LESSON 21 cortas

The hepatic lobule is a morphological unit of the liver, divisible into contiguous hexagonal spaces called lobules. Each lobule contains six portal spaces, located at angles and corners, each of which contains an arterial branch, venous branch, and a bile duct. The lobule is made up mainly of hepatocytes, which are polygonal cells forming rows (cords) with sinusoids in between. The lobule is also penetrated by trabeculae, which are branched connective tissue that forms thin branches and divides the liver parenchyma into lobules.

The perisinusoidal surface of hepatocytes has microvilli that facilitate the exchange of materials, allows hepatocytes to discharge endocrine secretions, and enables blood to enter via membrane receptors.

Sinusoids are discontinuous or continuous blood capillaries carrying blood from the artery and portal vein to the central vein. They are lined with endothelial cells and Kupffer cells. The endothelial cells are smaller cells that line the sinusoids, while Kupffer cells are larger cells that reside within the sinusoids and are involved in phagocytosis and releasing cytokines.

<p>Hepatocytes are polygonal cells, 20-30 µm in diameter, forming rows with sinusoids in between. They contain various organelles including ribosomes, RER, Golgi complex, mitochondria, peroxisomes/microsomes, SER, and cytoplasmic inclusions such as glycogen and lipids.</p> Signup and view all the answers

<p>Trabeculae are branched connective tissue penetrating the liver, forming thin branches and dividing the liver parenchyma into lobules. They are thickest in pork liver, making it tougher.</p> Signup and view all the answers

<p>Each lobule contains six portal spaces, located at angles and corners, and each contains an arterial branch, venous branch, and a bile duct. These portal spaces divide the lobule into functional units.</p> Signup and view all the answers

<p>The lateral surface of hepatocytes contains desmosomes, porous junctions, and labyrinthine intercellular spaces (bile canaliculi) that prevent the leakage of bile.</p> Signup and view all the answers

<p>Kupffer cells reside within the sinusoids and are part of the reticuloendothelial system. They are involved in phagocytosis and releasing cytokines.</p> Signup and view all the answers

<p>Endothelial cells are smaller cells that line the sinusoids and contribute to the structure of these blood capillaries, allowing for the exchange of materials and interactions with blood cells.</p> Signup and view all the answers

<p>Each portal space contains an arterial branch, venous branch, and a bile duct.</p> Signup and view all the answers

<p>Pig liver has clearly visible lobules, due to the presence of trabeculae, and has thicker trabeculae, making it tougher than other types of liver.</p> Signup and view all the answers

<p>The central vein carries blood that has passed through the sinusoids and is the site of convergence for the blood from multiple lobules. It plays a key role in draining deoxygenated blood from the liver.</p> Signup and view all the answers

<p>Kupffer cells are macrophages in the liver that play a role in waste elimination, immune response modulation, and inflammation.</p> Signup and view all the answers

<p>Ito cells provide structural support to the sinusoids, store lipids and vitamin A, and produce type III collagen fibers.</p> Signup and view all the answers

<p>The bile canaliculi form a labyrinthine network, joining to form larger bile ducts and emptying into the common hepatic duct. They are responsible for transporting bile from hepatocytes to the bile ducts.</p> Signup and view all the answers

<p>The liver has a dual afferent circulation, receiving oxygenated blood from the hepatic artery and nutrient-rich blood from the portal vein.</p> Signup and view all the answers

<p>The exocrine pancreas secretes digestive enzymes, while the endocrine pancreas produces hormones that regulate carbohydrate metabolism.</p> Signup and view all the answers

<p>The pancreatic parenchyma is surrounded by a thin capsule of irregular fibrous connective tissue and is divided into lobes and lobules by fibrous septa.</p> Signup and view all the answers

<p>The exocrine pancreas is a compound tubulo-acinar gland, with islets of endocrine cells called the endocrine pancreas or pancreatic islets or islets of Langerhans.</p> Signup and view all the answers

