Connective Tissue Functions and Composition

Connective Tissue Functions

• Connective tissue has several essential functions in the human body, including material exchange through blood vessels, support and binding of other tissues like epithelia, blood vessels, and nerves, protection against infection, inflammation, and immune response.
• Wound healing involves collagen types I and III, and connective tissues help regulate the behavior of cells, including migration, proliferation, and differentiation.

Connective Tissues Composition

• Connective tissues originate from mesenchyme, derived from the mesoderm in the embryo.
• They comprise an extracellular matrix (ECM) made up of ground substances and fibers, and cellular components including resident and transient cells.

Connective Tissue Ground Substances Composition

• Ground substance is an amorphous gelatinous material that fills the spaces between fibers and cells in the ECM.
• Hyaluronic acid, a polysaccharide, is a component of ground substance, contributing to its viscous, slippery nature, making it a good lubricant.
• Proteoglycans, composed of a core protein bound to glycosaminoglycans (GAGs), trap water within ground substances.
• Glycoproteins like fibronectin, laminin, and osteopontin act as adhesion proteins, linking the components of the ground substance and the cell surface.

Connective Tissue Fibrous Components

• Three major types of fibers make up connective tissue: collagen fibers, reticular fibers, and elastic fibers.

Collagen Fibers

• Collagen fibers are the most abundant type of connective tissue fiber, providing flexibility and high tensile strength.
• They appear as wavy fibers with variable width, and at least 29 types have been classified.
• Type I collagen is found in bones, tendons, and the dermis of the skin, and is produced by fibroblasts and osteoblasts.
• Type II collagen is a component of hyaline and elastic cartilage, synthesized by chondroblasts.
• Type III collagen forms reticular fibres in organs like skin, muscle, and blood vessels. It is the first collagen type produced during wound healing and is later replaced by type I collagen.
• Type IV collagen is involved in forming basement membranes, located in the basal lamina, and is produced by epithelial cells.
• Type VII collagen anchors the epidermis to the basal lamina, synthesized by keratinocytes and fibroblasts.

Wound Healing and Collagen

• Wound healing involves the interaction of different cell types and the production of specific collagen types.
• Macrophages play a crucial role in wound healing by clearing debris, recruiting fibroblasts for tissue reconstruction, and inducing the production of type III collagen as part of the provisional ECM.
• As tissue remodelling takes place, type III collagen is gradually replaced by the stronger type I collagen, with support from macrophages, fibrocytes, and myofibroblasts.

Reticular Fibers

• Reticular fibers are fine fibrils composed of type III collagen, not easily visible under standard H&E staining.
• They provide a supporting mesh framework for soft organs like the spleen, red bone marrow, liver, and lymph nodes.
• Special stains like silver and PAS stain reticular fibres black/brown and pink, respectively.

Elastic Fibers

• Elastic fibers contain elastin, a protein that allows them to stretch and recoil through cross-linking molecules.
• These fibers have a branching appearance with a wavy appearance when relaxed.
• Fresh elastic fibers have a yellow color.
• Elastic fibres are present in tissues like the aortic wall, larynx, and ligamentum flavum in the vertebral column.

Marfan Syndrome

• Marfan Syndrome is an autosomal dominant disorder caused by a defect in the gene encoding the protein fibrillin-1.
• This syndrome affects multiple tissues including the aorta, skin, ligaments, and ciliary zonular fibres of the lens.

Connective Tissues Resident Cells: Adipocytes

• Adipocytes are specialized cells that store fat.
• There are two major types of adipose tissue: white adipose tissue (WAT) and brown adipose tissue (BAT).
• WAT, predominantly found in adults, stores energy as triglycerides and is a major contributor to obesity.
• BAT, more prevalent in infants and smaller amounts in adults, generates heat through thermogenesis to maintain body temperature.

Connective Tissue Transient Cells: Macrophages

• Macrophages are phagocytic cells, derived from monocytes in the blood.
• They can be fixed or transient, playing a role in defense and immune response.
• They phagocytose pathogens, dead cells, and red blood cells.
• Macrophages also act as antigen-presenting cells, displaying antigens on their surface through MHC (major histocompatibility complex) molecules to stimulate an immune response.

Connective Tissue Transient Cells: Mast Cells

• Mast cells have numerous secretory granules that obscure the nucleus.
• These granules store vasoactive and immunoreactive substances like histamine and heparin.
• Mast cells mediate inflammatory and allergic reactions.

Connective Tissue Transient Cells: Plasma Cells

• Plasma cells develop from B-lymphocytes after activation.
• They are oval-shaped, with a prominent Golgi apparatus and extensive rER.
• Their nucleus, often eccentrically located, has a characteristic "clock-face" appearance.
• Plasma cells play a crucial role in antibody production.

Types of Connective Tissues

• Loose (areolar) connective tissue is characterized by a loose arrangement of fibers and cells, with abundant ground substance.
• Dense irregular connective tissue has abundant collagen fibers arranged in random directions, providing high tensile strength and elasticity.
• Dense regular connective tissue features densely packed collagen fibres arranged in a parallel orientation, enabling resistance to tensile forces in one direction.

This quiz covers the essential functions and composition of connective tissues in the human body. It explores the roles of extracellular matrix, ground substances, and cellular components, alongside the importance of these tissues in processes like wound healing. Delve into the crucial aspects that make connective tissues vital for overall health.