TISSUES Flashcards
Four Basic Tissue Types
Epithelial
Connective
Muscular
Nervous
cells producing very abundant ECM
Connective
composed of elongated cells specialized for contraction and movement
Muscular
cells with long, fine processes specialized to receive, generate, and transmit nerve impulses
Nervous
cells responsible for the organ’s specialized functions
PARENCHYMA
cells of which have a supporting role in the organ, always made up of connective tissue (except in brain and spinal cord)
STROMA
line all external and internal surfaces of the body.
All substances that enter or leave an organ must cross this type of tissue.
composed of closely aggregated polyhedral cells adhering strongly to one another and to a thin layer of ECM
forms cellular sheets that line the cavities of organs and coyer the body surface
EPITHELIAL TISSUE
PRINCIPAL FUNCTIONS OF EPITHELIAL
Covering, lining, and protecting surfaces (eg, epidermis)
Absorption (eg, the intestinal lining)
Secretion (eg, parenchymal cells of glands)
generally have elongated nuclei,
Columnar cells
have flattened nuclei,
Squamous cells
have more spherical nuclei
cuboidal or pyramidal cells
The basal surface of all epithelia rests on a thin extracellular, felt-like sheet of macromolecules referred to as the ___
a semipermeable filter for substances reaching epithelial cells from below.
BASEMENT MEMBRANES
Nearest the epithelial cells
Thin, electron-dense, sheet-like layer of fine fibrils
BASAL LAMINA
Beneath the basal lamina
More diffuse and fibrous
RETICULAR LAMINA
self-assemble into a two- dimensional network of evenly spaced subunits resembling the mesh of a window screen,
Type IV collagen
: These are large glycoproteins that attach to transmembrane integrin proteins in the basal cell membrane and project through the mesh ,formed by the type IV collagen
Laminin
a short, rod-like protein and a proteoglycan, both of these cross-link laminins to the type IV collagen network, helping to provide the basal lamina’s three-dimensional structure. to bind the epithelium to that structure, and to determine its porosity and the size of molecules able to filter through it.
Nidogen and perlecan
contains type III collagen and is bound to the basal lamina by anchoring fibrils of type Vil collagen, both of which are produced by cells of the connective tissue
RETICULAR LAMINA
SPECIALIZATIONS OF THE APICAL CELL SURFACE
MICROVILLI
STEREOCILIA
CILIA
In epithelia specialized for absorption. L. villus, tuft), usually of uniform length.
- In cells such as those lining the small intestine, densely packed __ are visible as a brush or striated border projecting into the lumen.
microvilli
- Much less common type of apical process, best seen on the absorptive epithelial cells lining the male reproductive system.
- Increases the cells’ surface area, facilitating absorption.
- __ are typically much longer and less motile than microvilli, and may show branching distally.
Stereocilia
are long, highly motile apical structures, larger than microvilli and containing internal arrays of microtubules.
exhibit rapid beating patterns that move a current of fluid and suspended matter in one direction along the epithelium.
Cilia
most (if not all) other cell types have at least one short projection called a___, which is not motile but is enriched with receptors and signal transduction complexes for detection of light, odors, motion, and flow of liquid past the cell
primary cilium
TYPES OF EPITHELIA
Covering (or lining) epithelia
Secretory (glandular) epithelia
Organized into one or more layers that cover the surface or line the cavities of an organ
- Classified according to the number of cell layers and the cell morphology in the outer layer.
COVERING (LINING) EPITHELIA
contain one cell layer
Simple epithelia
contain two or more layers.
stratified epithelia
Based on cell shape, simple epithelia are further classified as
squamous
cuboidal
columnar
thin cells
squamous
(cell width and thickness roughly similar),
cuboidal
(cells taller than they are wide).
columnar
The very thin surface cells of ___ can be “keratinized” (packed with keratin filaments) or “nonkeratinized” (with relatively sparse keratin).
