Lecture 8 Flashcards
What are the general features of epithelium?
- Avascular
- covers external body surfaces
- lines internal closed cavities
- lines body tubes
- forms secretory portion of ducts of glands (parenchyma)
- specialized cells function as receptors for special senses.
What are the three characteristics of epithelium
- the cells are closely apposed and adhere to each other
- exhibit functional and morphological polarity
- the basal surface is attached to an underlying basement membrane
What are the three surface domains of epithelial?
- free space / apical domain
- lateral domain
- basal domain
What are the junctional complexes of the lateral domain?
- Occluding junction
- anchoring junction
- communicating junction
Example of an occluding junction?
tight junction or zonula occludens
Example of anchoring junctions?
- adhering junctions (zona adherens)
2. Desmosomes (macula adherens)
Explain zona occludens?
Occluding junctional complex (cell to cell)
It is a tight junction
function:
- localized sealing of the PM of adjacent cells
What transmembrane proteins can be found in the zona occludens?
caludins- Forms backbone of ZO and forms/regulates aqueous channels
occludins- maintains barrier between apical and lateral cell surface
JAM- mediates interactions between endothelial cells and monocyte adhesions
ZO-1 = important link in transduction of signals
ZO-2- required in epidermal growth factor-receptor signaling
ZO-3 = Interacts with ZO-1. occludin, and actin
What domain separates the luminal space from the intercellular space and connective tissue?
zonula occludens
What domain establishes the functional domains: apical and basolateral?
zonula occludens
Explain the zonula adherens?
anchoring junctional complex (cell to cell)
lateral adhesion between cells
it is a continuous band that surrounds the entire cell. (beneath the tight junction)
What protein is found in the zonula adherens?
E-cadherin (calcium dependent)
helps to attach adjacent cells
interacts with actin
Explain the macula adherens?
anchoring junctional complex
macula adherens = desmosome
lateral, localized, spot adhesion
focal dense spots (macula)
Where is the macula adherens found?
Found below the zonula adherens
What proteins are found in the macula adherens?
Transmembrane protein:
desmocollin
desmoglein
(cadherin family, Ca dependent)
Intracellular plaque:
plakoglobins
desmoplakins
interacts with intermediate filaments
What are the functions of gap junctions
communicating junctional complex
help coordinate activity of adjacent cells
Where are gap junctions found?
epithelium
smooth and cardiac muscle
nerve tissue
What proteins make up the gap junction?
connexin- transmembrane protein subunits
connexon- half channel formed by 6 connexins
What do connexons do?
they align to form a communicating channel connecting the cytoplasm of adjacent cells
What are lateral interdigitations?
infoldings of cytoplasmic processes of adjoining cells
What is the purpose of lateral interdigitations?
Increase later cell SA
Where are lateral interdigitations common?
Common in cells engaged in fluid and electrolyte transport
tight junctions prevent fluid leak
What is focal adhesion?
Anchoring junction
This junction functions to anchor the actin cytoskeleton to the extracellular matrix.
What protein is present for focal adhesion?
Integrins
The hemidesmosome?
anchoring cell junction
helps to anchor epithelial cells to the basement membrane
interaction with intermediate filaments
hemidesmosome protein?
integrins
What is bullous pemphigoid?
A disease that is characterized by blister formation at epithelium attachment to basement membrane
What are the purpose of basal infoldings?
- increase cell SA of the basal domain
- allow for more transport proteins and channels
- well developed in cells that perform active transport
Structure of the basement membrane?
can be seen with a light microscope
amorphous layer at the basal surface of epithelia
found between epithelial cells and connective tissue
thick in respiratory epithelium
What comprises the basal lamina?
laminins
type IV collagen
proteoglycans and glycoproteins
What are the two layers of the basal lamina?
- lamina lucida (considered an artifact)
2. lamina densa (electron dense)
What is the basal lamina called in non-epithelial cells?
external lamina
What are the two major types of glands?
- exocrine- secrete onto a surface directly or through ducts that are connected to a surface
- Endocrine- secrete products (hormones) into the connective tissue and then enter bloodstream
What are three release mechanisms of glands?
merocrine- exocytosis of membrane bound vesicles
apocrine - product released at apical surface surrounded by envelope of PM
Holocrine - programmed cell death releases secretory products and cell debris
Explain paracrine vs autocrine?
paracrine signals nearby cells
autocrine is the same cell signaling
unicellular glands vs multicellular glands?
unicellular = 1 cell
Ex: goblet cell (secrets mucus)
multicellular = numerous cells
What are the shapes of secretory cells?
Tubular- tube
alveolar (acinar) - flask
tubuloalveolar - tube ends in a dilation
A duct can be simple or compound.. what does that mean?
Simple = no branching
compound = branching
Names of simple glands?
- simple tubular - intestine; straight tube
- simple coiled tubular - skin; deep in dermis
- simple branched tubular - stomach; secrete mucus
- simple acinar - urethra; single layer of secretory cells
- branched acinar - stomach/skin; opens directly into lumen
Names of compound glands?
- compound tubular- intestine; located deep in submucosa
- compound acinar- pancreas; pyramid shaped
- compound tubuloacinar - salivary gland;
What are the three classifications of exocrine glands?
- serous
- mucus
- mixed
Explain serous exocrine glands?
watery
nuclei are rounded or oval
Explain mucous glands (exocrine)?
viscous and slimy
extensive glycoslyation
nuclei are flattened and compressed to the base of the cell
PAS positive
Mixed exocrine glands?
contains both mucous and serous secretory components
