5 TOB Epithelia & Glands

• Epithelial cells: tightly packed in single/multi-layered sheets, have apical/basal polarity, make a SMALL amount of ECM components
• CT cells: more isolated, less polarized, make a VARIABLE amount of ECM components

• 1) covering and lining epithelia
• 2) glandular epithelia
• 3) sensory epithelia

there is little extracellular space between cells

using cell adhesion molecules that form specialized cell-cell junctions to prevent tearing

• a thin layer composed of the basal lamina (secreted by the epithelium) and the reticular lamina (secreted by the connective tissue)
• it provides physical support, a substrate for attachment, and a mesh for filtration

TRUE, blood vessels that nourish the epithelium are located in ADJACENT connective tissue

Yes. Ample nerve endings. 

it has a high capacity for renewal by stem cells, especially in epithelia that are subjected to wear and tear such as skin

ALL THREE! diverse in origin; derived from all three germ layers (ectoderm, mesoderm, & ectodeterm)

• the apical surface
• however in some cases (stratified or pseudostratified) not every cell in an epithelium reaches the surface
• the cells usually display apical-basal polarity

• apical surface
• (eg. microvilli in the intestine, stereocilia in the epididymis, cilia in the trachea)

it can be specialized for adhesion to underlying connective tissue, or folded and interdigitated with its neighbors (eg. kidney tubules)

• cell-cell junctions (3 types basically)
• 1) tight junctions: seal the epithelium
• 2) adherens junctions/desmosomes: bind neighbors together
• 3) gap junctions: allow intercellular communication

• basement membrane
• it's usually made up of two structures, the basal lamina & the reticular lamina

• forms a continuous 50-80 nm thick layer beneath the epithelial cell's basal plasma membrane
• it's composed of collagen type IV, laminin, heparan sulfate proteoglycan, & and a number of other proteins that form a finely fibrillar meshwork

• in addition to the basal lamina, the recticular lamina makes up the basement membrane
• it's an underlying layer of small collagen fibrils (reticular fibers, lots of collagen type IV) embedded in an amorphous matrix

planar cell polarity (the difference between apical & basal surfaces of epithelial cells) exists to build planar-patterned structures; skin, hair, auditory hairs cells, & cilia

• 1) protection:  e.g. epidermis of the skin provides mechanical protection, waterproofing & insulation
• 2) absorption: eg. epithelial lining of small intestine absorbs nutrients
• 3) reproductive: seminiferous tubule (epithelia contains sertoli cells)
• 4) secretion: eg. mucous by goblet cells
• 5) sensory reception: smelling, hearing, seeing
• 6) surface transport: eg. tracheal cilia cells move mucous from lungs toward oral cavity
• 7) trans-epithelial transport: kidney tubules transport salt & water from the lumen of collecting tubules back into bloodstream through the interstitial space
• 8) contraction of myoepithelial cells: eg. to squeeze milk from excretory lobules of mammary glands
• PARTTSS C

• 1) by the number of cell layers
• 2) by the shape/height of cells
• 3) whether they are ciliated or non-ciliated 

• signifies a single layer of epithelial cells
• typically found in tissues specialized for absorption & secretion but NOT subject to extensive wear & tear
• eg. endothelium, mesothelium, bowman’s capsule, distal and proximal convoluted kidney tubule, small intestine, lung alveoli

• many layers (two or more) of epithelial cells
• found in tissues SUBJECTED to wear and tear
• eg. skin, oral cavity, esophagus, anal canal, vagina

the shape of epithelium cells is classified by observing their most apical (outermost) layer

cells that are thin, flat & scale-like

cube-shaped cells

cell that are taller than they are wide

• a single layer of thin, flat & scale-like cells specialized for filtration, diffusion, osmosis & secretion
• 1. cells lining capillaries (endothelium)
• 2. serosal cells lining mesentery
• 3. cells lining Bowman's capsule of kidney
• 4. cells lining lung alveoli

• mesothelium - a form of simple squamous
• lines body cavities and allows passage of tissue fluids into and out of these cavity by diffusion (also lubricates to prevent friction)
• 

• endothelium - a form of simple squamous epithelia found in blood vessels
• these cells are specialized for passive transport (diffusion) of fluids

• endothelial cells of capillary (cross-section)
• simple squamous epithelium
• 

• a single layer of cube-shaped cells specialized for secretion and absorption
• 1. cells in kidney tubules

• collecting tubule in kidney made up of simple cuboidal epithelium 
• secretory, excretory & absorptive functions

• simple columnar epithelium of small intestine
• specialized for absorption

• single layer of cells whose height is greater than their width specialized for secretion and absorption
• these cells may or may not be ciliated
• 1. intestinal epithelium cells

• epithelial cells that appear to be stratified (have more than two layers) because cell nuclei look like they're in a different layer, however each cell actually rests on the basement membrane and there's really only a single layer of cells
• 1. ducts in the male reproductive system: EPIDIDYMIS 
• 2. respiratory tract: TRACHEA
• these cells may be ciliated, and if so are specialized for secretion and propulsion of mucus by beating ciliary action
• *when in doubt whether something is pseudostratified or stratified cuboidal or columnar, GUESSING pseudostratified means you will be right 99% of the time

