lesson 12 gritti Flashcards
the digestive tract proper is composed of
oral cavity, esophagus, stomach and intestine
where are water and electrolytes absorbed?
in the large intestine
where does most of the absorption take place?
into the small intestine
what is the thing that changes the most among the different structures of the GI tract?
the epithelium
Accessory parts of the GI tract
glands (liver, pancreas) that produce enzymes essential for the breakdown of macromolecules
cardiac valve
between the esophagus and the stomach
pyloric valve
between the stomach and the intestine
ileocecal valve
between the small intestine and the large intestine
general structure of the GI tract: layers
mucosa, submucosa, muscolaris propria and serosa (or adventitia)
mucosa is divided in 3 layers
epithelium, lamina propria and muscolaris mucosa
GALT
gut associated lymphoid tissue
part of the mucosa (specifically in the lamina propria) and serves as protection of the body from pathogens that enter the GI tract
ex: Peyer patches in the terminal ileum is part of the GALT
MALT
mucosa associated lymphoid tissue
formed by all the ALTs in multiple organs of the body
-protect the body from the pathogens that enter into the mucosal surfaces of the different organs
lamina propria
loose reticular connective tissue
a lot of cells (cells of the immune system, smooth muscle cells, small glands)
small fibers
in the stomach the lamina propria is well developed, why?
it contains the gastric glands fundamental for the stomach function
muscolaris mucosa
thin layer of smooth muscle that separate the mucosa from the submucosa
-very thin, not everywhere can be spotted
the epithelium
changes according to the function of the different parts of the GI tract
it will have to be of a more protective type in the oral cavity (due to mastication) and of a more absorptive or secretary type in the intestine
M cells
present in the epithelium that overlies GALT, such as Peyer patches.
these cells are specialized epithelial cells that
-take up antigens from the gut lumen by endo or phagoctosis
-antigens are delivered to Antigen presenting cells
-they process the antigen and present it to T and B cells
-there is the production of antibodies and the starting of a localized immune response
submucosa
-dense irregular connective tissue (more fibers than cells very disorganized)
-Meissner plexus or submucosal plexus: in the submucosa there is the innervation of the autonomic nervous system
-there are blood and lymph vessels
muscolaris propria
at least 2 muscle layers
-inner one: circular
-outer one: longitudinal
where is the meissner plexus?
in the submucosa
less organized than the myenteric one
where is the Myenteric (Auerbach plexus)?
in the muscolaris propria
what are the two nervous plexi that make up the entire nervous system of the GI tract?
the Myenteric (Auerbach) plexus in between the 2 layers of the muscolaris prpria and the Meissner plexus in the submucosa
which type of cell is present in both the plexi of the GI tract?
ganglion cells
rugae
foldings of the stomach that include both the mucosa and the submucosa
less visible when the stomach is full
serosa
-outermost layer
-loose connective tissue with different appearance depending on the organ we are looking at
-often surrounded by a thin layer of squamous epithelium called mesothelium
what do you have instead of the serosa in the organs not suspended in the abdominal cavity? such as the esophagus
-you have the adventitia
-connective tissue with a protective function that does not have the mesothelium
the serosa in the abdominal cavity is continuous with?
the mesenteries (membranes sorrounded by mesothelium on both sides that support the intestines) that are continuous with the peritoneum (a serous membrane that lies the abdominal cavity)
what is the epithelium characteristic of the whole oral cavity?
-STRATIFIED SQUAMOUS EPITHELIUM
-it has a protective function, weather it is keratinized or not
3 types of mucosa in the oral cavity
masticatory mucosa (hard palate, gingivel)
specialized mucosa (more at the back of the oral cavity)
lining mucosa (lips, soft palate…etc)
oral mucosa
epithelium (stratified squamous)
lamina propria (connective tissue)
NO muscolaris mucosa or muscolaris propria
-the structure is similar to the skin
epidermis->epithelium
dermis->lamina propria
the lining mucosa has a submucosa that contains different glands. which types?
salivary glands, lymphoid and sebaceous glands
simple or compound gland depending if?
the duct is branched or not
salivary glands are made of
-secretory acini and ducts
-compound glands because the duct is branched
-tubuloacinar ->the secretory portion has the shape of a tubule/ball
lips, divided in 3 layers
- internal mucus layer
thick stratified non keratinized squamous epithelium with minor salivary glands - red vermillion zone
thin keratinized stratified squamous epithelium
no glands
kept moist by the saliva in the tongue
its underlying connective tissue has an highly developed innervation - outer layer: thin skin, containing sweat glands, hair follicles and sebaceous glands
why are lips movable?
