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Tissue: Tissue is defined as the group of similar cells along with intracellular substances performing a specific function in the body.
Organ:Tissues arranged in a specific pattern form an organ. For example, stomach, heart, lungs
Organ system: When two or more organs interact by physical or chemical reaction in order to perform a common physiological function, is known as organ system. For example, digestive system, respiratory system.
Types of tissues:Based on the structure of cells, tissues are broadly classified into four different types namely, epithelial, connective, muscular and neural
Also known as epithelium, in which the cells are tightly packed with little intracellular space. The tissue has a free surface that faces the body fluid or the outside environment thus providing immediate lining for some part of the body. There are two types of epithelium tissue namely, simple and compound epithelium.
Simple epithelium: Composed of single layer of cells and is usually seen as a lining in body cavities, ducts and tubes. Based on the structural modification of the cells, it is further classified into three types, namely squamous, cuboidal and columnar epithelium.
A. Squamous B. Cuboidal C. Columnar D. Ciliated
Squamous epithelium: Usually found in walls of blood vessels and in air sacs of lungs, the squamous epithelium is made up of flattened, thin layer of cells with irregular boundaries. The cells of this epithelium generally perform functions like forming a diffusion boundary.
Cuboidal epithelium:As name suggests, this epithelium is made up of single layer of cube cells found usually in ducts of glands and tubular parts of kidneys. Their main function is to regulate secretion and absorption.
Columnar epithelium: As name suggests, these are single layer of tall and slender cells with their nuclei located in the base. These cells possess tall finger-like structures called microvilli which are seen in the walls of small intestine. They help in secretion and absorption.
Ciliated epithelium:Presence of cilia on cuboidal or columnar epithelium is defined as ciliated epithelium. They play a role in moving the particles in a specific direction. Usually found in nose, bronchioles and fallopian tubes.