Digestive System 2 Flashcards
What is the length of the digestive tract?
It extends from the mouth to the anus.
What does the wall of the digestive tract consist of?
- outer serosa (or an adventitia)
- muscularis externa
- submucosa
- inner mucosa
What does the “mucosa” layer constist of?
- inner epithelium
- middle lamina propria
- outer muscularis mucosae
Where is the muscularis mucosae absent?
- mouth
- pharynx
- portions of the esophagus
- rumen
What does the mouth lack? (which parts of the wall?)
- submucosa
- muscularis externa
What does the digestive tract consist of?
only TUBULAR organs!
What is the outermost layer of all tubular organs?
2 options:
- tunica serosa
- tunica adventitia
Is it possible to find both tunica serosa and tunica adventitia in one place in tubular organs?
NO!
Is it possible to find both tunica serosa and tunica adventitia in the same tubular organ?
yes, just at different locations!
What is the difference between tunica serosa and tunica adventitia from a histological perspective?
Tunica serosa = simple squamous epithelium
(squamous are very flat cells)
What is a special feature of tunica serosa cells?
all of the cells secrete SEROUS SECRETE!
simple squamous epithelium
What is serous secrete? What is its function?
- watery substance
- small fraction of proteins and other molecules
- necessary for the lubrication of outer surfaces
What lubricates internal organs?
tunica serosa cells
Where is tunica serosa found?
ONLY IN CAVITIES!
- pelvic
- abdominal
- thoracic
ser tylko w brzuchu = cavities
What is constant in all organs in a cavity?
- lubrication!
- covered by tunica serosa!
Explain the structure of tunica adventitia. What is its function?
- based on loose connective tissue
- attaches organ with the adjacent structure
Explain the surrounding layer of the esophagus.
Esophagus is located in the neck = not a cavity!
- highly attached to adjacent structures (muscles)
- surrounded by tunica adventitia
Explain the structure of the external layer of tissue of the digestive tract.
tunica serosa- simple squamous epithelium
tunica adventitia- loose connective tissue
State the functions of the external layer of the digestive tract.
Tunica adventitia:
- attaches organ to adjacent structures
Tunica serosa:
- prevents attachment
- provides lubrication + sliding movements
What layer comes after tunica serosa/adventitia?
Tunica muscularis (Muscular layer)
What is tunica muscularis based on?
smooth muscle cells
What is tunica muscularis based on?
2 layers!
1) Circular muscle layer
2) Longitudinal muscle layer
Which muscle layer is typically located on the inner side? Which on the outer side?
Inner- circular muscle layer
Outer- longitudinal muscle layer
Why are the two muscle layers necessary in the digestive tract?
Circular and longitudinal contractions provide the digestive tract with “PERISTALTIC MOVEMENTS”.
- allow food to move through the digestive tract
Why are the two muscle layers necessary in the uterus?
Contractions allow to push out baby during the birth process.
Which muscle layer is most important in blood vessels? Why?
- CIRCULAR muscle layer!
- regulates blood pressure (narrows and widens lumen)
What structures are the same in all tubular structures?
Tunica muscularis!
- circular muscle layer
- longitudinal muscle layer
What is a structure that is an exception to other tubular organs when it comes to tunica muscularis? Why? What are the layers? What order?
STOMACH:
- additional layer- OBLIQUE pathway
- located most inner
- muscle order (From center): oblique, circular and longitudinal layer
Why is the stomach an exception of the type of muscles in tunica muscularis?
- additional oblique muscle layer
- helps mix food within the stomach
What layer is located beneath the muscle layer (tunica muscularis)?
Tunica SUBMUCOSA
What type of tissue is tunica submucosa?
loose connective tissue
ifyou get subbed out then youre loosing!
What is the function of tunica submucosa?
loose connective tissue:
- mediator between tunica mucosa and tunica muscularis
What is the final (most inner) layer of the digestive tract? What is it composed of?
tunica MUCOSA
3 layers:
- epithelium (inner)
- lamina propria (middle)
- muscularis mucosa (outer)
What is the most important layer of the digestive tract wall?
tunica mucosa
What is the most important layer of tunica mucosa? Why?
- epithelial layer
- very related with the function of organs
- helps distingush between particular organs (epithelium differences allow to distinguish between types of organs)
What is the structure of lamina propria?
loose or dense connective tissue
lame vs proper = loose vs dense
Explain the structure of Muscularis Mucosae. Where is it located?
Muscularis Mucosae = outer layer of mucosa
- very thin layer
- few smooth muscle cell layers
What structure is different depending on the type of organ in which it is located? State examples.
INNER SURFACE OF MUCOSA (EPITHELIAL LAYER OF MUCOSA)
- general histological structure of mucosa may be the same, yet there are underlying architectual differences (infoldings, projections, etc.)
eg.
- intestine: projections (villi) for absorpion
- stomach: invaginations
What other components can be spotted in the digestive system? State an example. Provide a reason.
immune system components
- things which help fight infections (aggregations of immune system cells)
eg. LYMPHOID NODULE
kills pathogens and bacteria which enter the organism through the digestive tract.
