[Biology Class Notes] on Liver Pdf for EXAM

The liver is the largest gland in an animal or human body and the viscera of the body. In the carnivorous, omnivorous, and herbivorous, different sizes of the liver can be observed, due to the difference of role in metabolism. The weight as per body weight is more in young animals, as it changes with age. In the fetal stage, the liver is derived from the endoderm epithelium on the ventral duodenum. The liver produces red and white blood cells during the fetal state. The main function of a liver is to produce bile and metabolism of protein, fat, and carbohydrates.

Liver in the Human Body

In humans, the liver is in the upper right corner of the body. It is situated just below the diaphragm and is tilted towards the body cavity. The right portion of the stomach is above the small intestine and the left portion is above the stomach. 

Structure of Liver

• In animals, the structure of the liver is similar to humans.

• The liver is lined by the fibrous connective tissue. This capsule is called Glisson’s capsule. In animals, the liver is also considered to be derivative from the epithelial tissue. 

• The cellular structure of the liver is simple and it consists of the repetition of a simple structure called lobule. 

• The hepatocyte cells are organized in the anastomosed layer. These layers of hepatocytes are much thicker and fuse together to form a complex structure.

• Endocrine secretion of a large number of plasma proteins like lipoprotein and albumin is done by hepatocytes.

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Liver Anatomy:

The anatomy of the liver is as follows.

• The liver is divided into certain lobes namely the left lateral lobe, left medial lobe, and right lateral lobe, right medial lobe, quadrate, caudate, and papillary.

• Each lobe is further divided into eight segments and all of the segments contain 1000 lobules.

• Each of the lobules in the segment has a small tube. A tube from each lobule joins to make the common hepatic duct.

• The function of the hepatic duct is to transport bile made by the liver cells to the gallbladder and duodenum.

• Blood is supplied to the liver from two distinct sources; those are oxygenated blood flow from the hepatic artery and nutrient-rich blood flow from the hepatic portal vein. 

Liver Position in the Body:

At any given time, the liver retains around one pint (13 per cent) of the body’s blood supply. In the majority of animals, the liver is found underneath the diaphragm. Most of the blood which reaches the liver comes from the portal vein and due to heavy blood supply, the liver has a reddish colour.

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The Function of the Liver in the Human Body

The liver performs several activities in the human body. Some of the major functions of the liver are mentioned below:

• The liver helps to regulate the blood chemical levels.

• The liver produces bile, which helps to remove the waste product away and bile helps in the breakdown of fat in the small intestine.

• Bile is an essential watery outpouring of the liver that is generated by the hepatic cells and transported to the gallbladder for concentration, storage and is then delivered into the duodenum, the very first portion of the small intestine. Organic and inorganic solutes make up approximately 5 percent of bile. Its purpose is to assist the duodenum in fat digestion. Bile acts as detergents that play a critical role in the emulsification of fat as it lowers down the surface tension so that pancreatic juices and enzymes can have better action on food particles.  Bile is made up of bile acids and salts, phospholipids, cholesterol, pigments, water, and electrolyte molecules. Because of its constituents, the bile secretion is mildly alkaline with a pH range of 7–8. The hormones cholecystokinin, secretin, gastrin, and somatostatin, as well as the vagus nerve, regulate the quantity of bile secreted into the duodenum.

• The liver produces blood plasma proteins like albumin.

• The most prevalent circulation polypeptide within the plasma is albumin. One of the primary roles is to inhibit the leakage of plasma solutes. Increased capillary permeability causes albumin and other plasma solutes to escape into the interstitium in inflammatory situations such as trauma, illness, infection, and states where the organism is growing. This enhances the combined interstitial and intravascular space’s distribution volume. Albumin is a plasma component binding protein that is harmful in its unbound state. It also provides amino acids, serves as the primary extravascular scavenger, and is oxidised during inflammation.

• Glycogenesis, the process of storing excess glucose in the form of glycogen, occurs in the liver. Excess glucose is converted to glycogen for storage. For energy and to balance and generate glucose when needed, glycogen can be converted back to glucose.

• Haemoglobin is processed in order to make use of its iron content. The liver stores iron that is found in the heme group of blood haemoglobin.

• Cholesterol and specific proteins are produced to aid in the transport of fats throughout the body.

• The liver converts poisonous ammonia to urea which can be excreted by the urine. Urea is the end product of protein metabolism.

Role of Liver

The liver performs the filtration of blood that comes out from the digestive tract. In this process, the liver also detoxifies the blood. The absorption of drugs in our body also occurs in this particular process. The liver secretes bile which is a very important aspect of fat metabolism. The liver makes protein for blood. Blood proteins are important as they help in the clotting of the blood as without the presence of blood proteins minor wounds could be fatal due to immense blood loss.

Digestive Function of the Liver

The liver makes bile juice which helps in the digestion process and also helps to carry out the waste materials. Liver stores the glucose and releases it as per the requirement of the body through the process of glycogenolysis. In glycogenolysis, glycogen breaks down to form glucose. The liver also helps to clear bilirubin. The liver produces cholesterol and protein to carry fat through the body. 

Diseases of Liver

• Jaundice – When bilirubin gets stored in our body in an excess amount, then a yellow tint on the eye and skin is observed. This is known as jaundice. This disease is caused due to inflammation of the liver.

• Liver Cancer – If cirrhosis is present in the liver, then it may lead to liver cancer and the most common type of liver cancer is Hepatocellular Carcinoma.

• Hepatitis – This is caused by the viruses Hepatitis A, B, C, due to the inflammation of the liver.