Digestive System 3 Flashcards
What do the intestines of a mammal consist of?
- small intestine (duodenum, jejunum, ileum)
- large intestine (cecum, colon, rectum, anal canal)
What is the tissue found in the small intestine?
simple columnar epithelium
+ striated border
What tissue is the large intestine composed of?
simple columnar epithelium
+ striated border
What other cells, except of simple columnar epithelium, can be found in the intestines?
goblet cells
How is the tunica muscularis of the intestines organised?
What type of cells?
- inner circular layer
- outer longitudinal layer
smooth muscle cells
How do the intestines compare from a histological point of view?
They are very similar.
duodenum, jujenum, ileum are very similar; but also, small and large intestines are very similar.
What is the outermost layer of the intestines? Why?
Tunica Serosa
- serous cells provide secrete which lubricates the surface of intestines,
- allows intestines to glide against other organs
What is the second layer of the intestines (from the outside)?
Tunica Muscularis
- outer longitudinal layer
- inner circular layer
- (both layers = smooth muscle cells)
What is the 3rd layer (counting from the outside) of the intestines? What tissue is it based on?
Tunica Submucosa
- based on loose connective tissue
What is the final tissue layer of the intestines (most inner layer)? What cells is it composed of?
Mucosa:
- simple columnar epithelium
- striated border
What is meant by the “striated border” of the intestines?
“striated border” = microvilli
What are ‘microvillis’?
very small projections located on EACH simple columnar epithelial cell.
What do microvilli provide the intestines with? Why is this necessary?
- microvilli increase the intestinal surface area
- necessary to absorb water and nutrients more effectively
What is the major difference between the histological structure of the small and large intestine?
villi!
(only found in the small intestine)
What is the special structure of the small intestine?
villi
What are the differences in villi between species?
ruminants: short and thick
carnivores: long and slender
What is located at the bases of villi?
Invaginations of the epithelium called the intestinal glands.
What are the invaginations in the epithelium at the villi bases called?
intestinal glands
What occurs in the invaginations? How does it occur? What is a different name of the villi invaginations?
invaginations = intestinal glands
- replacement of the mucosal epithelium
- by cell division
By what process is mucosal epithelium replaced?
cell division
What is a distinctive feature of the small intestine?
Mucosa takes up a very large portion of the entire intestinal wall/organ.
- 80% of entire wall
- 20% remaining layers (tunica submucosa, muscularis and serosa)
What type of projections can be spotted in the small intestine?
outer projections: villi
inner projections: intestinal glands
What other organ has glands in the digestive system? What are their names?
stomach
gastric glands (in gastric pits)
What is the difference between glands in the stomach and small intestine?
stomach- gastric pits
small intestine- intestinal glands
stomach: invaginations (gastric pits) which only later open into gastric glands
What type of cells are located in intestinal glands?
- stem cells
- paneth cells
- enteroendocrine cells
- goblet cells
- enterocytes
What is the function of stem cells in intestinal glands? Why is it important?
- renewal of the intestinal epithelium,
- important because the simple columnar epithelium has a very limited lifespan
What are feces based on?
- dead epithelial cells
- only small portion is undigested food
What are paneth cells? What is their main function?
- innate immune system cells
- produces enzymes (lysozyme) (which breaks down bacterial walls and recognises viruses)
What is the function of the lyzosyme enzyme? What cell secretes it?
- paneth cells secrete lyzosymes
function:
- innate immune response
- break down bacterial walls
- recognise viruses
- phagocytosis (similar to macrophages and neutrophils)
Are paneth cells effective?
paneth cells secrete lyzosymes which are not 100% effective, however they do play a very good job in innate immune defence.
What is the function of endocrine cells in the intestinal gland?
- secrete hormones: secretin, cholecystokinin, GIP
SECRETIN:
- regulates secretions in the pancrease, liver, small intestines and stomach,
- regulates pH levels
What feature makes the intestines similar to the stomach?
endocrine cells (both the stomach and small intestine have hormone secreting cells in their glands)
What is the function of secretin in the small intestine? What is it released by?
secretin is released by enteroendocrine cells.
function:
- regulates secretions (pancrease, liver, small intestines and stomach)
- regulates pH levels
What is the function of goblet cells in the small intestine?
