Tissues in our body

 Introduction

Our body has a specific design supported by a structured framework of cells and tissues. A very basic unit of life is called a cell and many cells grouped together to form a tissue. Similarly, 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 of different body parts vary in their activity level, size and length, basing these which, parameters, the  4 principal types of tissues in our body are epithelial tissues, muscular tissues, nervous tissues, and connective tissues. This post takes you through the basic structural and functional description of each type of tissue. 

  

 

Classification of  tissues

Having said that the systematic aggregation of cells lead to tissues. Different cell types assimilate with their surroundings based on their size, shape, and the functions they need to carry out. Some of the tissues are long and slender, few are rounded but thick. Following sections describe the structure and functions of basic tissue types.

 

1. Epithelial tissues:

The epithelium is the most abundant tissue found in the human body. As the name suggests ( Epi-outer) covers the outer surfaces of many organs, mucous membranes, inner walls of blood vessels and fundamentally the skin.  Epithelium also encloses the visceral coverings of internal organs as well as almost all the areas of mucus membranes of glands. The epithelium is again classified into 2 broad types based on the size, shape, and arrangement of cells; accordingly, they are simple or compound type. Simple epithelium is again categorized as squamous, columnar, ciliated columnar and cuboidal epithelium. The simple epithelium has a single layer of cells whereas the stratified epithelium has a bundle of layers piled together in a certain pattern. Rarely, we also find a special type of epithelium known as the pseudostratified epithelium. The term pseudo indicates false meaning that a single layer of cells is presented in varying heights to give the appearance of being stratified. The outer epithelial layers do not necessarily require blood as most of the epithelial surface is keratin based. But the lower sides of the cells 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. Furthermore, the bulk of the organs and body parts have all the 4 types of tissues, however, each organ has its own proportion a particular epithelial type. For instance, if we take bones , they are surrounded by nervous tissues and  muscular tissues.

 

 

Different types of epithelium

 

 

2. Muscular tissues

Locomotion -body movement is an essential function mainly led by bones. Muscles Produce contraction and relaxation in order to help our body parts to move and they are present in almost every part of the body, but the type of muscles vary. 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 thinly distributed ones. Our muscular system is so unique that it has the ability to modify its length and thickness depending upon the degree of strength to be generated while moving a body part. Muscles can produce active and passive movement while the most common type being the active movement. Active motion helps in walking, running, jumping and many day-to-day chores whereas the passive motion helps in vital functions such as peristalsis,  heartbeat, respiratory movements etc.  There are 3 major types of muscle tissues: skeletal or striated muscles, non-striated or smooth muscles, and the cardiac muscles. Our skeletal muscles assist in the active movement of large muscles by means of their rhythmic contraction and relaxation while lifting heavy objects, sitting, standing, bending, and running. These are performed with the help of the large muscles found on the upper and lower limbs. Most of the skeletal muscles are voluntary in nature hence they are otherwise termed as voluntary muscles. They are also called striated muscles because of the alternate dark and light striations on their surface. Non-striated ones are the involuntary muscles lying close to the most of vital organs and some inner linings. Unlike the striated type, these muscles do not have striations. Going forward, cardiac muscles are the improvised version of skeletal muscles. They are one of the unique muscle types, very strong, highly contractile and above all they never stop contracting from birth till the death. They are well-known as heart muscles exclusively found in the myocardium( middle layer of the covering of the heart). They are elongated, fibrous and highly branched with rich blood supply to sustain their ability to contract. Cardiac muscle tissues are involuntary in nature. They look like striated muscles but are much stronger and dark red in colour because of its rich blood supply. Heart muscles receive blood supply through coronary arteries branching out from the aortic channel. The electrical stimulation generated from the SA node and AV node triggers 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 through neurons. Neural signals aids in sending and receiving the information necessary for the peripheral organs to act.  Nerve tissues are further classified into the central nervous system and the peripheral nervous system. The neuron is the structural and functional unit of the nervous system while many neurons piled 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 are 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 while cartilaginous tissues have tough and elastic cartilage. 

 

 

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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