Connective Tissues: Cells, Fibers, and Types

Posted on Mar 16, 2025 in Environmental Biology

Connective Tissue

  • Tissue
  • Formed from the mesoderm during embryonic development.
  • A set of tissues with the same function, tissue together, sustaining the body and protecting organs.
  • Tissue called connective tissue.
  • It consists of cells contained in an amorphous substance, the extracellular matrix, formed by H2O, salts, proteins, polysaccharides, and fibers that form a network.

Cells

  • Fibroblasts: Are responsible for the formation of extracellular structures. They secrete the extracellular matrix, protein, and fiber.
  • Adipocytes: These are cells of fat reserves.
  • Histiocytes: Migrant cells that become activated macrophages, with phagocytic function.
  • Lymphocytes: Manufacture antibodies.
  • Mast Cells: Contain heparin and histamine.
  • Monocytes: Migrant cells with phagocytic function.
  • Pigment Cells: Contain pigment.

Fibers

  • Collagen Fibers: These are the most abundant, are very resistant, and can be found in the skin, tendons, ligaments, cartilage, bone, blood vessels, etc.
  • Elastic Fibers: Very elastic networks. Found in the ligaments.
  • Reticular Fibers: Very fine and form a support network for organs.

Types of Connective Tissues

  • Loose Connective Tissue: Located throughout the body.
  • Dense Connective Tissue: Formed by elastic fibers, it is found in ligaments and arteries.
  • Reticular Connective Tissue: Formed by reticular fibers and localized to the lymph nodes.
  • Adipose Tissue: Formed by adipocytes that have shifted the core due to the drop of fat.
  • Cartilaginous Tissue: Composed of collagen fibers which provide firmness and elasticity. Cartilage forms the skeleton of all vertebrate embryos and in adults is replaced by bone.

Bone Tissue

  • Are the main skeletal tissue of vertebrates.
  • Rich matrix formed by calcium phosphate (Ca(PO4)3) and collagen fibers.
  • The cells themselves are the osteocytes and receive nutrients through a network of capillaries that crosses the bone.
  • There are two types of bone tissue:
  • Compact: With few gaps. Forms the central part of the long bones (diaphysis), filled with yellow bone marrow.
  • Spongy: Many spaces between the cells that give it a bored look. Usually, they are full of red bone marrow. Forms short bones, flat bones, or ends of long bones (epiphysis).
  • The cavities are filled with bone marrow, perhaps of 2 types:
  • Red: Manufactures blood cells (red blood cells, platelets, and white blood cells).
  • Yellow: Contains fats and has replaced the red over the years. In adults, red bone marrow is only found at the ends of long bones, femur, pelvis, sternum, vertebrae, and skull.

Blood

  • Composition: Blood is a red, watery fluid which represents 8% of total body weight.
  • Blood consists of plasma and cells:
  • Blood Plasma: Formed by 92% H2O and proteins, among which are:

– Fibrinogen antibodies or gammaglobulin (involved in clotting)
– Albumin (carrying molecules)

b) Blood Cells: Originated from stem cells of red bone marrow. There are 3 types:

  1. Red Blood Cells (Erythrocytes): During the ripening process in the marrow, they lose their nucleus, so their lifetime is about 4 months. They have hemoglobin inside, a vertebrate respiratory pigment with the function of transporting O2 and CO2.
  2. White Blood Cells (Leukocytes): Have no pigment. These are cells with a nucleus and different functions (phagocytic function and antibody-producing). Based on their appearance under an electron microscope, they are ranked as:

– Agranulocytes: Are uniform in appearance; these are the antibody-producing lymphocytes and monocytes (phagocytic function).
– Granulocytes: Have a pelleted aspect. These are neutrophils, eosinophils, and basophils, which are phagocytic.

  1. Platelets: Cytoplasm fragments involved in blood clotting. Formed in red bone marrow.