Cell Physiology and Function [epithelial tissue]

epithelial cells - covers the body's external surfaces and lines internal organs

structural features (5)

has high cellularity [cells are closely packed together]

is avascular [no blood vessels] - nutrients enter by diffusion or absorption

has cell polarity [have distinct surfaces]

has cell junctions

rapid regeneration [replace damaged and dead cells. Important for protection and secretion]

distinct surfaces

apical surface [free surface of an epithelial cell that faces a space or cavity] [TOP]

basal surface [attached to the basement membrane] [BOTTOM]

types of cell junctions and function (3)

tight junctions

-prevent movement of substances between cells

gap junctions

-allow movement of ions and small molecules between cells

desmosomes

-strongly attach neighbouring cells together

types of epithelial layers

-simple [one layer of cells]

-stratified [multiple layers of cells]

types of simple epithelium

-cell shape

-nucleus

-function

-where

simple squamous epithelium

-flat cell

-flattened nuclei

-diffusion and filtration

e.g. lung alveoli and capillaries

simple cuboidal epithelium

-cube-shaped cells

-round nuclei in the centre of cell

-secretion and absorption

e.g. kidney tubules

simple columnar epithelium

-tall cells

-oval/elongated nuclei

-secretion and absorption

e.g. stomach and small intestine

Pseudostratified epithelium

-single layer of irregular shaped and different sized columnar cells

-lines the respiratory tract and secretes mucus [contains goblet cells that secrete mucus and cilia that move mucus along the respiratory tract]

e.g. trachea

[all cells contact the basement membrane]

types of stratified epithelium

-function

-where

stratified squamous epithelium

-protection against abrasion

-e.g. skin, mouth and oesophagus

stratified cuboidal epithelium

-protection and secretion

-e.g. sweat glands and salivary glands

stratified columnar epithelium

-protection and secretion

-e.g. male urethra and some gland ducts

transitional epithelium

-allows the urinary arteries to stretch

-e.g. ureters and urinary bladder

types of stratified squamous epithelium

-surface cells

-where

Keratinised stratified squamous epithelium

-flat, dead surface cells [no nucleus]

-cells filled with keratin

-e.g. skin

Non-keratinised stratified squamous epithelium

-flat, living surface cells [have nucleus]

-cells are not filled with keratin

-e.g. mouth and oesophagus

stratified epithelium function

protects against physical and chemical damage

glandular epithelium- epithelium tissue that secrete chemical substances e.g. hormones, enzymes

types of glands

exocrine glands

-secrete substances into ducts [e.g. sweat, mucus]

endocrine glands [ductless]

-produce hormones directly into the blood and surrounding tissue

naming micrograph

[always look at the cell at the top when naming]

functions of epithelial cells (6)

-protection [protects underlying tissues from injury, pathogens and chemicals]

-absorption [absorbs substances into the body]

-secretion

-diffusion [allows substances to move across a thin layer]

-filtration

-excretion