epithelial tissue Flashcards
functions of epithelium
Covers body surface
Lines body cavities
Constitutes glands.
- Glands: secretes essential molecules such as hormones.
what is the traditional classification of epithelium is based on 2 factors
- no. of cells
- shape of surface cells
special categories:
- Pseudostratified
- Transitional
why does the pseudostratified looks like stratified epithelium
due to cells that does not reach the basal surface
what is the specific characteristics that transitional epithelium has
Distensible (stretchable)
- shape changes depending on the amt. of fluid it holds.
location and function of each epithelium tissue
transes
briefly explain the cell polarity
different sides that perform specific functions
- apical domain (top/ free surface)
- Faces the external environment or lumen
- Absorption, secretion or interaction with the external environment/ coordinate with free extracellular fluid. - lateral domain (sides)
- Located between neighbouring cells
- Facilitates cell-to-cell communication and adhesion
[cell stick tgt and communicate] - basal domain (bottom)
- Connects the cell to the underlying CT
- Anchoring the cell and facilitating molecular exchange with the CT
[keeping the cell stable and allowing nutrient exchange]
what are the structural surface modifications of the apical domain
microvilli
stereocilia
cilia
[these helps w absorption, movement or sensing environment]
Finger-like cytoplasmic projections on the apical surface of most epithelial cells.
microvilli
- tiny-finger-like projections
- 20 to 30 actin filaments
- found on cells that absorbs nutrients
key parts of microvilli
[actin filaments - the “bones” inside the microvillus
vilin: holds tgt at base
terminal web: network at the base, keep then stable]
- actin-building proteins
- fascin, epsin, fimbrin (tightly packed tgt) - myosin l
- binds actin filaments to the plasma membrane - terminal web
- horizontal network of actin filaments.
- spectrin stabilize actin filaments - myosin ll and tropomyosin
- slight movement by tightening or loosening the network
how does microvilli move
moves passively
do not actively move like cilia.
way slightly when the terminal web contracts
[like blades of grass swaying in the wind.]
where can stereocilia be found and its function
male reproductive system (epididymis & ductus defers) - absorption and fluid balance
inner ear (sensory E) -detect sound vibrations
what are the key parts of stereocilia
core: actin filaments (give structure and strength)
fibrin holds actin filaments tgt
📍 Stereocilia in the Genital Ducts (Epididymis & Ductus Deferens)
- contain ezrin and a-actin (help anchor)
📍 Stereocilia in the Sensory Epithelium (Inner Ear)
- contain epsin (connect to surrounding = can detect vibrations)
Hair-like extensions present on nearly every cell in the body.
cilia
- contains axoneme, made of microtubules arranged in organized pattern
- basal body anchors axoneme to the cell
briefly explain the different types of cilia
index card
A rare genetic condition in which the position of the heart and abdominal organs is reversed.
Situs inversus
- caused by absence or immotile nodal cilia
- aka primary ciliary dyskinesia.
[Nodal cilia are responsible for generating fluid flow that helps direct the placement of organs in the correct locations.
If the cilia don’t function properly, the organs can be positioned incorrectly.]
it is the specific structural components that make up the barrier and the attachment sites, and are responsible for joining individual cells together.
Junctional complex
3 types:
what are the 3 types of junctional complexes
Occluding junctions (aka tight junctions)
Anchoring junctions
Communicating junctions (aka gap junctions)
It forms tight seals between adjacent cells, effectively inhibiting the movement of large molecules and ions.
Occluding Junctions (Zonula Occludens)
- create a narrow region where the plasma membranes of two cells meet tightly, closing off the space between them.
- apical domains (top parts of cells) are often shaped like polygons, and their points create junctions where three cells meet.
Main Components of Occluding Junction
claudins:
These proteins are the backbone of tight junctions and help form small water channels between cells.
Example: In the kidneys, claudins help create channels that allow water to pass through cells, which is important for filtration and reabsorption.
occludin:
This protein helps maintain the barrier between cells.
It also restricts the movement of lipids and proteins between the top and side parts of the cells, helping keep the cell’s structure intact and properly functioning.
junctional adhesion molecule:
Part of the immune system’s protein family (IgSF).
JAM increases electrical resistance across the cell membrane, which helps control ion flow and keeps the balance of ions intact.
tricellulin:
This protein seals the weak points where three cells meet (called tricellular contacts), ensuring that the tight junction barrier stays strong and prevents leakage.
these are regulatory and signaling proteins that attach to the four proteins
PDZ domain proteins
- the 4 proteins are claudins, occludin, junctional adhesion molecule, tricellulin
(index card)
what are the junctionalcomplexes infections
bacteria:
Clostridium perfringens
Helicobacter pylori
virus:
Oncogenic adenovirus
Papillomavirus
miscellaneous parasites:
Dermatophagoides pteronyssisnus
- Aka dust mites.
- Release protein that can damage junctional complexes in the respiratory tract, leading to allergic reactions and respiratory issues.
it provides lateral adhesions between epithelial cells.
anchoring junction
2 types:
Zonula adherens
Macula adherens (desmosome)
5 major families of CAMs (Cell Adhesion Molecules) in anchoring junctions
index card
it is a transmembrane proteins that are part of anchoring junctions, and interact with CAMs of neighboring cells.
