epithelia lecture - BIO210 Anatomy

components of epithelial tissue

1) specialized cells

• stem cells develop into epithelial cells

2) extracellular protein

3) ground substance

• fluid around the cells

the majority of epithelia is:

cells - there is a large mass of cells

very little matrix

where is epithelial tissue?

sheets of cells that cover exposed surfaces, line body cavities, ducts and vessels

properties of epithelial tissue

• cellularity

• attachment to the basement membrane

• polarity

• avascularity

• regeneration

cellularity

the cells are closely bound to each other by cell junctions (tight junction, desmosome) making a wide sheet

attachment

the deepest (basal) layer is attached to the basement membrane

polarity

• opposite ends (superficial/deep) of the cells have distinct features

• the basal end of a cell is closer to the basement membrane (deep side)

• the apical end of the cell is closer to the superficial border

avascularity

lacking blood vessels. epithelia must be in close contact with other vascular tissue (usually connective tissue)

regneration

damaged tissue is regrown

layering of epithelial cells

• simple layer - 1 layer of cells (all cells contact the basement membrane)

• stratified layer - 2 or more cell layers deep, only the deepest touches the BM

• pseudostratified - 1 cell layer (layering appears to be stratified due to irregular shape)

cell shapes of epithelial tissue

• squamous

• cuboidal

• columnar

squamous shape

flat, irregular-shaped cells (eggs sunny side up)

cuboidal shape

cube-shaped cells

columnar

tall, thin cells (column-like)

1 cell layer names of epithelial tissue:

• simple squamous epithelia (flat irregular)

• simple cuboidal epithelia (cube-shaped)

• simple columnar epithelia (tall, thin cells)

2 or more cell layers of epithelial tissue:

• stratified squamous epithelia (flat, irregular)

• stratified cuboidal epithelium (cube-shaped)

• stratified columnar epithelia (tall, thin)

pseudostratified:

• only tall, thin cells

• pseudostratified columnar epithelial tissue

transitional epithelial tissue:

a stratified layering of multiple shapes

glandular epithelia

• exocrine glands - release secretions onto the surface of epithelia (like sweat or oil)

• glands are composed of epithelia cells

types of glands:

• serous glands

• mucous glands

• mixed exocrine glands

types of glands

• serous glands - secrete a serous solution - watery

• mucous glands - secrete a mucous secretion - mucus

• mixed exocrine glands - secrete both serous and mucus

mechanisms of exocrine release

• merocrine

• apocrine

• holocrine

merocrine

• secretions are released by exocytosis

• a vesicle fuses to the inside of the membrane releasing contents to the extracellular fluid

merocrine - exocytosis

• moving molecules out of the cell

• a vesicle fuses to the inside of the membrane releasing contents to the extracellular fluid

apocrine

• secretions are released when the apical end of the cell is shed

holocrine

• secretions are released when the cell membrane ruptures