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BASIC TISSUES - EPITHELIAL TISSUES (General properties (Covers and lines…
BASIC TISSUES - EPITHELIAL TISSUES
General properties
Covers and lines body
Functional units of secretory glands
Cells closely packed with little spaces between (effective barrier)
One free (apical) surface to outside or an open internal space (lumen)
Basement membrane anchors to underlying connective
Lack direct blood and lymphatic supply so receive from connective
Polarity (specific top and bottom)
Derived from ectoderm and endoderm (some meso)
Classification
Number of layer
Simple - one cell layer
Stratified - 2 or more
Pseudostratified - single irregularly shaped
Shape
Squamous - flattened
Cuboidal - square
Columnar - rectangular
Surface specialization
(non) keratinised
(non) ciliated
Types
Simple
Squamous
Function: diffusion and filtration
Lines all blood vessles, pulmonary alveoli
Cuboidal
Function: excretion, secretion and absorption
Line kindey, tubules, ducts
Columnar
Function: excretion, secretion and absorption
Lines digestive tract, uterine tubes and respiratory passageways
Stratified
Squamous
Function: keratin - protection (epidermis of skin) and non keratin - protection and pliability (lines oral and nasal cavity and vagina)
Cuboidal
Function: strengthening luminal wall (large ducts of sweat, pancreas and salivary glands
Transitional
Function:distension (walls of uterus and bladder)
Numerous layers of rounded cells
Pseudostratified
In bronchus
Several layers of nuclei
Cells in contact with basement membrane
Functions of covering epithelia
Protection - mechanical and infections
Selective permeability - prevent loss of fluid
Absorption
Active transfer
Removal of particles (cilia)
Surface specializations
Microvilli - Absorption
Cilia - Transport
Specialization in cell junctions
Tight junctions: closely associated areas of 2 cell membranes forming an impermeable barrier to fluid
Adherens junctions: mediate cell contact and participate on cellular communication, migration
Desmosomes: cell junctions and mediate strong adhesion between epidermal keratinocytes
Gap junctions: intercellular channels involved in cell communication and NB in keratinocyte growth and differntiation
Epithelial glands
Glands based on no. of cells
Unicellular - one celled gland
Multicellular
Many celled gland
Majority
Secrete mucous to protect
Organized collection of secretory epithelial cells
Most develop as epithelial outgrowths into underlying CT
Primarily involved in secretion
Exocrine - remain connected to surface by excretory ducts
Endocrine - lack excretory duct, product released into blood
Exocrine Gland
Simple - unbranched duct
Compound - branched duct
Secretory units simple tubes/ clusters of units = acini
Secretions through ducts
Classification
Simple tubular gland is straight and tubular
Simple branched tubular gland is branched and tubular
Simple coiled tubular gland is coiled
Simple alveolar gland is sac like
Simple branched alveolar gland is branched and sac like
Compound tubular gland is tubular
Compound alveolar gland is tubular and flask like
Compound tubuloalveolar gland is branched
Endocrine Gland
Lack ducts
May be discrete organs - primary function production and secretion of hormone eg. pituitary
Secrete hormones into capillaries/ lymphatic system
Types of secretion
Merocrine (exocytosis)
Glycoproteins, water and salt
Opens to surface
Cholinergic
Apocrine (pinching off)
Adrenergic
Milky soln and pheromones
Larger than merocrine glands
Excretory duct opens into canal of hair follicle
Secretion starts at puberty
Holocrine (shedding of whole cell)
Protective lipids
Inactive during childhood