digestive system V and VI Flashcards
name liver functions
endocrine secretion
exocrine secretion
inactivation or elimination of substances
conversion of substances
hemopoiesis
storage of substancesd
describe endocrine secretion - liver functions
secreted into blood
somatomedin - GH, tells liver to produce this and tells cells of epiphyseal plate - chondrocytes to grow and multiply, albumin, fibrinogen, prothrombin, transferrin - iron carrier, vldl = very low density lipoprotein, precursor of ldl
describe exocrine secretion - liver functions
not to circulation
goes to bile, bile acids, billirubin, it also secretes, phospholipids and cholesterol
describe inactivation/secretion of substances - liver functions
glucuronyl transferase conjugates glucuronic acid to bilirubin - goes to bile, also to barbituates, antihistaminics, anticonvulsants, insecticides, and other drugs,
endocytosis of hormones and cholesterol - ldl particles- bad cholesterol
liver has ldl receptors - way to eliminate toxins from body hormones go to target organ to trigger a function, hormone cannot be circulating forever so its removed by receptor mediated endocytosis - live has receptors for hormone
describe conversion of substances - liver functions
tetra-iodothyronine (t4. thyroxine, thyroid hormone) –> tri-idodthyronine (t3 - more potent) converted by liver cells
describe hemopoiesis - liver functions
production of rbcs
during fetal development
after birth - bone marrow takes over
describe storage of substances - liver functions
glycogen - sugar and lipids - cholesterol, triglycerides
describe capsule of ct of liver
penetrates at level of porta hepatis
glissons
separates liver into hepatic lobules = prismatic structures
what is porta hepatis
entrance of 2 branches of hepatic arteries (start in abdominal aorta and then branches)
exit of hepatic duct = brings bile synthesized in liver to gallbladder
describe common bile duct
ends at level of si
bile will go to intestines
Emulsifies fat - digestion of lipids
describe hepatic vein
exits through hepatic vein and drains blood into inferior vena cava
describe histology of liver
ct between lobules = across and down
bile duct goes in opposite directions of hepatic artery and portal veins
located in portal space =
branch of hepatic artery = arteriole
branch of portal vein = venule
portal space = ct blood vessels and bile ducts, large areas of ct
describe hepatic lobule
subdivided by chords of hepatocytes
describe hepatocytes
pale colour, forms row of cells separated by blood vessels - liver sinusoids - go from periphery to central vein
describe veins of hepatocytes
sinusoids
central vein opens into sublobular vein
which drains in hepatic vein
what are bile canaliculi
opens into bile duct and takes bile to common bile duct and gallbladder
bile released when fatty meal
describe sinusoids
see endothelial cells
separates hepatocytes
NO BM
only reticular fibers, irregular in size
Permeable capillaries
separated = no tight junctions
everything goes through easy
describe kupffer cell
phagocytic cells - old rbcs, particulate matter, bacteria
bigger than edothelial cell
processes can extend to sinusoids - long
what opens into sinusoids
arteriole - branch of hepatic artery and venule - branch of hepatic vein
describe cholangiole and bile duct
equivalent to intercalated duct = between lobes, interlobular
cholangiole opens into bile duct
bile secreted by hepatocytes
bile duct covered by columnar or cuboidal cells - depends on size of bile duct
describe nuclei of hepatocytes
can be binucleated
small cubes forms plate = communication between plates = opening
what is at the end of bile canaliculi
tight junctions
changes directions where bile circulates, since do not want bile to be in circulation
what is space of disse
between endothelial cells and hepatocytes = space of disse
where exchange happens
what are cholangioles also called
herings canals
bile ductules
what are sinusoids lined by
endothelial cells and kupffer cells sometimes
name main activities of hepatocyte
endocytic and secretory activities
describe endocytic activity of hepatocyte
receptor mediated endocytosis of ligands = hormones, ldl, hdl, chylomicrons
digested and stored as aas
triglycerides, monosaccharides etc
