The human liver is the largest exocrine gland in the body. As part of the digestive system, it is also the largest metabolic organ and a massive detoxification center for degrading alcohol and drugs. Essentially, it is composed of millions of hepatocytes, which are the parenchymal or fundamental cells of this organ. It is constituted by functional and structural units called liver lobules, which are roughly hexagonal in shape.
The liver is enclosed in a thin capsule of dense connective tissue and covered mostly by a visceral layer of peritoneal mesothelium. The liver is stimulated by three hormones: glucagon, insulin, and growth hormone. It is supplied by the hepatic artery and receives nutrient-rich blood from the hepatic portal vein. The nutrients brought in by the hepatic portal vein are the products of digestion in the small intestine and they are metabolized by the hepatocytes contained in the lobules.
Functions
The key functions of liver are manyfold. It manufactures and secretes cholesterol to repair damaged tissues as well as plasma proteins into the bloodstream It also metabolizes all nutrients that arrive through the portal system. It converts excess glucose into glycogen and triglyceride (fat). It metabolizes fatty acids into ketone bodies during famine and dietary conditions. It transforms glycerol and amino acid into glucose (when there is not carbohydrate consumption) through a process known as gluconeogenesis. It metabolizes ethanol (alcohol) into acetaldehyde. It also secretes bile to emulsify fats in the small intestine.
Anatomical Description
The liver occupies the right side of upper part of the abdominal cavity, lying immediately under the diaphragm. It is roughly triangular or wedge-shaped, with the wide portion on the right side of abdomen. The liver weighs 1,500 grams on average. Horizontally, from right to left, it measures between 26 and 30 cm in length, while the anterior-posterior thickness of the right portion is 22 cm. This organ has a convex upper and anterior surface, corresponding to the shape of the dome of diaphragm, while its lower surface has concave portions which are surrounded by sharp border. The posterior side is also slightly convex.
The liver is attached to the diaphragm through the falciform ligament, which is a sagittal fold that extends from the peritoneum. The falciform ligament divides the liver into two parts; the right lobe, which is the largest and the thickest, and a left lobe, which is smaller. The right lobe is under the right dome of diaphragm, while the left lobe lies under the left dome. A small cardiac impression is visible on the upper surface of left lobe, which corresponds to the position of the heart above the diaphragm.
The liver is arranged around structural units called lobules or acini, which consist of parenchymal cells called hepatocytes that form hepatic plates. In the center of each lobule, there is a central vein, while the interlobular artery and vein and the hepatic bile duct lie along the length and at one side of each lobule. These blood vessels are small branches of the hepatic artery and portal vein. The interlobular artery and vein are contained, together with the hepatic bile duct, in a triangular portal canal that runs the length of each lobule.
The interlobular artery and vein in turn give rise to interlobular capillaries, which enter the lobule where they are continuous with the hepatic sinusoids. The sinusoids contain mixed arterial and venous (portal) blood and drain into a central vein. The central vein of each lobule drains into the sublobular vein, which in turn drains into the right, middle, and left hepatic vein.
 |
| Anterior side of human liver |
0 Comments