Cell adhesion molecules (CAMs)
[found on the surface of cells. They help cells stick to each other and to the structures around them. CAMs are involved in creating anchoring junctions that keep cells connected.]
Heterotypic binding: When CAMs from different types of cells stick together.
Homotypic binding: When CAMs from the same type of cell stick together.
provide lateral adhesion between epithelial cells, and is composed mainly of cadherins and nectins.
Zonula adherens
- E-cadherin-catenin complex:
binds to vinculin and a-actinin. - Weak nectin-based adhering:
junctions are formed specialized areas where junctions are exposed to dynamic regulation.
provides localized spot-like junction between epithelial cells, and represent major anchoring cell-to-cell junction by providing anchoring sites for immediate filaments.
Macula adherens (desmosome)
- On the inside of the cell, there’s a desmosomal attachment plaque, which helps to connect the cell membrane to the skeleton.
- In the space between the cells, there are special proteins called desmogleins and desmocollins. These proteins belong to the cadherin family and help the cells stick together by forming a “cadherin zipper”.
- These proteins interact with plakoglobin and desmoplakin, which help connect the cell membrane to the cytoskeleton, making the junction strong and stable.
Desmosomes = Strong spot-like junctions.
Desmogleins and Desmocollins = Proteins that help cells stick together.
Plakoglobin and Desmoplakin = Help anchor the junction to the cell’s inner structure.
are the only known cellular structures that permit the direct passage of signaling molecules from one cell to another.
Communicating junctions (gap junctions, nexuses)
- formed by 12 subunits of connexin protein family = connexons
- signaling molecules (like ions or small chemicals) pass directly from one cell to another.
- channels can open and close in response to signals such as voltage changes, calcium levels, pH, or other chemical signals.
Why are plicae (folds) important in epithelial cells?
increase surface area, which helps in more efficient absorption, secretion, or communication in organs.
Where are morphologic modifications, like plicae, commonly found?
In organs where absorption, secretion, or communication are crucial, like the intestines or glands.
what are the several features that basal domain of epithelial cells is characterized by
Basement membrane
Cell-to-extracellular matrix junctions
Basal cell membrane infoldings
what are the special stains needed for the basement membrane to be seen under a microscope
PAS (+) Periodic Acid-Schiff: A stain that makes the basement membrane stand out.
Silver-reactive: Another stain that highlights the basement membrane.
Mallory stain: A stain that can also be used to see the basement membrane.
the 2 parts that basement membrane are made up of
basal lamina:
The part that is made by the epithelial cells.
[is the structural attachment site for overlying epithelial cells and underlying connective tissue.]
reticular lamina:
The part made by the connective tissue (CT).
what are the components oof the basal lamina
collagens (Types IV, VII, XV, and XVIII)
laminins
entactin/ nidogen
proteoglycans
what are the several anchoring structures used to connect the basal lamina to the underlying CT
Anchoring fibrils (Type VII collagen): These fibers hold the basal lamina in place and attach it to type III collagen in the connective tissue (the most common type).
Fibrillin microfibrils: These help attach the basal lamina to elastic fibers, giving more support.
Projections of the lamina densa: These are small extensions that connect the basal lamina to the connective tissue, helping to form additional bonds with type III collagen.
It maintains morphologic integrity of the epithelium-connective tissue interface.
Cell-to-Extracellular Matrix Junctions
(index card )
Focal Adhesions – Connect actin filaments inside the cell to the basal lamina (part of the basement membrane).
Hemidesmosomes – Anchor intermediate filaments inside the cell to the basement membrane, providing strong attachment.
[Focal adhesions connect cells to the extracellular matrix (outside the cell).
Desmosomes connect cells to each other, strengthening the tissue.]
What is the purpose of morphologic modifications in epithelial cells?
increase surface area (SA) to improve absorption, secretion, and adhesion.
Structural folds in the basal surface of epithelial cells that increase SA for better transport & absorption.
basal infoldings
- strengthen cell connections by involving structures like tight junctions, adherens junctions, & desmosomes.
Why do glands have morphologic modifications?
: To increase efficiency in secreting substances.
type of glands and their mechanism of secretion
exocrine glands
- holocrine
- apocrine
- merocrine
endocrine glands
paracrine glands
autocrine signaling
glands that release their secretions (like mucus, sweat, or digestive enzymes) onto a surface (e.g., skin, digestive tract).
Exocrine glands
- unicelular glands:
Made of just one cell that produces and releases substances. Example: Goblet cells in the intestine secrete mucus. - multicellular glands:
Made of many cells working together. They have different structures that help classify them further. Example: Salivary glands produce saliva.
mucous secretions vs serous secretions
Mucous secretions → Thick, sticky, and slimy (e.g., mucus from goblet cells in the respiratory tract).
Serous secretions → Thin, watery, and fluid-like (e.g., saliva from salivary glands).
Epithelial Cell Renewal
continuously renewing cell populations:
Surface epithelia (like skin and gut lining) have fast turnover (new cells form quickly).
For example, the small intestine renews every 4-6 days, and skin renews in about 47 days.
stable cell populations:
liver, cells don’t renew as quickly
stable cell population, meaning cell division happens rarely, and the cells live longer.