<p>Acinous cells in the pancreas have a high basophilia in their basal area, while the apical area is usually acidophilic. They contain a spherical nucleus located towards the geometric centre of the cell. Ultrastructurally, they exhibit characteristics of exocrine glandular cells of the serous type, including an abundance of rough endoplasmic reticulum (RER) arranged in parallel cisterns occupying the whole basal pole and a large quantity of zymogen granules (pancreatic enzymes) at the apical pole. During fasting, the cells are usually packed with zymogen granules.</p> Signup and view all the answers

<p>The formation of excretory ducts in the pancreas begins inside the pancreatic acini. These ducts have an intra-acinar portion called intercalated ducts, which are formed by squamous acinous cells or centroacinar cells. Ultrastructurally, these cells do not have secretory granules and have scarce rough endoplasmic reticulum (RER). The intercalated ducts merge to form the intralobular ducts, which converge to form the interlobular ducts. The interlobar ducts discharge their contents into the main pancreatic duct, which joins the common bile duct before opening into the duodenum at the level of the ampulla of Vater.</p> Signup and view all the answers

<p>The endocrine pancreas is located between the exocrine pancreatic acini as islands or islets of endocrine cells that discharge their secretion into a highly developed internal capillary network. The islets are separated from the exocrine tissue by a thin layer of reticulin fibers and contain little loose connective tissue associated with capillaries. The cells within the islets are arranged in irregular anastomosed cords and are of five types: A or alpha (α) cells, which secrete glucagon; B or beta (β) cells, which produce insulin; D or delta (δ) cells, which secrete somatostatin; F cells, which produce the pancreatic polypeptide; and C cells, which do not have secretory granules.</p> Signup and view all the answers

<p>The different endocrine cell types in the pancreas are not identifiable with usual laboratory techniques since they all show a very similar morphology. However, with immunohistochemical techniques, they can be precisely identified.</p> Signup and view all the answers

<p>The intralobular ducts are formed by the merging of intercalated ducts and converge to form the interlobular ducts. The interlobar ducts discharge their contents into the main pancreatic duct, which joins the common bile duct before opening into the duodenum at the level of the ampulla of Vater. These ducts play a crucial role in transporting the secretions from the exocrine pancreas to the duodenum for digestion.</p> Signup and view all the answers

<p>The islets of Langerhans are innervated by myelinated and unmyelinated fibers of the autonomic nervous system, which are located on the periphery of the blood vessels. They are also associated with a highly developed internal capillary network with fenestrated blood capillaries.</p> Signup and view all the answers

<p>Centroacinar cells do not have secretory granules and have scarce rough endoplasmic reticulum (RER). They play a role in the formation of the excretory duct system within the pancreas.</p> Signup and view all the answers

<p>During periods of fasting, acinous cells are usually packed with zymogen granules, which present a finely granular structure and contain pancreatic enzymes. The quantity and maturation of the granules may vary, showing more or less electron density based on their stage of development.</p> Signup and view all the answers

<p>The main functions of the liver are: 1. Exocrine function: Synthesize and secrete bile to the duodenum. 2. Endocrine function: Synthesize and secrete proteins into the blood. 3. Metabolic function: Of proteins, carbohydrates, fats, and haemoglobin. 4. Storage: Of triglycerides, glycogen, vitamins A and B. 5. Defence: Intravascular phagocytosis, drug detoxification. 6. Haematopoiesis: In the embryo and, potentially, in the adult. All these functions are carried out by only one type of cell, the hepatocyte.</p> Signup and view all the answers

<p>The liver is a parenchymatous organ with stroma and parenchyma. The stroma, from outside to inside, consists of the following parts: 1) Capsule: It is made of dense irregular connective tissue and is called Glisson's capsule. It is covered by peritoneum on its entire surface except at the level of the hilum, located on the caudal side of the organ.</p> Signup and view all the answers

<p>The liver is located in the upper right quadrant of the abdominal cavity for most species. The cranial or diaphragmatic face of the liver is convex and is divided into a variable number of lobes depending on the species. In all species except horses and birds, there is a vesicle associated with the liver called the gallbladder.</p> Signup and view all the answers

<p>The liver functions as both an exocrine and endocrine gland. As an exocrine gland, it synthesizes and secretes bile to the duodenum. As an endocrine gland, it synthesizes and secretes proteins into the blood, such as albumin and clotting factors.</p> Signup and view all the answers