Structural Organization in Animals

Summary: The structural organisation in animals or any other lifeform is the same at the fundamental level. Or in other words, all life currently living on earth are made up of cells. And when cells get together, they form tissues. Tissues, in turn, form organs and organ systems.

Cells   → Tissues   → Organs →   Organ system

Structural Organisation in Animals

As stated above, the structural organisation in animals starts from the smallest fundamental unit – the cell. And a group of cells that perform a similar function forms tissues. When tissues group together to perform specific functions, they form organs.

The fundamental unit that comprises structural organisation in animals and plants is the cell. Pictured above is a generic image of an animal cell

Cell

The cell is the smallest, structural and functional unit of an organism. The cell components are mainly involved in carrying out various life functions.  To carry out these functions, cells required specialized structures called cell organelles.

Main Article: Cells

Tissues

Tissues: The next level of structural organisation in animals, after the cell.

Tissues are an integrated group of cells which perform similar functions and possess similar cellular structure. These tissues provide a basic framework in multicellular animals.

Main Article: Tissues

There are four different types of tissues:

• Epithelial tissue
• Connective tissue
• Muscular tissue
• Nervous tissue

Epithelial Tissue

Epithelial tissues are characterized by the absence of blood vessels. Instead, it receives the required nutrition through diffusion.  They form the outer covering as well as the inner lining of many organs. In epithelial tissues, all cells are densely packed with little intercellular matrix between them. Epithelial tissue is classified into two types –  simple epithelium and compound epithelium. Moreover, epithelial tissue can be classified based on its shape as well – cuboidal, squamous, columnar.

Connective Tissue

They are the most abundant and widely distributed tissues in animals. All connective tissues, apart from blood cells, secrete collagen or elastin (fibrous proteins that provide structural support, flexibility, and elasticity.) Connective tissues are called so because of their special function of linking and supporting other tissues in the body. There are three different types of connective tissues: Loose connective tissue, dense connective tissue, and specialised connective tissue.

Muscular Tissue

These tissues are composed of long, tube-shaped fibres, which are structured in parallel arrays and are mainly composed of numerous fine fibrils, called myofibrils. Muscular tissues play a vital role in contraction, relaxation and other bodily movements. There are three different types of muscular tissues: skeletal muscles, smooth muscles, and cardiac muscles.

Nervous Tissue

Nervous tissues consist of neurons and neuroglial cells. The neuron is an excitable cell and a main component of the neural system. The neuroglia forms the rest of the neural system, which makes up double the volume of neural tissue in the human body. Nervous tissues have the greatest control over the body’s responsiveness to changing conditions.

The below table provides the complete details about tissue, origin and its functions.

Organ and Organ Systems

A collection of tissues form an organ; a group of organs that work together to perform one or more functions is called an organ system.

Every organ is composed of one or more type of tissues. A group of organs working together to perform a common function is called an organ system. Excretory system, reproductive system, endocrine system, circulatory system, respiratory system are examples of organ systems.

Also refer: Difference Between Tissues and Organs

For more information on cells, tissues, the structural organisation in animals and other related topics, explore BYJU’S Biology.