How can we distinguish that the digestive system is the primary immune system organ?
Through the large number of immune system cells.
What type of tissue is the epithelium of the mucosa made out of?
stratified squamous epithelium
What occurs to the stratified squamous epithelium in some places? What places?
keratinization
- dental pad
- surface of tongue
- hard palate
- cheek
- non glandular stomach of ruminants, horses and pigs
Where is simple columnar epithelium located?
mucosa in the:
- glandular stomach
- small intestine
- most of the large intestine
What is the structure of the epithelium of mucosa in the glandular stomach, small intestine, and most of the large intestine?
simple columnar
What type of tissue does the anal canal consist of?
stratified squamous
same like inner epithelium of digestive tract
What is the mucosa moistened by (from the mouth through the esophagus)? What are their types? What is the major type of gland?
SECRETIONS
- mucous
- serous
of various glands (especially salivary glands).
What other structures aid in the production of lubricating secretions? What cells?
STOMACH:
- surface mucous cells
- mucous neck cells
SMALL and LARGE INTESTINE:
- goblet cells
What is the beggining and ending part of the digestive tract lined by?
stratified squamous epithelium
What epithelium are the parts of most digestive actions lined by?
simple columnar epithelium
Why is the anus lined by stratified squamous epithelium?
- it has small contact with the external environemnt
- thick= protected from outer environmental factors: pathogens, chemical substances etc.
Why is the beginning of the digestive tract lined by stratified squamous epithelium? Which parts?
- all parts from mouth until the glandular stomach
- thick= protected from outer environmental factors: food! (hot, rough materials, very large amounts)
When does the change in epithelium occur? Why?
only in the glandular stomach (stratified squamous –> simple columnar)
- stomach: protection is not as much necessary because:
1) large: food fits (unlike in esophagus)
2) acidic environment
3) enzymes
Why are the small and large intestines not necessary protected?
- recieves ‘safe’ digested food
- equilized in temperature
What is an advantage of being lined with simple columnar epithelium for the intestine?
simple columnar epithelium is much thinner than stratified squamous epithelium –> absorption of molecules is effective
What is the oropharynx lined by?
stratified squamous epithelium
What does the oropharynx contain? What is an exception? Why?
MUCOUS glands
- except carnivores: MIXED glands
(stratified squamous epithelium)
What is the muscularis externa of skeletal mucle in the oropharynx surrounded by?
ADVENTITIA
- not in the cavity
- connects organ with surrounding muscle structures
What organ follows the mouth in the digestive tract?
oropharynx
Until what structure is the epithelium in the digestive tract stratified squamous?
the glandular stomach
What is the esophagus externally surrounded by in most of its length?
tunica ADVENTITIA
What part of the esophagus is special? Why?
Muscularis externa varies in composition:
- DOG: composed of skeletal muscle throughout its length (except of stomach in which skeletal muscle –> smooth muscle)
- RUMINANTS: entire muscle is skeletal muscle
- HORSE and CAT: skeletal –> smooth muscle in the caudal third of the esophagus
- PIG: skeletal –> smooth muscle (cranial to the diaphragm)
Why is a part of the esophagus not lined by adventitia? What is it lined by?
- serosa
- located in a cavity (before opening to stomach)
What is exceptional in the esophagus?
- muscular layer is not based on smooth muscle tissue!
- based on skeletal muscle!
- (mixture between skeletal and smooth muscle tissue)
What about the esophagus can inform one about the species of an organism?
- the proportion of skeletal muscle
- the position of glands
What is the mucosa of the esophagus lined by?
stratified squamous epithelium
What types of glands occur in the esophagus?
mucous and mixed glands
What about glands allows to distinguish between species?
- position
Explain the position of glands throughout the esophagus in different species.
CAT, HORSE, RUMINANT: glands at the junction of the pharynx and esophagus
PIG: glands occur anteriorly, no glands in the midregion, sparse glands in the caudal region
DOG: glands in the entire length of the esophagus + extend into the stomach (Short distance)
What is the major gland found in the esophagus?
Mucous glands (but mixed glands are also present)
Explain the differences in the stomach between different species.
HORSE, RUMINANT, PIG:
- forestomach: nonglandular
- stomach: glandular
RUMINANTS:
- forestomach: rumen, reticulum and omasum
- abomasum: glandular stomach
CAT, DOG:
- forestomach: absent
- stomach: glandular
What does the glandular stomach consist of in all species?
- cardiac gland region
- fundic gland region
- pyloric gland region
State a main feature of the cardiac gland region.
Small in all species but the pig.
What is the stomach lined by? Does it produce anything?
mucous producing SIMPLE COLUMNAR EPITHELIUM
What are all fore-stomachs lined by?
keratinized stratified squamous epithelium
What is the “real stomach”?
- glandular stomach
- digestion process is based on enzymes
Explain the structure of the forestomach. What is its purpose?
