The liver, a reddish-brown organ weighing approximately three pounds, resides in the upper right part of the abdominal cavity, beneath the diaphragm. It is the largest internal organ and gland in the human body, performing hundreds of functions. These roles range from processing nutrients to neutralizing harmful substances.
The Liver’s Role in Digestion
The liver is part of the digestive system, playing a central role in processing absorbed nutrients and producing substances crucial for digestion. Its primary digestive function is the continuous production of bile, a yellowish-green fluid. Bile contains bile salts, which emulsify fats in the small intestine, breaking large fat globules into smaller particles that digestive enzymes can process and absorb.
Bile travels from the liver through ducts, either directly to the duodenum or to the gallbladder for storage. When food enters the small intestine, the gallbladder contracts, releasing stored bile to aid in fat digestion. Beyond bile production, the liver receives nutrient-rich blood directly from the digestive tract via the hepatic portal vein. This blood carries absorbed carbohydrates, fats, and proteins, which the liver processes for the body’s use or storage.
Beyond Digestive Functions
The liver’s functions extend beyond digestion, contributing to many other bodily processes. It detoxifies harmful substances from the bloodstream, including medications, alcohol, and metabolic waste products. This detoxification occurs in two main phases: Phase I modifies toxins into intermediate products, and Phase II transforms these intermediates into water-soluble compounds, making them easier to excrete through bile or urine.
The liver also regulates metabolism. It maintains stable blood sugar levels by converting excess glucose into glycogen for storage and releasing glucose back into the blood when levels are low. It also synthesizes cholesterol and other fats, and produces important proteins like albumin, which helps maintain fluid balance, and clotting factors for blood coagulation. The liver also stores important nutrients, including glycogen, fat-soluble vitamins (A, D, E, K), vitamin B12, and minerals like iron and copper.
Liver Connections Throughout the Body
The liver’s functions create connections with many other organ systems, underscoring its systemic impact despite its primary classification within the digestive system. It interacts with the circulatory system by filtering a large volume of blood, processing substances before they circulate throughout the body. The liver also produces important blood proteins, including those involved in blood clotting, which are essential for maintaining circulatory integrity.
Connecting to the excretory system, the liver converts toxic byproducts of protein metabolism, such as ammonia, into urea through a process called the urea cycle. This less toxic urea is then released into the bloodstream and filtered out by the kidneys for excretion in urine. Within the immune system, the liver houses specialized immune cells called Kupffer cells. These cells act as macrophages, removing bacteria, foreign particles, and cellular debris from the blood that flows through the liver, forming a crucial defense barrier. The liver also participates in the endocrine system by metabolizing various hormones, influencing their levels and activity throughout the body.