Tissues are groups of similar cells that come together to perform a special function in the body. The study of tissues is called Histology or Microanatomy. There are different types of tissues in the human body; other animals and plants have tissues too but theirs will be described in another article.
Four Major Types of Tissues in Human Body
- Epithelial Tissue
- Connective tissue
- Nervous tissue
- Muscular tissue
The 4 tissues mentioned above are the main types of tissues in the body. Each of these basic tissue types have different types for example, there are different types of Epithelial tissue and there also different types of connective tissues and so on.
The Examples, Functions, Structures and Pictures of the Main Types of Tissues of the body listed above will be described briefly and each would be described in details in other articles.
- Tissues protect other tissues or organs in the body such as the skin protecting and covering other organs
- Tissues regulate temperature of the body such as the skin
- Some tissues help to control transport of nutrients and gases (such as oxygen and carbon dioxide) across other tissues and organs such as epithelial tissues lining the gastrointestinal tract (gut) and lungs.
- Some Tissues relay information from the brain to other tissues and vice versa such as thee nervous tissue
- Some tissues serve as a layer or background over which other tissues rest on it such as the connective tissue which serves as a matrix or ground for binding other tissues together.
- Some tissues help in transportation such as the blood which is a connective that helps in transportation of the cells needed to supply oxygen and also transport other nutrients in the body
- Some tissues enable humans to move, carry loads and facilitate respiration such as the muscular tissue. The muscles help in movement, grinding of food and movement of food through the gut (intestinal smooth muscles do this) while the muscles of the chest help in respiration.
Tissue Structure and Components
The structure of tissues varies according to the type of tissue. Remember that tissues are a group of cells that come together to carry out a special function for the body; there may be different types of cells that may come together to carry out a special function. In some tissues, the cells may be similar and in some, the cells may be different.
When cells come together, they do so within a confined space called the Extracellular Matrix or the Extracellular Space. You can visualize the Extracellular matrix or space as a community that has many houses and each house as a cell (each house may be similar but they perform special functions such as using some houses as rooms for sleeping, other houses are used as shops while others are used as offices). The Extracellular space is as the community where the houses are built on the land. In tissues, the extracellular matrix holds the different types of cells and provides a n enabling environment for the cells to perform their functions.
The reason why it is called the extra–cellular space or matrix is because the space is located outside the cells (extra cellular space). Even within the extracellular space, there are various proteins that form this space. This will be discussed while describing this space in details.
Therefore, a tissue can be said to have 2 major components the cells and the extracellular matrix.
Types of Tissues and their Functions
The 4 basic tissues mentioned have different functions in the body.
An Epithelial tissue is a sheet of cells that are joined together to a covering to other parts of the body. You can visualize the epithelial tissue as a blanket that covers the bed. The skin is an example of an epithelial tissue that covers other parts of the body and protects them.
A single epithelial tissue is called an Epithelium while many epithelial tissues are called Epithelia.
Where is Epithelial Tissue found?
The epithelial tissue can be found outside the body as the skin and inside the body as a lining to the organs in the body.
Locations of Epithelial tissue in the body
- There is an epithelial tissue lining the inner part of the intestines that are responsible for absorption of food. There are different types of this epithelial tissue. It will be described below under types of epithelial tissues.
- An epithelial tissue lines the lungs and it is called the Pleura
- The epithelial tissue that covers the outer parts of the intestines and other organs in the abdomen is called the Peritoneum
- The epithelial tissue that covers the outer part of the heart is called Pericardium and the one that covers the inner chambers of the heart is called Endocardium
- The epithelial tissue lining the outer parts of the body is called the Skin which looks different depending on the part it is covering. The skin covering the lower part of the feet looks harder or tougher than the one covering the face.
- The epithelial tissue lining the inner lumen of blood vessels is called Endothelium
Types of Epithelial Tissues
- Squamous Epithelium
- Cuboidal Epithelium
- Columnar Epithelium
- Transitional Epithelium
This type of epithelial tissue is composed of flattened cells that are joined together to form a continuous lining. There are two (2) types of squamous epithelium which are the Simple Squamous Epithelium and Stratified Squamous Epithelium.
