Connective Tissue: Cells, Fibers, and Functions
Connective Tissue
Derived from the mesenchyme, embryonic star-shaped cells establish contact through cytoplasmic extensions, forming a lattice structure. Mesenchyme originates from two tissue groups:
- Connective, cartilage, and bone tissues.
- Blood and hematopoietic tissues.
Connective Tissue Composition
Connective tissue comprises cells and fibers within a fundamental and immigrant substance.
Connective Tissue Cells
Connective tissue cells are numerous and varied, divided into two groups:
Fixed Cells
These cells maintain extracellular components and store energy reserves. They include:
- Fibrocytes: Large, branched, spindle-shaped cells with one or two nucleoli. They form connective tissue fibers.
- Adipocytes: Specialized cells that synthesize and store lipids. Abundant in the hypodermis.
Migrant Cells
These cells are involved in short-term reactions to tissue injury. They include:
- Macrophages (Histiocytes): Irregularly shaped cells with short, rounded extensions. They have high phagocytic capacity and abundant lysosomes.
- Plasma Cells (Cyanophils): Oval-shaped cells with an eccentric nucleus and radially disposed chromatin. They produce antibodies and contribute to resistance against microbial infections.
- Mast Cells: Identified by their cytoplasmic granules. They contain histamine (a vasodilator) and heparin (an anticoagulant).
- Lymphocytes: Can extravasate through endothelial pores into connective tissue for phagocytosis.
- Chromatophores (Pigment Cells): Irregularly shaped cells containing pigment granules (e.g., melanin in melanocytes).
Connective Tissue Fibers
Extracellular components that provide strength and determine tissue characteristics and functions. There are three types:
- Collagen Fibers: Formed by fibrocites, these fibers create a wide network. Their protein structure resembles a helix.
- Reticular Fibers: A fine network of intertwined threads surrounding and wrapping various organ structures. They are considered immature collagen fibers.
- Elastic Fibers: Independent fibers formed from elastin, capable of stretching and recoiling. Found in blood vessel walls.
Fundamental Amorphous Substance
A viscous gel-like solution surrounding fibers and cells, composed of mucopolysaccharides.
Varieties of Connective Tissue
- Collagenous Connective Tissue: Includes loose and dense types. Loose connective tissue fills spaces between organs and underlies the dermis. Dense connective tissue is rich in fibers and found in structures like eyelids.
- Reticular Connective Tissue: Characterized by abundant reticular fibers, forming a network that supports cells in organs like the spleen.
- Elastic Connective Tissue: Contains a preponderance of elastic fibers. Forms elastic ligaments and is found in the adventitia of blood vessels.