Tissues in our body

 Introduction

Our body has a specific organization supported by a structured framework made up of cells and tissues. A very basic unit of life is called a cell. Cells grouped together to form a tissue. Many tissues join together to form an organ and the organs result in the systems. Irrespective of the body part, tissues are present everywhere but the types of tissues vary between different parts of the body. Our body tissues are formed based on the structural and functional demands necessary for the individual. For example, lung parenchyma has a ciliated end because the ciliary cells help in easy expansion and contraction of the lungs. Tissues vary in their activity level, size and  length as there is individual difference exists between many subtypes. There are 4 principal types of tissues in our body, in fact in most of the mammals, tissues are more or less the same. The basic types of tissues are epithelial tissues, muscular tissues, nervous tissues, and connective tissues. This article briefs the basic structural and functional description of each type of tissue. 

  

Types of tissues

1. Epithelial tissues:

Epithelium is the most common tissue found in the human body. Epithelial tissues, as the name suggests ( Epi-outer) cover the outer surfaces of many organs, mucous membranes, inner walls of blood vessels and the skin.  Epithelium also covers the visceral coverings of internal organs as well as almost all the mucus membranes of internal glands. The epithelium is classified into 3 main types based on the size, shape, and arrangement of cells. Epithelium can be simple or compound type. Simple epithelium is of 4 subtypes; squamous, columnar, ciliated columnar and cuboidal epithelium. Simple epithelium has a single layer of cells, and a stratified epithelium has a bundle of layers attached together in a certain pattern. Rarely, we also find a special type of epithelium known as pseudostratified epithelium. This is pseudo ( false) because a single layer of cells is presented in varying heights to give the appearance of being stratified. Epithelial layers do not necessarily require blood sully as most of the epithelial surface is keratin based. But they receive their nourishment through the diffusion of substances from the underlying connective tissue. One of the largest organ-skin is made up of this type of epithelium. Most of the organs and body parts will have all the 4 types of tissues, however, an individual tissue type dominate the particular organ or part of the body. For instance, bones have connective tissues, nerve supply as well as the surrounding muscular tissues.

 

Different types of epithelium

 

2. Muscular tissues:

Locomotion -body movement is an essential function. Without the help of muscle tissue, it is impossible to survive because muscles help in supporting, contracting and relaxing the body parts to produce necessary movement.  Muscles are present in almost every part of the body, but they are not the same everywhere. Some of the actively moving parts such as arms, shoulders, legs have a thicker band of muscular tissues. On the contrary, parts like skull, joints and some bony prominences have a limited supply of muscular tissues, except in a few bony areas. Our muscular system is so unique that it can contract and relax which in turn produces the rhythmically and pattern of body motion. The body can have active and passive motion. Active motion helps in walking, running, jumping and many other vigorous activities. Passive motion is in action while we are on the rest, for example, during peristalsis, our heartbeat, etc.  There are 3 types of muscle tissues: skeletal or striated muscles, non-striated or smooth muscles, and the cardiac muscles. Skeletal muscles assist in the active movement of large muscles through their rhythmic contraction and relaxation. For instance, lifting heavy objects sitting, standing, bending, and running are performed with the help of the muscles present on the upper and lower limbs. Most of the skeletal muscles are voluntary in nature hence they are otherwise termed as voluntary muscles or striated muscles( because of the alternate dark and light striations). Non-striated muscles are involuntary in nature and these are found near the vital organs and some inner linings. Non-striated muscles, unlike striated type, do not have striations. Cardiac muscles are one of the unique muscle types, very strong, highly contractile and above all they never stop contracting from birth till the death. In general, they are known as heart muscles exclusively found in the myocardium( middle layer of the covering layers of the heart). Cardiac muscles are elongated, fibrous and highly branched with a rich blood supply to sustain their ability to contract. Cardiac muscle tissues are involuntary in nature. They look like striated muscles but much stronger, and they appear dark red because of the rich blood supply. Heart muscles receive blood supply through coronary arteries branch out from the aortic channel. Electrical stimulation generated from SA node and AV node which in turn trigger the individual muscles to contract and relax. 

 

 

Muscular tissues-image from wiki commons

 

 

3. Nervous tissue:

Our nervous system is very complex, sensitive and highly coordinated with other bodily systems such as muscular systems, sense organs, and skeletal systems. Nervous tissues help in the control and coordination of our body by sending and receiving neural signals. Neural signals are important to send and receive the information necessary for the organs to act.  Nerve tissues are divided both centrally and peripherally hence the names, central nervous system and the peripheral nervous system. The neuron is the unit structural and functional unit of the nervous system; piling many neurons end to end result in nerves.  Neurons have the ability to detect sensory feelings from the external environment. Some of the feelings such as heat, cold, pressure, the sharpness of an object is perceived by nerve endings of the skin surface and this is a part of the peripheral nervous system. The central nervous system has the brain and the spinal cord.  Nerves help us by assisting in moving, hitting, kicking, standing and running.  For more information on the brain click here.

 

4. Connective tissue:

As the name suggests, they help in connecting, supporting, or separating a body part from its adjacent structures. Connective tissue can be cartilaginous, bone, adipose tissue and the blood. Blood is the only liquid connective tissue in our body. Anatomically they can be either loose or dense. Adipose tissue has more fatty layers beneath while cartilaginous tissues have a tough and elastic cartilages. Blood is the only liquid connective tissue that connects all the parts by its circulation.

Connective tissues-images from Google

 

 

 

Read more

1    

Structure and functions of bone tissue

2

Epithelial tissues

3

Connective tissues

4    

Adipose tissues

 

Questions

  1. Define tissue and explain the functions of tissues in our body 

  2. Classify tissues. Which is the most abundant tissue in our body?

  3. Explain the structural difference between simple epithelium and stratified epithelium.

  4. Briefly explain about connective tissues.

  5. What are the different types of muscular tissues in our body? Explain the difference between striated and non-striated muscles?

  6. What is a neuron?

 

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