the presence of a non-keratinising stratified squamous epithelium (but this is found in the mouth as well), lymphocytes in the submucosa, and mucinous glands in the submucosa that have squamous-lined ducts.
Note: Although the textbook states that the gland ducts are lined by columnar epithelium, this is wrong – it is squamous (or, at most, in places, cuboidal)
How can you determine that a certain mucosa is from the gastric antrum
the long crypts that branch, lined by mucous-secreting cells, and the lack of parietal cells (which rules out body and fundus). The superficial zone of the mucosa occupies more than half the thickness in the antrum and pylorus, but about 50% in the cardia. The duodenal mucosa has a villous architecture.
What do parietal cells secrete?
Gastric parietal cells secrete hydrochloric acid (the surface mucous cells secrete a bicarbonate-rich mucous) and intrinsic factor.
Intrinsic factor plays a role in the absorption of Vitamin B12, which enters via the diet (it is not secreted by parietal cells!).
Chief cells secrete pepsinogen, which is cleaved to active pepsin in the gastric lumen.
What do Brunner’s glands secrete, where are they found and why
Brunner’s glands secrete an alkaline mucus that helps neutralise gastric acid. Chyme is the name given to digested food that leaves the stomach.
How to differentiate the ileum;s mucosa from the duodenum and jejunum
the villous architecture and the prominent lymphoid aggregates (Peyer’s patches) in the submucosa and mucosa. These lymphoid aggregates are not present in the jejunum or duodenum. The appendix and colon do not have a villous architecture.
Which statement about the histology of the colon is true?
Auerbach’s plexus lies in the muscularis propria
It has a prominent brush border
It is lined by a serous epithelium
The caecum has a different histology to the ascending colon
The muscularis propria has three layers
Auerbach’s plexus lies in the muscularis propria
Two autonomic nerve plexuses innervate the gastrointestinal tract: Meissner’s plexus lies in the submucosa, Auerbach’s plexus lies between the layers of the muscularis propria.
The colon has a double-layered muscularis propria – inner circular, outer longitudinal.
The epithelium comprises a simple columnar layer of mucus-secreting enterocytes.
The histology of the different parts of the colon is the same.
A prominent brush border is a feature of the small intestine, not the colon.
This is colonic mucosa how can you tell this
the epithelial stem cells lie at the base of the crypts of Lieberkhun. You cannot tell which part of the colon it comes from, as the entire colon looks the same. The colon does have a muscularis mucosa, immediately below the lamina propria. The colon is supplied by the superior mesenteric artery and the inferior mesenteric artery. Vitamin B12 is absorbed in the terminal ileum.
