Epithelial Glands Flashcards
Give the general characteristics of epithelium
Avascular
- No blood vessels in epithelium
- Oxygen & nutrients by diffusion from underlying connective tissue
Covers exterior body surfaces
-skin
Lines internal closed cavities
-endothelium of blood vessels of cardiovascular system
Lines body tubes
- gastrointestinal tract
- respiratory tract
- genitourinary tracts
Forms secretory portion (parenchyma) & ducts of glands
Specialized cells function as receptors for special senses
-smell, taste, vision
What are the 3 principle characteristics of epithelium ?
- Cells are closely apposed & adhere to each other
- Specialized cell to cell junctions
2. Exhibit functional & morphological polarity
3 surface domains
1. Free surface/ apical domain
2. Lateral domain
3. Basal domain
- Basal surface attached to underlying basement membrane
- cell to matrix junctions
What are the lateral specializations of cells ?
Lateral surface/domain
- Occluding junctions.
- tight junction (zonula occludens)
- Anchoring junctions
- Adhering junctions (zonula adherens)
- Desmosomes (macula adherens)
- Communicating junctions
- Gap junctions
Describe Zonula Occludens
Occluding junctions complex (cell to cell)
- Zonular occludens = tight junctions
- Localised sealing of the plasma membrane of adjacent cells
- Network of anastomosing strands that completely surround the apical cell borders
- Transmembrane proteins= Claudins & occludins
- Interaction with action cytoskeleton via ZO-1
What are the major proteins included in the zonula occludens junctions?
- Occluding
- Claudin
- JAM
- ZO-1
- ZO-2
- ZO-3
What are the associated protein partners and function of Occludin?
Occludin, ZO-1,ZO-2, ZO- 3, Vapp33, actin
Function: is present in most occluding junctions: maintains barrier between apical and lateral cell surface
What are the associated protein partners and function of Claudin?
Claudin, ZO-1, JAM
forms backbone of zonula occludens strands: forms and regulates aqueous channels used for paracellular diffusion
What are the associated proteins and function of JAM?
JAM, ZO-1, Claudin
Function: present in endothelial cells; mediates interactions between endothelial cells and monocytes adhesions
What are the associated proteins and function of ZO-1?
Associated proteins: ZO-3,ZO-2, Occludin, Claudin, JAM, cingulin, actin, ZONAB, ASIP, AF-6
Function: important link in transduction of signals from all transmembrane protein; interacts with actin filaments, has tumor suppressor actin
What are the associated proteins and function of ZO-2?
ZO-1, Occludin, cingulin, 4.1R
Function: Required in the epidermal growth factor-receptor signaling mechanism
What are the associated proteins and function of ZO-3?
Associated proteins: ZO-1, Occludin, actin
Function: interacts with ZO-1, Occludin, and actin filaments of cell cytoskeleton
In detail, explain the function of zonula occludens
Zonula occludens separates the luminal space from the intracellular space and connective tissue compartment
Paracellular pathway: across the zonula occludens between two cells
Transcellular pathway: across the plasma membrane of the epithelial cell
Establishes functional domains in the plasma membrane
- Apical
- Basolateral
Explain detail the function of the zonula adherens
Anchoring Junctional Complex(Cell to Cell)
-Lateral adhesion between epithelial cells
-Continuous band or belt that surrounds the entire cell, found just beneath the tight junction
- Transmembrane protein = E cadherin
- calcium dependent - Helps to attach adjacent cells (15-20nm apart)
- Interaction with actin cytoskeleton
What are the functions of macula adherens in detail?
Anchoring junctional complex
-macula adherens= desmosome
- lateral, localised, spot adhesion between epithelial cells about 30nm apart
- Focal dense spots (macula)
-Found beneath the zonula adherens of cells
- Transmembrane protein= desmocolin & desmoglein
- Cadherin family, calcium dependent - Intracellular plaque=plakoglobins & desmoplakins
- Interaction with intermediate filaments of cytoskeleton
What are gap junctions, where are they found?
