Tissues in Animals – Epithelial Nervous, Connective, Bone Tissues

Tissues in Animals

A tissue (from Latin texere = weave) is a group of cells that collaborate to carry out one or numerous functions in organisms such as plants and animals. These cells communicate and follow one another by direct cell-cell contacts and through intermediary particles like those that form the extracellular matrix. Each organ of the body is formed by numerous kinds of tissues.

The part of science handling plant and animal tissues is referred to as histology. It is a mostly detailed discipline that utilizes light and electron microscopy to explain tissue morphology. The anatomy and organization of tissues are vital to understanding the regular physiology and pathology of the organs.

In the bodies of animals, there are 4 major classifications of tissues: epithelial tissue, connective tissue, muscle tissue, and nervous tissue.


Epithelial tissue

Epithelial tissue is comprised of layers of tightly packed cells that line the surfaces of the body for protection, secretion, and absorption. Examples of epithelial tissue consist of the skin, the lining of the mouth and nose, and the lining of the gastrointestinal system. This tissue has many types on the basis of the shape of cells in addition to the number of cell layers. Some types include:


Squamous epithelium

Consists of a single layer of flat cells. It is present in the lungs, heart, and blood vessels. Here, it permits the movement of materials across it.

Cuboidal epithelium

Consists of a single layer of cube-shaped cells. It is found in kidney tubes, small glands, etc. where it makes secretions.

Columnar epithelium

It has elongated cells. It is found in the alimentary canal, gall bladder, and so on where it makes secretions.

Ciliated columnar epithelium

It has elongated cells with cilia. It is present in the trachea and bronchi and propels mucous.

Stratified squamous epithelium

It has many layers of flat cells. It exists in the lining of the esophagus and mouth and also over the skin. It safeguards the inner parts.

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General functions of epithelial tissue
  • Provides a barrier between the external environment and the organ it covers.
  • Specialized to operate in secretion and absorption.
  • Protects organisms from bacteria, injury, and fluid loss.
  • Excretes waste products such as sweat from the skin.
Muscle Tissues

Muscle tissue consists of bundles of long cells called muscle fibers. It is the most abundant tissue in an animal. The cells of this tissue have the ability to contract. There are 3 types of muscle tissue:

Skeletal muscles or striated muscles are attached to bones. Their cells are striated (striped) and contain many nuclei. They are responsible for the movements of bones.

Smooth muscles are found in the walls of the alimentary canal, urinary bladder, blood vessels, and so on. They contain smooth (non-straited) cells, each with a single nucleus. They are accountable for the motion of substances.

Cardiac muscles are present in the wall of the heart. Their cells are also striated but there is a single nucleus in each cell. They produce heartbeat.

Skeletal muscles are voluntary in action i.e., their contraction is under the control of our will. Smooth and heart muscles are uncontrolled in action i.e., their contraction is not under the control of our will.


Nervous tissue

Cells making up the central nervous system and peripheral nervous system are classified as nervous tissue. In the central nervous system, nervous tissue forms the brain and spine. In the peripheral nervous system, the nervous tissue forms the cranial nerves and spinal nerves, which include the sensory and motor nerve cells.


The function of nerve tissue is to transfer nerve impulses around the body. Nerves include a cell body (soma), dendrites, which receive impulses, and axons that send out impulses. The axons of nerve cells are surrounded by a myelin sheath. The myelin sheath consists of layers of myelin, a white fatty substance. The myelin sheath’s primary function is to insulate nerve fibers and it likewise increases the speed of the impulses transferred by the afferent neuron. There are 3 kinds of nerve cells: sensory neurons, interneurons, and motor neurons.

Connective Tissue

Connective tissues are comprised of fibrous cells. Blood and Bone are good examples of specialized connective tissues. The cells of the connective tissue are separated by non-living material called the extracellular matrix. These tissues help to hold other tissues together throughout the formation of organs and have the capability to stretch and contract positively.

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Bone Tissues

Bones consist of various types of tissue, including compact bone, spongy bone, bone marrow, and periosteum.

Compact bone comprises the thick external layer of bone. Its functional unit is the osteon. Compact bone is very hard and strong.

Spongy bone is present inside bones and is lighter and less dense than compact bone. This is due to the fact that spongy bone is porous.

Bone marrow is a soft connective tissue that produces blood cells. It is found inside the pores of spongy bone.

The periosteum is a difficult, fibrous membrane that covers and protects the outer surfaces of bone.

Cartilage is a kind of thick connective tissue, made from tough protein fibers, that offers a smooth surface area for the motion of bones at joints. Found in joints, nose, breast bone, trachea.

A ligament is a band of fibrous connective tissue that holds bones together and keeps them in place.


Blood is regarded as a specialized form of connective tissue because it comes from the bones and has some fibers. Blood is composed of red blood cells, leukocyte,s and platelets. These elements are suspended in a yellow fluid known as plasma.

Red blood cells: also known as erythrocytes are made in the red bone marrow. They do not have a nucleus and are biconcave in shape. Their biconcave shape makes them flexible so that they can squeeze through narrow blood vessels. It likewise provides a larger surface area to volume ratio, so that they absorb and release gases quicker. The red cell has a brief life span of around 120 days. Red blood cells contain the protein referred to as hemoglobin.

White blood cells: Are commonly known as leukocytes and are produced in the yellow bone marrow and lymph nodes. The cells have several nuclei. White blood cells are slightly larger than red blood cells and are more irregular in shape. Their main function is to protect the body from disease. There are numerous kinds of white blood cells.

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Platelets: Also called thrombocytes are produced in the bone marrow and are fragments of bone marrow cells. They have no nuclei. Platelets help in the clotting of blood and prevent excessive bleeding.

Plasma: Plasma is the pale-yellow element of blood that allows the remainder of the components of blood to drift in suspension. It makes up about 55% of total blood volume. It includes dissolved proteins, hormones, urea, and CO2. Its main functions are to carry nutrients, cells, and metabolic waste items and preserve blood volume.



The sheet of tightly packed cells which perform the same task and function in an organized fashion is tissue. In animals, due to the complexity of life activities, there are advanced tissues and categorize into four types.

Epithelial tissues cover the outside of the body. These act as barriers and safeguard the body against mechanical stress or trauma, invasion of microorganisms and body fluid loss. They are further classified on the basis of their shape and number of cell layers.

Then there are connective tissues which mainly bind and support other tissues. Major types are loose, fibrous connective tissues, cartilage, bones and blood. Loose connective tissues have strong, flexible fibers. They help in holding organs.

Cartilage is hard flexible tissue and bones are much harder and stronger. Both function in providing support and movement to the body. Blood transports various substances throughout the body.