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Tissues are present exclusively in vascular animals and plants, which have acquired them with the course of evolution independently and, therefore, they present differences between them although, in essence, they are homologous.
This Green Ecologist article explains what they are and the general characteristics of the different types of animal tissues, as well as its functions. Finally, animal and plant tissues will be compared, describing their most obvious differences.
Animal tissues: what are they and their characteristics
In biology, tissue is a level of biological organization consisting of a material made up of an organized series of cells (the same or different from each other) of the same nature, with an embryonic origin and a common physiological behavior.
Animals are characterized by highly specialized cells. The more evolved an organism is, the more differentiation its cells will present. The association of these specialized cells gives rise to the tissues that, in turn, make up the organs of animals. These present specific functions and can be categorized into four types of animal tissues: epithelial, conjunctive, muscular and nervous.
Types of animal tissues and their functions
The 4 types of animal tissues they are listed below, along with their functions and features.
Epithelial tissue
It covers the body's surface, lines its internal cavities, and forms the secretory portions of the body's glands, which secrete substances such as hormones and enzymes. It's about a non-vascularized tissue (for nourishment, it depends on the underlying connective tissue), whose constituent cells are characterized by:
- Being attached to each other by means of specific molecules that establish intercellular bonds.
- Possess morphological and functional polarity.
- Present a basal surface attached to a basement membrane, which separates them from the connective tissue, while its apical part is exposed to the external environment or the body cavity.
Epithelia are classified according to the amount of cell strata in simple (if they only have one layer of cells) or stratified (if it has several layers) and according to the shape of the epithelial cells (which can be flat, cubic or cylindrical).
Conjunctive tissue
Originating in the mesenchyme, the term "connective tissue" includes various types of tissues with different functions (mechanical and functional support, immunological protection, energy reserve and transport). The cells that form them are separated from each other by collagen, reticulin and elastin fibers and by an extracellular matrix, these three elements being the components of these tissues. The extracellular matrix is a complex structural network secreted by connective tissue cells (which it surrounds and supports), which influences extracellular communication and is composed of protein fibers (collagen and elastic) and the so-called fundamental substance (which consists of proteoglycans, multi-adhesive glycoproteins and glycosaminoglycans, in addition to water, dissolved substances and plasma proteins).
There are several types of connective tissue: adipose, bone, blood (liquid type, driven by the heart and vascular walls), cartilaginous, hematopoietic and lymphatic.
Muscle tissue
Its function is the body movement and the change in size and shape of the organs (muscle contraction). It has mesodermal origin and is formed by elongated cells called muscle fibers, which contain actin and myosin and whose functional characteristics are excitability, conductivity and contractility. These muscle cells have a cytoplasm called the sarcoplasm, bounded by a membrane called the sarcolemma. In sarcoplasm, microfibrils stand out, which can be smooth or striated. There are three types of muscle tissue:
- Striated muscle tissue: it is associated with the bones and moves the different parts of the body.
- Cardiac muscle tissue: appears in the heart, promoting blood and lymphatic circulation throughout the body.
- Smooth muscle tissue: It is found in the walls of the hollow organs and is involved in the internal movements of the body.
Nervous tissue
Composed of neurons, which receive stimuli from others, conduct the electrical impulse to other tissues and store information, and also formed by support cells, which are in contact with the former and provide protection, electrical isolation and metabolic exchange mechanisms between blood vessels and neurons.
The nervous system is divided into Central Nervous System, which is made up of the brain and spinal cord, and the peripheral nervous system, formed by cranial, spinal and peripheral nerves (which transmit and receive impulses from and to the central nervous system) and ganglia. Supporting cells form neuroglia in the central nervous system, while in the peripheral nervous system they are represented by Schwann cells and satellite cells. This tissue coordinates the functions of the body, since the nervous system allows the response to environmental stimuli and controls the activities of organs and devices.
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Differences between animal tissues and plant tissues
The component cells of animal and plant tissues are different, since, obviously, the former are animal cells and the latter are plant cells, which implies a series of intrinsic differences. These are the main differences between cells of animal and plant tissues:
- Animal cells are mobile and plant cells are not.
- Animal cells lack chlorophyll, unlike plant cells.
- Animal cells are heterotrophic (and consuming) and plant cells are autotrophic (and producing).
- Animal cells are of limited growth and plant cells are of unlimited growth.
- Animal cells have only a plasma membrane, while plant cells also have a cell wall that gives them rigidity and turgor.
- Plant cells have vacuoles in the cytoplasm that do not appear in animals.
- Animal cells have centrosomes and plant cells, for the most part, do not.
- In plant tissues, most cells can differentiate from one tissue to another, whereas, in animal tissues, cells are usually not capable of this.
In this other Green Ecologist article you can learn much more about the Similarity and difference between animal and plant cells.
In addition to those already mentioned with respect to the cells themselves, these are more differences between animal tissues and plant tissues:
- Plant tissues are made up of living and non-living cells, while animal tissues only have living cells. This is why plant tissues require less energy than the latter.
- Animal tissues differ in epithelial, connective, muscular, and nervous, while plant tissues differ in growth, parenchymal, protective, supporting, conductive, and secretory tissue.
- In plants, tissues provide structural maintenance, while in animals tissues are involved in locomotion.
If you want to read more articles similar to Types of animal tissues, we recommend that you enter our category of Animal Curiosities.
