Tissue (Epithelial) Flashcards
What does epithelial tissue do
-protects tissues from mechanical and thermal injury
-provides immune defenses, physical barriers, and prevents invasion by microorganisms
What are the additional functions of the epithelial
-Secretion: forms glands that produce hormones and oils; secreted into blood or ducts
-Transport into other tissues: selectivity permeable membrane; substances can cross through passive or active transport and enter other tissues
-Sensation: rich nerve supply; detects changes in internal and external environment
Taste buds are an example of specialized epithelial cells
What do epithelial tissue consist of
-consists of tightly packed cells linked by tight junctions and desmosomes
This makes cells impermeable and resistant to physical stresses and mechanical injury
Are epithelial tissue vascular or avascular
It is avascular (lacks blood vessels); it obtains nutrients and oxygen by diffusion from deeper tissue; limits thickness
Epithelium components: what does the basement membrane consist of?
Basal lamina - ECM is created by epithelial cells and has collagen fibers and ground substance
Reticular lamina - created by underlying connective tissue and has reticular fibers and ground substance
These two glue epithelial tissue to underlying connective tissue; anchor underlying blood vessels in place; provides barrier between epithelia and underlying tissues
What is the epithelium classified by?
It is classified by the number of cells and the shape of cells in the layers
Simple epithelial - single cell layer
Stratified epithelial - more than one cell layer
What are the classifications of the simple epithelial layer
Squamous cells - flattened
Cuboidal cells - short
Columnar cells - tall and elongated
Describe simple epithelial
-one layer thick
-adapted for transportation of substances between different tissues (some have microvilli for increased surface area, some have cilia for moving substances through hollow organs)
Describe this type of simple epithelial: simple squamous epithelium
-thin single layer of cells
-fried egg appearance
-rapid diffusion of substances (ions, oxygen, carbon dioxide, fluids) in air sacs of lung
-specific segments of kidney, tubules, and lining blood vessels
Describe simple cuboidal epithelium
-single layer of cube-shaped cells
-is thin so substances can diffuse across rapidly
-lines structures where diffusion is needed (certain kidney tubules, respiratory passages, the ducts of many glands, and thyroid gland
Describe simple columnar epithelialum
-single layer of rectangular-shaped cells
-has nuclei in basal portion of cell
-microvilli (small intestine) or cilia (uterine tubes and segments of respiratory tract) on apical plasma membrane
Describe pseudostratified columnar epithelium
-looks layered because nuclei is at various heights
-one layer thick with basal plasma membrane in contact with basement membrane
-in segments of respiratory tract and nasal cavity
-ciliated
What are the two transport processes in the epithelia
Paracellular transportation - substances leak in epithelial membrane; limited due to tight junctions that makes spaces between cells nearly permeable
Transcellular transportation - substances enter cell by crossing plasma membrane; diffuses across cytosol; exists cell through plasma membrane at opposite side
What is stratified epithelium
-more than one layer of cells
-protective barrier where subjected to high degrees of mechanical stress
What are the types of stratified epithelium
Keratinized stratified squamous epithelium
Nonkeratinized stratified squamous epithelium
Stratified cuboidal epithelium
Stratified columnar epithelium
What is transitional epithelium
It is a subtype of stratified epithelium; only found in urinary system; lines kidney, ureter, bladder, urethra; has cuboidal basal cell layers; ability of apical cell layers to flatten allows tissues to stretch
Describe glandular epithelial
-structure of epithelial; creates and secretes product from secretory cells
-is from epithelial tissue that migrated to underlying connective tissue
-classified by shape or how product is released
-is released by endocrine and exocrine
Describe exocrine glands of grandular epithelial
-products released onto surface of epithelium or lines hollow organ
-is secreted through epithelial lined duct
-local effects on cells in grand vicinity
Describe endocrine glands in epithelial
-secretes products, usually hormones; directly into bloodstream with or without ducts
-allows products to have systemic effects on other distant cells
What are the exocrine glands that help secrete products
Merocrine, Holocrine, Apocrine
What does merocrine do
Merocrine - used by majority of exocrine glands; products packaged by secretory vesicles for release by exocytosis into ducts
What does holocrine do
Holocrine - used by sebaceous gland in skin to secrete sebum; releases product when cell ruptures and dies; mitosis in gland base
What does apocrine do
Apocrine - rare secretion; parts of cytoplasm pinched off; lactates mammary gland
Describe keratinized stratified squamous epithelium
Keratinized stratified squamous epithelium - apical cellular layers are dead; no nuclei; has protein keratin; tissue is rough and resistant to friction; adapted for outer layers of skin
Describe Nonkeratinized stratified squamous epithelium
Nonkeratinized stratified squamous epithelium - apical cellular layers has nuclei; subjected to mechanical stresses where surface must remain moist; mouth, throat, esophagus, anus, vagina
Describe stratified cuboidal epithelium
Stratified cuboidal epithelium - rare in humans; two cell layers; lines ducts of sweat glands
Describe stratified columnar epithelium
Stratified columnar epithelium - rare in humans; part of certain exocrine glands; underlying basal lamina
