Biological Functions of Connective and Skeletal Tissues

Connective Tissue Functions and Components

Connective tissues provide a frame to attach the other tissues of the body, such as body structures, and to protect the internal organs. The intercellular substance of these tissues is very important and is reinforced by a matrix of fibers dispersed and interwoven, and a transparent amorphous extracellular matrix.

Specialized Cell Types

• Fibroblasts: Fixed cells, which are variable.
• Adipocytes; Monocytes: Accumulate fat; WBC migrants. When inflammation occurs, they turn into macrophages that engulf microbes.
• Lymphocytes: Produce antibodies.
• Mast cells: They produce heparin (anticoagulant function) and histamine, which increases the permeability of capillary walls.
• Chromatophores: Stem cells that are very bulky.

Fibers of Connective Tissue

• Collagen fibers: Abundant, very tough, and resistant to traction forces (found in skin, tendons, and ligaments).
• Elastic fibers: They are branched and merged, forming networks.
• Reticular fibers: Very thin and branch, forming nets; they are supporting structures of some organs.

Classification of Connective Tissues

• Loose connective tissue: Found throughout the body, in the mucous membranes and surrounding blood vessels. Combined with the adipose tissue, it is the subcutaneous layer of skin attaching to the underlying tissues.
• Dense: Very strong and very flexible, with many collagen fibers grouped in bundles (e.g., tendons attached to bone).
• Elastic: Formed by parallel bundles of elastic fibers.
• Reticular connective tissue: Comprising a network of reticular fibers, it underpins the red marrow.
• Adipose (Fat): Little substance formed by low extracellular fibrils; their cells are adipocytes, which serve as important energy reserves and only occur in insects and mammals (e.g., surrounding the kidney and heart).

Cartilaginous Tissue and Its Varieties

Cartilaginous tissue is skeletal tissue where the ground substance is formed by a network of collagen fibers in a gelatinous matrix that provides strength and elasticity (to form the bones of the embryo).

Types of Cartilage

• Hyaline cartilage: White appearance with few collagen fibers; it forms the skeleton of the fetus.
• Fibrocartilage: Has a lot of collagen fibers that provide much resistance; it is part of the intervertebral discs (pads and meniscus).
• Elastic cartilage: Many elastic fibers; it is found in the epiglottis and larynx.

Bone Tissue and Skeletal Structure

Bone tissue is the tissue of vertebrate skeletons; it provides rigidity, as the intercellular substance is impregnated by minerals precipitated as calcium phosphate, providing resistance. In this, there are spaces called "bony gaps": small cavities connected by some fine canaliculi. They contain bone cells, osteocytes.

Compact and Spongy Bone

• Compact bone tissue: The most durable and hard, found in the shaft of long bones and the outside of all bones. Intermolecularly, this is where osteocytes reside in concentric bony plates around Haversian canals with blood vessels and nerves.
• Marrow: Located inside the shaft and loaded with fat; this is yellow bone marrow.
• Periosteum: The connective tissue responsible for bone growth in thickness.
• Bone tissue (spongy): The inside of the short bones, flat bones, and long bone epiphyses form sheets that are projected in 3D. It produces large amounts of blood cells.