Because epithelial tissue forms a protective barrier, anything entering or leaving the body must cross it, playing a crucial role in regulating exchanges with the external environment and within the body.
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Epithelial tissue cells are tightly packed, forming a continuous sheet with a small amount of cementing material between them and almost no intercellular spaces.
Epithelial tissues can be found in the skin, the lining of the mouth, the lining of blood vessels, lung alveoli, and kidney tubules.
Epithelial tissues cover most organs and cavities within the body, forming a barrier to keep different body systems separate and regulate the exchange of materials.
The oxygen we inhale is absorbed in the alveoli, tiny air sacs in the lungs, where it diffuses into the bloodstream to be transported to the rest of the body.
Oxygen is transported to body cells by binding to hemoglobin in red blood cells, which are carried through the bloodstream to tissues where oxygen is released for cellular respiration.
Cells need oxygen for the functions of mitochondria, which are involved in energy production.
Blood collects waste from all parts of the body and carries it to the liver and kidneys for disposal.
Muscle cells facilitate movement through their contraction and relaxation.
Muscle cells are responsible for the movement of our chest during breathing, as their contraction and relaxation cause the chest to expand and contract, facilitating the process of inhalation and exhalation.