Dissociation of ligand and then receptor will be recycled to cell surface to continue cycle - important, liver degrades these substances after since they should not be circulating
describe secretory activity of hepatocyte
rer = synthesizes apolipoproteins and sends to golgi - ser stores long chain fatty acids, triacylglycerols, phospholipids and cholesterol and sends to golgi
golgi = packs complex and secrets into space of disse and lumen vldl - apolipoprotein complex, contains cholesterol secreted by liver, produced by hepatocytes
why is removing ldl important
could lead to plaque in artery
what are other functions of hepatocytes
peroxisome
ser
describe peroxisome of hepatocyte
similar to lysozyme - has crystalline structure
catalyses reaction - turns hydrogen peroxide to water and oxygen
removes hydrogen peroxide
beta oxidation of long fatty acid chains - FA - by product = hydrogen peroxide
catabolism of alcohol
breakdown of purines amp/gmp to uric acid - eliminated by kidneys
cholesterol synthesis
describe SER of hepatocyte
synthesized bile cholesterol + taurine = taurocholic acid
bilirubin conjugated to glucuronic acid
will be elimated at level of bile canaliculi - do not want it to go to circulation
describe a portal lobule
surrounded by portal spaces
3 central veins all drain into the same portal space = makes portal lobule
describe hepatic acinus
metabolic effects
hepatocytes closer to portal space = metabolically active since closer to oxygen
as go towards central vein = less oxygen and more elements from waste metabolism
what do all bile ducts drain into
hepatic duct and all goes to gall bladder
what is turnover of hepatocytes
150 days
very low
expanding - expanding population of cells
what is mitotic index
1 cell every 20 000
what is surgical excision
cells divide actively until organ reaches normal size
describe repeated damage to hepatocytes
like alcoholism = results in proliferation of ct = cirrhosis - liver will not recover and be small
what is hepatitis
tight junctions affected and bile leaks out = leads to jaundice
describe pancreas
The pancreas is a mixed exocrine & endocrine gland
endocrine portion is composed of islets of langerhans
exocrine portion is a compound acinar gland similar in structure to parotid gland
describe exocrine pancreas
exocrine pancreas produces a slightly alkaline fluid & proteins consisting 15 or more of main enzymes (mainly) & pro-enzymes (zymogens - Zymogenic granules) capable digesting the components of ingested food in small intestine
i.e. Carbohydrates (breakdown to mnosaccharides lipids (to triglycerides), proteins to amino acids) & nucleic acids (phosphate group Remove from nucleic acids by enzymes - like alkaline phosphatase)
both pancreas and salivary glands derive from…
evaginations of endodermal lining of embryonic primitive intestine
describe accessory pancreatic duct
drains secretory products into duodenum
describe main pancreatic duct
join to common bile duct coming from gallbladder
Together = drain into duodenum
what does bile promote
digestion of fat and pancreas provides lipids and other zymogens or enzymes
describe exocrine and endocrine pancreas
endocrine = islets of langerhans
serous acini = exocrine
describe formation of pancreas
blind ended tubules are lined by undifferentiated simple columnar epi cells which undergo sequential branching - many ducts
epithelial rudiments begin to organize into acini and lobules
some cells further differentiate from these forming acini = form islets of langerhans
describe exocrine pancreas
Divided in lobes and lobules
compound acinar = similar to salivary glands
describe ct of pancreas
capsule penetrates at level of pancreatic duct and separates liver into lobes and lobules
describe interlobar duct and ct
large amounts of ct
large ducts
describe interlobular duct and ct
thin septi of ct = subdivides lobe into small lobules
describe intercalated duct
drain into small lobular duct - equivalent to intercalated duct of salivary glands
short cells, pale, sometimes cuboidal or squamous
connected to serous acini
describe interlobular duct and ct of adult pancreas
line by columnar ep
cells pale
dont stain well
describe serous acini
exocrine pancreas
pyramidal shaped cells, round nucleus, tends to be basophilic, apex = acidophilic due to zymogen secretory granules with enzymes - picks up eosin
