TISSUES OF THE HUMAN BODY: TYPES AND THEIR CHARACTERISTICS - BIOLOGY - 2025

The tissues in the human body are elements that comprise groups of cells, highly organized, to fulfill a specific task and work as a unit. These are grouped into organs, which in turn are grouped into systems.

The major animal tissues are grouped into four types, namely: connective, nervous, muscular, and epithelial. In this article we will deal with the most relevant characteristics of each organizational system.

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The science in charge of studying the characteristics, structure and function of tissues is called histology. Specifically, the discipline that is responsible for the study of human body tissues is animal histology. The four types of tissues that we will explore in this article are also found in other animals.

Connective tissue

Connective tissue consists of a set of cells that are loosely arranged on an extracellular matrix of varying consistency and that can be gelatinous or solid. The matrix is ​​produced by the same cells that are part of the tissue.

-Function

Connective tissue serves as a link between different structures within the human body. Its presence gives shape, protection and resistance to the rest of the animal tissues. It is a fairly variable fabric; Next we will describe the most important characteristics and functions of each subtype.

-Classification

This tissue is classified taking into account the nature of the matrix in which the cells are immense, and can be loose, dense, fluid or supportive.

Loose connective tissue

It is composed of an arrangement of fibrous proteins in a soft matrix. Its main function is to keep organs and other tissues together; hence the name "connective". It is also found under the skin.

Dense connective tissue

We find it in the tendons and ligaments that are responsible for joining the muscles, bones and organs.

Fluid connective tissue

The cells are surrounded by an extracellular matrix of a totally liquid consistency. We are closely related to the example of this tissue: blood. In it we find a heterogeneous series of cellular elements floating in the extracellular matrix called plasma.

This fluid is responsible for transporting materials throughout the human body and is mainly composed of red, white blood cells and platelets immersed in plasma.

Supporting connective tissue

The extracellular matrix of the last connective tissue is firm and supports other structures. These include the bones and cartilage that support the human body, in addition to protecting important organs; like the brain, which is protected inside the cranial box.

Nervous tissue

Nervous tissue is made up mainly of cells called neurons and a series of additional supporting cells. The most outstanding characteristic of neurons is their ability to transmit electrical impulses, produced by a change in the permeability of the cell membrane to certain ions.

Support cells have various functions, such as regulating the concentration of ions in the space surrounding neurons, feeding neurons with nutrients, or simply (as the name implies) supporting these nerve cells.

Function

Living organisms exhibit a unique property of responding to changes in the environment. In particular, animals have a finely coordinated system that controls behavior and coordination, in response to the various stimuli to which we are exposed. This is controlled by the nervous system, made up of nervous tissue.

Neurons: units of the nervous system

The structure of a neuron is very particular. Although it varies depending on the type, a general scheme is as follows: a series of short branches surrounding a soma where the nucleus is located, followed by a long prolongation called the axon.

Dendrites facilitate communication between adjacent neurons and the nerve impulse runs through the axon.

We will use this example to note that in biology we find a close relationship between the form of structures and function. This does not apply only to this example, it can be extrapolated to all the cells that we will discuss in this article and to a wide range of structures at different levels of organization.

When we appreciate an adaptive structure (which helps in the survival and reproduction of the individual, as a result of natural selection) in an organism it is common to find that the various characteristics of its structure are correlated with function.

In the case of neurons, the long axon allows the rapid and effective passage of information to all places in the human body.

Muscle tissue

Although plants present a series of subtle movements (or not so subtle in the case of carnivores), one of the most striking characteristics of the animal kingdom (and therefore of humans) is their extensively developed ability to move.

This occurs thanks to the coupling of muscle and bone tissue, responsible for orchestrating different types of movements. The muscles correspond to a unique innovation of animals, which does not appear in any other lineage of the tree of life.

-Function

These cells with the capacity of contraction manage to transform chemical energy into mechanical energy, producing movement.

They are responsible for moving the body, including voluntary body movements, such as running, jumping, etc.; and involuntary movements such as heartbeats and movements of the gastrointestinal tract.

-Classification

In our body we have three types of muscle tissue, namely: skeletal or striated, smooth and cardiac.

Skeletal muscle tissue

The first type of muscle tissue plays a crucial role in most body movements, as it is anchored to the bones and can contract. It is voluntary: that is, we can consciously decide whether or not to move an arm.

It is also known as striated muscle tissue, since it presents a kind of stretch marks due to the arrangement of the proteins that make it up. These are the actin and myosin filaments.

The cells that compose them contain multiple nuclei, in the order of hundreds to thousands.

Smooth muscle tissue

Unlike previous tissue, smooth muscle tissue does not have stretch marks. It is found lining the walls of some internal organs such as blood vessels and the digestive tract. With the exception of the urinary bladder, we cannot voluntarily move these muscles.

Cells have a single nucleus, which is located in the central zone; and its shape is reminiscent of a cigarette.

Cardiac muscle tissue

It is the muscular tissue that is part of the heart, we find it in the walls of the organ and it is in charge of propelling the heartbeat. The cells have a series of branches that allow the electrical signals to be dispersed throughout the heart, thus achieving the production of coordinated beats.

The muscle cells that we find in the heart have a single central nucleus, although in some we can find two.

Epithelial tissue

The last type of tissue that we find in our body is the epithelial, also known simply as the epithelium. We find it covering the outside of the body and covering the internal surface of some organs. It is also part of the glands: organs responsible for the secretion of substances, such as hormones or enzymes, and also mucous membranes.

Cells frequently die

One of the most outstanding characteristics of epithelial tissue is that its cells have a fairly limited half-life.

On average they can live from 2 to 3 days, which is extremely short, if we compare them with the cells that make up the tissues mentioned in the previous sections (such as neurons or muscle cells), which accompany us throughout our lives.

However, these multiple events of programmed cell death (apoptosis) are in fine balance with regeneration events.

Function

The main function of this tissue is very intuitive: the protection of the body. It acts as a protective barrier that prevents the entry of potential unwanted substances and pathogens. It also exhibits secretory functions.

For this reason (remember the concept of structure-function that we discussed in the previous section), we find that the cells are very close together and compact. Cells are closely linked by a series of connections called desmosomes, tight junctions, among others, which allow communication and adhesion.

Cells of the epithelium exhibit a polarity

Epithelial cells have a polarity, which indicates that we can distinguish between two extremes or regions within the cell: the apical and the basolateral.

The apical side faces other tissues or the environment, while the basolateral portion faces the interior of the animal, connecting it to the connective tissue through the basal lamina.

Classification

The number of layers that make up the epithelium allows us to establish a classification into two main epithelial tissues: the simple epithelium and the stratified one. The first is formed by a single layer of cells and the second by several. If the epithelium is made up of multiple layers, but these are not ordered, it is known as pseudostratification.

However, there are other rating systems based on other characteristics such as the function of the epithelium (lining, glandular, sensory, respiratory or intestinal) or according to the shape of the cellular elements that compose it (squamous, cubic and primary).

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