- not specific to the small intestine (can be found in almost the entire digestive tract)
function:
- production of mucous (necessary to lubricate food)
What is the most important cell of the small intestine?
enterocyte
What is enteritis?
- the inflammation of intestines
- affects enterocyte cells
What is present in the lamina propria and submucosa of the small intestine?
Peyer’s patches
What are “payers patches”? Where are they found?
- aggregations of lymphatic nodules
- present in the lamina propria and submucosa of the small intestine (especially ileum)
Where are peyer’s patches most common?
- small intestine
- ileum
What is the function of peyer’s patches?
- guarantee immune surveillance of the intestinal lumen
- facilitate the production of an immune response within
To what system do the intestines qualify too? Why? What cells are present?
immune system
- most exposure to pathogenic bacteria and viruses takes place within the digestive tract
cells:
- lymphocytes (deeper to the mucosa)
- peyer’s patches
- paneth cells (lysozymes)
What other glands (apart from intestinal glands) can be found in the intestines? Where exactly are they found? What other name can they be reffered to as?
Brunner’s glands (Duodenal glands)
- found in the duodenum
- within the submucosa and lamina propria
compound tubular submucosal glands
What type of glands are Brunner’s glands?
compound tubular submucosal glands
What is the main function of Brunner’s glands? Why do they do what they do?
- produce a mucous-rich alkaline secretion (i.e. mucous containing bicarbonate) –> protects the duodenum from the acidic content (introduced by the stomach)
- provide an alkaline condition for intestinal enzymes to be active –> enable absoption to take place
State the species differences of Brunner’s glands.
carnivores, sheep, and goats:
- limited to the initial or mid region of the duodenum
horses, pigs, and cows:
- extend into the jejunum
What is opposite in the stomach and intestines?
the pH levels!
- stomach= very low (acidic)
- intestines= high (alkaline)
Why are the intestines alkaline?
Due to Brunner’s glands secreting alkaline mucous.
Why do the intestines have to have a basic pH?
To allow intestinal enzymes to be active and therefore enable the absorption of nutrients.
What would happen if Brunner’s glands wouldn’t exist?
- high pH would not be maintained in the intestines
- proper digestion would not take place
Explain the structure of the large intestines.
- similar to the small intestine
- lack villi
What additional structure does the large intestine have? Where is it located?
- prominent LYMPHATIC NODULES
- present in the submucosa
What type of cells increase in the intestinal epithelium? Why?
- GOBLET CELLS
- increase the production of mucous (increase lubrication)
- additional lubrication is required as water is removed from the intestinal contents (in preparation for defecation)
What happens to intestinal contents in preparation for defacation?
water is removed
How to distinguish the large intestine easily?
- villi are absent
- equal layer proportions (tunica mucosa=tunica submucosa=tunica muscularis=tunica serosa)
- has invaginations (crypts)
- no paneth cells
- more goblet cells
What cells line the large intestine?
- the same cells that line the small intestine (simple colimnar epithelium)
- NO PANETH CELLS
- stem cells
- enteroendocrine cells
- MORE GOBLET CELLS
- enterocytes
What cells are absent in the large intestines?
paneth cells
What is the effect of the lacking paneth cells in the large intestines?
- large intestine is not less effective in immune responses
- instead, there is a greater number of other immune system cells= LYMPHOCYTES
What are the pear patches below the mucosa of the intestines?
lymphocytes
What are the species differences of the cecum?
carnivores: small
herbivores: well developed (simpler stomach)
What type of bands are present in the tunica muscularis of the large intestine? What are their latin names?
Taeniae ceci:
- outer layer
- longitudinal bandss of smooth muscle
- vary in number
Taeniae coli:
- longitudinal bands of smooth muscle
- PIGS and HORSES ONLY
Which way does the rectum course?
retroperitoneally
As the rectum courses retroperitoneally, what changes?
tunica serosa –> tunica adventitia
What type of component is taeniae?
- anatomical
- it can be sen with the naked eye
- smooth muscle cells combined in a very thick string
- in tunica muscularis
- longitudinal muscle bands
What is special about the rectum?
the rectum is no longer positioned inside a cavity:
tunica serosa –> tunica adventitia
- attaches rectum to outer structures
- more stable, doesn’t move
How to distinguish the large instestine from the stomach?
