5.1: The Study of Tissues

Histology

Study of tissues and how they are arranged into organs; microscopic anatomy

Organ

Made up of 2 or more types of tissues with a discrete boundary, that work together to serve a particular function

4 Primary Tissue Classes

Epithelial, Connective, Muscular, and Nervous

Tissue

A group of similar cells or cell products that arise from the same region of the embryo and work together to perform a specific structural of physiological role in an organ; composed of cells and matrix

Matrix

(extracellular fluid); composed of fibers (fibrous proteins) and a clear gel (ground substance, tissue fluid, extracellular fluid (ECF), interstitial fluid, or tissue gel. Composed of water, gases, minerals, nutrients, wastes, and other chemicals); amount varies depending on type of tissue

Embryonic Tissues

Single cell (fertilized egg); produces lots of identical, smaller cells then organizes into layers

Primary Germ Layer

Gives rise to all of the body’s mature tissues; most organs are composed of 2 or more primary germ layers

Ectoderm

Outer layer of primary germ layer; gives rise (develop into) to the epidermis and nervous systems

Mesoderm

A layer of loosely organized cells; middle layer of primary germ cell that gives rise to mesenchyme , gives rise to muscle, bone, and blood, among other tissues

Mesenchyme

Composed of fine, wispy collagen (protein) fibers and fibroblasts (branching cells) embedded in a gelatinous ground substance

Endoderm

Inner primary germ layer that gives rise to the mucous membranes of the digestive and respiratory tracts, digestive glands, and other tissues

Interpreting Tissue Sections

Histologists used preserving, sectioning (slicing), and staining tissues to study and show the tissues

Fixative

A chemical (formalin) that prevents decay or preserves a specimen(s)

Histological Sections

2-dimensional; specimen is cut into very thin slices (only 1-2 cells thick; thin enough for light to pass through); mounted on slides and artificially colored with histological stains to bring out detail

Longitudinal Section (l.s.)

Tissue cut in the long direction

Cross Section (c.s. or x.s.)

tissue cut perpendicular to the l.s.

Oblique Section

Tissue cut at an angle between l.s. and c.s.