Organs in the Body - Diagram, List, and Functions (2025)

This entry was posted on January 8, 2025 by Anne Helmenstine (updated on January 19, 2025)

Organs in the body each perform specific functions vital for life and overall well-being. They work in harmony within organ systems to maintain the body’s homeostasis and facilitate growth, reproduction, and survival. Understanding what organs are, how they are organized, and their roles in the body provides insight into the intricacies of human anatomy.

What Are Organs?

An organ is a group of tissues that work together to perform a specific function. Organs are distinct structures with unique shapes, sizes, and purposes, ranging from the heart’s role in circulating blood to the liver’s function in detoxification.

Organs are not:

  • Cells: While organs contains cells, they often contain other structures, too. A cell is the fundamental building block of a living organism,
  • Tissues: Tissues are collections of similar cells that form the building blocks of organs.
  • Systems: Organ systems are groups of organs working together for a larger function, such as digestion or circulation.

What Are Organ Systems?

Organ systems are groups of organs that collaborate to perform broad biological functions. The human body has 11 major organ systems:

  1. Circulatory System: Includes the heart and blood vessels, transporting blood, oxygen, and nutrients.
  2. Respiratory System: Composed of the lungs and airways, facilitating oxygen intake and carbon dioxide removal.
  3. Digestive System: Includes the stomach, intestines, liver, and other organs that break down and absorb nutrients.
  4. Nervous System: Composed of the brain, spinal cord, and nerves, controlling body functions and responses.
  5. Muscular System: Encompasses all muscles, enabling movement and maintaining posture.
  6. Skeletal System: Consists of bones and joints, providing structure and support.
  7. Endocrine System: Includes glands that release hormones for regulation of processes like growth and metabolism.
  8. Reproductive System: Involves organs like the ovaries and testes, facilitating reproduction.
  9. Excretory System: Composed of the kidneys and bladder, removing waste from the body.
  10. Immune System / Lymphatic System: Includes the lymph nodes and spleen, defending against pathogens.
  11. Integumentary System: Includes the skin, hair, and nails, protecting the body and regulating temperature.

How Many Organs Are in the Human Body?

The exact number of organs in the human body varies depending on the definition of what constitutes an organ. Traditionally, there are about 78 organs, but some classifications count accessory organs and microstructures like glands, leading to numbers over 100.

What Are the Vital Organs?

Vital organs are those necessary for survival. They include:

  1. Brain: Controls body functions and cognitive processes.
  2. Heart: Pumps blood to deliver oxygen and nutrients.
  3. Lungs: Facilitate breathing and oxygen exchange.
  4. Liver: Detoxifies the body and produces bile.
  5. Kidneys: Filter blood and produce urine.

Which Organs Can a Person Survive Without?

While all organs contribute to health, some are not essential for survival:

  1. Gallbladder: Removes bile, but its absence doesn’t prevent digestion.
  2. Appendix: Once thought vestigial, its removal doesn’t impair health significantly.
  3. One Kidney: A person can survive with one kidney.
  4. One Lung: You can survive with just one.
  5. Spleen: Its removal increases susceptibility to infections but isn’t life-threatening.
  6. Reproductive Organs: Necessary for reproduction but not survival.
  7. Eyes: Necessary for vision, but not essential for survival.

Location of Organs in the Body

When you look at a person from the outside, it appears the body displays bilateral symmetry. Inside, it’s a different story. There are different organs on the right and left sides of the body.

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  • Centrally Located Organs:
    • Brain
    • Heart (slightly left)
    • Small intestine
    • Bladder
  • Organs on the Right Side:
    • Liver
    • Appendix
    • Gallbladder
  • Organs on the Left Side:
    • Spleen
    • Pancreas
    • Stomach
  • Paired Organs (one on each side)
    • Kidneys
    • Eyes
    • Lungs
    • Ears
    • Reproductive organs (testicles, ovaries)

What Are Accessory Organs?

Accessory organs assist in bodily functions but are not part of the primary system they support. Examples include:

  • Gallbladder: Stores and releases bile.
  • Pancreas: Produces enzymes aiding digestion and hormones regulating blood sugar.
  • Salivary Glands: Aid in digestion by producing saliva.
  • Breasts: Aid the reproductive system by producing milk.

Largest and Smallest Organs in the Body

  • Largest Organ: The skin is the largest organ, covering the entire body and serving as a protective barrier. Skin accounts for around 15% of body weight. The largest internal organ is the liver.
  • Smallest Organ: The pineal gland in the brain, about the size of a grain of rice, regulates sleep through melatonin production.

Complete List of Human Organs in the Body and Their Functions

Here is a comprehensive list of the organs in the human body with their functions:

Central Nervous System:

  • Brain: Controls body functions and processes.
  • Spinal Cord: Transmits signals between the brain and body.

Circulatory System:

  • Heart: Pumps blood throughout the body.
  • Blood Vessels (arteries, veins, capillaries): Transport blood.

Respiratory System:

  • Lungs: Facilitate oxygen intake and carbon dioxide removal.
  • Trachea: Connects the throat to the lungs.
  • Bronchi: Passageways for air into the lungs.

