unit 1 Flashcards
epithelium
avascular tissue that covers the exterior body surface, lines internal closed cavities and body tubes that communicate with the exterior
epithelium forms what portion of glands?
the secretory portion and their ducts
epithelium provides
a selective permeable barrier between the external environment and underlying connective tissue
three principal characteristics of epithelium
closely apposed to each other by cell-to-cell adhesions via cell junctions
exhibit functional and morphological polarity
basal surfaces attach to an underlying basement membrane
what are the two extracellular structures separating epithelium from CT
basal lamina and basement membrane
basal lamina
structural attachment site for over-lying epithelial cells and underlying CT
what is the basement membrane
basal lamina and the underlying contributions of the connective tissue
all epithelia rest upon what
a basement membrane
are basal lamina and basement membrane synonymous?
no
what are the three layers of the basement membrane
lamina lucida, lamina densa, lamina fibroreticular
what are components of the basement membrane
type IV collagen, laminin
what is classification of epithelium based on?
number of cell layers and shape of the surface cells
simple squamous cells are usually joined together by what
intercellular junctions
where can simple squamous cells be found
lining Bowman’s capsule, blood and lymphatic vessels, pleural and abdominal cavities
what do simple squamous epithelium permit
diffusion and bidirectional movement of gases, fluids, and nutrients from the free surface to underlying tissue
simple cuboidal epithelium
provides protection, forms conduits for gland ducts, may be specialized for active secretion and absorption
where are simple cuboidal epithelium found
in glands, salivary ducts, pancreas and kidney
simple cuboidal epithelium may have
microvilli or cilia
where are simple columnar epithelium mainly found
in areas engaged in protection of wet surfaces, nutrient absorption, and secretion
simple columnar epithelium often have what on free surfaces
microvilli
where are stratified squamous epithelium found
in areas that need protection from abrasion, i.e. skin
where are stratified cuboidal epithelium usually found
lining ducts of sweat glands and exocrine glands
where are stratified columnar epithelium usually found
pharynx, larynx, conjunctiva of eyelids, major ducts of exocrine glands, anorectal junction, parts of the male urethra
two special classifications of epithelium
psuedostratified and transitional
pseudostratified epithelium
some cells do not reach the free surface, but all rest on the basement membrane
transitional epithelium
lines lower urinary tract, extends from major calyces to proximal part of urethra
microvilli
cytoplasmic projections on the apical surface of most epithelial cells
anchored to villin at the tip of the microvillus
terminal web
composed of actin filaments stabilized by spectrin, which anchors it to the apical cell membrane
stereocilia, in the repro track
immotile microvilli of an unusual length, function to facilitate absorption
stereocilia, in the ear
sensory epithelium that are sensitive to mechanical vibration, serve as mechanoreceptors
high density of actin cross-linked by espin
stereocilia organization
internal bundles of actin filaments that are cross-linked by fibrin
organization is similar to microvilli, longer, anchored by ezrin to the plasma membrane
cilia
hair-like extensions of the apical plasma membrane
primary cilia
function as signal receptors that sense the flow of fluid in organs - mechanoreceptors
mutations in PKD affect the development of primary cilia, leads to disease
nodal cilia
present only embryologically, establishes the left-right asymmetry of internal organs
glands are either
exocrine or endocrine
exocrine glands
release their secretory product into a duct or lumen of a hollow organ
endocrine gland
release their secretion into the circulation which distributes it to the target organs
three types of junctional complexes
occluding junctions, anchoring junctions, communicating junctions (gap junctions)
other names for occluding junctions
zonula occludens, tight junctions
anchoring junction types
zonula adherens, macula adherens, focal adhesions, hemidesmosomes
structural integrity of epithelium is maintained by
adhesion of the constituent cells both to each other and to structural extracellular matrix
adhesions are maintained by what two systems
cell membrane proteins that act as adhesion molecules
specialized areas of cell membranes are incorporated in cell junctions
occluding junctions function
establish a barrier between different compartments of the body and allow epithelial cells to function as selective barrier
occluding junction proteins
4 groups of transmembrane proteins:
Claudins
occludin
junctional adhesion molecule
tricellulin
anchoring junctions function
mechanical stability, through anchoring the cytoskeleton of one cell to the cytoskeleton of an adjacent cell
play a role in cell-to-cell recognition, morphogenesis and differentiation
types of cell-to-cell adhesion
zonula adherens, macula adherens
zonula adherens
interacts with network of actin filaments
requires Ca++
cadherins and nectins
macula adherens
interacts with intermediate filaments
desmogleins and desmocollins provide linkage between cell-to-cell membrane
types of anchoring cells to CT
focal adhesions, hemidesmosomes (found where cells anchor to extracellular materials like basal lamina)
gap junctions
allow for movement of larger molecules between cells
formed by connexin proteins, six connexin make a connexon
integument
includes the skin, nails, hair, sweat glands, and sebaceous glands
layers of the skin
epidermis, dermis, hypodermis
skin categorization
thick or thin
rete ridges
form evagination of epidermis into the underlying dermis
cell types of the epidermis
keratinocytes, melanocytes, Merkel cells, Langerhans cells
layers of epidermis
stratum corneum
stratum lucidum (only in thick skin)
stratum granulosum
startum spinosum
stratum basale
stratum basale
single layer of cells that rests on the basal lamina and continuously divides to replace cells
has extensive cell junction (desmosomes & hemidesmosomes)
also contain melanin, is transferred to melanocytes
keratinocytes in stratum spinosum
keratinocytes with intercellular bridges and centrally located nucleus
larger, several layers thick with apparent cytoplasmic processes or spines
stratum spinosum function
resist abrasion and shearing forces
many desmosomes connect cytoplasmic processes
where is an increase of keratin produced?
