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Health topic
Plain-language guides to the organs and systems of the human body — heart, lungs, brain, kidneys, liver, glands and more — and how they work.
50 articles · Open in the article library · All topics
Body Organs
When people think about vital organs, the heart, brain and lungs usually come first. The intestines rarely get the same attention, yet almost every nutrient that keeps the body alive passes through them. They digest food, absorb what the body needs, ho...
5 min read
Body Organs
Beyond the skeletal muscle responsible for voluntary movement, the body contains two other distinct types of muscle tissue, cardiac and smooth muscle, each suited to a very different role than the muscles that move th...
2 min read
Body Organs
Cartilage is a firm yet flexible type of connective tissue found in several places throughout the body, including joints, the rib cage, the ears, the nose, and the airways. Unlike bone, it has no blood supply of its o...
2 min read
Body Organs
Tendons and ligaments are both made of tough, fibrous connective tissue, and while they're often mentioned together, they serve distinct roles in how the body moves and stays structurally stable.
2 min read
Body Organs
Bone marrow is a soft, spongy tissue found within the hollow spaces of many bones throughout the body. Despite being tucked away out of sight, it performs one of the body's most essential ongoing tasks: producing bloo...
2 min read
Body Organs
The tonsils are small clusters of lymphatic tissue located at the back of the throat, forming part of the body's immune system. Most people are referring to the palatine tonsils, the pair visible on either side of the...
2 min read
Body Organs
The placenta is a temporary organ that develops during pregnancy, attaching to the wall of the uterus and connecting to the developing baby via the umbilical cord. It exists only for the duration of pregnancy and is e...
2 min read
Body Organs
The penis is an external organ that forms part of the male reproductive and urinary systems, serving two distinct functions: the passage of urine and a role in reproduction.
3 min read
Body Organs
The vagina is a muscular, elastic canal that forms part of the female reproductive system, connecting the external genital area to the cervix and uterus above it.
3 min read
Body Organs
The cervix is the lower, narrow portion of the uterus that connects to the vagina, forming a passageway between the two structures. Though relatively small, it plays several distinct roles across different stages of t...
3 min read
Body Organs
The fallopian tubes are a pair of narrow, muscular tubes that connect the ovaries to the uterus, forming an essential link in the female reproductive system.
2 min read
Body Organs
The prostate is a small, walnut-sized gland that forms part of the male reproductive system, located just below the bladder, surrounding part of the urethra, the tube that carries urine and semen out of the body.
2 min read
Body Organs
The parathyroid glands are four tiny, pea-sized glands located directly behind the thyroid gland in the neck. Despite their small size and close proximity to the thyroid, they perform an entirely separate function, fo...
3 min read
Body Organs
The mammary glands are specialized glands located within breast tissue, present in both sexes but functionally active primarily in females, particularly during and after pregnancy. Their core role is producing milk to...
3 min read
Body Organs
Hair and nails are often thought of as purely cosmetic, but both are living structures — or rather, structures produced by living cells — that serve genuine physiological purposes.
2 min read
Body Organs
The uterus is a muscular, pear-shaped organ located in the pelvis, central to the female reproductive system. It's one of the few organs in the human body designed to change dramatically in size and structure over rel...
3 min read
Body Organs
The testes are a pair of oval-shaped organs that form the core of the male reproductive system, responsible for producing sperm and the primary male reproductive hormone, testosterone.
2 min read
Body Organs
The ovaries are a pair of small, oval-shaped organs located on either side of the uterus, forming a central part of the female reproductive system. They serve two main roles: producing eggs and producing key reproduct...
2 min read
Body Organs
The lymphatic system is a network of vessels, nodes, and organs that runs alongside the circulatory system, playing key roles in fluid balance and immune defense. Though less well known than the circulatory system, it...
2 min read
Body Organs
Blood is a specialized fluid that circulates continuously through the body, carrying oxygen, nutrients, waste products, and immune cells to and from every tissue. An average adult has roughly five liters of it, made u...
2 min read
Body Organs
Blood vessels form an extensive network throughout the body, carrying blood to and from every tissue. Laid end to end, the blood vessels in an average adult would stretch tens of thousands of miles — a vast transpor...
2 min read
Body Organs
The diaphragm is a large, dome-shaped muscle situated beneath the lungs, separating the chest cavity from the abdomen. Though often overshadowed by the lungs themselves in discussions of breathing, the diaphragm is th...
2 min read
Body Organs
The larynx, commonly known as the voice box, is a structure located in the neck, at the top of the trachea. It serves two essential functions: protecting the airway during swallowing and producing the sound used in sp...
2 min read
Body Organs
The nose is the primary entry point for air into the respiratory system, and together with the sinuses, a set of connected air-filled cavities within the skull, it plays a larger role in preparing air for the lungs th...
2 min read
Body Organs
The appendix is a small, narrow, finger-shaped pouch attached to the large intestine, near where the small and large intestines meet. For a long time it was considered a vestigial structure with no real function — b...
