Epithelia II Flashcards
Cilia contains dynein arms.
Centrioles in contrast have 9 triplets (cilia do not).
..
Stereocilia
- Definition
- Where are they located? (2)
- What supports them?
- Long, immotile branched microvilli.
- Located in the epididymis, proximal vas deferens (facilitate absorption/passive movement of fluid).
- Located in the Sensory hair cells of inner ear (bend in response to movements of the basilar membrane of the cochlea).
- Supported by internal bundle of actin filaments cross linked by actin-binding proteins.
**NO MICROTUBULES EVEN THOUGH THEY HAVE CILIA IN THE NAME!
Zonula occludens is located where?
Another name?
Extends around the entire perimeter of the cell at the apex (highest layer)
Also known as “terminal bars” or “tight/occluding” junctions
Look at pictures of PAS stain
Zonula occludes can be rapidly formed and disassembled. This is important for paracellular transport/WBC diapediesis. Epithelia are classified either as “tight” or “leaky” based on the permeability of the zonula occludes.
**Important in the blood/brain barrier
..
proteins in zonula occludens?
occludins/ZO 1,2, 3
Tight Junctions (zonula occludins) block lateral movement of lipids and membrane proteins to keep a cell polarized! (cell is more open on the basolateral surface.
…
Transcellular pathway occurs across the PM of the epithelial cell.
Transport is what?
Active! It requires specialized energy-dependent transport of proteins and channels.
ZO separates the luminal space from the connective tissue compartment.
…
Paracellular pathway occurs ACROSS the ZO between two epithelial cells. The amount of water, electrolytes, small molecules transported depends upon…what?
Paracellular transport is bidirectional!!!
The tightness of the ZO.
Permeability of the ZO depends on molecular composition.
Zonula adherens is also known as what?
Belt desmosome or Intermediate Junction
Microvilli are covered with a layer of glycocalyx. The glycocalyx is what…?
An area with enzymes that begin to break down carbs/ proteins, etc before they are taken up by epithelial cells.
Zonula adherents are located below what?
The zonula occludens!! (tight junctions)
Zonula Adherens are located in what cells?
Epi cells, between smooth muscle cells, and between intercalated discs of the cardiac cells.
Main protein in zonula adherens?
E-Cadherins (outside)
Actin & Catenins are inside
Zonula Adherens - adjacent PM are separated by a small gap filled with an electron dense plaque containing a glycoprotein localized only in the membrane.
THERE IS A SPACE WITH ZONULA ADHERENS! NOT IN ZONULA OCCLUDENS.
…
Macula adherens are also called….?
Desmosomes
Tonofilaments are…?
intermediate keratin filaments
desmosome means what in latin?
binding body
Macula Adherens/Desmosomes are…..
bipartitie structures of apposing cell membranes; an attachment plaque of nthe cytoplasmic side anchors tonofilaments which are intermediate keratin filaments
Which molecules facilitate cell-cell adhesion in desmosomes?
cadherins
Keratin are inside the cell
FORMS A DENSE PLAQUE (strong point of adhesions between cells) - small gap still of 25-35 nm
Desmosomes/Macula Adherens are discrete units. They are located on the basal lateral portion of the cell.
….
Apical Junctional complex consists of what? Give correct order.
Tight, Adherens, Desmosome
target of pathogenic agents
Intermediate filaments dock into which structures…?
desomosomes and hemidesmosomes
Desmosomes/Hemidesmosomes help to dissipate what?
Physical Forces applied to the epithelium
traction forces
Hepatitis C Virus… How does it target the junctional complex?
OCCLUDIN is required for post binding step in Hep C virus entry and infection of hepatic cells
Clostridium perfringens (Bacteria)…How does it target the junctional complex?
produces?
results in what disease?
principle effect?
- produces an ENTEROTOXIN that attacks the ZONULA OCCLUDENS junction in the intestines
- results in food poisoning
- dehydration is a result of massive movement of fluids via the PARACELLULAR pathway into the lumen of the intestines
Helicobacter pylori (bacteria)…How does it target the junctional complex?
binds where?
targets which enzyme?
results in what change in the cell?
causes damage to what?
Binds to extracellular domains of ZONULA OCCLUDENS proteins in the stomach and diminishes its capacity for TYROSINE KINASE SIGNALING resulting in CYTOSKELETAL REARRANGEMENTS.
Causes damage to the protective barrier which leads to the development of gastric ulcers and carcinomas.
Reovirus affects what?
GI system and respiratory tract
Reovirus affects junctional complex by targeting what protein?
What does it trigger with this interaction?
JAM (junctional adhesion molecule) protein of the zonula occludens.
Triggers a cascade of cellular events leading to APOPTOSIS!
Parasite that affects junctional complex?
Dermatophagoides pteronyssinus (common house dust mite)
Dermatophagoides pteronyssinus…. How does it effect junctional complexes?
Effects what junction?
Effects what part of the body leading to what reaction?
- Fecal pellets are inhaled with dust particles; the peptidases in the fecal pellets cleave proteins of the zonula occludens
- Loss of this barrier in the lungs exposes the lung (alveoli) to inhaled allergens and initiates an immune response that can lead to severe asthma attacks
Gap junction is also called what?
Nexus /Connexons (made of 6 connexins)
They separate cells by 2-3 nm and allow direct electrical and chemical communication.
Gap junctions = sites of electronic coupling. It is the only type of junction that mediates flow of current between cells.
….
