Wednesday, January 27, 2021

Human Anatomy:The Liver

A free Educational Medical Resource from Medika Life

The liver is an organ in the upper right-hand part of your abdomen. It sits under the diaphragm, and on top of the stomach, right kidney, and intestines.

The liver is a dark reddish-brown color, and is shaped a bit like a wedge. It weighs about 3 pounds. The liver has 2 lobes. Both are made up of 8 segments that have of 1,000 small lobes called lobules. These lobules are connected to small tubes (ducts) that lead to larger ducts that form the common hepatic duct. The common hepatic duct sends the bile made by the liver cells to the gallbladder and the first part of the small intestine (duodenum) through the common bile duct.

The liver holds about 1 pint (13%) of your body’s blood supply. There are 2 blood vessels that send blood to the liver. They are:

  • Hepatic artery. This sends oxygen-rich blood to the liver.
  • Hepatic portal vein. This sends nutrient-rich blood to the liver.

Functions of the liver

The liver has more than 500 vital functions. All the blood leaving the stomach and intestines passes through the liver. The liver processes this blood. It breaks down, balances, and creates nutrients. It also processes medicines and other chemicals. The liver:

  • Makes bile, which helps carry away waste and break down fats in the small intestine during digestion
  • Makes certain proteins for blood plasma
  • Makes cholesterol and proteins to help carry fats through the body
  • Converts excess glucose into glycogen for storage and makes glucose as needed 
  • Controls blood levels of amino acids, which are the building blocks of proteins
  • Processes hemoglobin for its iron and then stores the iron
  • Converts ammonia to urea, which is then excreted in urine
  • Clears medicines, drugs and other substances from the blood
  • Controls blood clotting
  • Helps prevent infections by making immune factors and removing bacteria from the blood
  • Clears bilirubin from the blood 

When the liver has broken down harmful substances, this waste is excreted into the bile or blood. Waste in bile enters the intestine and leaves the body in the form of feces. Waste in blood is filtered out by the kidneys, and leaves the body in the form of urine.

Anatomical Position

The liver is predominantly located in the right hypochondrium and epigastric areas, and extends into the left hypochondrium.

When discussing the anatomical position of the liver, it is useful to consider its external surfaces, associated ligaments, and the anatomical spaces (recesses) that surround it.

Anatomical Structure

The structure of the liver can be considered both macroscopically and microscopically.

Macroscopic

The liver is covered by a fibrous layer, known as Glisson’s capsule.

It is divided into a right lobe and left lobe by the attachment of the falciform ligament. There are two further ‘accessory’ lobes that arise from the right lobe, and are located on the visceral surface of liver:

  • Caudate lobe – located on the upper aspect of the visceral surface. It lies between the inferior vena cava and a fossa produced by the ligamentum venosum (a remnant of the fetal ductus venosus).
  • Quadrate lobe – located on the lower aspect of the visceral surface. It lies between the gallbladder and a fossa produced by the ligamentum teres (a remnant of the fetal umbilical vein).

Separating the caudate and quadrate lobes is a deep, transverse fissure – known as the porta hepatis. It transmits all the vessels, nerves and ducts entering or leaving the liver with the exception of the hepatic veins.

Microscopic

Microscopically, the cells of the liver (known as hepatocytes) are arranged into lobules. These are the structural units of the liver.

Each anatomical lobule is hexagonal-shaped and is drained by a central vein. At the periphery of the hexagon are three structures collectively known as the portal triad:

  • Arteriole – a branch of the hepatic artery entering the liver.
  • Venule – a branch of the hepatic portal vein entering the liver.
  • Bile duct – branch of the bile duct leaving the liver.

The portal triad also contains lymphatic vessels and vagus nerve (parasympathetic) fibres.

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