Histology of Liver, Gallbladder, and Pancreas Flashcards
What are the ligaments of the liver?
Falciform ligament
Triangular ligaments
Coronary ligaments
What is Glisson’s capsule?
A layer of connective tissue surrounding the liver
Ensheaths the hepatic artery, portal vein, and bile ducts within the liver
also called the hepatobiliary capsule
How much of the cardiac output does the liver recieve at rest?
25%
What sets the liver apart from the other abdominal organs?
Recieves dual blood supply
- hepatic arteries = oxygen rich blood (20-30%)
- hepatic protal veins - nutrient rich blood from digestive tract (70-80%), break down of hemoglobin from the spleen
What is the central role of the liver?
removing unwanted material from blood and otherwise maintaining the bloods normal composition
Lobule Architecture of liver
Central vein
peripheral portal triad
Roughly heaxagonal
connective tissue septum
What does the portal triad in the lobule contain?
branches of hepatic artery, vein, one or two bile ductules, lymphatic vessels and branches of the vagus nerve
What is the blood flow in the liver?
portal triad -> central vein (terminal hepatic venule) -> sublobular vein -> collecting vein -> hepatic veins -> inferior vena cava
describe the sinusoids of the liver?
Fenestrated lining (endothelial cells)
Hepatic macrophages in sinusoid walls
Bile ducts in the lobule recieve bile from where?
canaliculi
classic hepatic lobule drains blood from where?
from the portal vein and the hepatic artery to the hepatic or the central vein
(drains inward)
portal lobule drains bile from?
hepatocytes to the bile duct
(drains outward)
How do hepatocytes recieve oxygenated blood?
From hepatic acinus
flows inward
Zone 3 (centrilol) is least oxygenated
Zone 2 (Midzonal)
Zone 1 (periportal) is the most oxygenated
Acinus of Rappaport
these are the hepatic acinus
encompases an oval to diamond shaped region from two or three classical lobules and is divided into three zones in the parenchyma
Most functional way (both physiological and biochemically) to conceptualize the liver lobule based on blood flow
Liver Sinusoidal Endothelial Cells (LSEC)
thin lining of specialized endothelial cells
large and Fenestrated
Mixed blood from oxygen rich hepatic artery and nutrient rich blood from portal vein.
Blood flow = through sinusoids -> central vein of lobule -> central vein coalesce into hepatic veints -> vena cava
What is the relationship between sinusoids and hepatocytes?
Blood in sinusoids bathes hepatocytes and provide for exchange of substances betwen blood and liver cells
Basolateral surface of hepatocyte faces _______ sinusoids, apical surfce face ______ ______.
sinusoids
bile canaliculi
When blood passes freely through fenestration of sinusoids where does it go?
Into perisinusoidal space (Space of Disse)
What are hepatocytes?
Liver cells that are cuboidal
Polarized
arranged in a flat, irregular plates (cords) that are organized radially, like the spokes of a wheel.
What is the content of a hepatic plate?
Contains one or two rows of hepatocytes and these lie in between the sinusoids
The nucleus of the hepatocyte is?
Has a prominent nucleolus
Dispersed chromatin
Polyploidy
Describe the cytoplasm of the hepatocyte?
Glycogen lacey appearance
fat sphreical vacuoles
Riosomes and RER basophilia
Mitochondria - eosinphilic
Lysosomes
Golgi complex
Peroxisomes
Most of the glucose absobed from a meal is stored where?
In the liver as glycogen ( also in muscles)
In the liver glycogen makes up 5-6% of the organs fresh weight and an adult can store about 100-120 grams of glycogen
About how much glucose is present in the blood at all times?
4 grams
What allows glucose to enter the hepatocytes?
GLUT2
a plasma membrane glucose transporter
Storage of Glycogen
the human body can store up to 450 g of glycogen (1/3 of this in the liver)
What is the purpose of liver glycogen?
