Types of Animal Tissue

The tissue is a group of cells connected to each other that collectively perform similar functions in an organism. All contents of the body including structures and various organs are made of tissues. 

The animal body comprises of four basic types of tissues, all of which vary in their origin and function. They are: 

  • Epithelial Tissues- Made of tightly packed cells layer together, epithelial tissues line the body surface. Their functions include protection, absorption, and secretion. Epithelial tissues can be found in the lining of the mouth and nose, digestive system lining, and the skin. 

  • Muscle Tissues- These are of three types, smooth muscle tissue- found in inner linings of organs, skeletal muscle tissue- found attached to the bone and helps in body movement and cardiac muscle tissue- found in the heart. These tissues help in changing the size of a cell. 

  • Nervous Tissues- Made up of neurons (nerve cells in the brain), these tissues form the entire nervous system, including the spinal cord and the brain. 

  • Connective Tissues- Made of various cells that are involved in lending support to the body, connective tissues are namely the fat, bone, blood and cartilage in an animal body. 

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Epithelial Tissues

These tissues form the lining of body surfaces and also account for glands. The cells along these tissues are tightly connected to each other. The epithelium does not contain blood vessels and hence depends on the other connective tissues to derive its nutrients and other essentials. 

It is found along the edges of the organs and has two prominent surfaces, namely, the apical surface which is on the exterior and lies open to the body cavity, and the basal surface which lies adjacent to the underlying tissue.  

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Epithelial cells can be either squamous, cuboidal, or columnar in shape. The number of cell layers along with the combination of cell shapes decides the classifying features of epithelial tissue. 

Types of Epithelial Tissues and Their Functions

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Epithelial Tissues are always located on the inner or outer surfaces of organs, and their functions largely depend on the exact position of their locations. These are of the following types:


Squamous Epithelium 

Closely packed with one another, these are thin and flat cells that mostly like the esophagus, blood vessels, alveoli and the inner cavities of the mouth. The squamous epithelium tissue lends protection against mechanical injuries, while also blocking any sort of germs from entering. 


The squamous epithelium may also be arranged in multiple layers, in which case it is known as the stratified squamous epithelium tissue. These tissues are usually found in the lining of the esophagus and the skin. 


Cuboidal Epithelium Tissue

These are cuboidal in shape, hence rightfully deriving their name. Found in kidney tubules, salivary glands, and sweat glands, the functions of the cuboidal epithelium tissue are secretion, protection and absorption. 


When the cuboidal epithelium is arranged in multiple layers, it is known as the stratified cuboidal epithelium tissue, and found on the inner side of the salivary glands and pancreatic ducts. 


Columnar Epithelium Tissue 

Mostly with column-like or pillar-like cells, these can be found in the intestine and lining of the stomach. Important functions of the columnar epithelium tissue include secretion and absorption. 


Ciliated Epithelium Tissue

The columnar epithelium tissues often have cilia; this is when they come to be known as ciliated epithelium tissues. These can be found in kidney tubules, the respiratory tract and lining of the trachea. Their function is to help in the movement of material in a given direction.


Glandular Epithelium Tissue

These are majorly modified columnar epithelial tissues whose main function is secretion. They can be found in the sweat glands and tear glands. 


Muscle Tissues

Muscle tissues are specialised tissues found in animals, responsible for applying force to various parts of the body by using the method of contraction. Thin and elongated cells called muscle fibres make up the muscle tissues. 


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The structure of a muscle tissue contains three distinct elements- the cytoplasm in the muscle fibres, called the sarcoplasm, a membrane network known as the sarcoplasmic reticulum, and surrounding membrane of the muscle fibres known as the sarcolemma. 


Important properties of muscle tissues are as follows-

  • Extensibility- the ability of a muscle to stretch itself

  • Contractibility- the ability of the muscle cells to forcefully shorten themselves 

  • Excitability- the ability of a muscle tissue to respond to a stimulus given by any hormone or a motor neuron

  • Elasticity- the ability of a muscle to recoil to it's usual length after being stretched


Types of Muscle Tissues and Their Functions 

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Mostly responsible for initiating movement of an organism, muscle tissues have a range of other functions based on their types. These are:


Skeletal Muscle Tissues 

Voluntary muscle and striated in nature, skeletal muscle tissues have neatly arranged bundles and have tendons anchoring them. These have an impact of the skeletal movements of an organism that include posture and locomotion. 


Smooth muscle tissue 

These are involuntary and non-striated in nature and have tapered ends. They are mostly located in the blood vessel walls like arteries and veins, urinary tract, trachea and digestive system. Smooth muscle tissues help in peristalsis to move food up and down the alimentary canal. 


Cardiac muscle tissues 

These majorly comprise of making up the heart. Involuntary and striated, these are branched out at irregular angles to help with coordinated contractions occurring inside the heart. 


Nervous Tissues 

Nervous tissues are the cells that form the central and peripheral nervous system. While in the central nervous system, the nervous tissues form the spinal cord and the brain, in the peripheral nervous system, the nervous tissues make up the cranial and spinal nerves, also including the motor and sensory neurons. 

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The most important function of the nerve tissues are to transmit and carry nerve impulses in various parts of the body. Impulses are often sent by axons and received by dendrites. 

Nerve cells can be of three types- sensory neurons, motor neurons and interneurons. 


Connective Tissues 

These are tissues that support, connect or separate various other kinds of tissues and organs inside the body. They are made up of cells, fibres like collagen and extracellular matrix. Collective tissues can be found abundantly located inside the body in a freely arranged form or in a matrix. 

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Types and functions of connective tissues 

The various types include areolar, adipose, bone, cartilage and fat. All cells are involved in the secretion of collagen except for blood. 


Areolar Connective Tissues 

These are found under the skin, surrounding nerves and blood vessels. Their function is to repair tissues and provide support. 


Adipose Tissues 

These can be found in the organs and skin. Composed of fat globules, their function is to insulate the body with the fat presence. 


Bones 

These form the skeletal structure of the body and have a characteristic of being rich in calcium and collagen fibres. They protect the body and are the location of blood cell production. 


Cartilage

These can be found in the ear tips, vertebral column, bronchi and are made of chondrocytes that are comprised of flexible intercellular materials. 


Blood

The functions of blood include putting up a defence system, transportation and most importantly homeostasis. Blood is composed of blood cells that include platelets, RBC and WBC along with plasma.