• pseudostratified columnar epithelium (of the trachea)
• specialized for propelling mucus & debris toward the throat

• consists of flattened (squamous) cells on the surface of multiple layers of cells; usually protective
• 1. keratinized/cornified: differentiating cells formed by mitosis at the basal layer that make a lot of keratin, lose their nuclei, & move apically to replace the outermost squamous layer of cells (eg. skin)
• 2. non-keratinized/non-cornified (moist): cells that produce less keratin & apical squamous cells do not lose their nuclei (eg. esophagus)

• stratified squamous keratinizing epithelium of thin skin
• specialized for protection, waterproofing

• stratified squamous keratinizing epithelium of thick skin
• top layer = stratum corneum (dead)

• stratified squamous NON-keratinizing (hypokeratinizing) epithelium
• found in vagina, oral cavity, esophagus & anal canal 
• nuclei present in surface layer

• multiple layers of cube-like cells found in epithelium lining large glandular ducts
• they're specialized for protection

• stratified cuboidal epithelium
• lines large excretory ducts of exocrine glands such as salivary gland; functions in protection

• multiple layers of cells whose height is greater than their width specialized for secretion and protection
• 1.epithelium lining of very large glandular ducts.
• 2. portions of male urethra
• (others: ocular conjunctiva of the eye, parts of the pharynx & anus, female's uterus, male's vas deferens)

stratified columnar epithelia

• unusual stratified cuboidal epithelium whose appearance varies depending on whether it's contracted or expanded
• it's specialized for distension and contraction to accommodate the changes in volume of urine 
• apical cells are dome shaped, some are bi-nucleated
• 1. lining of renal pelvis
• 2. ureter
• 3. urinary bladder
• 4. initial part of urethra

• transitional epithelium of urinary bladder
• has umbrella cells & occasional bi-nucleated cells in superficial layer; is specialized for waterproofing, distention

• single or groups of cells specialized for secretion
• glands are derived from epithelia (glandular epithelia)

exocrine and endocrine

• glands that secrete secretions into the bloodstream through the interstitial space
• they do NOT have ducts and are NOT all derived from epithelia

glands that release their secretions into ducts continuous with the surface epithelium of an organ (eg. in skin or gastrointestinal tract)

• 1. the number of cells in the gland: unicellular or multicellular
• 2. the duct system: simple or compound
• 3. architecture of terminal branches: tubular or acinar
• 4. nature of secretion: mucous or serous
• 5. mode of secretion: merocrine, apocrine, holocrine

• either do not branch or branch only once
• type of exocrine gland classification

• branch repeatedly to form a branched tree
• type of exocrine gland classification

• form terminal tubular lobules
• type of exocrine gland classification

• form terminal rounded, grape-shaped, lobules
• type of exocrine gland classification

• compound acinar gland
• the branched duct system means it's compound

watery

serum-like

• a branched compound tubuloacinar salivary gland whose secretory portion contains BOTH mucus and serous cells
• 

• secretion by exocytosis
• eg. mechanism for the secretion of mucus by goblet cells by mucus or serous by salivary glands
• type of secretion done by exocrine glands

• secretion by decapitation of cells’ apical region
• mechanism for the production of milk in mammary gland
• type of secretion done by exocrine glands
• 

• secretion of whole cells’ content following apoptosis
• mechanisms for the production of sebum (mixture of lipids) by the sebaceous gland
• type of secretion done by exocrine glands

• Goblet cell - UNIcellular gland found in the intestinal epithelium that helps keep it moist
• uses merocrine (secretory vesicles, exocytosis) to secrete mucus

• is a common inherited autosomal recessive disorder caused by malfunctioning of the cystic fibrosis transmembrane conductance regulator (CTFR), small chloride channel,
• the CFTR channel is found in the apical membrane of epithelial cells of many organs including the lung, liver, pancreas, digestive tract, reproductive track & skin 
• the membrane protein normally moves Cl- OUT of an epithelial cell to the covering mucus. 
• absence of the channel results in imbalance of ion concentrations across the cell membrane and more viscous mucus

• lobular carcinomas - most common types of breast cancer originates from the epithelial cells lining the milk-producing secretory lobules in the mammary gland
• ductal carcinomas - less common types of breast cancer originates from epithelial cells lining the ductal system

• simple sqamous - very flat cells
• small arterial (blood) vessel
• this type of tissue specializes to allow diffusion of gasses into/out of the tissue

• mesothelium will generally line entire body cavities
• endothelium is seen lining smaller things, such as blood vessels

• simple squamous epithelium
• cells that line the Bowman's capsule of a kidney glomerulus

simple columnar epithelium

simple columnar; probably plasma cells (surrounding CT)

• little black lines: simple columnar epithelium of the intestinal vili
• the dark red/large outer cells: goblet cell
• connective tissue is in the middle of the whole structure

• simple columnar
• cross-section of villi 
• connective tissue is in the center
• green = goblet cells

pseudostratified epithelium