Serves as a maintenance of the blood glucose level
it declines to zero in periods of fasting that last more than one day.
What are the different processes that occur in the liver?
- Synthesis and secretion of plasma proteins (RER) - albumin, fibrinogen, and thrombin
- Synthesis and secretion of bile (SER) - bile acids from cholesterol, elimination of bilirubin, secretion of secretory IgA
- Metabolism of carbohydrates (SER, cytosol)
- Maintenance of normal level of blood glucose
- Metabolism of lipids (RER)
- Maintenance of normal level of blood lipids - VLDL
What is the function of the smooth endoplasmic reticulum?
Function - metabolic processes - synthesis nad hydrolysis
Enzymes - synthesis of lipids, oils, phospholipids, steroids, and sex hormones
Hydrolysis of glycogen into glucose (in liver)
Detoxification of drugs and poisons (in liver)
Pumps calcium uons for muscle funciton
What are bile canaliculi?
spaces present between plasma membran of adjacent liver cells
Describe the flow of bile
Bile canaliculi > canals of Hering > intrahepatic bile ductule (inportal triad) > interlobular ducts > left and right hepatic ducts > common hepatic duct joins with cystic duct > bile duct > duodenum
What cell lines the sinusoids and is considered a type of fixed macrophage?
Kupffer Cells
What is the function of Kupffer cells?
They continuosly sample the blood traveling through the sinusoid, phagocytosing antigens, microorganism and damaged RBC.
Identifying Kupffer cells in conventionally stained sections is not easy. When are they identifable and stand out?
When they are full of phagocytosed ink particles
What is Space of Disse?
Perisinusoidal space/Subendothelia
between heptacytes and sinusoidal lining cells
microvilli of hepatocytes project into space
space continuous with sinusoids
The space of Disse drains into?
lymphatics of portal triad
What cells are found in the Space of Disse?
Fat storing (Ito, stellate) cells
They also store vitamin A
Reticular connective tissue
Type II collagen = reticular fibers
lots of proteoglycan (flexibility)
form a delicate network within the space of Disse
seen with silver stain
Ito (stellate cells)
Located in the perisinusoidal space
long cytoplasmic processes that extend below the endothelial cells
contain actin and myosin
store fat and vitamin A
The Ito cells contract in response to what?
In response to endothelian and substance P
this contributes to regulation of the diameter of the sinusoid and hence regulates blood flow
When do Ito cells proliferate?
When activated by Kupffer cells and hepatocytes
In pathologial conditions Ito cells change into?
Collagen producing cells
Secrete Type I collagen leading to progrssive fibrosis of the liver
When do Ito cells change into myofibroblast?
Progressive fibrosis of the liver is occuring and as it advance the Ito cells turn into myofibroblast.
This constrict the lumen of the sinusoid and increase vascular resistance
Increase in resistance to blood flow in the hepatic sinusoids = portal hypertension
What are the changes that occur during liver injury?
Activated stellate cells
deposition of scar matrix
Kupffer cell activation
Loss of fenestration
Loss of hepatocyte microvilli
What are the histological changes with Cirrhosis?
Fibrous Septa
Regenerative nodules
Fatty Cyst
Nerosis
What makes up the endocrine pancreas and the exocrine pancreas?
Endocrine - Islet of Langerhans
Exocrine- Acini
The pancreas is seperated into lobules by connective tissue. What is in that connective tissue?
Blood vessels
nerves
The lobule is the what of the pancrease?
Secretory Unit
Exocrine Pancreas
The portion that makes and secretes digestive enzymes into the duodenum.
Includes:
Acinar and duct cells with associated connective tissue, vessles, and nerves
makes up 95% of the pancreatic mass
The acini in the exocrine pancreas contain what?
Each acini consist of a single layer of epithelial cells surrounding a cavity where the secretory granules (zymogen granules) within the acinar cells delivers secretions to the lumen of the acinus.
