State University of Medicine and Pharmacy “Nicolae Testemitanu” LIVER GALL BLADDER PANCREAS Department of Histology, Cytology and Embryology Tatiana Globa
The Liver Largest gland of the body Two principal lobes: right and left Right lobe further subdivided: Quadrate lobe and caudate lobe Is surrounded by a capsule of connective tissue (Glisson’s capsule).
Functions of the Liver Digestive and Metabolic Functions synthesis and secretion of bile storage of glycogen and lipid reserves maintaining normal blood glucose, amino acid and fatty acid concentrations synthesis and release of cholesterol bound to transport proteins inactivation of toxins storage of iron reserves storage of fat-soluble vitamins
Functions of the Liver Non-Digestive Functions synthesis of plasma proteins synthesis of clotting factors synthesis of the inactive angiotensinogen phagocytosis of damaged red blood cells storage of blood breakdown of circulating hormones (insulin and epinephrine) and immunoglobulins inactivation of lipid-soluble drugs
The morpho-functional unit of the liver “classical liver lobule” portal lobule liver acinus
LIVER LOBULE Hexagonal-shaped liver lobule (classical lobule) is the traditional description of the liver parenchyma organization Composed of hepatocyte (liver cell) plates(cords) radiating outward from a central vein Between the plates of hepatocytes there are sinusoids Has a central vein Portal triads are found at each of the six corners of each liver lobule
Sublobular veinDistributing veinCentral veinPlates of hepatocytes
PORTAL TRIADSPortal triads (also called portal areas or portalcanals) are located at the corners of liver lobules.Each portal area contains three (hence the termportal triad) more-or-less conspicuous tubularstructures all wrapped together in connectivetissue. a branch of the bile duct a branch of the portal vein - interlobular vein a branch of the hepatic artery - interlobular artery
Hepatocytes are cuboidal cells with one or two large euchromatic nuclei and with abundant, grainy cytoplasm that stains well with both acid and basic dyes (reflecting the abundance of various cellular constituents). they may accumulate abundant lipofuscin (yellow- brown "wear-and-tear" pigment), especially with advancing age. a typical hepatocyte has two surfaces with microvilli
Hepatocyte ultrastructure• all cytoplasmic organelles are very well developed• cell membrane facing a bile canaliculus and the perisinusoidal space forms microvilli
Hepatocytes are located in flat irregular plates (cords) that arearranged radially like the spokes of a wheel around a branch of thehepatic vein, called the central vein or central venule since it reallyhas the structure of a venule. Each hepatic plate contains 2 rows ofhepatocytes. Between 2 rows of hepatocytes of the plate there is bilecanaliculus. Between the plates of hepatocytes there are sinusoidscapillaries.
Bile canaliculusHepatocytes form2 rows Sinusoid Space of Disse Hepatocytes Microvilli
Sinusoids capillaries are larger than conventional capillaries and less regular in shape. They are lined by thin endothelial cells and lacks a basement membrane (is absent over large areas except the periphery and center of the hepatic lobule) Also residing on the sinusoidal walls are macrophages called Kupffer cells. These are phagocytic cells that remove particulate material and old red blood cells from circulation. Kupffer cells are members of the mononuclear phagocyte system. Pit cells are attached to the Kupffer’s cells. These cells contain granules and they are like large lymphocytes, killer cells. They make an anticancer effect. The space between the fenestrated endothelium and the cords is named the space of Disse.
Perisinusoidal space (space of Disse)It contains microvilli of hepatocytes, blood plasma, processes of the Kupffer’s cells lipocytes (adipose cells, commonly called an Ito cells). They are located between some hepatocytes. These cells have been shown to be the primary storage site for vitamin A. They also can produce connective tissue fiber in the large amount at the cirrhosis. In the fetal liver, the space between blood vessels and hepatocytes contains islands of blood-forming cells.
The blood circulation through the liver System of inflow: the liver receives blood from the hepatic artery (supplies oxygen-rich blood to the liver) and portal vein (carries venous blood with nutrients from digestive viscera). They branch into lobar, segmental, interlobular, distributing branches. System of circulation: the distributing branches of vessels contribute blood to the sinusoids which provide the exchange of substances between the blood and liver cells. Sinusoids contain the mixed blood. System of outflow: sinusoids drain blood from the periphery of the classical hepatic lobule toward its center, into the central vein. Outside hepatic lobules central veins drain into the sublobular (intercalated) veins, which join 3-4 together and drain into the hepatic vein. It drains into the inferior vena cava.
