Tissues

Looking back on the topic, Hierarchy of the Body, one can define tissues as clusters of cells with similar functions within an organism. There are four main types of tissues: the epithelial, muscle, nervous, and connective tissues.

Muscle tissues aid in movement by contracting and responding to stimulations. The main types of muscle tissues are the skeletal muscles (which can be contracted voluntarily and is attached to the bones by tendons), the cardiac muscle (involuntary muscle in the heart responsible for its contraction), and the smooth muscles (involuntary muscles in the internal organs such as the kidney, digestive tract, and bladder).

Meanwhile, the epithelial tissues’ primary roles are to protect, secrete, and absorb. These are made up of a layer or layers of tightly packed cells. These are commonly seen as linings and coverings of organs and cavities, such as lungs, kidneys, skin, and mucous membranes. These tissues help in transcellular and intercellular transportation. They are bounded by special proteins, desmosomes, and hemidesmosomes. They gain their nutrition from the cellular membrane because they are not bounded by blood capillaries. They develop from the endoderm and mesoderm, or ectoderm from the embryological germ layer. Examples of epithelial tissues include the simple cuboidal epithelium tissue and the pseudostratified columnar epithelium tissue, which are personally illustrated through a 2D drawing below.

Lastly, the connective tissues support, connect various tissues and organs. They help in the function of the blood and lymph and muscle and bone formation. They develop from the mesoderm and are surrounded by blood capillaries. Connective tissues do not show any sort of arrangement for they are simply scattered in the matrix. They are bounded by the blood capillaries and they gain their nutrition from there. These can be found in the bones, nerves, ligaments, tendons, and blood. Examples of connective tissues include the areolar tissue, dense fibrous tissues, cartilage, adipose tissue, blood, and bone. The blood and the bone are personally illustrated through a 2D drawing below.