Acinar cells
Pyramidal shaped, round nucleus at the base of cell
basal cytoplasm is basophilic due to abundance of RER
basal membrane receptors for Cholecystokinin from duodenum
Apex contains secretory granules (zymogen) - eosinophilic
release granules of digestive enzymes
What do the zymogen granules contain?
digestive enzymes and proenzymes
trypsinogen, chymotrysinogen, carboxypeptidase, amylase, lipase, nuclease
Human Acinar cells
most pancreatic enzymes are produced as inactive molecules = symogens
this helps minimize the risk of self digestion within the pancreas
Pancreatic juice is composed of two secretory products critical to proper digestion. What are they?
digestive enzymes (synthesized and secreted from the exocrine acinar cells)
bicarbonate (secreted from the epithelial cells lining small pancreatic ducts)
When is Secretin secreted?
In response to acid in the duodenum, which stimulates duct cells to produce water and bicarb
Merocrine secretion of proenzymes by the acinar cells is regulated by?
Secretin and Cholecystokinin from the enteroendocrine cells of the duodenum and jejunum with nerve stimulation from the vagus
Stomach cells secrete which two things?
Pepsin and HCL
Pancreatic acinar cells secrete what?
Trypsin
Chymotrypsin
Elastase
Sodium Bicarbonate
Intestinal Cells secrete what?
Secretin
Cholecystokinin (CCK)
In the small intestine (duodenum) the epithelial cells contain membrane bound enteropeptidase (enterokinase). What does this do?
Convert Trypsinogen -> Trypsin (has a negative feedback mechanism)
Trypsin then activates more tyrpsinogen,
converts Chymotrypsinogen -> Chymotrypsin
and
Procarboxypeptidase -> Carboxypeptidase
What is the Gallbladder?
A sac for bile storage
80-90% of electrolytes are absorbed in the gallbladder leaving bile acids and cholesterol
Bile from the gallbladder empties where?
Empties into the common bile duct under hormonal stimulation (cholecystokinin)
how is the cystic duct different from other duct?
It contains spiral valves
Describe the direction of duct drainaige between the lier, gallbladder, and the pancrease
- The left and right hepatic ducts merge to form a common hepatic duct.
- Common hepatic and cystic ducts merge to form a common bile duct
- Main pancreatic duct merges with common bile duct at the hepatopancreatic ampulla, which extends into the duodenum
- Bile and pancreatic juices enter duodenum at the major duodenal papilla
Cholecystokinin (CCK) stimulates the gallbladder. How does the gallbladder respond?
Responds by contracting and delivering more bile to the duodenum through the sphincter of Oddi, which relaxes in response to CCK
CCK is secreted by?
Intestinal mucosa
(I cells)
Increase in Fatty acids in the Duodenum leads to what?
Increase in CCK sectrion
this leads to a increase in plasma CCK
increase in plasma CCK causes contraction of the Gallbladder and relaxation of the sphinter of Oddi
=
increase in bile flow into common bile duct and increase in bile flow into duodenum
What is bile?
the excretion of cholesterol, phospholipids, bile salts, conjugated bilirubin and electrolytes
What is the function of bile?
Contributes to fat absoprtion in the intestinal lumen
Transports IgA to the intestinal mucosa by the enterohepatic circulation
Exretion of metabolic products of drugs and heavy metals processed in hepatocytes
Conjugated bile acids inhibit what?
The growth of bacteria in the small intestine
The Gall bladder has 4 layers. What are they?
Lining epithelium - simple columnar
Presense of Microvilli give brush border appwarance to epithelium (facilitates absorption of water
Lamina propria - rich in elastic fibers and blood vessels
Muscularis - consist of circularly arranged smooth muscle fibers mixed with connective tissue rich in elastic fiber
Serosa/Adventitia
What are Rokitansky-Aschoff sinuses?
herniation of mucosa into muscular wall of the Gallbladder
Seen in Chronic cholecystitis
