the human body contains more than two hundred different types of cells, each of which is unique. Dividing them into groups called tissues allows a similar structure and origin, as well as the functions performed. Tissues are the next hierarchical level of human anatomy after cells. They are a symbiosis of cells and intercellular space, the structure of which allows them to perform the functions assigned to them, thereby supporting the normal vital activity of the body.
In humans, 4 types of tissues are distinguished: epithelial, connective, muscle and nervous. Each of them is formed as a result of cell differentiation during the formation of the organism. What are the features of tissue anatomy, how do they interact and what functions do they perform? Anatomical reference will help you understand these issues!
Human tissue anatomy: from homogeneous cells to a highly differentiated organism
Formation of tissues, maintaining their shape and performing general functions is a complex process programmed in the body by DNA molecules. It is thanks to genetic information that cells are capable of differentiation – a biochemical process, as a result of which initially homogeneous units acquire specific features that subsequently allow them to perform certain functions. Thanks to this process, 4 types of tissues with similar anatomy and physiology appear in the body.
It is noteworthy that after differentiation, tissue cells retain their inherent features even in a new environment. To prove this, in 1952, experts at the University of Chicago carried out a visual study by dividing the cells of a chicken embryo and cultivating them in special enzymes. As a result of this experience, new colonies were formed, but at the same time the reactions and “behavior” of cells in the new structural environment were typical for the particular type of tissue from which they originally originated.
To understand how cells interact in the human body, consider the tissue anatomy in more detail.
Epithelial tissue forms the outer covers of the body – skin and mucous membranes, lines the internal cavities of organs and participates in the formation of glands. Epithelial cells adhere tightly to each other, intertwining into a single strong structure. There is practically no intercellular substance between them. This structure allows the epithelium to cope with the functions assigned to it, including:
- protection of the internal environment of the body from destructive factors acting from the outside;
- delineation of organs and their cavities, maintenance of their shape and structure;
- the production of special body fluids: saliva, some enzymes and hormones;
- participation in metabolic processes, including the absorption of certain molecules from the environment and the release of decay products.
Due to its special structure, epithelial tissues are capable of rapid regeneration. Even with serious damage, they gradually recover, forming colonies of new cells in the injured area.
Features of the anatomy of epithelial tissue allow it to be divided into two subspecies:
- The glandular epithelium forms glands of external and internal secretion. Tissues of this type are present in the thyroid, lacrimal, and salivary glands. Thanks to them, the secretion of certain hormones and enzymes that maintain balance within the body is carried out.
- The superficial epithelium is the outer covers of the body, as well as the lining of the cavities of the internal organs. Depending on the anatomical features, it can be single-layer or multi-layer, keratinizing and non-keratinizing. The keratinized epithelium is present only on the surface of the skin and is called the epidermal layer. Non-keratinizing, in turn, acts as a mucous barrier.
In addition, the epithelium is classified according to the type of cells present in its composition. Based on this criterion, cubic, flat, ciliary, cylindrical and other subtypes are distinguished.
The name of this type of fabric reflects its essence and functional features. Connective tissue includes a variety of cellular structures and a large amount of intercellular substance, consisting of an amorphous mass, collagen, protein and elastin fibers. This structure allows it to fill all the available gaps between the functional units of the body – organs and other tissues. It can also perform nutritional, protective, support, plastic, transport and other functions, depending on the location.
Connective tissue represents more than 50% of the total weight of a person. Depending on the anatomical location, it is classified into the following types:
- the connective tissue itself: dense and loose, reticular and adipose;
- skeletal formations;
- trophic fluids of the internal environment.
Dense fibrous tissue contains a high percentage of collagen and elastin, thanks to which it is able to maintain its current shape. Tendons, ligaments, fascia of muscle fibers and the periosteum (the surface layer of bones) are formed from it. Loose tissue, on the other hand, contains a high percentage of amorphous substance, therefore it is able to fill any necessary space. Together with dense tissue, it forms the dermis of the skin and the lining of the blood vessels.
Reticular tissue is similar to a kind of network of dendritic cells and fibers. It occupies a key place in the processes of hematopoiesis and, together with dense and loose connective tissue, forms the liver, red bone marrow, spleen and lymph nodes.
Adipose tissue also refers to connective tissue. Adipocytes – fat cells – line the internal organs, providing additional cushioning between them. In addition, adipose tissue is present in the subcutaneous tissue and performs a deposit function, storing fats for subsequent breakdown in conditions of a deficit of energy resources.
Skeletal formations, represented by connective tissue, form bone and cartilage structures. Bone tissue is denser, since its intercellular substance contains up to 70% mineral salts. Due to this, the bones of the skeleton are highly durable and stable. Cartilage tissue is more flexible, since elastin and collagen fibers prevail in its composition. From it articular surfaces, rings that support the shape of the airways, the auricle and other cartilage of the human body are formed.
A muscle group includes fibers that can respond to arousal, contract and relax, depending on the circumstances. Each individual muscle group has a certain, often elongated, shape and is separated from the others by a special bag – the fascia. Thanks to their rhythmic sequential contraction, the human body is able to take any acceptable posture and move in space. In addition, muscle tissue contributes to the contraction of the walls of some internal organs, including the heart, thereby supporting many vital functions.
Like other types of tissue, muscle has its own classification:
- Smooth muscles – myocytes – contract involuntarily and rhythmically. They form the basis of hollow internal organs and blood vessels – arteries, esophagus, bladder, etc.
- The striated musculature forms the skeletal and facial muscles, the diaphragm, the larynx, the tongue, and the muscles of the mouth. A separate type of it is cardiac muscle tissue: although it belongs to striated, each individual myocardial cell has 1–2 nuclei, unlike typical multinucleated cells of other muscles of this subgroup.
Nerve fibers are the connecting link between different parts of the body and the environment, due to which the entire anatomical system works harmoniously and synchronously. They are able to respond to excitement and conduct nerve impulses in a matter of fractions of seconds, providing a lightning-fast response of a person to changes occurring within him or acting from the outside.
Individual cells of the nervous system (neurons) are intertwined into a single network that extends to the entire body through two types of processes – dendrites and axons. Dendrites receive a nerve impulse and transmit it to the body of a neuron, while axons, on the contrary, emit it to other cells. This process occurs instantly, due to which the resulting impulse quickly reaches the final goal.
Depending on the influence that neurons have on the final goal, they are divided into several types:
- excitatory cells secrete a mediator that provokes excitement;
- inhibitory neurons synthesize an inhibition mediator;
- neurosecretory hormones are capable of releasing into the bloodstream.
Small slit-like spaces between neurons are filled with neuroglia – the intercellular substance of the nervous tissue. It performs a nourishing, protective and insulating function in relation to the structural units of the tissue.
Is tissue anatomy important?
p style=”background-color: white; box-sizing: border-box; color: #444444; font-family: "PT Serif", Georgia, Cambria, "Times New Roman", Times, serif; font-size: 18px; line-height: var(–line-article); margin: 0px 0px 24px; overflow-wrap: break-word; text-align: justify;”>Despite the seeming uniformity, the tissues of the human body have their own characteristics, which are formed in the process of embryogenesis. The result of their balanced interaction – the full-fledged vital activity of the organism – depends on how fully each of them will perform the assigned functions. A more detailed study of tissue anatomy allows you to understand how organs and systems interact with each other, what their performance is based on and how to achieve the most important moment – maintaining their health and functionality.