2 min read
Body Organs
The teeth and tongue work closely together at the very start of the digestive process, handling the mechanical breakdown of food and playing a central role in speech and taste.
2 min read
Body Organs
The salivary glands are a set of glands located around the mouth and jaw that produce saliva, the fluid that plays a surprisingly active role in the very first stage of digestion.
2 min read
Body Organs
The peripheral nervous system is the vast network of nerves extending out from the brain and spinal cord to every other part of the body — muscles, skin, organs, and glands. While the brain and spinal cord make up t...
3 min read
Body Organs
The spinal cord is a long, cylindrical bundle of nerve tissue that runs from the base of the brain down through the spinal column, protected by the surrounding vertebrae. It serves as the primary communication pathway...
2 min read
Body Organs
The pineal gland is a tiny, pea-sized structure located deep within the brain, near its center. Its main job is producing melatonin, a hormone closely tied to the body's internal sense of time.
2 min read
Body Organs
The thymus is a small gland located in the upper chest, just behind the breastbone. Unlike most organs, it's most active early in life and gradually shrinks with age, playing a critical but time-limited role in buildi...
2 min read
Body Organs
The hypothalamus is a small region located deep within the brain, just above the pituitary gland to which it's directly connected. Despite being roughly the size of an almond, it serves as a critical link between the ...
2 min read
Body Organs
The pituitary gland is a pea-sized structure located at the base of the brain, connected to the hypothalamus just above it. Despite its small size, it's often called the body's "master gland" because the hormones it r...
2 min read
Body Organs
The eyes are complex sensory organs that convert light into the electrical signals the brain interprets as vision. Each eye is roughly the size of a ping-pong ball, though only about a sixth of it is visible from outs...
2 min read
Body Organs
The esophagus is a muscular tube, roughly ten inches long, connecting the throat to the stomach. Its sole function is to transport food and liquid from the mouth to the stomach, but it does so through an active, coord...
2 min read
Body Organs
The gallbladder is a small, pear-shaped pouch tucked just beneath the liver, on the right side of the abdomen. Its role is narrow but important: storing and concentrating bile, a fluid essential to digesting fat.
2 min read
Body Organs
The bladder is a hollow, muscular organ located in the lower abdomen, functioning as the body's storage tank for urine before it's eliminated.
2 min read
Body Organs
The adrenal glands are two small, triangular glands, each sitting atop one of the kidneys. Despite being only a few centimeters across, they produce a range of hormones that influence stress response, metabolism, and ...
2 min read
Body Organs
The thyroid is a small, butterfly-shaped gland located at the front of the neck, just below the voice box. Despite its modest size, it produces hormones that influence the pace at which nearly every cell in the body o...
2 min read
Body Organs
The skin is the body's largest organ, covering an area of about two square meters in an average adult. Far from being a simple covering, it performs a range of active functions that make it essential to survival.
2 min read
Body Organs
The spleen is a fist-sized organ tucked under the rib cage on the upper left side of the abdomen. Though less discussed than organs like the heart or lungs, it plays an important dual role in filtering blood and suppo...
2 min read
Body Organs
The pancreas is a long, flat gland tucked behind the stomach, in the upper abdomen. It performs two distinct jobs — one related to digestion, the other to regulating blood sugar — making it both a digestive organ ...
2 min read
Body Organs
The large intestine, also called the colon, is a wide, roughly five-foot-long tube that forms the final section of the digestive tract, framing the small intestine on three sides of the abdomen. By the time material r...
2 min read
Body Organs
The small intestine is a long, coiled tube, roughly 20 feet in length, occupying most of the space in the abdomen. Despite its name, referring to its narrow diameter rather than its length, it's the primary site where...
2 min read
Body Organs
The stomach is a J-shaped, muscular sac located in the upper abdomen, positioned between the esophagus and the small intestine. It serves as both a temporary storage tank for food and the first major site of chemical ...
2 min read
Body Organs
The kidneys are a pair of bean-shaped organs, each roughly the size of a fist, located toward the back of the abdomen, one on either side of the spine. Their primary role is filtering blood to remove waste and excess ...
2 min read
Body Organs
The liver is the body's largest internal organ, sitting on the right side of the abdomen just beneath the rib cage. It performs hundreds of distinct functions, which is why it's often described less as a single-purpos...
2 min read
Body Organs
The brain is the body's command center, a roughly three-pound organ made up of tens of billions of nerve cells, or neurons, constantly exchanging electrical and chemical signals.
2 min read
Body Organs
The lungs are a pair of spongy, air-filled organs that sit in the chest, protected by the rib cage. Their essential task is gas exchange: pulling oxygen into the body and pushing carbon dioxide out.
2 min read
Body Organs
The heart is a muscular organ about the size of a closed fist, sitting slightly left of center in the chest. Its job is simple to state and remarkable in execution: keep blood moving through the body, every second, fo...
2 min read