Overview of the Four Basic Tissue Types
Epithelial Tissue 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).
Embryonically, most epithelial tissues are derived either from ectoderm (e.g.,
epidermis) or endoderm (e.g., epithelium of trachea and lung).
Connective Tissue 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).
Embryonically, connective tissues derive from mesoderm or mesenchyme.
Nervous Tissue 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.
Muscle Tissue is specialized for gross movement by means of cellular contraction.
Embryonically,
muscle derives from mesoderm or mesenchyme.
A note on pathology nomenclature:
source tissues.
The names of neoplasms reflect the fundamental nature of their
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.
everything else -- connective tissue, blood vessels, nerves, ducts.
Stroma is
The parenchyma / stroma
distinction provides a convenient way to circumvent the listing of tissue types when discussing
an organ.
Examples:
1. The parenchyma of the kidney is epithelial tissue (renal tubules and corpuscles).
The blood vessels, nerves,
and supporting connective tissue of the kidney comprise the stroma.
2. The parenchyma of the spleen is connective tissue (mostly lymphocytes and other blood cells).
The
supporting fibrous connective tissue of the spleen comprises the stroma.
3. The parenchyma of the heart is muscle tissue (cardiac muscle cells).
connective tissue of the heart comprise the stroma.
The nerves, intrinsic blood vessels, and
4. The parenchyma of the brain is nervous tissue (nerve cells and glia).
The blood vessels within the brain and
the connective tissue associated with these blood vessels are stroma.
5. 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.
stroma.
If an organ is inflamed, the signs of inflammation appear first in the
(For an example of inflammation from liver, see WebPath.)
Historical note:
Ignoring inconspicuous tissue features can have consequences.
capillaries are seldom evident in tissue specimens.
they are often ignored and forgotten.
Stromal
Nothing calls them to one's attention, so
Unfortunately, just such inattention may have delayed for
decades the realization that interfering with tumor vasculature might powerfully inhibit tumor
growth.
(From: http://www.siumed.edu/~dking2/intro/4basic.htm)