The simple squamous epithelium is the type that lines the blood vessels, lungs, and the heart as mentioned above. This type of epithelial tissue helps to ensure exchange of gases and nutrients from one tissue to another or from one organ to another organ.
The stratified squamous epithelium is the type that lines the intestines (gut), the vagina and oral cavity. This type of epithelial tissue undergoes continuous sloughing off and is being replaced with new cells underneath. It is called Stratified because it has different layers (strata) two or more layers of cells the way blocks are arranged while building a house.
This is composed of cube like cells that are joined together. They are found in small ducts of the body such as the salivary glands and the kidney tubules. Their function is for secretion or absorption of nutrients. There may be simple cuboidal epithelium
This type of epithelial tissue is composed of taller cells than the cuboidal epithelium. The look rectangular or form columns of cells that are joined together. This form of epithelial tissue helps in absorption of nutrients such as in the gastrointestinal tract and also helps to clear secretions such as the ones in the airways. The cells that form the columnar epithelium have fingerlike projections called microvilli that increase the area use for absorption.
This type of epithelial tissue consist of a mixture of cuboidal or squamous cells with columnar cells that are joined together to form layers. It is called Transitional because as you look at the top, there may be squamous cells that gradually change to either cuboidal or columnar cells as you go down the layers. The transitional epithelium is found in the urinary tract and in the bladder.
Connective tissues are groups of cells that come together to perform the special function of binding other tissues of the body together. The connective tissue serves as a support for other tissues to perform their functions. Without the connective tissue, other tissues cannot be joined together.
The connective tissue is like the foundation over which a house is built. The epithelia tissue rests on the connective tissue that was the matrix I described above. The extracellular matrix is part of the connective tissue. Other tissues also rest on the connective the nerves and bound by connective tissue, the muscles are also bound by connective tissue.
Types of Connective Tissue
- Loose connective tissue (Areolar connective tissue)
- Dense connective tissue (consisting of the dense irregular connective tissue and the dense regular connective tissue)
- Specialized connective tissue
Loose connective Tissue (Areolar Connective tissue)
The loose connective tissue is also called the Areolar connective tissue. It is called loose connective tissue because the packing of this tissue is loose and not tight. It serves as a packing material of the body that helps to anchor different organs and parts of the body such as anchoring blood vessels, nerves and organs.
This type of connective tissue is composed of cells called Fibroblasts. The fibroblasts help to secrete collagen fibers and elastic fibers (made of a protein called elastin) that serve as ropes or threads that bind other tissues together.
Dense connective tissue
The dense connective tissue has tight packing. The dense connective tissue forms the tendons (that join one bone to another), the ligaments (that join muscles to bones) and fascia (the tough whitish covering of muscles).
Specialized Connective Tissue
Specialized connective tissue have special functions that are not entirely for binding alone but also help with other functions in the body.
Types of specialized connective tissues
- Bone:the strongest and rigid form of connective tissue in the body that provides support and structure to the body
- Blood:the blood is a type of connective tissue. It is a liquid form of connective tissue that helps to transport cells such as red blood cells, white blood cells and nutrients
- Lymph:a liquid form of connective tissue just as the blood.
- Cartilage:semi rigid connective tissue that helps provide structure to the ears, nose and other parts of the body
The muscular tissue is a type of tissue in the body that helps to facilitate movement. There are different types of muscular tissue.
Types of muscular tissue
- Skeletal muscles
- Smooth muscles
- Cardiac muscles
The skeletal muscles can be controlled by man (voluntary muscles) and enable movement and carrying of objects.
The smooth muscles of the intestines help in movement of food down the gut.
The cardiac muscles enable the contraction of the heart. This type of muscle cannot be controlled by humans and automatically contracts by itself (involuntary muscle) to help pump blood round the body.
The Nervous Tissue
The nervous tissue is the tissue that enables relay of information from the brain to other organs or tissues. It is the nervous tissue that helps us to know when we touch something hot, cold or warm. It helps us perceive and communicate with the environment and also has protective function as it can help you to remove your hand or feet when you touch something hot to avoid burns and also helps you to close your eyes to prevent an insect or objects from entering the eyes. The two cells that make up the nervous tissue are the Neurons (the functional unit of the nervous tissue that relay information) and Neuroglia (supports the neurons).