Digestive System:

  • Stomach: Breaks down food for digestion.
  • Small Intestine: Absorbs nutrients from food.
  • Large Intestine: Absorbs water and forms feces.
  • Liver: Detoxifies chemicals and metabolizes drugs.
  • Pancreas: Produces digestive enzymes and hormones like insulin.
  • Gallbladder: Stores bile for fat digestion.

Excretory System:

  • Kidneys: Filter blood to produce urine.
  • Ureters: Transport urine from kidneys to bladder.
  • Bladder: Stores urine.
  • Urethra: Removes urine from the body.

Endocrine System:

  • Pituitary Gland: Regulates other glands and growth.
  • Pineal Gland: Produces melatonin for sleep regulation.
  • Thyroid Gland: Controls metabolism.
  • Parathyroid Glands: Regulate calcium levels.
  • Adrenal Glands: Produce hormones like adrenaline.
  • Pancreas (dual function): Regulates blood sugar.
  • Ovaries/Testes: Produce sex hormones.

Immune and Lymphatic Systems:

  • Spleen: Filters blood and supports immunity.
  • Lymph Nodes: Filter lymph and produce white blood cells.
  • Thymus: Matures T-cells for the immune system.

Reproductive System:

  • Ovaries: Produce eggs and hormones.
  • Testes: Produce sperm and testosterone.
  • Uterus: Supports fetal development.
  • Prostate Gland: Produces seminal fluid.

Integumentary System:

  • Skin: Protects the body and regulates temperature.
  • Hair: Insulates and protects skin.
  • Nails: Protect the tips of fingers and toes.

Sensory Organs:

  • Eyes: Enable vision.
  • Ears: Facilitate hearing and balance.
  • Tongue: Detects taste and aids in speech.
  • Nose: Detects smell.

Skeletal System:

  • Bones (206 total): Provide structure and support.
  • Bone Marrow: Produces blood cells.

The list currently omits smaller or less prominent organs that are essential but often overlooked in traditional classifications. Here are examples of organs that could be added to reach a more comprehensive list:

  • Salivary Glands (Parotid, Sublingual, and Submandibular): Produce saliva for digestion and oral health.
  • Lymphatic Structures (such as Tonsils and Adenoids): Play roles in immunity and filtering pathogens.
  • Mesentery: A fold of tissue anchoring the intestines, now recognized as an organ.
  • Adipose Tissue: Fat stores, recently classified as an endocrine organ due to its hormonal activity.
  • Vas Deferens and Seminal Vesicles: Male reproductive organs aiding in sperm transport and seminal fluid production.
  • Bartholin’s and Skene’s Glands: Female reproductive glands involved in lubrication.
  • Inner Ear Structures (e.g., Cochlea and Vestibular System): Responsible for hearing and balance.

How Organs in the Body Develop

During embryonic development, organs form through a process called organogenesis. This begins with the differentiation of germ layers:

  • Ectoderm: Forms the brain, spinal cord, skin, and sensory organs.
  • Mesoderm: Develops into muscles, bones, the heart, and blood vessels.
  • Endoderm: Forms the digestive tract, lungs, and liver.

Stem cells play a critical role in the early stages of development, giving rise to the specialized cells that make up each organ. This tightly regulated process ensures proper organ placement and function.

Organ Transplants and Artificial Organs

Organ transplants involve replacing a failing organ with a healthy one from a donor. Common transplants include the kidney, liver, and heart. Advances in medicine have led to:

  • Artificial Organs: Devices like artificial hearts and dialysis machines that mimic natural organ functions.
  • 3D Printing: The potential to create custom organs using biocompatible materials.
  • Stem Cell Research: Exploring the regeneration of damaged tissues and organs.

Comparative Anatomy: Organs in Other Organisms

Comparative anatomy highlights evolutionary adaptations that suit each species’ environment and lifestyle. Human organs share similarities with those of other species, but adaptations exist:

  • Gills in Fish: Allow aquatic respiration by extracting oxygen from water.
  • Crop in Birds: A storage organ for food before digestion.
  • Cloaca in Reptiles and Birds: A multipurpose organ for excretion and reproduction.
  • Spiracles in Insects: Openings that allow gas exchange without lungs.

FAQs About Organs

Here are answers to some common questions about organs in the body:

  1. What defines an organ? An organ is a collection of tissues that perform a specific function.
  2. What organ is unique to humans? While most organs are common across mammals, the human brain’s cognitive capacity sets it apart.
  3. How do organs regenerate? Some organs, like the liver, have a remarkable capacity for regeneration. Others, like the heart, regenerate minimally.
  4. Can a person have extra organs? Yes, conditions like situs inversus or accessory spleens result in additional organs.

References

  • Griffith, Oliver W.; Wagner, Günter P. (2017). “The placenta as a model for understanding the origin and evolution of vertebrate organs”. Nature Ecology & Evolution. 1 (4): 0072. doi:10.1038/s41559-017-0072
  • Kent, Michael (2000). Advanced Biology. Oxford: Oxford University Press. ISBN 0199141959.
  • Widmaier, E. P.; Raff, H.; Strang, K.T. (2014). Vander’s Human Physiology (12th ed.). McGraw-Hill Higher Education. ISBN 978-0-07-128366-3.

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