tissues Flashcards
four main tissue types
epithelia, connection, muscle and neural
epithelial tissue
covers exposed surfaces, lines internal passageways and chambers
-forms glands
connective tissue
fills internal spaces, provides structural support for other tissues, transports materials within the body and stores energy reserves
ie. blood and adipose
muscle tissue
specialized for contraction!
neural
carries information from one part of body to another in form of electrical impulses (TRAVELS!)
what does epithelia include and where is it found
- epithelia: layers of cells covering internal or external surfaces
- glands: structures that produce fluid secretions
locations:
- cover exposed surface of body (skin; outside world)
- form surface of skin
- line digestive, respiratory, reproductive and urinary tracts
- line internal cavities and passageways (chest cavity, fluid-filled spaces in brain, inner surfaces of BV, and chamber of heart
epithelial tissue characteristics
- cellularity: composed almost entirely of generalized cells bound closely by cell junctions
- polarity: has exposed (apical = free side) and attached (basal = part of tissue that almost always attaches to CT) surface; cytoplasmic components are unevenly distributed but tend to go towards basal to prevent damage
- attachment: base bound to basal lamina = basement membrane
- avascularity: lacks BV therefore obtaining nutrients via diffusion or absorption
- regeneration: high rates of cell division (mitosis); continuously replaced through division of stem cells in epithelium
epithelial tissue functions
- provide physical protection - protects internal and exposed surfaces from abrasion, dehydration, and destruction by chemical/biological agents
- control permeability - substances entering or leaving; barrier regulated and modified by response to stimulus (ie when calluses form on hands)
- provide sensation - have large sensory nerve supple that provide info about external and internal environments
- provide specialized secretions - gland cells produce secretions (secretions released onto surface of epithelium or onto surrounding interstitial fluid & blood)
specializations of epithelial cells
microvilli
- cells which line internal passageways
- abundant where absorption and secretion occur
- ie. digestive and urinary tracts (small intest.)
cilia
- moves substances across cell membrane
- lining respiratory tract (move mucus from lungs towards throat - swallowed or expelled by coughing)
-damage by abrasion or toxic compounds can stop movement, block flow of mucus, leading to infection of disease
intercellular connections: extensive areas of PM
cell adhesion molecules (CAMs)
- transmembrane proteins interconnection large areas of opposing PMs
intercellular cement
- thin layer of proteoglycans binds adjacent cells
intercellular connections: cell junctions
tight junctions, gap junctions, and desmosomes
tight junctions
lipid portion of 2 PMs tightly bound by interlocking membrane proteins
- * prevents passage of water and solutes btwn cells
- isolated contents of lumen from basolateral surface of ephithelium
keeps enzymes, acids, and wastes of digestive tract lumen from damaging underlying tissues and organs
gap junction
interlocking proteins = connexons (channel proteins)
- allows small molecules and ions to pass quickly from one cell to another
- in cardiac and smooth muscle; allows for coordinated muscle contractions
desmosomes
transmembrane; CAMs and proteoglycans link opposing PMs
- * bound/anchored by cytoskeleton (give strength)
- very strong, can resist stretching and twisting
- in areas exposed to mechanical stresses: stretching, twisting, bending
- in superficial layers of skin (damaged skin lost in sheets vs. individual cells: peel not flake after a sunburn)
classifying epithelia
layers = simple (single layer), stratified (more than one layer), pseduostratified (one layer than looks like multiple; columnar in shape
shapes = squamous (squished), cuboidal (cubes/square), columnar (rectangle), transitional (stratified and no cell shape)
simple squamous
- fragile most delicate (smallest distance from apical to basal)
- in protected areas where diffusion occurs
- location: lining of small BV and lungs
stratified squamous
- where mechanical stresses occur (toughest)
- surface to skin (keratin used to keep skin strong and protective)
simple cuboidal
- where secretion and absorption occur (often organized in rings)
- glands, ducts (pancreas and salivary glands)
pseudostratifed ciliated columnar
lining portions of respiratory tract (upper parts)
- sometimes have cilia
- nuclei doesnt line up giving it the appearance of multiple layers when it is just one layer
simple columnar
fx. = protects, secretes, and absorbs
- lining of stomach, intestine, gallbladder, uterine tubes
stratified columnar
fx. = protects
- small areas of pharynx, epiglottis, anus, mammary gland, salivary gland duct
glandular epithelia
glands= collection of specialized cells or cells derived from epithelia cells that produce secretions
endocrine glands and exocrine glands
endocrine glands
ductless glands - make hormones
- release hormones which enter bloodstream
- exocytosed into ECF to have its effects
ex. thyroid gland, pituitary gland
can be..
- part of epithelial surface (lining of GI tract)
- or found in separate organ (pancreas, thyroid)
exocrine glands
has ducts! produce exocrine solutions; no hormones (made and released directly into duct…travel via duct… end up on epithelia surface)
ex. enzymes entering digestive tract perspiration on the skin, tears in the eyes, milk from mammary gland
exhibit several methods of secretion
- classified by mode of secretion and by structure of gland cells and associated ducts
