Veterinary Histology: Epithelial Cells

Front 1

Mucosa

Back 1

-the innermost layer of tubular organs
-epithelial cells make up the mucosal surfaces
-protected by a layer of mucus which is secreted by goblet cells
-consists of 3 layers: epithelium, lamina propria, muscularis mucosa

Front 2

Mucosal Epithelium

Back 2

-composed of stratified squamous columnar (oral cavity, esophogus), pseudostratified ciliated columnar (respiratory tract), transitional (urinary tract)
-rests on a basement membrane

Front 3

Lamina Propria

Back 3

-layer of the mucosa
-connective tissue immediately below the epithelium
-consists of cells that prduce collagen, elastic and reticulin fibers

Front 4

Muscularis Mucosa

Back 4

-layer of the mucosa
-inconstantly present layer
-assists the expression of secretion from muscosal glands

Front 5

Submucosa

Back 5

-composed of connective tissue similar to that found in the lamina propria but collagen fibers are denser

Front 6

Muscularis

Back 6

-next layer in from mucosa in tubular organs
-layer of smooth or skeletal muscle
-important in movement of lumen contents

Front 7

Serosa

Back 7

-innermost layer of tubular organs
-single layer of simple squamous epithelium (mesothelium)
-

Front 8

Adventitia

Back 8

-present in organs lacking a mesothelial covering
-adventitia is an outer layer connective tissue

Front 9

Histogenesis of epithelium

Back 9

-contribution from all 3 germ layers
-ectoderm, endothelium, endodermal cells

Front 10

Embryonic ectoderm

Back 10

-consists of surface ectoderm and neuroectoderm

Front 11

Neuroectoderm

Back 11

-forms the neural tube which gives rise to the CNS and sensory epithelium of eye, ear and nose
-neural crest cells are included in this category

Front 12

Endothelium/Mesothelium

Back 12

-derive from the mesoderm
-no continuity with exterior surfaces (unlike epithelium)
-mesoderm derives mesenchymal cells

Front 13

Endodermal cells

Back 13

-endodermal cells of thyroid and parathyroid glands develop as epithelial outgrowths of the floor of the pharynx that become detached from this site of origin

Front 14

Epithelium Classification Based on Cell Shape

Back 14

-squamous: width>height
-cuboidal: width=height
-columnar:height>width

Front 15

Epithelium Classification Based on Cell Layers

Back 15

-simple: one layer
-stratified: 2 or more layers
-pseudostratified
-transitional

Front 16

Is epithelial tissue supplied by blood vessels?

Back 16

-NO!
-epithelial cells are supplied with nutrients that pass through the basement membrane

Front 17

Occluding junctions/Tight junctions/zonula occludens

Back 17

-limit the movement of water and other small molecules into intercellular space
-located in apical region of lateral surface of the cell
-appear as dark staining, bar-like structions

Front 18

Anchoring junctions (2 types)

Back 18

-both provide lateral adhesion between adjacent cells
-zonula adherens: interacts with actin filaments
-macula adherens/desmosome: interacts with intermediate filaments
-desmosomes result in a shrinkage artifact in 10% formalin

Front 19

Cell adhesion molecules (CAMS)

Back 19

-play an important role in cell to cell adhesion and in cell adhesion to the intracellular matrix

-each stage of tissue differentiation in the embryo is defined by the expression of specific CAMS

-4 categories:
Cadherins: Ca2+ depending in the zonula adherens
Integrins:interact with extracellular matrix molecules such as collagen
Selectins: found on leukocytes and endothelial cells
Immunoglobulin superfamily: glycoproteins with a wide array of functions

Front 20

Communicating or gap junctions

Back 20

-consist of open regions or pores in the membrane
-allow passage of ions, amino acids, sugars, nucleotides and messengers
-helps support homeostasis
-connexin proteins form the channels
-present in most cells, but particularly important in cardiac muscle

Front 21

Basement membrane junctions

Back 21

-Hemidesmosones

Front 22

Cell Polarity (General)

Back 22

-there are distinct morphologic and biochemical properties associated with the apical, lateral and basal domains

Front 23

Apical Domain

Back 23

-directed toward surface of the lumen, enclosed cavity or tube lined by epithelial cells

-microvilli: finger like cytoplasmic projections that increase the surface area for absorption in the GI tract and renal tubules

-cilia:
-fine, hair-like structures capable of moving fluid and microscopic particles along epithelial surfaces
-found in respiratory tract, tail of sperm
-look like tangle, hair-like structures under a light microscope
-the electron microscope allows you to see the 9+2 (or 9+0) pattern of microtubules

Front 24

Ciliary Diskinesia

Back 24

-during gastrulation the clockwise rotation of monocilium on the ventral surface of the embryonic disk generates sensory changes on the left side of the body that are different from the right side
-so, if the cilia are non-motile or absent the organs will be displaced

Front 25

Basal Domain

Back 25

-at the basal surface of epithelial cells that make contact with the underlying connective tissue there is a sheet of extracellular matrix called the basement membrane
-easily seen in the trachea and urinary bladder
-hemidesmosomes anchor the basal region of epithelial cell membranes to the basement membrane

Front 26

Basement Membrane vs. Basal Lamina

Back 26

-basement membrane is seen with the light microscope and basal lamina is seen with the electron microscope
-basal lamina has two layers: lamina lucida and lamina densa (both synthesized by epithelial cells)

Front 27

Exocrine glands

Back 27

-secrete products onto a surface directly or through epithelial ducts that are connected to a surface

Front 28

Endocrine glands

Back 28

-lack a duct system and secrete their products into the surrounding connective tissue which are then taken up by the bloodstream and taken to their target cells

Front 29

Paracrine glands

Back 29

-produces secretion that does not enter the bloodstream, but effects other cells within the same epithelial surface
-reaches the target cell by diffusing through the extracellular space

Front 30

Types of exocrine gland secretion

Back 30

-merocrin, apocrine, holocrine

Front 31

Merocrine secretion

Back 31

-secretory product is delivered in membrane-bound vesicles to the apical region of the cell
-the vesicles fuse with the membrane and release their content by exocytosis
-occurs in pancreatic acinar cells

Front 32

Apocrine secretion

Back 32

-secretory product is released at the apical region of the cell surrounded by a thin layer of cytoplasm and a portion of the cell membrane
-occurs in mammary glands and ceruminous glands of the ear canal

Front 33

Holocrine secretion

Back 33

-secretory product accumulates within the cell which undergoes apoptosis so both the secretory product and remains of the cell are discharged into the lumen
-occurs in sebaceous glands of the skin

Front 34

Naming multicellular exocrine glands

Back 34

-simple: has an unbranched duct
-compound: has a branched duct
-tubular: has a tube-shaped secretory portion that may be straight, branched or coiled
-acinar/alveolar: has a flask or globe-shaped secretory portion that may be single or branched

Front 35

Liver cell Regeneration

Back 35

-liver cells are called hepatocytes but are actually a type of epithelial cell
-they have no basement membrane, a portal blood supply and a duct system of canaliculi and ducts
-can regenerate using multipotential stem cells