STRATIFIED SQUAMOUS EPITHELIUM
Lining of vessels (endothelium); serous lining of cavities: pericardium,pleura, peritoneum, (mesothelium)
simple squamous
Facilitates the movement of the viscera (mesothelium), active transport by pinocytosis (mesothelium & endothelium), secretion of biological active molecules (mesothelium)
simple squamous
Covering the ovary, thyroid
simple cuboidal
covering, secretion
simple cuboidal
Lining of intestine, gallbladder
simple columnar
Protection, lubrication, absorption, secretion
simple columnar
Epidermis
FUNCTION: Protection; prevents water loss
Stratified Squamous Keratinized
Mouth, esophagus, larynx, vagina, and canal
FUNCTION: Protection, secretion; prevents water loss
Stratified Squamous nonkeratinized
Sweat glands, developing ovarian follicles
FUNCTION: Protection, secretion
Stratified cuboidal
Ladder, ureters, renal calyces
FUNCTION: Protection, distensibility
Stratified TRansitional
Conjunctiva
FUNCTION: protection
Stratified Columnar
Lining of trachea, bronchi, nasal cavity
FUNCTION: Protection, secretion, cilia-mediated transport of particles trapped in mucus out of the air passages
Pseudostratified
(layers of cells with nuclei at different levels; not all cells reach surface but all adhere to basal lamina)
Pseudostratified
*is found mainly in the epidermis of skin, where it helps prevent dehydration from the tissue).
* Its cells form many layers, with the less differentiated cuboidal cells near the basement membrane.
* These cells become more irregular in shape and then flatten as they accumulate keratin in the process of keratinization and, are moved progressively toward the skin surface, where they become thin, metabolically inactive packets (squames) of keratin lacking nuclei.
STRATIFIED SQUAMOUS KERATINIZED EPITHELIUM
lines moist internal cavities (eg, mouth, esophagus, and vagina) where water loss is not a problem.
Here the flattened cells of the surface layer retain their nuclei and most metabolic functions.
Stratified squamous nonkeratinized epithelium
occurs in the excretory ducts of salivary and sweat glands.
Stratified cuboidal epithelium
is seen in the conjunctiva lining the eyelids, where it is both protective and mucus secreting
Stratified columnar epithelium
lines much of the urinary tract, extending from the kidneys to the proximal part of the urethra, and is characterized by a superficial layer of large, dome-like cells sometimes called umbrella cells.
Urothelium
Tall, irregular cells all are attached to the basement membrane.
. Their nuclei are at different levels and not all cells extend to the free surface, giving a stratified appearance.
* Example: lining of the upper respiratory tract
PSEUDOSTRATIFIED COLUMNAR EPITHELIUM
function mainly to produce and secrete various macromolecules may occur in epithelia with other major functions or comprise specialized organs called glands.
- may synthesize, store, and release proteins (eg, in the pancreas), lipids (eg, adrenal, sebaceous glands), or complexes of carbohydrates and proteins (eg, salivary glands).
SECRETORY EPITHELIA & GLANDS
abundant in the lining of the small intestine and respiratory tract, which secretes lubricating mucus that aids the function of these organs
Goblet cell
remain connected with the surface epithelium, the connection forming the tubular ducts lined with epithelium that deliver the secreted material where it is used.
Exocrine glands
lack ducts. Thin-walled blood vessels (capillaries) adjacent to endocrine cells absorb their secreted hormone products for transport in blood to target cells throughout the body
Endocrine glands
Glands can be:
Simple
Compound
Secretory portions can be ___, ___
Secretory portions can be tubular (either short or long and coiled) or acinar (rounded and saclike):
TYPES OF SECRETION
Merocrine
Holocrine
Apocrine
This is the most common method of protein or glycoprotein secretion and involves typical exocytosis from membrane-bound vesicles or secretory granules.
Merocrine secretion
Here cells accumulate product continuously as they enlarge and underga terminal differentiation, culminating in complete cell disruption that releases the product and cell debris into the gland’s lumen.
This is best seen in the sebaceous glands producing lipidrich material in skin.
Holocrine secretion
Here product accumulates at the cells apical ends, portions of which are then extruded to release the product together with small amounts of cytoplasm and cell membrane, Lipid droplets are secreted in the mammary gland in this manner
Apocrine secretion:
are key sites for ion and water transport, maintaining the body’s overall balance of salts and water.
Epithelia of kidney tubules
