Chapter 4: Tissues – Structure and Function in the Human Body

Tissues

Introduction to Tissues

Tissues are groups of cells with similar structure and function that work together to perform specific activities in the body. The study of tissues is known as histology.

• Definition: A tissue is a collection of similar cells and their extracellular matrix from the same origin that together carry out a specific function.

• Importance: Understanding tissues is fundamental to comprehending how organs and organ systems function.

The Four Basic Tissue Types

Main Categories

The human body is composed of four primary tissue types, each with distinct roles:

• Epithelial Tissue: Covers body surfaces, lines cavities, and forms glands.

• Connective Tissue: Supports, protects, and binds other tissues together.

• Muscle Tissue: Responsible for movement.

• Nervous Tissue: Initiates and transmits electrical impulses for communication.

Connective Tissue

Overview

Connective tissue is the most abundant and widely distributed tissue type in the body. It provides structural and metabolic support for other tissues and organs.

• Major Classes: Connective tissue proper, cartilage, bone, and blood.

Functions of Connective Tissue

• Binding and Support: Connects and supports other tissues (e.g., tendons, ligaments).

• Protection: Cushions organs and defends against pathogens (e.g., bone, adipose tissue).

• Insulation: Maintains body temperature (e.g., adipose tissue).

• Transportation: Transports substances throughout the body (e.g., blood).

Characteristics of Connective Tissue

• Common Origin: All connective tissues arise from mesenchyme, an embryonic tissue.

• Extracellular Matrix: Unlike other tissues, connective tissues are largely non-living extracellular matrix, which separates the living cells. This matrix is composed of ground substance and fibers.

Structural Elements of Connective Tissue

• Ground Substance: Unstructured material that fills the space between cells and contains fibers.

• Fibers: Provide support and include collagen, elastic, and reticular fibers.

• Cells: The primary cell types include fibroblasts (connective tissue proper), chondroblasts (cartilage), osteoblasts (bone), and hematopoietic stem cells (blood). Other cells include white blood cells, plasma cells, and macrophages.

Ground Substance

The ground substance is the medium through which solutes diffuse between blood capillaries and cells.

• Components:

  • Interstitial (tissue) fluid

  • Cell adhesion proteins (e.g., fibronectin, laminin)

  • Proteoglycans (e.g., glycosaminoglycans or GAGs)

• Function: Acts as a molecular sieve for nutrient and waste exchange.

Fibers

• Collagen Fibers: Tough and provide high tensile strength.

• Elastic Fibers: Long, thin fibers that allow for stretch and recoil.

• Reticular Fibers: Short, fine, highly branched fibers that form supportive networks.

Cells of Connective Tissue

• Fibroblasts: Produce fibers and ground substance in connective tissue proper.

• Chondroblasts: Produce matrix in cartilage.

• Osteoblasts: Produce matrix in bone.

• Hematopoietic Stem Cells: Give rise to blood cells.

• Other Cells: White blood cells, plasma cells, macrophages, and mast cells are involved in immune defense and tissue maintenance.

Areolar Connective Tissue: Model

Areolar connective tissue is a loose connective tissue that serves as a universal packing material between other tissues. It contains a variety of cell types and all three fiber types (collagen, elastic, reticular) in a gel-like ground substance.

• Key Cells: Fibroblasts, macrophages, mast cells, white blood cells, fat cells, plasma cells, lymphocytes, and nerve fibers.

• Function: Wraps and cushions organs, holds tissue fluid, and plays a role in inflammation.

Example: Areolar tissue is found beneath the skin and surrounding blood vessels, nerves, and organs.

Additional info: The provided diagram illustrates the cellular and fibrous components of areolar connective tissue, showing the relationships between different cell types and fibers.