1 How do hepatocytes (& Kupffer cells) get access to slow-moving blood?
2 How is bile produced and collected as a fluid separate from blood?
Thanks!
1. Hepatocytes (liver cells) and Kupffer cells (specialized immune cells in the liver) get access to the slow-moving blood through a unique circulatory system called the hepatic portal system.
To understand how this works, we first need to know that the hepatic portal system is responsible for directing blood from the abdominal organs, including the intestines, spleen, and pancreas, to the liver. This system helps in the processing and detoxification of substances absorbed from the intestines.
Here's a step-by-step explanation of how hepatocytes and Kupffer cells obtain slow-moving blood:
1. After digestion, nutrients and toxins are absorbed into the bloodstream from the small intestine.
2. Absorbed substances then enter the mesenteric veins, which collect blood from the intestines.
3. The mesenteric veins merge together to form the portal vein.
4. The portal vein carries the nutrient-rich blood to the liver.
5. In the liver, the portal vein branches out and forms a network of small blood vessels called sinusoids.
6. These sinusoids are lined with hepatocytes, which are the main functional cells of the liver.
7. Kupffer cells, which are specialized immune cells, are also present in the sinusoids.
8. As the blood flows sluggishly through the sinusoids, hepatocytes and Kupffer cells come into close contact with the blood, allowing them to perform their functions.
9. Hepatocytes metabolize nutrients, produce various enzymes, and detoxify potentially harmful substances.
10. Kupffer cells help in immune responses and remove debris and bacteria from the blood.
In summary, hepatocytes and Kupffer cells gain access to slow-moving blood through the hepatic portal system, which directs nutrient-rich blood from the abdominal organs to the liver.
2. Bile production and collection as a separate fluid from blood involve several steps in the liver:
1. Hepatocytes (liver cells) produce bile within specialized structures called bile canaliculi. These canaliculi form a network within the liver tissue.
2. Hepatocytes secrete bile salts, bile pigments, cholesterol, and other components into the bile canaliculi.
3. As bile travels through the canaliculi, it merges to form small bile ducts within the liver.
4. These small bile ducts join together to form larger ducts known as hepatic ducts.
5. The hepatic ducts eventually combine to form the common hepatic duct, which carries bile out of the liver.
6. The common hepatic duct then joins the cystic duct, which connects to the gallbladder.
7. Within the gallbladder, bile is stored and concentrated until needed.
8. When required, the hormone cholecystokinin (CCK) is released in response to the presence of food in the small intestine. CCK stimulates the contraction of the gallbladder, causing bile to be released into the common bile duct.
9. The common bile duct merges with the pancreatic duct and enters the small intestine at the sphincter of Oddi.
10. Once in the small intestine, bile aids in the digestion and absorption of fats.
In summary, bile is produced by hepatocytes in the liver, collected into bile canaliculi, and transported through the bile duct system. It eventually reaches the gallbladder, where it is stored and concentrated until needed for digestion in the small intestine.