due to their well developed striated muscle
the tongue is composed of?
adipose tissue, connective tissue, glands and skeletal muscle.
the mucosa is characterized by a stratified squamous epithelium non keratinized or partially keratinized
sulcus terminalis
-V shaped
-divides the tongue in an anterior 2/3 and a posterior 1/3
what’s present in the anterior 2/3 of the tongue?
projections of the mucosa called papillae
filiform papillae
-very numerus
-thin, elongated conical projections
-keratinized tips
-facilitate the disintegration of food
fungiform papillae
-less numerous
-non or lightly keratinized
-associated to Taste buds
circumvallate papillae
-larger
-at the bottom(in the cleft) you have the opening of von ebner’s glands
->serous glands
-associated to taste buds
what is in common between fungiform papillae and circumvallate papillae?
both associated to taste buds->fundamental ovoid structures that allow us to taste different flavor/chemical composition of the food we ingest
taste buds, are made of?
- taste receptor cells
50-100 each bud and characterized by apical microvilli - support cells that support the taste pore (little opening onto the surface)
- basal cells that are stem cells that renew both these cell types (7-10 days turnover)
NB: different receptor cells according to the different taste they can sense
these taste buds are enwrapped by?
afferent sensory axons that form synapses with taste receptor cells
what are the 2 receptors that a receptor cell can have?
GPCRs and ion channels
type of epithelium that characterizes the esophagus
stratified squamous non keratinized epithelium, very thick
esophagus main characteristics
-25cm tube with the function of taking the food swallowed into the stomach
-large nucleus despite it being quite closed due to foldings of the mucosa
name of glands of the esophageal lamina propria
esophageal cardiac glands
name of glands in the esophageal submucosa
esophageal mucous glands
what do you see in the upper part of the esophagus in terms of muscularis external?
upper third: only skeletal muscle, voluntary contraction
middle third: a mix of smooth and skeletal muscle
going downards we see only smooth muscle (involuntary peristalsis)
instead of the serosa in the esophagus we have?
the adventitia, it is attached to the other organs.
in the last cm (in the abdomen) we have the serosa
cardia
transitional zone between the esophagus and the stomach
contains cardiac glands
->mucous secreting glands
pyloric part
connects the stomach with the small intestine
the pyloric part ends at the pyloric sphincter
the sphincter relaxes when the chyme is ready to go to the duodenum
-contains pyloric glands that secrete 2 types of mucus+ the hormone gastrin
esophageal-gastric junction
easily identifiable due to the change in epithelium (stratified squamous non keratinized->simple columnar epithelium)
body and fundus
histologically are very similar
have gastric glands that produce the acidic gastric juice
where are the cardiac glands located?
and gastric glands?
in the cardia
between the lamina propria and the muscolaris mucosa
in the fundus/body of the stomach
between lamina propria and muscolaris mucosa
name of the invaginations of the stomach mucosa
gastric pits
serve as openings for the gastric glands that secrete gastric juice
how many layers of muscles in the muscolaris external of the stomach?
3
how many layers of muscles in the muscolaris external of the esophagus?
2
surface mucous cells
located in the epithelium of the gastric pit.
produce mucous to protect the mucosa from the acidic gastric juice and from the abrasive effect of food
isthmus
transitional zone that connects the gastric pit to the gastric glands
contains stem cells that can renew the epithelium
secretory epithelial cells of the gastric glands
-neck mucous cells
mucus less alkaline than surface mucous cells
-chief cells
lipase and pepsinogen for the digestion of lipids and proteins
-parietal cells
HCI
-G cells
endocrine cells
why do parietal cells have a lot of mitochondria?
they need a lot of ATP to catalyze active transporters for bicarbonate, H+ and CL- (to synthesize HCI in the gastric lumen and transport bicarbonate in the lamina propria->acidic ph in the lumen, higher ph in the mucosa)
where are the granules positioned in chief cells? and in enteroendocrine cells?
- into the apical part
- in the basal part (in contact with the basal membrane, the products have to be released in order to enter the circulation)
type of connective tissue of the adventitia and serosa?
loose connective tissue
serosa is lined by mesothelium: simple squamous epithelium
