Histology

Histology is a branch of anatomy. The term histology literally means "the study of the tissues" of the body, but it has come to mean the study of the structure of the body with microscopes. Tissues, which can be thought of as the components of organs, are anatomical structures composed of cells, extracellular matrix, and interstitial fluid. Tissues are precisely defined by the requirement that the tissue be composed of cells that are similar in form and function. Four basic tissue types are recognized: epithelial, connective, muscular, and nervous tissues. Each of the basic tissue types has several subtypes.

Stained histological preparation on a microscope stage. Source: WikiMedia Commons.

Other Names

Related Terms

Microscopic anatomy
Microscopy

Types

Histology subject areas

• General histology
• Special histology

Histological technologies

• Light microscopy
• Electron microscopy

Description

Histology is traditionally divided into two fields of study: general histology and special histology. General histology is the study of the tissues themselves, whereas special histology is the microscopic study of the structure of organs of the body.

General Histology

General histology examines the composition of each of the tissue types, including the nature of its cells and extracellular matrix. Tissues types are classified as subtypes of four basic tissue types: epithelial, connective, muscular, and nervous tissues.

Epithelial tissues

Epithelial tissues cover and line surfaces of body parts, and make up the secretory units of endocrine and exocrine glands. Epithelial tissues are composed of sheets or clusters of contiguous cells with little extracellular matrix, except a basal lamina beneath the basal surface of the epithelial cells. Epithelial tissues are classified into the following groups:

• Surface epithelium
• Glandular epithelium
  • Exocrine glandular epithelium
  • Endocrine glandular epithelium
• Sensory epithelium

Connective tissues

Connective tissues bind together, support and protect body structures. They are composed of cells and extracellular fibers (collagen and elastic fibers), embedded in ground substance and interstitial fluid. Connective tissues are classified into the following groups:

• Connective tissues proper
  • Fibrous connective tissues
  • Adipose tissues
• Specialized connective tissues
  • Cartilaginous tissues
  • Bony tissues
  • Dentin and Cementum of teeth
  • Hematopoietic tissue
  • Lymphoid tissue
  • Connective tissues in fluid or gel form, e.g., Blood and Lymph

Muscular tissues

Muscular tissue is the basic tissue characterized by the ability to contract upon stimulation. Muscular tissues are composed of elongated, excitable, and contractile cells, usually arranged in parallel. Muscular tissues are classified into the following types:

• Smooth muscle tissue
• Striated muscular tissues
  • Skeletal muscle tissue
  • Cardiac muscle tissue

Nervous tissues

Nervous tissue is the principal component of the nervous system. Nervous tissues are composed of excitable cells (neurons) with long processes that make synaptic interneuronal connections, and supporting cells (glia). The nervous tissues can be classified into the following types:

• Central nervous system tissues
  • Gray matter
  • White matter
  • Reticular formation
  • Ependyma
• Peripheral nervous system tissues
  • Nerve fascicle
  • Ganglion

Special Histology

Special histology is the microscopic anatomy equivalent of systemic anatomy in gross anatomy. Thus special histology is also known as histology of the organ systems, and is usually subdivided into the following areas:

• Histology of the Skeletal System
• Histology of the Articular System
• Histology of the Muscular System
• Histology of the Alimentary System
• Histology of the Respiratory System
• Histology of the Urinary System
• Histology of the Genital Systems
• Histology of the Endocrine Glands
• Histology of the Cardiovascular System
• Histology of the Lymphoid System
• Histology of the Nervous System
• Histology of the Sense Organs
• Histology of The Integument

Related Professions

A histologist is a scientist who studies the structure of the body using a microscope.
An electron microscopist is a scientist who studies the structure of body parts with an electron microscope.
A pathologist is a medical doctor who examines samples of body parts to look for signs of disease, usually with a microscope.
A histotechnologist is a professional who produces histological preparations for anatomical or pathological examination.

History

Histology was a very active field of biological research in the 19th century. Improvements in microscope construction and the introduction of staining procedures led to the rise of the field pioneered earlier by Malpighi and Bichat.
Marcello Malpighi (1628-1694) is sometimes called the "Father of Microscopic Anatomy". Using a primitive compound microscope, he was the first to described pulmonary alveoli, capillaries, renal corpuscles, splenic corpuscles, and the Malpigian layer of the skin.
Marie François Xavier Bichat (1771-1802) can reasonably called the "Father of Histology" as he was the first to systematically study the tissus ("textures"), which he considered to be the elemental building blocks of the body. Eschewing the use of microscopes, Bichat used dissection to identify 21 tissues.
The development of achromatic lenses, which reduced chromatic and spherical aberrations, in the 1820s permitted the production of improved compound microscopes. After a couple of decades of growth of the histological literature, Rudolph Albert von Kölliker (1817-1905) was able to produce a landmark textbook, Handbuch der Gewebelehre des Menschen (1852).
Advances in histology in the late 19th century were largely driven by the development of empirical and histochemical staining procedures^[1], embedding media, and microtomes^[2]. Joseph von Gerlach's (1820-1896) stain (a solution of ammonia carmine and gelatin) was the first published staining protocol (1858).
The 20th century saw further progress in histochemistry, including the development of enzyme histochemistry, autoradiography, immunohistochemistry and in situ hybridization. Important innovations were also made in light microscopes, leading to phase contrast microscopy, differential interference microscopy, fluorescence microscopy, and confocal microscopy. The electron microscope was invented in the mid-century, and developed into transmission and scanning electron microscopes that allowed studies of the fine structure of cells and organelles.

How Histology Was Named

in Über Histologie und eine neue Eintheilung der Gewebe des Menschlichen Körpers (1819), August Mayer (1787-1865) coined the term histologie^[3] to mean "the study of the tissues of the body", from the Greek words ἱστός (histos, "web" or "warp") and λόγος (logos, "word" or "treatise"). The term came into common usage in the 1840s. The English word histology probably came from the German histologie via the French histologie.

Other Resources

Mills SE. Histology for Pathologists, 3rd ed. Baltimore: Lippincott Williams & Wilkins, 2006.

References

1. ↑ Clark G and Kasten FH. History of Staining. Philadelphia, Williams & Wilkins, 1983.
2. ↑ Bracegirdle B. A History of Microtechnique: The Evolution of the Microtome and the Development of Tissue Preparation. London: Heinemann, 1978.
3. ↑ Bracegirdle B. The history of histology: A brief survey of sources. Hist Sci. 1977; 15:77-101.

External Links

Histology-World
Dr. H. Jastrow's Electron microscopy atlas of cells, tissues, and organs
Bergman, Afifi & Heidger's Atlas of Microscopic Anatomy - A Functional Approach, 2nd ed.
Moran & Rowley's Visual Histology Text-Atlas
National Organization for Histotechnology