GALL BLADDER functions storage of bile concentration of bile acidification of bile send bile to the duodenum in response to cholecystokinin secreted by from enteroendocrine cells in small intestine
Tunics (layers) of the Gall Bladder TUNICA MUCOSA: When the gall bladder is empty, this layer is extremely folded. When full, this layer is smoother but still has some short folds. lamina epithelialis: composed of simple columnar epithelial cells with numerous microvilli on their luminal surfaces and connected by tight junctions near luminal surfaces. lamina propria: composed of loose connective tissue rich in reticular and elastic fibers to support the large shape changes that occur in the lamina epithelialisl; lamina propria may contain compound tubuloalveolar glands. May be mucous or serous. lamina muscularis mucosae: not present TUNICA SUBMUCOSA: present and typical TUNICA MUSCULARIS: contains much smooth muscle, poorly organized TUNICA SEROSA: present and typical
Pancreas Exocrinegland (97%)– PROENZYMES for digestion of carbohydrates, proteins & fats (amylase, trypsin, lipases) Endocrine gland (3%)– INSULIN and GLUCAGON (carbohydrate metabolism)
The exocrine pancreas The exocrine portion of the pancreas is a compound acinar gland It has many small lobules, each of which is surrounded by connective tissue septa through which run blood vessels, nerves, lymphatics, and interlobular ducts. Exocrine secretion by the pancreas is controlled by hormones and nerves.
The exocrine pancreas Acini: The secretory cells of the pancreas are arranged around Acini a small lumen. The pancreatic acinar cells are highly active in protein synthesis for export and this high activity is reflected in their bizonal staining properties. The basal region of these secretory staining cells usually stains intensely with hematoxylin reflecting the presence of large amounts of endoplasmic reticulum where the protein is being synthesized on ribosomes – homogen zone. The presence of numerous zymogen granules containing high concentrations of protein is reflected in the intense eosin staining in the apical region of the secretory cells – zymogen zone. These granules are most abundant during fasting or between meals and least abundant after a meal has been ingested.
Centroacinar cell These cells form the first part of the intercalatedZymogen ductgranules
The exocrine pancreas Ducts: The secretory product of the acinar cells is carried out of the pancreas by a duct system as in other exocrine glands. The first part of the duct system is called the intercalated The first part of the duct system is called the duct or intralobular duct. It is lined with cuboidal epithelial cells that secrete bicarbonate ion into the secretory product. This duct actually extends into the acinar lumen, where its walls consist of the pale staining centroacinar cells. walls consist of the pale staining Intercalated ducts have very little connective tissue around them but they lead into larger interlobular ducts which lie them but they lead into larger within more prominent connective tissue septa. Interlobular ducts are lined with a low columnar epithelium that may contain goblet cells. Interlobular ducts empty into the main pancreatic ducts that exit the pancreas.
Pancreatic juice trypsin,chymotrypsin and carboxypeptidase hydrolyse proteins into smaller peptides or amino acids; ribonuclease and deoxyribonuclease digest the corresponding nucleic acids; pancreatic amylase digests carbohydrates; pancreatic lipase digests lipids; cholesterol esterase breaks down cholesterol esters into cholesterol and a fatty acid.
The endocrine pancreas. The cells of the endocrine portion of the pancreas are arranged either in round-to-oval shaped areas rich in blood vessels known as the islets of Langerhans or they may be scattered throughout the exocrine portions of the pancreas near the acini or ducts.
Island of Langerhans• β-cells (75%) which secrete insulin (stimulates the synthesis of -cellsglycogen, protein and fatty acids; facilitates the uptake of glucose into cells; activates glucokinase in liver cells). They are located in the central part of the island.• α-cells (20%) which secrete glucagon (effects opposite to those of -cellsinsulin). They are generally located peripherally in the islets. • δ-cells (5%) which secrete somatostatin, a locally acting hormone which -cellsinhibits α -, β-cells. •a few other endocrine cells, which secrete • pancreatic polypeptide, which stimulates chief cell in gastric glands, inhibits bile and bicarbonate secretion – PP-cells, PP-cells • vasoactive intestinal peptide (VIP), which has effects similar to glucagon, but also stimulates the exocrine function of the pancreas and decrease the arterial blood pressure – δ1-cells, 1-cells • secretin, which stimulates the exocrine pancreas, and motilin, which increases GIT motility – EC-cells (enterochomaffin cells). EC-cells