Structure and function of accessory organ-2

Liver

The liver, which weighs between 1.2 and 2.3 kg, is the body's largest glandular organ (average 1500 gm). It makes up roughly 2.5% of an adult's entire body weight. When it functions as a hematopoietic organ in a mature fetus, it is roughly twice as big (5% of body weight). It occupies the majority of the right hypochondriac region, a portion of the epigastric region, and extends into the left hypochondriac region in the right upper quadrant of the abdomen, immediately below the diaphragm. It is almost entirely concealed by the ribs, however during inspiration, the lower edge can be felt along the right costal margin. It is a delicate, "wedge-shaped" organ with a reddish-brown appearance from the abundant blood that flows through it.

Organ Associated With the Liver

• Superiorly and Inferiorly
  • Abdomen's anterior wall and diaphragm.
• Inferiorly
  • Stomach, bile duct, duodenum, right kidney, right colon's hepatic flexure, and adrenal gland.
• Posteriorly
  • Esophagus, vertebral column, aorta, gall bladder, inferior vena cava, and diaphragm
• Laterally
  • Diaphragm and lower ribs.

Surfaces of the Liver

The liver has two surfaces, except posteriorly, which are divided from one another by a sharp inferior border.

• The anterior, superior, and posterior surfaces of the diaphragm.
• The inferior direction of the visceral surface.

Diaphragmatic Surface

The liver's smooth, conical diaphragmatic surface rests up against the inferior diaphragmatic surface. The hepatorenal and subphrenic recesses are connected to it:

• The falciform ligament, a structure formed from the ventral mesentery in the embryo, divides the subphrenic recess into right and left sections and separates the diaphragmatic surface of the liver from the diaphragm.
• The right side of the peritoneal cavity contains the hepatorenal recess, which is situated between the liver, right kidney, and right suprarenal gland. The hepatorenal and subphrenic recesses run together anteriorly.

Visceral peritoneum covers the liver's diaphragmatic surface, with the exception of the posterior region of the bare liver, where it is in direct contact with the diaphragm.

Visceral Surface

• Except for the gallbladder fossa and the porta hepatis, the visceral surface of the liver is covered by visceral peritoneum, and it is connected to the right kidney, right suprarenal gland, esophagus, right anterior part of the stomach, superior part of the duodenum, lesser omentum, gallbladder, right colic flexure, and right transverse transverse colon. The portal vein and hepatic arteries enter the liver through the porta hepatis, which also acts as the location where the hepatic ducts leave the liver.

Structure of the Liver

The right, left, quadrate, and caudate lobes of the liver are its four divisions. The huge right lobe and the smaller, wedge-shaped left lobe are the two that are most noticeable. The caudate and quadrate lobes are parts of the posterior surface that make up the other two. The falciform ligament, a piece of mesentery that suspends the liver from the diaphragm and anterior abdominal wall, separates them from one another.

The round ligament, also seen anteriorly, is a fibrous remnant of the umbilical vein, which supplies blood to the fetus's liver from the umbilical cord. The Glisson's capsule, a layer of connective tissue that surrounds the surface of the liver, encloses it. The liver's lobes are built up of minuscule functional units, known as lobules, that are hardly perceptible to the unaided eye. Hepatocytes, cubical-shaped cells with a hexagonal shape that are arranged in pairs of columns radiating from a central vein to form liver lobules, give these structures their hexagonal shape. Sinusoids (blood vessels with an incomplete wall) that carry a mixture of blood from the small branches of the portal vein and hepatic artery are located between two cells in a column of cells.

This configuration enables the mixing and close contact of the liver cells with the portal venous blood, which contains a significant amount of nutrients. Hepatic macrophages (Kupffer cells), which have the job of ingesting and eliminating worn-out blood cells and any foreign particles present in the blood flowing through the liver, are found among the cells lining the sinusoids.

Sinusoids release blood into the central or centrilobular vein. These eventually grow into the hepatic veins, which leave the liver and empty into the inferior vena cava, by joining with the veins from other lobules. Bile secretion is one of the liver's activities. Each day, the liver secretes 500 to 1000 ml of bile, which helps to emulsify fat and facilitates digestion. Accordingly, each column of hepatocyts has a bile canalicolus on one side and a blood sinusoid on the other.

Bile ductules and bile ducts are created by the joining of the bile canaliculi. The right and left hepatic ducts, which remove bile from the liver, are finally formed when the bile ducts combine. Each lobule also contains lymphoid tissue and a network of lymph vessels.

Blood Supply of the Liver

• The liver receives blood from the portal vein and hepatic artery. Variable numbers of hepatic veins exit the posterior surface and quickly enter the inferior vena cava right below the diaphragm to return venous blood.

Functions of the Liver

An incredibly active organ is the liver. The primary duties include:

• Carbohydrate Metabolism
  • Plasma glucose levels are maintained in large part by the liver. Following a meal, when blood glucose levels rise, the insulin hormone causes the liver to convert glucose into glycogen and tryglycerides for storage. When blood sugar levels drop later, the liver converts glycogen to glucose and releases it into the blood, keeping levels within the normal range.
• Fat Metabolism
  • To produce ATP, lipoproteins, cholesterol, and some triglycerides, the liver breaks down fatty acids.
• protein synthesis
• amino acid deamination
• Urea is created from the nitrogenous component of the amino acid that is removed because it is not necessary for the production of new protein and is extracted in urine.
• produces uric acid by breaking down nucleic acids, which is excreted in the urine.
• Transamination
  • Removes the amino acid's nitrogenous component and attaches it to other carbohydrates to create new non-essential amino acids.
• Most blood clotting factors and plasma proteins are made from amino acids.
• Erythrocyte Disintegration and Microbe Defense
  • In the sinusoids, phagocytic hepatic macrophages (Kupffer cells) perform this function. Spleen and bone marrow are other sites of red blood cell lysis.
• Detoxification of Drugs and Toxic Substances
  • These include alcohol and the toxins made by alien organisms, such as microbes. Some medications, such as glyceryl trinitate, are heavily inactivated by the liver and are therefore ineffective when taken orally.
• Inactivation of Hormones
  • These include sex hormones and insulin, glucagon, cortisol, aldosterone, and thyroid hormones.
• Production of Heat
  • The liver consumes a sizable amount of energy and generates a lot of heat. Thus, it serves as the body's primary organ for producing heat.
• Secretion of Bile
  • Bile salts are produced by the hepatocytes and are necessary for the emulsification and absorption of lipids.
• Storage
  • Glycogen, fat-soluble vitamins A, D, E, and K, iron, copper, and some water-soluble vitamins like vitamin B12 are among the many things that the liver stores.