stratum spinosum, assembled into keratin filaments that make the cytoplasm eosinophilic
what projects into the spines of the keratinocytes? what do they do?
tonofibrils (large bundles of keratin), connect to desmosomes at tip and link to spine of neighboring cells
keratinocytes of stratum granulosum
stratified layer 2-5 cells thick, most superficial nonkeratinized epidermis
cytoplasm contain non-membrane bound granules that are strongly basophilic
keratohyalin granules
cystine and histidine rich proteins
precursors of flaggrin
flaggrin
promotes tonofibril formation and keratinization
what are lamellar bodies? what do their contents form?
cytoplasmic secretary granules
lipid-rich contents form extracellular sheets to create a barrier impermeable to water
when do cells undergo apoptosis in the epidermis?
as they exit stratum granulosum
stratum lucidum
only a few cell layers thick and only found in thick skin
highly refractive, contains eosinophilic cells where keratinization is well advanced
stratum corneum
15-30 layers thick
dead, flattened, desiccated cells filled almost entirely with keratin filaments
what is desquamation
when the most superficial cells of stratum corneum are shed
what is the major contributor to the protection/barrier function of epidermis?
stratum corneum
what is the predominant cell in the epidermis?
keratinocyte
how are melanocytes distributed??
to keratinocytes by phagocytosis
Merkel cell
ovoid cells with dense cytoplasmic granules
how do you get a Merkel disc?
Merkel cell + associated sensory nerve ending
mechanoreceptor, LIGHT TOUCH!
where are Langerhans cells found?
in all layers of the epidermis, but primarily stratum spinosum
Langerhans cells
star shaped, dendritic type cell
process and present cutaneous antigens to lymphoid cells
what are Langerhans cell essential for?
immune surveillance in skin
what are the two layers of the dermis?
papillary and reticular
what are the two parts of the epidermal-dermal junction?
dermal papillae and epidermal ridges (rete ridges)
what does the papillary layer of the dermis consist of?
loose CT, less abundant collagen fibers, fibroblasts, abundant mast cells and macrophages, some lymphocytes
what layer of the skin are blood vessels not found in?
epidermis
reticular layer of dermis
thicker, less cellular than papillary
dense irregular CT with abundant blood vessels and nerve fibers, thick bundles of type I collagen, and course elastic fibers
hypodermis
loose CT often with abundant adipose, large blood vessels and nerve fibers are observed in this layer
what does the hypodermis do?
loosely binds skin to underlying organ and structures
what is the most common nerve supply to the skin?
free nerve endings (lack CT or Schwann cell)
where do free nerve endings terminate?
in stratum granulosum, often reach stratum corneum
what sensations do free nerve endings convey?
fine touch, heat, cold, pain
what are the encapsulated sensory receptors?
pacinian corpuscles, meissner’s corpuscles, Ruffini’s corpuscles
what are pacinian corpuscles?
deep pressure sensors found in deep dermis/hypodermis
nerve endings surrounded by concentric layers of support cells
what are meissner’s corpuscles?
fine touch, vibration, and pressure sensors found in dermal papillae layer
nerve endings spiral thru corpuscle surrounded by few support cells
what are Ruffini’s corpuscles?
encapsulated mechanoreceptor that detects pressure, temp, and stretching
found in reticular layer of dermis
matrix cells
cells that give rise to keratinizing cells of hair shaft
dermal papilla (hair bulb)
tuft of loose CT at base of the hair bulb - vascular supply to hair follicle
where are sebaceous glands located?
between a hair follicle and its arrestor pili muscle in dermis
sebum
secretary product of lipid rich decomposed cells
what are sebaceous gland ducts composed of?
stratified squamous epithelium
what are eccrine sweat glands?
coiled secretory unit located deep in the dermis and straight duct that opens into the skin
what are the lumens of the secretory portion of the eccrine sweat gland lined by?
pseudostratified epithelium
what are the lumens of the ductus portion of the eccrine sweat gland lined by?
stratified cuboidal epithelium
stain darker!!
what system controls eccrine sweat glands and what are they used for?
autonomic control, thermoregulation (heat and stress)
what do apocrine sweat glands do?
secrete a thick, odorous fluid into hair follicles for an unknown function
apocrine sweat glands
large lumen tubular glands associated with hair follicles
what epithelium lines the secretory portion of apocrine glands?
simple cuboidal
goblet cell
terminal bar
cilia
keratinized cell
urothelium
dome shaped cell on top, tear drop shaped cell lower
mucous cell
elongated nuclei, clear cytoplasm
serous cell
acinus
meissner’s corpuscle
paccini corpuscle
sebaceous gland
apocrine gland
sebaceous gland