- no glands
- entire digestive process is based on microorganisms
Explain the distribution of gastric glands in the stomach.
cardiac zone (nearest to esophagus)- cardiac glands
pyloric zone (final part)- pyloric glands
fundic part (body)- corpus-fundic glands
What glands are mucous glands?
cardiac and pyloric glands
What is special about the fundic part of the stomach?
gastric pits are present
What are gastric pits?
Tubular structures formed where the epithelium of the glandular stomach invaginates into the lamina propria.
What empties into gastric pits?
tubular glands
What are glands constructed mostly of in the fundic gland region? What is their function?
- parietal cells (secrete HCl)
- chief cells (secrete pepsinogen)
What type of glands are present in the pyloric gland region?
mucous type with interspersed parietal cells
What type of glands are present in the cardiac gland region?
mucous glands with occasional parietal cells
In easy words what is a gastric pit?
invagination of the stomachs internal surface
What is important to note about gastric pits?
The gastric pit is not the gland itself!
- glands open into gastric pits
Are mucous cells part of gastric pits?
not always, which is why they are called “surface mucous cells”.
What is the name of the mucous producing cell of the gastric pit?
mucous neck cell
What is in between of the mucous neck cells? What are their functions?
stem cells
- in charge of renewing superficial epithelium and other cells within the gastric pits
What do parietal cells secrete? What is their structure?
- large triangular shape
- secrete HCl and an interinsic factor
- may have 2 nuclei
What do chief cells secrete? What is it a precursor of? What is their struture?
- secrete pepsinogen (primary precursor of pepsin)
How is pepsin created?
pepsinogen + HCl
What is the difference between pepsin and pepsinogen?
pepsinogen= inactive form of pepsin (cannot function in digestion)
What is a G-cell? What does it produce? Function?
produces and secretes gastrin (hormone),
- maturation of entire fundal growth
- stimulation of gastrin –> formation of more gastric pits –> more effective digestive process
- cause chief cells to produce more pepsinogen
- impacts the mobility and contractions of muscles within the digestive tract (impacts peristaltic movements and stomach contractions)
What allows the stomach to be part of the endocrine system?
the presence and secretion of the hormone GASTRIN by G-cells.
What cells can be found within a gastric pit?
- surface mucous cells
- mucous neck cells
- parietal cells
- chief cells
- G-cells
- stem cells
What lies beneath gastric glands in the stomach?
STARTUM COMPACTUM:
- layer of dense connective tissue
What is stratum compactum?
- layer of dense connective tissue
- beneath gastric glands
- CARNIVORES
What is special about the stomach of a horse? What is its name? What is it lined by?
Large non-glandular region between the esophagus and glandular stomach.
- demarced from the glandular stomach by the MARGO PLICATUS junction
- lined by heavily keratinized stratified squamous epithelium
What is special about the stomach of a dog?
STRATUM COMPACTUM (layer of dense connective tissue beneath gastric glands)
What is special about the stomach of a pig?
small non-glandular region
pigseat a lot, so they need a large glandular stomach
What is not typically found in the digestive system? Where is it found as an exception?
dense connective tissue
- found in the stratum compactum in carnivores
State the main features of the stomach (simple).
- lined by simple columnar epithelium
- inner surface has gastric pits
- simple tubular glands in gastric pits (secreting acids and enzymes)
- muscle layer beneath glands (3 layers: oblique, circular and longitudinal)
- serosa (final layer)
What can be found in gastric pits?
simple tubular glands
What is the name of the fore stomach of ruminants?
Rumen
What is the rumen lined by? Into what structures does it continue?
- keratinized stratified squamous epithelium
- continues into the reticulum and omasum
What are pillars of the rumen?
Large forlds of the tunica mucosa which contain smooth muscle from the tunica muscularis.
What is the name of the large forlds of the tunica mucosa which contain smooth muscle from the tunica muscularis.
pillars
Explain the surface of pillars.
smooth
What is the name of conical projections of the mucosa?
papillae
What do the papillae cover?
- the rest of the inner surface of the rumen
What is the core of a ruminal papilla made of? What does it lack?
- contains connective tissue
- lacks a lamina muscularis
Explain the structure of the reticulum. Distinctive features?
- mucosal folds form honeycomb like chambers
- reticular crests
- reticular papillae (crests and floor of chambers)
distinctive features:
- larger
- lamina muscularis in mucosa
- lamina muscularis is isolated (doesnt continue, no juctions
What can be found on the crests and the floor of the chambers of the reticulum?
Reticular papillae
How is the lamina muscularis organized within the crests? (reticulum)
isolated patches of smooth muscle (tips of folds)
Expain the structure of the omasum.
Tunica mucosa of the omasum forms long omasal laminae which extends into the lumen
What extends into the core of the laminae to what?
lamina muscularis and tunica muscularis extend into the core of the laminae to form 3 laters of smooth muscle.
- not isolated! all muscles are connected!
Where are the papillae present in the omasum?
- on the surface of the laminae
- between laminae
How to distinguish between omasum and reticulum?
check if the muscles are isolated or connected.
omasum= connected
reticulum= isolated