Where are gap junctions found?
osteocytes, astrocytes (glial cells of nervous system), cardiac muscle, smooth muscle, and endocrine cells
Also on the lateral aspect of cells!
Cancer cells generally do not have what type of junction? This explains their uncontrolled growth.
Gap junctions! Therefore, their cells fail to communicate their mitotic activity to each other, which may explain their uncontrolled growth
Gap junctions can rotate to open/close! This is how they are regulated (calcium mediates this - causes closing). Twisting action
….
Connexin 26 mutation causes..
Highly expressed in inner ear
Deafness
Connexin 32 mutation causes…
Expressed in PNS - Causes degenerative disease - Charcot -Marie-Tooth
This is a problem with myelination - short circuiting of action potentials.
Connexin 50 mutation causes…
Congenital Cataracts / Blindness
Avascular lens becomes opaque if no gap junctions - depends on diffusion from this!!
Basement Membrane
What is it made by? and other definitions
- Thin sheet of extracellular material at the basal surface of all epithelia
- Separates epithelia from the underlying CT
- Structural attachment site for its overlying epithelial cells and its underlying CT
- Synthesized primarily by overlying epithelial cells!! (part of ECM)
- Not just associated with epithelia… “external lamina” in other tissues (muscle cells, adipocytes, and schwann cells”
Basal membrane is visible with light microscope but to see what you need EM?
Basal lamina!!!
Basement membrane consists of what two components?
1) Basal lamina
2) Reticular lamina
All epithelial cells have a basement membrane and they secrete it.
…
Functions of the basement membrane
- Adhesion of epithelial cells to underlying CT
- Selective permeability (<50 kD)
- NOT a diffusion barrier aka allows for diffusion (remember that eli is avascular!)
- good substrate for cell migration (during wound healing/embryonic development)
- barrier that is critical to “metazoic potential” of epithelial cancer cells (Carcinomas)
(carcinomas in situ have not yet breached the BM)
Specilizations on the basal surface
Hemidesmosomes and Focal Adhesions
Hemidesmosome definition
- occur in which epi?
- Anchors the INTERMEDIATE FILAMENTS of the cytoskeleton into the BM (basal surface)
- occur in epithelia that require strong, stable adhesion to the CT (skin, mucosa of the oral cavity)
Pathology example of the hemidesomosomes?
Bullous Pemphigoid
What is bullous pemphigoid?
- autoimmune disease
- Ab against hemidesmosomes!
- layers of skin separate and subepidermal blistering occurs
Focal Adhesions… mainly FYI! Anchor actin filaments into the BM
..
Strength of the epidermis to resist abrasions comes from what connection?
Hemidesmosomes!
Lamina Propria
- ALL EPI CELLS POSSESS THIS!
- CT located immediately beneath the BM
- serves as a support to the epi, and as a vascularized CT bed containing blood vessels, lymph vessels, and nerves
Nerve fibers/Blood vesselss…which penetrates the BM?
only nerves!
Exocrine glands?
Open onto surface - exhibit diff methods of secretion
Endocrine glands?
Release products into bloodstream
Glands are derivatives of epithelium!
..
Formation of glands from covering epithelium…. Epithelial cells proliferate and penetrate connective tissue. If the gland is endocrine, the cells can be arranged in cords or in follicles.
….
What are the three mechanisms of product release? Just the names
Merocrine/eccrine
Apocrine
Holocrine
Merrocrine/eccrine release?
release of product with the cell membrane remaining intact (pancreas/pituitary)
EXOCYTOSIS WITH VESICLES!
Apocrine
Involves constriction and pinching off of a portion of the apical cytoplasm containing secretory granules (mammary glands/smelly sweat glands)
Holocrine
Cell rupture
Bulk release of whole cells or discharge of their cytoplasm into the glandular excretory duct (sebaceous glands)
Unicellular Glands
- exs
- found where
- Mucuous or goblet cells
- Found in simple columnar cells of intestine and pseudo-stratified columnar epithelium of the respiratory system
What is the theca?
Cup shaped rim of cytoplasm filled with secretary droplets, MUCINOGEN, that takes a clear blue basophilic stain and is PAS positive
(unicellular glands)
How long do unicellular glands live?
4 days
Secretion is continuous within this time
Maybe accelerated by parasympathetic nerves
What is an acinus?
small saclike cavity in a gland surrounded by secretory cells
Lubricating, viscous fluid rich in mucopolysaccharides?
mucous
Which salivary gland uses mucous and serous?
Sublingual gland?
Mucous glands have a light purple appearance. Serous secretion cells are more of a violet shade.
..
Watery secretion rich in ENZYMES (pancreas, parotid glands)
Serous secretion
Thin, flat layer of squamous epithelial cells moistened by exudates FROM UNDERLYING BLOOD VESSELS!
Serous Membrane
Moist epithelial surface, usually columnar, but may be cuboidal or squamous, that is moistened by secretions produced by glands formed by the epithelium itself.
Mucous Membrane
Small intestine gets cell renewed after how many days?
3-6 days.
Stem cell are located in intestinal crypts.
Unidirectional cell flow (move to surface of villus)
Stem cells at bottom of crypt are constantly undergoing mitosis.
Stratum Germinativum of the skin..what is it?
The stem cells of the skin! Constantly undergo mitosis. Takes 28 days to get to skin surface.
Reversible conversion of one mature epi cell type to another mature epi cell type (usually going to stratified squamous). ADAPTIVE RESPONSE to stress, chronic inflammation, or other abnormal stimuli
Epithelial metaplasia.