Communicating junctional complex (cell to cell)
- present in a variety of tissues
- epithelium
- smooth & cardiac muscle
- nerve
-help coordinate activity of adjacent cells
Differentiate between connexins and con exons for gap junctions
Connexin- Transmembrane protein subunits
Connexons -half channel formed by 6 connexins
Connexons align to form a communicating channel connecting the cytoplasm of adjacent cells
Explain the lateral morphological specialization of lateral cell surface
Lateral interdigitations
-in foldings (plicae) of cytoplasmic processes of adjoining cells
-increased lateral cell surface area
- common in cells engaged in fluid and electrolyte transport
- Ex. Gall bladder, small intestine
- Sodium ions are pumped out of cytoplasm by Na+/K+ -ATPases
-Fluid accumulates in the intracellular space until driven into underlying connective tissue
Tight junctions prevent fluid escape in apical direction
Explain focal adhesion
Anchoring junctional complex
- cell to extracellular matrix junctions
- helps to anchor epithelial cells to basement membrane
Transmembrane proteins= integrins
- Link between actin microfilaments of cytoskeleton and extracellular matrix
- Important role during cell migration
Explain the function of the hemidesmosomes
Anchoring junctional complex
- cell to extracellular matrix junctions
- helps to another epithelial cells to basement membrane
- Half the component of a desmosome
- Transmembrane proteins= integrins
- Interaction with intermediate filaments of cytoskeleton
What is Bollus pemphigod?
Disease characterized by blister formation at epithelium attachment to basement membrane
-Antibodies directed against BP320 & type XVII collagen
Describe basal in folding s as a morphological modification
- Significantly increase the surface area of the basal domain
- Allow for more transport proteins and channels to be present
- Well developed in cells performing active transport of molecules
- kidney tubule
- striated ducts of exocrine glands
- Mitochondria arranged vertically in these folds
- Light microscopy- “striated” appearance
Explain the function of the basal membrane
- Can be visualized with light microscope
- Amorphus layer at basal surface of epithelia
- Found between epithelial cells and underlying connective tissue
- Especially thick in respiratory epithelium
- H&E x450
The basal lamina is called __________ in noneoithelial cells
External lamina
How can the basal lamina be visualized?
By electron microscopy
What is the function of the basal lamina?
Structural attachment site for overlying epithelial cells and underlying connective tissue (fibroreticulsr lamina)
Describe the composition of the basal lamina
Composition :
- lamins
- type 4 collagen
- proteoglycans & glycoproteins
2 layers
- Lamina lucida (rara)-considered an artifact
- Lamina densa- electron dense
What is an exocrine gland?
Secrete onto a surface directly or through ducts that are connected to a surface
What are the release mechanisms of exocrine glands?
- Merocrine- exocytosis of membrane bound vesicles(most common )
- Apocrine-product released at Apical surface surrounded by envelope of plasma membrane
- Bleb
- Ex. Lactating mammary gland
- Holocrine
-programmed cell death releases secretory product & cell debris
Ex: sebaceous glands of skin
What is an endocrine gland?
Secrete products (hormone) into the connective tissue & then enter the bloodstream
- paracrine=nearby cells
- autocrine= same cells
Explain the classifications of exocrine glands
Unicellular glands
1 single cell
-Ex goblet cells
-mucus secreting cells
Multicellular glands
-numerous cells
Sub classification
- Shape of secretory cells
- tubular-tube
- alveolar(acinar)= flask
- tubuloalveolar= tube ends in a dilation
- Presence or absence of branching duct
- simple= unbranched duct
- compound = branched duct
What are the classsifications based on type of secretion produced by exocrine gland ?
- Serous
- Mucous
- Mixes
What are serous exocrine glands?
Watery
-poor or nongoycosylated protein secretion
- Nuclei within cells are typically rounded or oval
- Apical cytoplasm filled with zymogen granules is stained with eosin
- Perinuclearcytoplasm is basophilic due to extensive rER
- Ex. exocrine pancreas & parotid salivary glands
What are mucous exocrine glands?
- viscous/slimy
- extensive glycisylation
- Nuclei within cells are flattened & compressed to the base of the cell
- PAS positive due to anionic oligosaccharides
- Mucinogen granules
- store mucus
- water soluble oligosaccharide is poorly preserved
- Appear empty in H & E staining
Describe mixed exocrine glands, give an example
Contains both mucus and serous secretory components
-Ex. Submandibular & sublingual salivary glands
Submandibular gland
-serous> mucus
Compound tubuloacinar gland
Sublingual gland
-mucus>serous