1) GASTRIC PITS:
stomach: glands opening into gastric pits
large intestine: no glands opening into invaginations
2) TUNICA MUSCULARIS:
stomach: 3 layers (inner oblique, middle circular, outer longitudinal)
large intestine: 2 layers (inner circular, outer longitudinal)
What is the liver? What does it divide into?
- large lobed gland
- divided into lobes
- lobes divide into numerous classic lobules
What is each lobe covered by? What is beneath it?
- covered by mesothelium
- beaneath: CAPSULE OF THE LIVER (thin connective tissue layer)
What is the “capsule of the liver”?
thin layer of connective tissue below the mesothelium
What do classic lobules consist of?
- sinusoids
- hepatocytes (plates of parenchyma cells radially organised about a central vein)
What are hepatocytes?
plates of parenchyma cells radially organised about a central vein
What are the species differences of the liver? What allows one to distringuish between species?
ALL ANIMALS (except pig):
- lobules are indistinctly seperated from one another
PIG:
- boundries of connective tissue between lobules clearly identify their boundries
swinie sie widocznie roznia od innych
What type of organ is the liver? Why?
- parenchymal organ
- it does not have a lumen
What is a parenchymal organ? What structural components do parenchymal organs have?
1) only 2 components: parenchyma and stroma
PARENCHYMA: part of organ responsible for its function
STROMA: connective tissue providing organ shape and mechanical protection
What are the functions of the liver? What part of the organ are they based on? What cells qualify to this part?
parenchyma of the liver (hepatocytes)- responsible for function
- produce immune system components
- provide metabolism for incoming substances (drugs, medication, alcohol, toxic substances)
- provide physiological metabolism (produce fat, glucose)
- produces bile (necessary for digestion)
- storage of blood
What cells in the liver function as the parenchymal part?
hepatocytes
What is the parenchyma of an organ?
functional unit
What is an organs stroma?
- connective tissue
- shapes an organ (combines cells)
- provides protection from the mechanical aspect
Explain the stroma of the liver.
stroma always begins with:
- CAPSULE of dense connective tissue
capsule has branches, that go deeper into the organ dividing the organ into:
- LOBES
smaller branches go deeper into the organ, dividing it into:
- CLASSIC LOBULES
What shape do classic lobules have?
hexagonal or pentagonal
What part of the liver do its lobules divisions qualify to as?
stroma
What type of component are the liver’s lobules?
structural, not functional.
Are ‘lobules’ visible in animals other than pigs? What structure helps orientation?
connective tissue between parts, seperating lobules into lobules is not visible.
BUT it is possible to orient where a lobule would be, as each lobule structure has a CENTRAL VEIN.
What structure allows one to distinguish where a classic lobule is placed, and its borders?
the central vein
What are the interlobular connective tissues of the liver?
- bile duct
- hepatic artery
- portal vein
What is the ‘portal triad’?
How else can it be referred to as?
the interlobular connective tissue, consisting of:
- bile duct
- hepatic artery
- portal vein
also known as: hepatic triad, and liver triad
Explain the flow of liquids in the portal triad.
Blood travels in one direction, while, bile travels in the opposite direction (billary system).
What does blood travel in in the liver?
enters:
- hepatic artery
- portal vein
through:
- hepatic sinusoids
exits:
- central vein
- –> sublobular vein
- –> hepatic vein
How does blood travel into the liver?
through the hepatic artery and portal vein
How does blood travel within the liver?
through sinusoids
How does blood travel out of the liver?
through the central vein into the sublobular vein and finally into the hepatic vein.
Where does blood enter when using the hepatic artery and portal vein?
into hepatocytes
What are hepatic sinusoids?
capillaries, specific to the liver (gaps in their walls)
Why are sinusoids capillaries ‘specific to the liver’?
they have gaps in their walls
What is important to note about the blood going through the liver?
only a minor part goes through the system, a major part leaves the blood stream and enters hepatocytes.
What happens to blood in the liver? What can it be compared to?
blood is filtered through hepatic cells (like through a sponge).
What is the purpose of having two main blood insertions (ie. hepatic artery and portal vein) having the same direction of blood stream?
where does portal vein blood come from?
hepatic artery:
- oxygenated blood
- provides oxygen for hepatic cells (ie. parenchyma)
portal vein:
- nutrient rich blood
portal vein blood comes from the intestines.
