Tissues: Epithelium Flashcards
Tissue
group of specialized cells
Four primary Tissues
Epithelium, Connective, Muscle, Nerve
Ematopoisis
formation of blood cells
Epethilium
sheet of tissues that covers a body surface or lines body cavity
- basal surface attached to basement membrane
- always connected to connective tissue
- avascular and inervative
- rapid regeneration (GOOD- are prone to lots of friction)
Two types of epithelium
covering/lining
glandular (protection, lubrication, chemical signaling)
Apical Surface
surface that is either on the outside or inside a lumen
Basement membrane
seperates the epethilium from the connective tissue
Functions of Epithelial Tissue
protection barrier permeability sensation absorption
Classification : Cell Layers
simple = one cell layer stratified = more than one layer pesuedostratified = really simple columnar
Classification : Cell Shape
Squamous = flat Cuboidal = square Columnar = tall
Squamous Epithelium
Simple Squamous
thin and flat
- 1 layer thick (delicate)
- found in linings of blood vessels and lungs (absorption)
Stratified squamous
- forms many layers thick (against physical and chem attacks)
- found on outside of body (epidermis, dermis)
Keratinized stratified squamous epithelium
apical layers of skin cells (tough and water resistant)
- packed with fibrous protein keratin
Nonkeratinized stratified squamous epithelium
resists abrasions but dries out (must be well lubricated)
- found in vaginal and oral cavities
Cuboidal Epithelium
Simple cubodial
occurs where secretion or absorption takes place (lining of kidney tubules)
Stratified cubodial
RARE, but found in ducts of sweat and mammary glands
Transitional Epithelium
tolerate repeated cycles of stretching without damage (urinary bladder)
- called transitional because cell layers change appearance (from stratified to more as they stretch)
Columnar Epithelium
Simple columnar
found where absorption or secretion occur (stomach small intestine, large intestine)
Pseudostratified columnar
cilia bearing cells found in portions of respiratory tract (nasal, trachea, bronchi)
Stratified columnar
RARE, but protect portions of pharynx, epiglottis, anus and urethra
Glands
typically multicellular and specialized for secretion
-goblet cells secrete mucus (trachea and parts of digestive tract)
Endocrine Glands
release hormonal secretions into interstitial fluid which then moves to blood (thyroid and pituitary gland)
NO DUCTS
Exocrine Glands
release secretion into ducts that carry it to an epithelial surface (skin)
HAVE DUCTS
Classification of Exocrine Glands (NTK! 86 & 87)
Merorcrine secretion: exocytosis (sweating)
Apocrine secretion: cell pinches off secretion (mammary glands but also exocytosis)
Holocrine secretion: fills a gland and bursts; no repair (sebum- gland that produces oil) ==> have to have a population of stem cells behind the gland to produce more cells
DUCTS
1 ducts = simple tubular glands and simple alveolar gland
Branching ducts = compound tubular glands and alveolar
Cell Connections
Tight Junctions
Gap Junctions
Desmosomes
(A) Gap Junctions
- cells held together by channel proteins
- allows free diffusion of ions and small molecules between cells (cardiac muscle- contractions)
(B) Tight Junctions
- close; prevent water and solutes between cells (permeability)
- lipid plasma membranes fused together with proteins in membrane
(C) Desmosomes
- strongest; allows cell to bend and twist without seperating
- like cable connection (one cell to another)
Ability of epithelial tissue to maintain and repair itself
(1) epithelium exposed to toxins, chemicals, pathogens, abrasions
(2) rapid regeneration (miotic life cycle)
(3) stratified epithelium, new cells arise from stem cells located in basal layer of tissue
Differentiation
non specialized cells (stem cells: hemocytoblasts) undergo genetically guided changes to become more specialized cells
First Body TIssues
Ectoderm
Mesoderm
Endoderm
Goblets
only type of unicellular gland in the body
