There are many different organs in the human body, and there are also a couple of different ways of classifying them. One of the most common and simplest schemes arranges them as external or internal; sometimes they’re also divided by function, such as digestive, respiratory, and blood-related. Some scholars also think in terms of vitality or overarching importance. In these cases, certain organs, the brain and the heart in particular, are called “vital,” whereas others that perform more complementary roles can be labeled “accessory.” This classification system is often harder to work with since the body relies on almost all organs in different ways. It’s often the case that the vitals depend on the accessories to get their jobs done. Additionally, though people can sometimes live without certain organs like the pancreas or the kidney, this is usually only possible with the help of medications and therapies.
External Organs
The most obvious organs in the human body are those that are visible on the outside. Getting a sense of human anatomy usually requires a look at what’s going on inside, either through surgery or diagnostic imaging, but this isn’t the case with those parts that sit externally, either in part or in full.
Skin is the largest of the organs in the human body and weighs more than twice as much as the brain. Depending on the person, the average weight of the skin is about 8 pounds (approximately 3.6 kg). It's responsible for protecting the body from a variety of dangers including sunlight and chemicals. The skin is comprised of three layers: the base layer is the subcutis, the middle layer is the dermis, and the outer layer is the epidermis.
Eyes are usually also considered an external organ, though a lot of things happen near the optical nerve, which is inside the face. Humans blink approximately 10,000 times per day, or on average, about 12 times each minute. The eyes start to develop about 26 weeks after conception. It's believed that the eyes focus on 50 things per minute.
The Reproductive System
In males, the reproductive organs are almost entirely outside of the body. They include the penis and the testicles, which protrude from the body; together these produce and deliver sperm, which are genetic materials essential to conception. The female reproductive system is focused on egg production, fertilization, and gestation, and is made up of the cervix, the uterus, and the ovaries, all of which are internal. They open into the vagina, which is the only part that can be seen externally.
Internal Organs
The bulk of the body’s organs reside in the torso, usually in or just beneath the ribcage. One of the main roles of the ribcage is actually to protect these organs from accidental damage or injury. Most of the digestive and respiratory systems are housed here. The stomach, for instance, which is located between the small intestine and esophagus, is responsible for processing food and moving it along to the intestines. The liver, located on the right side of the body under the ribs, is responsible for making bile, processing nutrients from food, and removing toxins from the body. Lungs, which are located in the center of the chest, bring oxygen into the body and remove carbon dioxide. Two kidneys are located in the middle of the back below the rib cage and are responsible for taking water and waste from the blood in order to form urine.
The Heart
The human heart is perhaps the most essential and complex human organ, though again a lot of this depends on perspective. It is responsible for pumping blood to every part of the body through a network of veins and arteries. There are four chambers that make up the heart, two ventricles and two atria, and together the organ is about the size of an adult fist. It’s typically set at an angle, and is located behind the sternum on the left side of the body. In most people it beats about 100,000 times a day, or about 40 million times a year.
The Brain
The brain is another organ that often comes to mind when people think about things that are essential. It is responsible for controlling all the actions of the body and regulating chemical activity, particularly hormonal balance; it is also crucial for things like language processing and communication. It weighs about 3 pounds (1.36 kg). The cerebrum is what makes up 85 percent of its total weight, and the brain as a whole is comprised of about 75 percent water. There aren’t any pain receptors here, though pressures and growths can have serious implications on health and lifestyle in other ways.