Digestive system L 4. Lecturer Dr. Firdous M. Jaafar Department of Anatomy/Histology section

Transcription

1 Digestive system L 4 Lecturer Dr. Firdous M. Jaafar Department of Anatomy/Histology section

2 objectives 1-Describe the structure of liver. 2-Define liver lobule, and identify its zones. 3-Define portal lobule. 4-Define hepatic acinus. 5-Describe hepatocyte. 6-Describe bile canaliculae and sinusoids. 7-Define space of Disse, and describe its structure. 8-Discuss the blood supply of the liver. 9-Describe the structure of pancrease; a-exocrine part: serous acini and ducts. b-endocrine part: islet of Langerhan. 10-Describe the structure of gall bladder.

3 Liver The liver is located in the peritoneal cavity below the diaphragm. Function: 1- produces bile and plays a major role in lipid, carbohydrate, and protein metabolism. 2- Inactivates and metabolizes many toxic substances and drugs. 3- participates in iron metabolism

4 Liver The liver is composed of two lobes; right and left, and covered by a thin connective tissue capsule (Glisson's capsule), that send trabeculae subdividing the liver into lobes and lobules. In man the trabeculae are very incomplete.

5 Liver

6 Liver Human liver lobule Pig liver lobule

7 Hepatic lobule hepatic lobules are polygonal units showing plates of epithelial cells called hepatocytes radiating from a central venule The plates are separated by hepatic sinusoids.

8 irregularly dilated vessels consist only of a discontinuous layer of fenestrated endothelial cells, separated from hepatocytes by a thin, discontinuous basal lamina and a very narrow perisinusoidal space (the space of Disse). Hepatic sinusoids

9 Reticulin (collagen type III) fibers running along the plates of hepatocytes are the major support for the sinusoids and central venules. Hepatic sinusoids

10 Hepatic sinusoids/sem

11 Hepatic sinusoids Two types of cells are present in the wall of sinusoids: 1- Kupffer cells: macrophages. 2- Ito cells(fat storing cells).

12 MEDICAL APPLICATION In chronically diseased liver, Ito cells proliferate and acquire the features of myofibroblasts, with or without the lipid droplets, and play a major role in the development of fibrosis, including the fibrosis secondary to alcoholic liver disease.

13 Hepatic lobule/portal triad At the corners of the lobule, there is the portal canals or portal triad.each portal canal contains: 1- portal venule (a branch of portal vein) 2- hepatic arteriole (a branch of hepatic artery) 3- bile duct and lymphatic vessels. These structures are surrounded by loose connective tissue.

14 Hepatocytes are large polyhedral cells, with six or more surfaces, and typical diameters of µm. Rich in mitochondria, with large spherical one or two nuclei. Hepatocyte

15 Hepatocyte Has three surfaces: 1- Sinusoidal surfaces: are separated from the sinusoidal vessel by the space of Disse, where material is transferred between the sinusoids and the hepatocyte 2- Canalicular surfaces: are the surfaces across which bile drains from the hepatocytes into the canaliculi. 3- The intercellular surfaces: are the surfaces between adjacent hepatocytes

16 the first portions of the bile duct system, limited only by the plasma membranes of two hepatocytes, and collect bile towards portal space(triad). bile canaliculi empty into bile ductules which will end at bile ducts, which will end at R&L hepatic ducts. Bile canaliculi

17 Bile canaliculi/em

18 Blood supply of the liver 1- Portal vein system: Portal vein gives portal venule, which gives distributing venules, which give inlet venules, which empty into sinusoids. Sinusoids run towards central or centrolobular vein, then sublobular vein then hepatic vein, which empties into inferior vena cava.

19 Blood supply of the liver 2- Arterial system: hepatic artery gives interlobular arteries, which gives inlet arterioles, which ends in the sinusoids.

20 structure-function relationships in liver.

21 MEDICAL APPLICATION Blood always flows from the periphery to the center of each hepatic lobule, so the properties and function of the periportal hepatocytes differ from that of the centrolobular cells. Hepatocytes near the portal areas can rely on aerobic metabolism and are often more active in protein synthesis, while the more central cells are exposed to lower concentrations of nutrients and oxygen and are more involved with detoxification and glycogen metabolism.

22 MEDICAL APPLICATION Jaundice: occures When bilirubin or bilirubin glucuronide is not excreted properly by liver. Neonatal hyperbilirubinemia: is one of the frequent causes of jaundice in newborns due to underdeveloped state of the smooth ER in their hepatocytes. Gallstones (cholelithiasis): is an Abnormal proportions of bile acids.it can block bile flow and cause jaundice.

23 MEDICAL APPLICATION Liver cirrhosis is a process of replacement of damages liver tissue by excess amount of connective tissue. It is caused by ethanol, drugs or other chemicals, hepatitis virus (mainly types B, C, or D), parasites, and autoimmune liver disease. It is a progressive and irreversible process, causes liver failure, and is usually fatal. The fibrosis is diffuse, affecting the entire liver.

24 Liver regenaration liver has a strong capacity for regeneration, by a process of compensatory hyperplasia. The regenerated liver tissue is usually well organized, with the typical lobular arrangement, and replaces the functions of the destroyed tissue. one liver lobe can often be donated by a living relative for surgical transplantation and full liver function restored in both donor and recipient.

25 Pancreas The pancreas is a mixed exocrine-endocrine gland that produces both digestive enzymes and hormones. A thin capsule of connective tissue covers the pancreas and sends septa into it, separating the pancreatic lobules. The secretory acini are surrounded by a basal lamina that is supported by a delicate sheath of reticular fibers and a rich capillary network.

26 Pancreas

27 Pancreas Exocrine part is composed of : serous acini, and intercalated ducts(similar to parotid gland). centroacinar cells constitute the intraacinar portion of the intercalated duct and are found only in pancreatic acini. Intercalated ducts merge to form larger interlobular ducts lined by columnar epithelium. No ducts in the pancreas are striated.

28 Pancreas Exocrine part Centroacinar cells

29 Pancreatic acinar cell(em)

30 Medical application In acute necrotizing pancreatitis, the proenzymes may be activated and digest pancreatic tissues, leading to very serious complications. Possible causes include infection, gallstones, alcoholism, drugs, and trauma.

31 Pancreas Endocrine part is composed of : pancreatic islets (islets of Langerhans) which are compact spherical or egg-shaped masses of endocrine tissue embedded within the acinar exocrine tissue of the pancreas. A very thin capsule of reticular fibers surrounds each islet.

32 Pancreas/Islet of Langerhan

33 Pancreas/Islet of Langerhan Types of cells: 1-α or A cells: secrete primarily glucagon. 2-β or B cells: secrete insulin. 3- δ or D cell: secrete somatostatin. 4- F or PP cell: secrete pancreatic polypeptide.

34 MEDICAL APPLICATION Insulin-dependent or type 1 diabetes (juvenile diabetes) results from partial or total autoimmune destruction of cells and subsequent lack of insulin. Insulin-independent diabetes or type 2 diabetes occurs later in life, results from a failure of cells to respond to insulin, and is frequently associated with obesity.

35 Biliary tract & Gallbladder

36 Gallbladder saclike structure that stores and concentrates bile, and releases it into the duodenum after a meal. The wall consists of: 1- mucosa: simple columnar epith.,with lamina propria. 2- muscular layer: thick. 3- adventitia, or serosa.

37 Gallbladder Wall of GB EM of epithelial cell