1. DIGESTIVE SYSTEM
LIVER
PANCREAS

2. Blood supply to the liver
The hepatic portal vein (hpv) and the hepatic artery send blood to the liver.
Their branches form the interlobular vessels which branch into distributing vessels that are located at the periphery of the lobule.
The interlobular vessels that form the smallest portal triads send blood into the sinusoids.
In the sinusoids the blood flows centripetally toward the central vein.
The central vein courses through the central axis of the classic liver lobule and empties into a sublobular vein.
Several sublobular veins converge to form larger hepatic veins that empty into the inferior vena cava

3. BLOOD SUPPLY TO THE LIVER

4. DIAGRAM OF A “CLASSIC” LOBULE

5. Liver acinus
The liver acinus described as diamond shaped, is the smallest functional unit in the hepatic parenchyma.
The short axis of the acinus is defined by the terminal branches of the portal triad that lie along the border between two “classic” lobules.
The long axis is a line drawn between the two central veins closest to the short axis.
The liver acinus provides the best correlation among blood perfusion, metabolic activity, and liver pathology.

6. DIAGRAM OF A LIVER ACINUS
The cells in zone 1 are the first to receive both nutrients and toxins in the blood and are the first to show morphologic changes following bile stasis. These cells are also the last to die and the first to regenerate.
The cells in zone 3, on the other hand, are the first to show ischemic necrosis. They are last to respond to toxic substances and to bile stasis
The cells in zone 2 have all characteristic between zones 1 and 3.
The hepatocytes in each liver acinus are described as being arranged in three concentric elliptical zones surrounding the short axis. Thus,
Zone 1 is closest to the axis. Zone 2 is farthest from the axis. Zone 2 lies between zones 1 and 3.

7. Sinusoids
Hepatic sinusoids are lined with a thin discontinuous endothelium.
Hepatic sinusoids have Kupffer cell or the stellate sinusoidal macrophage.
The Kupffer cells may be involved in the final breakdown of some damaged or senile red blood cells that reach the liver from the spleen.

8. Schematic diagram of a plate of hepatocytes interposed between hepatic sinusoids

9. Hepatocytes
Hepatocytes make up the anastomosing cell plates of the liver lobule.
Hepatocytes are large polygonal cells that constitute about 80% of the cell population of the liver.
Nuclei of hepatocytes are large and spherical and occupy the center of the cell.
Liver cells are capable of considerable regeneration when liver substance is lost to disease or surgery.

10. Peroxisomes functions:
1. Specific oxidative functions in: -gluconeogenesis -metabolism of purines -metabolism of alcohol -metabolism of lipids 2. About one-half of the ethanol that one might drink is converted to acetaldehyde by enzymes contained in liver peroxisomes 3. In humans catalase and D-amino acid oxidase, as well as alcohol dehydrogenase are found in peroxisomes.

11. Lysosomes
Lysosomes concentrated near the bile canaliculus correspond to the peribiliary dense bodies. They have varied contents including:
-pigment granules (lipofuscin)
-myelin figures
-partially digested cytoplasmic organelles
may be a normal storage site for iron.

12. Biliary tree
The bile canaliculus is small canal formed by grooves in neighboring cells.
The bile canaliculi form a ring about the hepatocyte and drains into small bile ducts, the canals of Hering, these in turn, drain into the bile duct of the portal canals.
Bile flows in the canaliculi centrifugal. The flow of bile is in a direction opposite to the flow of blood, i.e. from the region of the central vein toward the portal canal.

13. Diagram of the blood and bile flow in the liver

14. Bile
Structure:
About 90% of the bile salts a component of bile is reabsorbed and resecreted by the hepatocytes.
Bile also consists of cholesterol, lecithin, bile pigments, water and electrolytes.

15. PANCREAS

16. The exocrine component of pancreas
The exocrine portion of the pancreas is a compound acinar gland with serous type of secretion
The initial portion of the intercalated duct begins within the acinus.
The intercalated duct cells located inside the acinus are called centroacinar cells.
Cells which composed pancreatic acini are called acinar cells.
They are characterized by acidophilic zymogen granules.

17. Diagram of a pancreatic acinus and its duct system

18. Duct system
The intercalated ducts are short and drain to intralobular collecting ducts.
The network of intralobular ducts drains to the larger interlobular ducts.
The interlobular ducts, in turn, drain directly into the main pancreatic duct.
A second large duct, the ductus choledochus (accessory pancreatic duct) arises in the head of the pancreas.

19. Endocrine pancreas Structure:
The islets of Langerhans, the endocrine component of the pancreas, are scattered throughout the organ.
The islets constitute about 1-2% of the volume of the pancreas.

20. The B cells They constitute about 70% of the total islet cells.
They are generally located in its central portion.
Functions:
They secrete insulin which stimulate:
uptake of glucose from the circulation
utilization and storage of glucose by all cells

21. The D cells
They constitute about 5-10% of the total pancreatic endocrine tissue.
They are also located peripherally in the islets.
Functions:
They secrete somatostatin which inhibit:
insulin and glucagon secretion

22. Diagram of an islet of Langerhans

23. The minor cells of islets
The PP cells secrete pancreatic polypeptide.
It stimulates gastric chief cells
It inhibits bile secretion and intestinal motility.
It inhibits pancreatic enzymes and bicarbonate secretion.

24. The minor cells of islets
The EC cells secrete secretin, motilin and substance P.
Secretin acts locally to stimulate bicarbonate secretion in pancreatic fluid and pancreatic enzyme secretion.
Motilin increases gastric and intestinal motility.
Substance P function is unclear.