The Human body consists of at least 200 distinct types of cells. These cells contain essentially the same internal structures yet they vary enormously in shape, size, and functions.
The different types of cells are not randomly distributed throughout the body; rather they occur in organized layers, a level of an organization referred to as tissue or we can say that tissue is a group of cells with their extracellular matrix.
The two separate branches of anatomy basically deal with the study of tissues i.e. Histology (the study of normal tissues) and the histopathology which is the branch of science which deals with the study of abnormal or diseased tissues.
The word “tissue” comes from the French word “,tissu” which is actually meant as “woven”.
French anatomist and pathologist Marie François Xavier Bichat introduced the term in 1801, stating that body functions could be understood better if they were studied at the level of tissues rather than organs.
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Types of tissues
The human tissue is classified into four basic categories: epithelial tissue, connective tissue, muscle tissue, and nervous tissue.
These all types of tissues derived from embryonic tissue (ectoderm, mesoderm, endoderm) and sometimes they vary according to species.
Epithelial Tissues
- Cells of epithelial tissue form sheets that cover the body and organ surfaces.
- In all animals, most epithelium derives from the ectoderm and endoderm, except the epithelium, which derives from the mesoderm.
- Examples of epithelial tissue include the skin surface and the linings of the airways, reproductive tract, and gastrointestinal tract.
- There are several kinds of the epithelium, including simple squamous epithelium, simple cuboidal epithelium, and columnar epithelium.
- Functions include protecting organs, eliminating waste, absorbing water and nutrients, and secreting hormones and enzymes.
Connective Tissues
- Connective tissue consists of cells and non-living material, called the extracellular matrix.
- The extracellular matrix may be either fluid or solid. Examples of connective tissue include blood, bone, adipose, tendons, and ligaments.
- In humans, cranial bones derive from the ectoderm, but the other connective tissues come from the mesoderm.
- Functions of connective tissue include shaping and supporting organs and the body, allowing body movement, and providing oxygen diffusion.
Muscle Tissues
- The three types of muscle tissue are skeletal muscle, cardiac muscle, and smooth (visceral) muscle.
- In humans, muscles develop from the mesoderm. Muscles contract and relax to allow body parts to move and blood to pump.
Nervous Tissues
- Nervous tissue is divided into the central nervous system and peripheral nervous system.
- It includes the brain, spinal cord, and nerves. The nervous system derives from the ectoderm.
- The nervous system controls the body and communicates between its parts.
The Embryonic Origin of Tissues
- The fertilized egg or zygote is also known as single-celled. It is formed by the fusion of an egg and sperm.
- The zygote undergoes too rapid mitotic cycles, and forms the embryo by generating many cells.
- The first embryonic cells generated have the ability to differentiate into any type of cell in the body and, as such, are called totipotent, meaning each has the capacity to divide, differentiate, and develop into a new organism.
- As cell proliferation progresses, three major cell lineages are established within the embryo.
- Each of these lineages of embryonic cells forms the distinct germ layers from which all the tissues and organs of the human body eventually form.
- Each germ layer is identified by its relative position: ectoderm (Ecto- = “outer”), mesoderm (Meso- = “middle”), and endoderm (endo- = “inner”). shows the types of tissues and organs associated with each of the three germ layers.
- Note that epithelial tissue originates in all three layers, whereas nervous tissue derives primarily from the ectoderm and muscle tissue from mesoderm.
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Different types of tissue membrane
The two broad categories of tissue membranes in the body are
- Connective tissue membranes, which include synovial membranes, and
- Epithelial membranes, which include mucous membranes, serous membranes, and the cutaneous membrane which means the skin.
Tissue regeneration
- When tissue regeneration occurs it is essential that some of the original cells are available to replicate by mitosis.
- The extent to which regeneration is possible depends on the normal rate of physiological turnover of particular types of cells.
- Those with a rapid turnover regenerate most effectively. There are three types.
1.) Labile cells
Labile cells are those in which replication is normally a continuous process. They include cells in:
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- epithelium of e.g. skin, mucous membrane, secretory glands, ducts, the uterus lining
- bone marrow
- blood
- spleen and lymphoid tissue.
2.) Stable cells
Stable cells have retained the ability to replicate but do so infrequently. This includes:
- liver, kidney and pancreatic cells
- fibroblasts
- Smooth muscle cells
- osteoblasts and osteoclasts in bone.
3.) Permanent cells
Permanent cells are unable to replicate after normal growth is complete. This includes:
- nerve cells (neurons)
- skeletal and cardiac muscle.
Frequently Asked Questions (FAQs)
What is the definition of tissues and its types?
Tissues are groups of similar cells that work together to perform specific functions in the body. There are four main types of tissues: epithelial, connective, muscle, and nervous. Epithelial tissue covers and lines surfaces, connective tissue supports and connects structures, muscle tissue allows for movement, and nervous tissue transmits and processes information.
What is the importance of tissues?
Tissues are important because they are the building blocks of organs and organ systems in the body. They allow for the specialization of cells and the division of labor, enabling more efficient and effective functioning of the body as a whole. Tissues also provide structural support, regulate biochemical processes, and protect against injury and disease. Without tissues, the complex functions and interactions of the human body would not be possible.
What is the most important tissue?
It is not possible to determine a single “most important” tissue, as all tissues play critical roles in maintaining the proper functioning of the human body. Each tissue type has its unique structure and function, and all work together to ensure the proper functioning of organs and organ systems. However, some tissues, such as nervous and muscle tissue, are particularly essential for specific functions, such as movement and sensory perception.
Who discovered tissue?
Marcello Malpighi, an Italian physician and biologist, is credited with the discovery of tissues in the 17th century. In his studies of plants and animals, Malpighi observed that tissues were composed of cells and identified the distinct characteristics of various tissue types. He is considered a pioneer in the field of histology, the study of tissues, and his work laid the foundation for modern understandings of the structure and function of tissues in living organisms.
What is the study of tissues called?
The study of tissues is called histology. It is a branch of biology and medicine that focuses on the microscopic structure of tissues and their functions in living organisms. Histology involves the use of specialized techniques and instruments to examine the structure and composition of tissues at the cellular and molecular levels, including staining, sectioning, and microscopy. Histological studies are critical for understanding the normal functioning of tissues and organs, as well as the pathological changes that occur in disease states.
What is the structure of tissue?
The structure of tissues can vary depending on the specific tissue type. However, all tissues are composed of cells that are organized in a specific way to perform a particular function. In addition to cells, tissues may also contain extracellular matrix, which is a complex mixture of proteins, sugars, and other molecules that support the structure and function of the tissue.