describe centroacinar cells
pale
center of serous acini
describe islets of langerhans
surrounded by thin capsule of ct - fibrocytes, reticular fibers, diagnostic - use as landmark
describe serous acinus cell
no myoepithelial cells in serous acini
secreting into lumen so tight junctions
describe serous acinar cell
pyramidal
tight junctions
ribosomes - ribonucleoproteins, react well with hematoxylin so basophilic at base
rer - well devlopped and mitochondria - active cell
golgi prominent - packs enzymes into condensing granule
zymogen granules - has protein, dark in em, electron dense, fully mature
exocytosis
describe pancreatitis
medical emergency
can happen after excess alcohol = enzymes start to dissolve own pancreas - leaks out, enzymes more powerful than stomach
what regulates the exocrine pancreas
cck
secretin
Unconstituted, only when digestion
describe cck
produced by enteroendocrine cells of duodenum
promotes exocytosis
describe secretin
stimulates secretion of water and bicard
produced by enteroendocrine cells of duodenum
what do centroacinar cells produce
water and bicarbonate
describe zymogen granules
contain proenzymes
all converted by enterokinase
trypsinogen to trypsin (remove aa from trypsinogen and convert to active trypsin)
procarboxypeptidase to carboxypeptidase
proelastase to elastase
pro phospholipase a to phospholipase a
describe enterokinase
located in microvilli of enterocytes of duodenum
small enzyme - protease
describe active enzymes of pancreas
15 active enzymes
lipase - important of tj, role in pancreatitis
amylase
RNase
DNase
what is role of trypsin inhibitor
Secreted by centroacinar cells
prevents early activation of trypsin
provides protection against reflux of trypsin from gut
describe endocrine pancreas
Islets of langerhans
will organize in 2 ways = follicles like in thyroid or cords associated to fenestrated capillaries
pancreatic cells of islets of langerhans associated to fenestrated capillaries
how many islets of langerhans in pancreas
5x10^5-10^6 = 2% of pancreas
200um in diameter
considered to be endocrine microunits
name cell types
alpha
beta
delta
pancreatic polypeptide cells
describe alpha cells of endocrine pancreas - %, size, location, hormone, function
15-20%
large
periphery
glucagon
glycogen breakdown and gluconeogenesis
describe beta cells of endocrine pancreas - %, size, location, hormone, function
70% smaller
central
insulin - opposite of glucagon
uptake of glucose by liver and lower glucemia when eating
only one gene encodes insulin
describe delta cells of endocrine pancreas - %, size, location, hormone, function
5%
large
periphery and central
somatostatin
inhibits release of glucagon and insulin via paracrine action and HCl secretion by parietal cells
describe pancreatic polypeptide cells of endocrine pancreas - %, size, location, hormone, function
1%
large
periphery and central
pancreatic polypeptide
stimulates activity of chief cells
describe role of glucagon
plays major role in maintaining normal concentrations of glucose in blood and has opposite effect of insulin
what is glucagon. synthesized as
proglucagon and proteolytically processed ro glucagon within alpha cells of pancreatic iselts
final product = linear peptide of 29 aas
primary sequence highly conserved in vertebrates
where is proglucagon expressed
also expressed within intestinal tract where it is processes to glucagon, like peptides = enteroglucagon - not into glucagon
what is major effect of glucagon
major effect of glucagon = increase blood concentration of glucose as brain has an
absolute dependence on glucose as fuel
When blood levels of glucose begins to fall below normal Range -glucagon stimulates
breakdown of glycogen stored in liver and/or activates hepatic gluconeogenesis
like when asleep
why are fenestrations important in islet cells
allows passage of hormones into lumen of capillary
what does chronic ingestion of alcohol lead to
acute pancreatitis = due to obstruction of duct system and activation of trypsin or release of enzymes into intercellular space
explain type 1 diabetes
insulin dependent diabetes mellitus develops before age of 15 which is apparently cause by an autoimmune destruction of the beta cells of islets
