The Human Liver
The liver is an internal organ which lies in the abdominal cavity of the body of animals. In humans, it is the largest glandular organ of the body, and generally weighs about 3 lb (1.35 kg).
Physically, the liver looks like a large reddish brown lump which is divided into four unequal lobes. Liver tissue is made up of hepatic cells (hepatic is an adjective denoting something concerned with the liver) which are grouped into lobules; each lobule is served by a capillary which is a minute subdivision of the two large vessels which supply the liver with blood: the hepatic artery which brings blood full of oxygen from the aorta; and the portal vein, which brings blood full of digested food from the small intestine.
From its strategic location between the gut and the rest of the body, the liver plays many important roles in the body, which can be grouped into three broad areas:
- metabolism: The liver metabolizes carbohydrates, fats, proteins from digested food, storing them, using them to synthesize new proteins, or excreting them. It manufactures and secretes bile, which is stored in the gall bladder and released into the small intestine, where it is used to emulsify fats. The liver handles the conversion of glucose to glycogen for storage and regulates the proper level of glucose in the blood. As it breaks down digested proteins, it produces and eliminates urea, thereby removing ammonia from bodily fluids. Essentially, the liver helps maintain homeostasis in the body, regulating the body's supply of important nutrients and hormones.
- filtration: The liver contains phagocytic Kupffer cells, which remove substances from the blood for excretion - bacteria, endotoxins, viruses, antigens, and lots of other harmful stuff, including bilirubin, the degredation product of the red dye in blood. The liver detoxifies the body of drugs.
- storage: The liver generally stores about 600 ml of blood, though it can hold more if it needs to, for example in times of emergency; in addition, it stores vitamins and minerals.
Liver disease encompasses a wide range of conditions. The most common are hepatitis, an inflammation of the liver that can have chronic effects, and cirrhosis, a chronic progressive inflammation that leads ultimately to liver failure. In addition, long term alcohol abuse can negatively impact the liver. There are also rarer genetic disorders that harm the liver, including hemochromatosis, Wilson's disease, and cystic fybrosis.
The first liver transplant was performed in 1963, and today the operation has become common, with the majority of patients surviving the dangerous first year. In 1994 a bioartificial liver, part cloned liver cells, part machine, was used; it's kind of like a kidney dialysis machine, and can support patients with liver failure who are waiting for transplants. In addition, a liver can regenerate, and up to 75% of it can be safely removed and will grow back again. This procedure, called liver resection, provides a way to cure patients with tumors of the liver.
The Metaphoric Liver
The liver has long been seen as an important organ of emotion and even thought. The Greek philosopher Galen, whose second century ideas remained the basis for western medical thinking till the seventeenth century, viewed the liver as the seat of the vegetative soul, an ancient plant-based soul which was retained by higher beings. The liver, he thought, received food and converted it to natural spirits, which it then sent to the heart, from whence it reached the rest of the body.
Shakespeare saw the liver as a seat of bitter anger and bile. Old English used the adjective liverish to refer to a crabby or grouchy person, based on the belief that the liver could produce an excess of bile, giving someone a reddish complection and peevish manner.
The Edible Liver
People have long eaten liver from cows or calves, pigs, lambs, chickens, and geese; livers from younger animals will tend to be more healthy, because the livers of older animals have had much longer to accumulate nasty chemicals, hormones, and medicines that the animal might have been fed. In addition, liver from younger animals will be paler in colour, with a milder flavour and odour and more tender texture than the liver of adult animals.
Goose liver is the most expensive of the edible livers; it's usually known by the swishy French name foie gras, and, though delicious, the ways that geese are fattened and slaughtered can be reprehensible. *Sigh*
Liver should be cooked quickly, for example by lightly sauteing; cooking longer tends to toughen it. Liver is rich in iron, protein, and vitamins A and B.
Ode to the Liver
fragment of a poem by Pablo Neruda, translated by Oriana Josseau Kalant
I sing to you
and I fear you
as though you were the judge
and if I can not
surrender myself in shackles to austerity,
in the surfeit of
or the hereditary wine of my country
to disturb my health
or the equilibrium of my poetry,
giver of syrups and of poisons,
regulator of salts,
from you I hope for justice;
I love life: Do not betray me! Work on!
Do not arrest my song.