histology- the digestive tract Flashcards
what is liver and pancreas composed of
glandular epithelial cells
functions of the liver
most divers tissue in the body
detoxification of metabolic waste products, toxins and drugs
synthesising cholesterol, bile
etc
varied
portal vein
capillary bed at one end and at the other end
how fast reaches the liver
thoracic duct dumped into venous circulation
porta hepatis
groove a deep fissure in the inferior surface of the liver through which all the neurovascular structures (except hepatic veins) and hepatic ducts enter or leave the liver
incoming blood
arrives in segments in different place to where the outgoing blood drains
liver capsule
covered by collagenous connective tissue
liver structure
made up of segments called lobules
each lobule if approximately hexagonalk and has a branch of the hepatic vein called the centrolobular vein (central vein) at its centre and portal triads at each corner
sinusiods
blood hyperfrolirates till gets into central veins
blood entering in portal tracks
spill into all the different lobules
difference between human and pig lung
pig doesn’t have clear connective tissue septa between lobules
portal triad
branches of the vessels which enter at the porta hepatis that is the hepatic portal vein and the hepatic artery. They are also called the portal triad because they also include a third ‘tube’, a branch of the conduit which leaves the liver at the porta hepatis, the bile duct.
what does portal tracts include
branches of
hepatic portal vein
heptatic artery
bile ductale- lined by simple cuboidal cells called cholangiocytes
tracts also typically include lymphatic vessels
lymph producer
liver largest producer in the body
large structure with lots of fluid
can see thin walled lymphatic vessels in lab
looking for bile ducts on cells
cuboidal cells
hepatocytes
main cells of the liver
these polyhedral epithelial cells form what appear in sections to be cords of liver cells but in fact are plates or sheets of cells with spaces in between for blood to flow through
these blood channels are called sinusoids
the lobule
classic lobules- centred on central veins surrounded by triads
liver acinus- two portal tracks in centre of attention
when toxins enter body arrive at this point so good to see as a way of understanding how liver works
direction of blood flow
central vein- 5 triads surrounding it and blood flows towards each of the 5 triads
sinusoids ultrasound
sinusoids are lined by endothelial cells- sit slightly away from hepatocytes- space is called the space of disse or the perisinusiodal space
microvilli of the hepatocytes project into this space
hepatocytes and sinusoidal ultrasound
stuffed with mitchocondria need energy
connective tissue of the liver
place of disse- find type 1 collagen
portal tracts
hepatic stellate cells
also called ito cells
found scattered in the space of disse
modifies fibroblasts and make connective tissue
also store vitamin A within fat droplets in their cytoplasm
in some pathological conditions they transform into myofibroblasts and produce scar tissue in the liver
Kupffer cells
these are resident macrophages scattered within the sinusoids
they act to remove particulate matter from the blood and help remove worn out red blood cells
bile
an alkaline solution containing water, ions, phospholipids, bilirubin and bile salts
all heaptocytes produce bile
bilirubin
a pigment which results from the breakdown of hemoglobin in the spleen, and when excreted in the bile, is the principal cause of the brown colour of feces.
the bile salts
necessary for the emulsification of fats in the digestive tract. Primary bile that is produced by the hepatocytes is modified in several ways (e.g. addition of bicarbonate ions and water) by the cholangiocytes, the cells that line the biliary tree.
bile travel
Bile flows via bile canaliculi toward the bile ducts in the portal tracts and thence to the hepatic ducts.
bile canaliculi
small channels (1µm dia.) formed by tight junctions in the cell membranes of adjacent hepatocytes
gall bladder
a muscular sac which is
lined by simple columnar epithelial backed by a lamina propria of loose connective tissue rich in blood vessels and lymphatic vessels, a coat of smooth muscle and an outer collagenous layer of adventitia.
Stores bile.
Has a folded mucosa when empty – this flattens when distended.
Modifies the bile stored within it.
volume of bile arriving from the liver
About 80%-90% of the volume of the bile arriving from the liver is removed by the gall bladder. This is done by actively pumping Na and Cl ions from the bile into the spaces between adjacent epithelial cells. Water then follows due to the increase in osmotic pressure in these spaces, which become distended with fluid when the gall bladder is actively concentrating bile. The water is carried away, largely by the lymphatic vessels of the lamina propria.
gall balder contraction
The gall bladder is stimulated to contract and deliver bile to the duodenum, both under nervous control (chiefly vagal), and via release of the hormone cholecystokinin by endocrine cells of the duodenum when fatty food enters it.
cholecystitis
inflammation of the gall bladder is not uncommon. Here gallstones have obstructed the cystic duct leading to expansion of the gall bladder, thickening of the muscle layers and inflammation
pancreas
both and exocrine and an endocrine gland
.
pancreas endocrine gland
The endocrine pancreas consists of small, scattered islands of tissue called islets of Langerhans, which produce a number of hormones including insulin and glucagon. Islets make up about 1%-2% of the pancreas
pancreas exocrine gland
The exocrine pancreas produces about a litre of digestive juices containing proteases to break down proteins, lipases to break down lipids, nucleases to breakdown DNA/RNA, amylase to break down starch, etc, each day. These enter the duodenum via the pancreatic duct
pancreas on microscope
thin connective tissue capsule that is continuous with connective tissue septa that divide the glands into lobules
exocrine cells
basal part- typically basophilic- more purple due to extensive RER
apical part- eosinophilic- prescience of zymogen (pre-enzyme granules)
centroacinar cells
duct cells within the acini
smallest ducts doesn’t begin at end of acinus but in the middle of the acinus and carries on
he hepatopancreatic ampulla (of Vater).
The main pancreatic duct joins the common bile duct and opens into the duodenum on a papillae:
