Blood is a liquid connective tissue, filling the cardiovascular system of vertebrate animals, including humans and some invertebrates. It consists of a liquid part plasma and formed elements: leukocyte cells and post-cellular structures: erythrocytes, and platelets. It circulates through the system of vessels under the action of the force of the rhythmically contracting heart and does not directly communicate with other tissues of the body due to the presence of histohematological barriers.
Tear is a fluid produced by the lacrimal gland of the eye of mammals. Transparent, slightly opalesces, has a weakly alkaline reaction. The main part (up to 99%) is water, the rest consists of inorganic substances (sodium chloride, sodium carbonate and magnesium, as well as sulfuric and phosphoric calcium). Bactericidal properties are given to tears by the enzyme lysozyme. The composition of tears also includes 0.1% other proteins.
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