Multicellular organisms are a system of cells whose individual function contributes to success of the organism as a whole Your body is composed of about 100 trillion cells classified into about 200 types based on variations of structure and functionDifferentiation is the process in which a cell develops from an unspecialized to a specialized state2Image copied from: Nerkar AA and Gadegone MM. 2013. J Basic & Applied Zool. 66(3): 148-153.
Tissues are groups of similar cells that function together to perform specialized activitiesPrimary types of tissue–Nervous tissue–Muscle tissue–Epithelial tissue –Connective tissue3Fox SI. Human Physiology. 14thed. New York NY: The McGraw-Hill Companies Inc, 2016. p 11 and 12.
(intestinal epithelium)Intercellular junctions contribute to the structure and function of tissues4Tortora GJ. Principles of Human Anatomy. 9thed. New York: John Wiley & Sons Inc, 2002. p 57.Randall DJ, Burggren WW and French K Eckert Animal Physiology: Mechanisms and Adaptations. 5th ed. New York: W.H. Freeman, 2002. p 105.Hemidesmosome
Epithelial tissues consist of cells arranged in continuous sheetsEpithelial membranes consist of an epithelial layer anchored to an underlying basement membrane –Cutaneous membranes line body surfaces–Serous membranes line organs–Mucous membranes line the lumen of hollow organs open to the external environmentStratified epithelial membranes are specialized for protection