This section describes the tissues and their structures.

Histology: The Study of Tissues

Seeley pg. 136

Introduction

• The human body is composed of four levels of organization: cells, tissues, organs and body systems.
• Cells of similar structure & function are organized into tissues.
• There are four primary types of tissue in the human body:
  1. epithelial
  2. connective
  3. muscle
  4. neural.

Epithelial Tissue

Seeley pg. 102

• Structure of Epithelial Tissue

Epithelial tissue covers most internal & external surfaces of the body. In addition, epithelial tissue also forms many glandular structures as well. Epithelium consists almost exclusively of cells with very little extracellular material between them. Epithelial tissue often has one free surface that is not associated with other cells and a basal surface which is attached to a basement membrane. Epithelial tissue are avascular. Blood vessels do not penetrate the basement membrane to the reach the epithelium. Therefore, all gases, nutrients & waste products must diffuse across the basement membrane to & from blood vessels in the underlying connective tissue.

Tortora pg. 95

• Epithelial cells retain their ability to reproduce and therefore are capable of generating new cells to replace damaged epithelial cells.

• Classification of Epithelium

  • Epithelial tissue are classified according to the arrangement of cell layers & cell shape.

    • Arrangement of layers:

      1. Simple epithelium- consists of a single layer of cells with each cell extending from the basement membrane to the free surface.

      2. Stratified epithelium- consists of more than one layer of cells & only one of which is adjacent to the basement membrane.

      3. Pseudostratified epithelium- consists of a single layer of cells that are all attached to the basement membrane yet only some of the cells reach the free surface.

• Function of Epithelial Tissue

  • Functionally, epithelial tissues play an important role in diffusion, filtration, secretion, absorption, protection, movement of mucus and are also capable of great stretching.

Connective Tissue

Seeley pg. 113

Structure of Connective Tissue

• The essential characteristic that separates connective tissue from the other three tissue types is the presence of an abundant amount of extracellular matrix or material between its cells.

• The extracellular matrix has three major components:

  1. Protein fibers (ie. Collagen, reticular & elastin)

  2. Ground substances consisting of nonfibrous proteins and other materials

  3. Fluid

Classification of Connective Tissue

• The extracellular matrix is the basis for the classification of connective tissue into the three following subgroups:

  1. Matrix with mainly protein fibers (ie. Adipose)

  2. Matrix with protein fibers and ground substance (ie. Bone)

  3. Matrix with mainly fluid (ie. Blood)

Adipose Tissue

Bone

• Bone is a hard connective tissue that consists of living cells ( osteocytes) & mineralized matrix.

• Bone tissue is classified into two types:

  Compact (Dense) bone

Cancellous (Spongy) bone

Structure: Network of scaffolding characterized by bone trabeculae with large spaces between them that are filled with hemopoietic tissue. Osteocytes are located within the trabeculae. Function: Acts as a scaffolding to provide strength & support without the weight of compact bone. Location: Interior bones of the skull, the vertebrae, sternum, pelvis & also in the ends of the long bones.
	Seeley pg. 118

Blood

Structure: Various blood cells and a fluid matrix. Function: Transports O2, CO2, hormones, nutrients & waste products. Protects the body from infections, and is involved in temperature regulation and the clotting process.
	Tortora pg. 112

Muscle Tissue

• Structure of Muscle Tissue

• Muscle tissue consists of long, thin cells or fibers known as myocytes which are constructed to generate a force for contraction.

• Based on location and certain structural & functional characteristics, muscle tissue is classified into three categories:

  Smooth

Skeletal

Cardiac

Neural Tissue

McCance pg. 39

Structure of Neural Tissue

• Neural tissue is composed of highly specialized tissue called neurons.

• Neurons are composed of three major parts:

  1. Cell body- contains the nucleus & is the site of general cellular function.

  2. Dendrites- receives electric signals (action potentials) and then conduct these signals toward the cell body.

  3. Axons- conducts action potentials away from the cell body.

Basic Study Questions

  1.  What is the definition of histology?

  2.  What are the four primary tissues of the human body?

Additional Study Questions