Where do the two blood sources unite?
the hepatic artery and portal vein unite at the central vein.
What do hepatocytes produce? What direction does it flow in? Where to? What is its final destination?
- hepatocytes produce bile.
- bile flows in the opposite direction to the blood stream
- bile is collected in the bile duct
- goes further into the bile duct system, and then is collected in the gall bladder
What is the classic hepatic lobule? Shape? Cells?
- structural lobule of the liver
- hexagonal mass
- liver cells
What is the portal lobule? What else is it referred to as?
- territory of the liver tissue around a portal triad.
- nutritional lobule of the liver.
What are the hepatic acinus of Rappaport? Shape? Function?
- diamond shaped area of the liver parenchyma
- forms the structural and metabolic function of the liver
Explain the structure of the liver acinus. How many zones is it divided into? What is the zone division based on?
- divided into 3 zones
- based on the gradient of blood supply
ZONE 1:
- around the vascular backbone
- well oxygenated
ZONE 2:
- intermediate zone
- moderately oxygenated
ZONE 3:
- close to the central vein
- least oxygenated
Explain the 3 zones of the liver acinus. Location and oxygenation.
ZONE 1:
- around the vascular backbone
- well oxygenated
ZONE 2:
- intermediate zone
- moderately oxygenated
ZONE 3:
- close to the central vein
- least oxygenated
What are the three concepts of liver lobules?
- classical hepatic lobule
- portal lobule
- hepatic acinus of Rappaport
1) normal with dot inside; 2) between 3 dots (PORTAL); 3) between 2 dots
What is the name of the structural lobule of the liver?
classical hepatic lobule
What is the name of the nutritional lobule of the liver?
the portal lobule
What serves metabolic and structural functions of the liver?
hepatic acinus of Rappaport
What is the only type of lobule which can be seen?
classical hepatic lobule
Why are zones important in the acinus of Rappaport?
Different zones have different functions.
i.e.
zone 1: highly oxygenated blood –> generation of glucose molecules
zone 3: limited oxygen –> conversion of lipids
What is the pancrease? What is it surrounded by?
- an organ
- surrounded by thin connective tissue which extends between lobules of the parenchyma
What is scattered around the pancrease?
- endocrine pancreatic islets
- exocrine acinar cells
What are the exocrine secretory units? What do they secrete?
Exocrine acinar cells produce trypsinogen and chymotrypsinogen.
What type of glands are present in the pancrease? What does each part contain?
both endocrine glands and exocrine glands.
endocrine glands- pancreatic islets
exocrine glands- acinar cells
Explain the exocrine part of the pancrease.
stroma components:
- connective tissue capsule (dense regular connective tissue)
- branches dividing pancrease into lobes and lobules (not clear shape like the liver!)
What type of cells make up acini? How are acini connected?
acini:
- pyramidal shaped cells
- connected by a duct system
What is the initial portion of the exocrine duct system known as? What is it lined by?
the intercalated duct
- lines by flattened simple cuboidal epithelial cells
What does the intercalated duct connect with? What is it lined by?
the intercalated duct connects with the intralobular duct,
- lined by simple cuboidal epithelium
What else is located in the connective tissue between lobules? What is it lined by?
except: intralobular duct, intercalated duct
interlobular duct
- lined with simple columnar epithelium
What are the three ducts in the pancrease? Order? Cells?
1) intercalated duct (lined by flattened simple cuboidal epithelial cells)
2) intralobular duct (lined with simple cuboidal epithelial cells)
3) interlobular cells (lined with simple columnar epithelium)
What is the parenchyma of the pancrease based on? What are they composed of? Shape?
acinuses (composed of pancreatic acinar cells- triangular in shape)
What do acinar cells secrete? Active or inactive? What occurs later?
trypsinogen and chymotrypsinogen:
- inactive forms of enzymes
- activated in the small intestine (due to high pH levels)
Why does the pancrease not have active enzymes?
to prevent the pancrease from digesting itself.
How are enzymes transported from the pancrease to the small intestine?
through the duct system
- intercalated duct
- intralobular duct
- interlobular duct
What is the difference between the exocrine and endocrine part of of the pancrease?
Exocrine part has ducts.
Endocrine parts has no ducts and duct systems!
