Liver

-
.
Liver, largest internal organ of the human body. The liver, which is part of the digestive system, performs more than 500 different functions, all of which are essential to life. Its essential functions include helping the body to digest fats, storing reserves of nutrients, filtering poisons and wastes from the blood, synthesizing a variety of proteins, and regulating the levels of many chemicals found in the bloodstream. The liver is unique among the body’s vital organs in that it can regenerate, or grow back, cells that have been destroyed by some short-term injury or disease. But if the liver is damaged repeatedly over a long period of time, it may undergo irreversible changes that permanently interfere with function.

The human liver is a dark red-brown organ with a soft, spongy texture. It is located at the top of the abdomen, on the right side of the body just below the diaphragm—a sheet of muscle tissue that separates the lungs from the abdominal organs. The lower part of the rib cage covers the liver, protecting it from injury. In a healthy adult, the liver weighs about 1.5 kg (3 lb) and is about 15 cm (6 in) thick.

Despite its many complex functions, the liver is relatively simple in structure. It consists of two main lobes, left and right, which overlap slightly. The right lobe has two smaller lobes attached to it, called the quadrate and caudate lobes.

Each lobe contains many thousands of units called lobules that are the building blocks of the liver. Lobules are six-sided structures each about 1 mm (0.04 in) across. A tiny vein runs through the center of each lobule and eventually drains into the hepatic vein, which carries blood out of the liver. Hundreds of cubed-shaped liver cells, called hepatocytes, are arranged around the lobule's central vein in a radiating pattern. On the outside surface of each lobule are small veins, ducts, and arteries that carry fluids to and from the lobules. As the liver does its work, nutrients are collected, wastes are removed, and chemical substances are released into the body through these vessels.

Comments

Post a Comment

Popular posts from this blog

Cellular Respiration

-
Cellular Respiration, process in which cells produce the energy they need to survive. In cellular respiration, cells use oxygen to break down the sugar glucose and store its energy in molecules of adenosine triphosphate (ATP). Cellular respiration is critical for the survival of most organisms because the energy in glucose cannot be used by cells until it is stored in ATP. Cells use ATP to power virtually all of their activities—to grow, divide, replace worn out cell parts, and execute many other tasks. Cellular respiration provides the energy required for an amoeba to glide toward food, the Venus fly trap to capture its prey, or the ballet dancer to execute stunning leaps. Cellular respiration occurs within a cell constantly, day and night, and if it ceases, the cell—and ultimately the organism—dies. Two critical ingredients required for cellular respiration are glucose and oxygen. The glucose used in cellular respiration enters cells in a variety of ways. Plants, algae, and cer
Read more

The Human Eye

-
Image
Structure of the Eye The amount of light entering the eye (right) is controlled by the pupil, which dilates and contracts accordingly. The cornea and lens, whose shape is adjusted by the ciliary body, focus the light on the retina, where receptors convert it into nerve signals that pass to the brain. A mesh of blood vessels, the choroid, supplies the retina with oxygen and sugar. Lacrimal glands (left) secrete tears that wash foreign bodies out of the eye and keep the cornea from drying out. Blinking compresses and releases the lacrimal sac, creating a suction that pulls excess moisture from the eye’s surface. The entire eye , often called the eyeball, is a spherical structure approximately 2.5 cm (about 1 in) in diameter with a pronounced bulge on its forward surface. The outer part of the eye is composed of three layers of tissue. The outside layer is the sclera, a protective coating. It covers about five-sixths of the surface of the eye. At the front of the eyeball, it is continuo
Read more

Respiratory System

-
. Respiratory System, in anatomy and physiology, organs that deliver oxygen to the circulatory system for transport to all body cells. Oxygen is essential for cells, which use this vital substance to liberate the energy needed for cellular activities. In addition to supplying oxygen, the respiratory system aids in removing of carbon dioxide, preventing the lethal buildup of this waste product in body tissues. Day-in and day-out, without the prompt of conscious thought, the respiratory system carries out its life-sustaining activities. If the respiratory system’s tasks are interrupted for more than a few minutes, serious, irreversible damage to tissues occurs, followed by the failure of all body systems, and ultimately, death. While the intake of oxygen and removal of carbon dioxide are the primary functions of the respiratory system, it plays other important roles in the body. The respiratory system helps regulate the balance of acid and base in tissues, a process crucial for the norma
Read more