Types of tissue in the brain

can greatly simplify your understanding of the cellular composition of the many organ systems.

Overview of the Four Basic Tissue Types

covers body surfaces (epi, on + thelium, surface). Epithelial tissue consists of cells attached to one another to form an uninterrupted layer of cells that separates the underlying tissues from the outside world. The body's epithelium not only covers its obvious surfaces (such as the epidermis of the skin and the linings of respiratory, urinary, and digestive tracts) but also extends into all of the complex invaginations which form lungs, kidneys, sweat glands, digestive glands, liver, etc. Epithelial tissue provides the essential functions of protection; containment of body fluids; and transport in and out across body surfaces (absorption and secretion).

supports other tissues. Connective tissue consists of several cell types and extracellular products which, together, provide essential functions of mechanical reinforcement, immune surveillance, transport/diffusion of nutrients and wastes, and energy storage (fat).

is responsible for rapid long-distance signalling, coordination, and "thinking". Nervous tissue consists of highly specialized nerve cells and support cells which are derived from embryonic neuroectoderm and neural crest. [More]

A note on pathology nomenclature: The names of neoplasms reflect the fundamental nature of their source tissues. Thus a carcinoma is a cancer of epithelial origin, while a sarcoma is a cancer of mesenchymal (connective tissue or muscle) origin.

Parenchyma / Stroma: The parenchyma of an organ consists of that tissue which conducts the specific function of the organ and which usually comprises the bulk of the organ. Stroma is everything else - connective tissue, blood vessels, nerves, ducts. The parenchyma / stroma distinction provides a convenient way to circumvent the listing of tissue types when discussing an organ.

Examples:

  • The parenchyma of the kidney is (renal tubules and corpuscles). The blood vessels, nerves, and supporting connective tissue of the kidney comprise the stroma.
  • The parenchyma of the spleen is (mostly lymphocytes and other blood cells). The supporting fibrous connective tissue of the spleen comprises the stroma.
  • The parenchyma of the heart is (cardiac muscle cells). The nerves, intrinsic blood vessels, and connective tissue of the heart comprise the stroma.
  • The parenchyma of the brain is (nerve cells and glia). The blood vessels within the brain and the connective tissue associated with these blood vessels are stroma.
  • The parenchyma of the malignant neoplasm is cancer cells. Other tissues, including blood vessels, which grow to support the tumor are stroma.

Parenchyma is interesting. Because organ-specific function usually centers on parenchymal cells, histological (and physiological) accounts often emphasize parenchyma. Unfortunately, stroma is commonly ignored as just boring background tissue.

Pay attention to the stroma. No organ can function without the mechanical and nutritional support provided by the stroma. If an organ is inflamed, the signs of inflammation appear first in the stroma. (For an example of inflammation from liver, see .)

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