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Biology 2nd Baccalaureate

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1.3. Tissues


Unicellular beings are characterized because, with a single cell, they are capable of carrying out their vital functions. Remember that prokaryotes and some eukaryotes of the protoctist kingdom (protozoa and algae) and the fungal kingdom (yeasts) are unicellular.

Multicellular beings, on the other hand, are made up of a set of cells that have originated from the egg or zygote cell. From this cell, the others have arisen, all with the same DNA but, through cell differentiation, they have specialized to give rise to the different types of cells existing in the body.

Interactive activity: Tissues, organs and devices or systems.

tissue is made up of a set of cells that work together to carry out a function in an organism. Different tissues associate with each other to perform even more complex functions, and form the organs. In turn, the bodies that collaborate to perform the same function constitute an system.

Interactive activity: The tissues.

The histology is the part of biology that is responsible for the study of tissues. Animal tissues are classified into four types:

Epithelial tissue

The epithelial tissue is made up of a set of tightly knit, flat polyhedral cells, without leaving spaces between them, which line the internal and external body surfaces, and which also form glands. Epithelial tissue can be:

  • Coating. It has a protective function, covering internal (digestive tract, respiratory tract) or external (skin) surfaces of the body.
    • Epidermis: made up of many layers of cells that make up the outer part of the skin.
    • Mucous membranes: they protect the walls of the internal cavities such as the digestive tract or the respiratory tract.
    • Endothelium: made up of a layer of cells that covers the inner surfaces of the blood vessels and the heart.
  • Glandular. Formed by cells specialized in producing substances that they release to the outside. Sometimes they form structures called glands, such as the salivary glands.

Connective tissues

The connective tissues are mainly structural and protective function:

  • The connective tissue is a resistant tissue with a structural function, it joins tissues or organs. It is made up of cells called fibroblasts, responsible for synthesizing fibers such as collagen, which make up ligaments and tendons.

    A particular type of connective tissue is blood tissue, made up of cells ( red and white blood cells ) embedded in a matrix (plasma).

  • The adipose tissue is composed of cells called adipocytes. They have a protective function, as in the case of the kidney or the heart, and an energy reserve for the body.
  • The cartilage is a supporting tissue. Its cells form hard but elastic structures. It forms the skeleton in embryos and in adults, they are found covering the bones of the joints, in the ears, the trachea, the nose and the intervertebral discs.
  • The bone is formed by cells called osteocytes surrounded by a hard mineralized matrix. It is a supportive tissue and forms the skeleton of adults. Unlike cartilage, bone tissue is highly irrigated by the circulatory system.

Muscle tissue

Muscle tissue is made up of elongated cells called muscle fibers, characterized by their ability to contract, which is why they are responsible for the movement of the body, forming muscles. There are several types of muscle tissues:

  • Striated muscle tissue: Its contraction is voluntary, it allows movement of the skeleton.
  • Smooth muscle tissue: Its contraction is involuntary, it is responsible for the movement of organs such as the stomach or uterus.

The heart muscle tissue is a type of striated muscle tissue but involuntary contraction.

Nervous tissue

The nervous tissue is formed by specialized cells called neurons and other cells that work with them called glial cells or glia. They form the nervous system, responsible for transmitting the nerve impulse and coordinating the functioning of the body.

Interactive activity: The tissues.

Interactive activity: Tissues.

Answer in your notebook

1.8.- Make a table in which the names of the main types of fabrics and their function appear.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.