Organ (biology)

A collection of tissues joined in a structural unit to serve a common function

Diagram of internal organs in the human body

An organ is a collection of tissues that structurally form a functional unit specialized to perform a particular function or group of functions. Organs are found in most multicellular organisms, including animals and plants. In the hierarchy of biological organization, an organ lies between tissues and an organ system.

Structure and Function

Organs are composed of main tissue, parenchyma, and "sporadic" tissues, stroma. The main tissue is that which is unique for the specific organ, such as the myocardium in the heart. The sporadic tissues include the connective tissue, blood vessels, and nervous tissue.

In animals, organs are typically composed of several types of tissues. For example, the heart is made up of muscle tissue, connective tissue, and nervous tissue. Each type of tissue contributes to the overall function of the organ. The heart's primary function is to pump blood throughout the body, which it accomplishes through the coordinated contraction of its muscle tissue.

In plants, organs include structures such as roots, stems, and leaves. Each of these organs has specific functions that contribute to the plant's survival and reproduction. For example, leaves are primarily involved in photosynthesis, the process by which plants convert light energy into chemical energy.

Examples of Organs

The liver of a sheep

Animal Organs

• Heart: Pumps blood through the circulatory system.
• Liver: Processes nutrients, detoxifies harmful substances, and produces bile.
• Lungs: Facilitate the exchange of oxygen and carbon dioxide between the air and the blood.
• Kidneys: Filter blood to produce urine, removing waste products from the body.
• Brain: Processes sensory information and coordinates bodily functions.

Plant Organs

• Roots: Anchor the plant and absorb water and nutrients from the soil.
• Stems: Support the plant and transport nutrients and water between roots and leaves.
• Leaves: Conduct photosynthesis and gas exchange.
• Flowers: Reproductive structures that produce seeds.

Development and Evolution

Diagram showing the origin of major organs on the animal phylogeny

The development of organs is a complex process that involves the differentiation of cells and tissues during embryogenesis. In animals, this process is regulated by gene expression and signaling pathways.

The evolution of organs is a key aspect of the diversification of life on Earth. Organs have evolved to perform specific functions that enhance the survival and reproduction of organisms. For example, the evolution of lungs allowed vertebrates to exploit terrestrial environments, while the development of flowers in plants facilitated more efficient reproduction through pollination.

Also see

• Tissue (biology)
• Organ system
• Anatomy
• Physiology
• Embryogenesis