About tissues in the human body

Today we talk about tissues in the human body. Muscle tissue is classified in three ways based on the tissue’s function, shape, and structure:

Smooth muscle tissue: So-called because it doesn’t have the cross-striations typical
of other kinds of muscle, the spindle-shaped fibers of smooth muscle tissue
do have faint longitudinal striping. This muscle tissue forms into sheets and
makes up the walls of hollow organs such as the stomach, intestines, and bladder.
The tissue’s involuntary movements are relatively slow, so contractions last
longer than those of other muscle tissue, and fatigue is rare. Each fiber is about
6 microns in diameter and can vary from 15 microns to 500 microns long. If
arranged in a circle inside an organ, contraction constricts the cavity inside the
organ. If arranged lengthwise, contraction of smooth muscle tissue shortens
the organ.

Cardiac muscle tissue: Found only in the heart, cardiac muscle fibers are
branched, cross-striated, feature one central nucleus, and move through involuntary
control. An electron microscope view of the tissue shows separate fibers
tightly pressed against each other, forming cellular junctions called intercalated
discs that look like tiny, dark-colored plates. Some experts believe intercalated
discs are not cellular junctions but rather special structures that help move an
electrical impulse throughout the heart.

Skeletal muscle tissue: This is the tissue that most people think of as muscle.
It’s the only muscle subject to voluntary control through the central nervous
system. Its long, striated cylindrical fibers contract quickly but tire just as fast.
Skeletal muscle, which is also what’s considered meat in animals, is 20 percent
protein, 75 percent water, and 5 percent organic and inorganic materials. Each
multinucleated fiber is encased in a thin, transparent membrane called a sarcolemma
that receives and conducts stimuli. The fibers, which vary from 10
microns to 100 microns in diameter and up to 4 centimeters in length, are subdivided
lengthwise into tiny myofibrils roughly 1 micron in diameter that are suspended
in the cell’s sarcoplasm.

Now you know about tissues in the human body


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