The liver is the second largest organ in the human body (after the skin) and the largest gland (weighing an average of 1500g).
The liver is an extremely busy and hard-working organ as evidenced by its huge blood flow – blood passes through the liver at a rate of around 1.4 litres (3 pints) per minute.
The healthy liver is such a busy organ that its activities create a large amount of heat, increasing body temperature. That’s why you will often feel hot after a large meal.
The liver is sheltered by the ribs and is tucked away in the right side of the upper abdomen. It has two anatomical parts called “lobes” and the right lobe is approximately 6 times larger than the left. The right and left lobes of the liver are separated by fibrous tissue known as the Falciform ligament. The large right lobe can be divided into smaller lobes, known as the largest right lobe proper, and the quadrate lobe and the caudate lobe, which can be seen on the underside or under surface of the liver.
The liver is not only unique by virtue of its large size, but also by its dual blood supply. It is the only organ to have two separate sources of blood supply: the hepatic artery bringing freshly oxygenated blood from the heart and the portal vein bringing blood from the stomach and intestines which is laden with nutrients from your food.
The hepatic artery and portal vein enter the liver together through a fissure in its base called the porta hepatis and at this point divide into branches to supply the left and right lobes of the liver. Once inside the liver those blood vessels continue dividing further like the branches of a tree bringing blood to every part of the liver.
These tiny branches of blood vessels eventually empty into microscopic spaces between the rows of liver cells. These spaces are called sinusoids and they are vitally important for liver-cleansing and nourishment. The sinusoidal spaces are lined by special cells such as fat-storing cells, pit cells, endothelial cells and the most amazing cells of all – the Kupffer cells.
The Kupffer cells are highly specialised and are not easy for your liver to replace. One could say the Kupffer cells are the garbage collection service of the liver, and we all know what happens to our neighbour if the local council’s garbage collection service goes on strike. Kupffer cells are mobile and look somewhat like a tiny octopus as they travel around cleaning up the blood and lymphatic fluid inside the sinusoid.
Kupffer cells engulf and ingest dead cells, cancer cells, yeasts, viruses, bacteria, parasites, artificial chemicals, incompletely digested or denatured proteins and dangerous foreign particles.
Once the Kupffer cell has its dangerous victim ingested, it chews up with enzymes and puts it to rest. If these Kupffer cells are worked too hard for too long they may become overloaded with toxins so that the liver’s task of keeping your bloodstream claim is not achieved.
In such cases many different symptoms of poor health may occur, especially allergies, headaches and chronic fatigue.
After coursing in and out among the columns of liver cells, the sinusoids empty into central veins which in turn empty into larger hepatic veins that carry blood away from the liver back to the heart. Thus the cleanliness of the blood returning to your heart is dependent upon the efficient functioning of your liver cells and senior sinusoids.
WHAT IS BILE?
The liver produces a yellow-green substance called bile which is necessary for the emulsification and absorption of fats from the small intestine. The liver cells produce bile and secrete into tiny ducts which lie between the clumps of liver cells; these tiny gaps that collect the bile are called bile canaliculi and they in turn join into larger ducts that join to form the right and left hepatic bile ducts, which in turn join to form the common hepatic duct.
The gallbladder is a storage sac that connects to the common hepatic duct via the cystic duct. The gallbladder has two main functions: to store bile and to concentrate bile, so that it becomes much stronger by the time it is needed. Bile is concentrated five-fold while stored in the gallbladder. The liver might manufacture bile, but the gallbladder makes it potent.
Bile is then transported to the intestine via the common bile duct. Bile is a liquid consisting of water, bile salts, cholesterol, bile pigments, lecithin, lipids and electrolytes. Bile salts are made by the liver cells from cholesterol which either comes from the diet or is synthesised during fat metabolism. Cholesterol itself is found in bile as a byproduct of bile-salt metabolism, but higher amounts in the bile are due to excessive saturated fats in the diet.
People who eat a high-fat diet have a tendency to develop gallstones from the high amount of cholesterol in their bile.
Bile cholesterol is ideally kept in a soluble form by combining with bile salts and lecithin to form soluble particles called micelles. If there is too much cholesterol in the bile it will not be able to stay soluble and may precipitate into gallstones.
Bile salts are made from cholesterol through a sequence of chemical reactions in the liver cells so forming the necessary bile acid cholic and chenodeoxycholic acids. These bile acids are combined with the amino acids taurine and glycine. This combination is called a conjugated bile acid. A bile salt is a bile acid that has lost a hydrogen ion and gained a potassium and sodium ion. Yes, the production of bile in the liver is a very finely tuned process and can be deranged by poor diet, and also by deficiencies of the amino acid taurine. All good liver tonics should contain taurine and lecithin as well as liver tonic herbs.
Bile pigments such as bilirubin give the bile a yellow-green color. If the bile ducts or liver cells are damaged so that bilirubin cannot be excreted in the bile and thus through the intestines, the bilirubin pigment builds up in the body giving the skin and eyes a yellowish colour – this is known as jaundice.
FUNCTIONS OF THE LIVER
The liver is very versatile and performs a host of metabolic and regulatory functions.
Regulates carbohydrate metabolism – turns glucose into glycogen for storage in the liver. Liver glycogen can release glucose into the blood to maintain blood sugar levels if required. If the body is low in carbohydrates the liver can manufacture more carbohydrates from fat or proteins.
Has storage functions – stores glycogen, vitamin A, vitamin D, many of the B complex environments, including vitamin B12, iron, and copper.
Regulates protein metabolism – the liver manufactures many body proteins such as albumin and blood clotting factors such as prothrombin that cause the blood to clot when needed. It makes sex hormone binding globulin which is the protein that binds the steroid sex hormones. A healthy liver is essential for a good sex drive (libido) and if your liver is producing excessive amounts of the protein sex hormone binding globulin (SHBG) your libido may be poor.
The liver makes many proteins for the purpose of transporting substances (such as fats, iron, hormones and drugs) around the bloodstream. One particular liver protein called high density lipoprotein (HDL) is checked frequently in blood tests – a high reading is beneficial in reducing your risk of heart disease. This is because HDL transports cholesterol out of the blood-vessel walls back to the liver for excretion. Thus a healthy liver is required for healthy blood vessels.
Detoxifies many toxic substances – either by the Kupffer cells or by adding a chemical substance to the toxin for its elimination or deactivation. It metabolises biotransforms drugs, steroid hormones, and waste products of the body such as toxic ammonia. Ammonia is formed in the body from the breakdown of protein and a healthy liver is able to break it down into urea which is then excreted via the kidneys. The most important enzyme system in the liver’s detoxification process is the cytochrome P-450-dependent microsomal oxidase system. Thankfully, you don’t need to remember this system of liver enzymes, but it’s important to note that it is highly dependent upon vitamin C and taurine and most of us do not ingest these nutrients in sufficient quantities.
In cases of toxic overload the liver cannot keep up with detoxification requirements and thus the liver itself bears the brunt of these toxins.