Question 1: Define a tissue ? Describe various type of epithelial tissue ?

A tissue is an organized group of cells, similarly modified for a specific function.
Epithelial tissue covers surface, lines cavities and farms glands. Based on function epithelial tissue can be grouped into two. They are covering and lining epithehum and glandular or secretory epithelium.
Covering and lining epithelium :- Based on the number and arrangement of cell layers these are three kinds of covering and lining epithelium. They are
1. Simple epithelium :- single layered, specialized for secretion, absorption and filtration.
2. Compound or stratified epithelium :- Multi layered and specialized for protection.
3. Pseudostratified epithelium :- Single layered but the arrangement of cells give a stratified appearance, cells are specialized for secretion, discharge of mucus, elimination of foreign particles etc. Based on the shape and size and arrangements cells covering and lining epithelium are of four main types.
They are
1. Squamous epithelium :- Composed of thin, flat , disc
shaped and broad cells, arranged very closely like tiles on a
floor. It is specialized for diffusion , osmosis and filtration. It
is found in blood vessels, kidney tubules,
buccal cavity , vagina , urethra etc.

2. Cubical epithelium :- formed of cube like or prism like cells. This epithelium is specialized for excretion , secretion and absorption. It is found in glands and glandular ducts.
3. Collinear epithelium :- formed of tall column like or pillar like cells having striated free borders. Its function includes protection , absorption and secretion. It lines the pharynx , stomach , intestine , uterus etc.
4. Ciliated epithelium :- It is a modified columnar or cuboidal epithelium. Free borders ofcells are ciliated. These cilia are useful to move particles ofmucus in definite direction. It is found in nasal cavities, larynx, trachea etc.
Sensory and germinal epithelia are two modifications ofcov g and lining epithe-
5.Glandular epithelium  :- The cells are modified as glands. Based on the nature of products there are two types of glands namely secreting: glands and excreting glands .Eg. for secreting glands are salivary glands, liver, pancreas etc. and for excreting glands are kidney sweat glands etc. Glands can be unicellular or multicellular . Based on the presence or absence of ducts glands are grouped into exocrine glands are ducted glands and endocrine glands are ductless glands. The three kinds of exocrine glands are holocrine, merocrine and apocrine