3 Functions of epithelium
1. Covering, Lining, and protecting surfaces2. Absorption3. Secretion
Basic Characteristics of epithelium (6)
1. Polyhedral cells that are tightly attached to each other2. Forms sheets of cells which coat the outer surface of body and line various organs3. Forms glands and other secretory tissues4. Undergoes mitosis and is avascular.5. Relies on diffusion from blood vessels in adjacent CT6. Its a polar tissue and has two faces; the apical pole, or side by lumen, and the basal pole, the side by the CT.
What is the Basement Membrane
A thin sheet of ECM that contains contributions from both the CT and epithelium.
What anchors basement membrane to the cells?
how thick is the basement membrane?
what are the zones of the basement membrane?
1. Lamina Lucida (by the cell and made of laminin, enactin, and integrins)2. Lamina Densa (Collagen IV)3. Lamina Fibroreticularis (Depends, Collagen III)
Naming epithelium is based on which two factors?
1. Layering2. Shape of cells at surface
Simple squamous epithelium is found where in the body?
Areas of high diffusion (blood/lymph vessels, kidney glomeruli, lung alveoli)
Simple cuboidal epithelium is found where in the body?
Secretory cells lining glands and ducts, kidney tubules. Basically anywhere secretion of proteins is happening.
Simple columnar epithelium is found where in the body?
Mucous secreting absorptive surfaces (GI tract, bronchi of the lungs, uterine tubes) In bronchi and uterine tubes they are ciliated.
psuedostratisfied ciliated columnar epithelium is found where in the body?
Mucosal surfaces where they can secrete mucous. They are ciliated to push the mucous along.(Sperm ducts, ducts of larger glands, trachea and upper resp. tract.)
Stratified squamous epithelium is found where in the body?
If keratinized, its found on the skin and attached gingiva. If not keratinized, lining mucosa of the mouth, esophagus and vagina. So anything that might encounter abrasive forces on a regular basis.
Stratified cuboidal epithelium is found where in the body?
Rare, found in ducts of large sweat glands, salivary glands and mammary glands.
Stratified columnar epithelium is found where in the body?
Fairly rare. Found in male urethra, salivary glands. Sometimes its transitional between simple columnar and stratified squamous epithelia.
Urothelium is found where in the body?
Bladder lining, its stretchy.
What are microfilaments composed of?
How big in diameter are microfilaments?
What are the functions of microfilaments?
1. structural2. Microvilli3. For movement of a cell ( ex. filopodia)4. Gives shape to the cell5. Forms tracks for myosin, giving contractility
What are intermediate filaments composed of?
It depends on the tissue, but mostly vimentin ( in mesenchymal cells) and cytokeratin.
How big in diameter are intermediate filaments?
Around 10 nm in diameter.
What are the functions of intermediate filaments?
1. Anchors2. structure(it is non-contractile)
What are microtubules composed of?
How big in diameter are microtubules?
What are the functions of microtubules (2)?
1. Kenesins (monorail system)2. Movement (like Cilia and flagella using dynein)
What is a tight junction?
An interaction between two similar membrane proteins on adjacent cells.
What are characteristics of tight junctions (4)?
1. There are very narrow gaps between the joined cells. This controls the movement of stuff between them.2. They maintain cell polarization3. They bind to actin filaments.4. They play roles in various signaling pathways (like "contact inhibition")
What are 3 different types of tight junctions?
1. Claudins2. Occludins3. JAMs
What are Adhesive Junctions?
They hold cells to each other.
What are some of the components of adhesive junctions?
1. one Catherine (on outside) bind to two catinins (one on the inside of each cell) linking them together.2. Two nectins on outside of cells are bound together and each of them are bound to an Afadin on the inside of each cell (Nectin-Afadin complex). This plays a role in contact inhibition.3. Viniculin and actinin attach to actin filaments, which help link everything together.
How big of a gap are between two cells joined by cell to cell adhesive junctions?
20 nm (stuff can move through, mostly)
What are Focal adhesion junctions?
They are similar to cell to cell adhesions, but they are cell to ECM adhesions.
What are the major components of focal adhesion junctions?
1. integrins (they replace cadherins used in cell to cell adhesions as the transmembrane component.)2. viniculin, actinic and talon attachments to actin filament.3. Integrin receptors that play a role in cell signaling.4. Integrins also interact with many ECM proteins (collagen, fibronectin etc...)
What are desmosomes?
Cell to cell adhesions that look more "button-like."
What are some components of desmosomes?
1. Cadherins on the outside of the cell are called "desmoglein and desmocollin" They attach to cations (inside each cell) called desmoplakin, plakoglobin and plakophilin.2. They form lines externally and plaques internally visible as dark bands (electron dense)3. They attach to intermediate filaments in the cell to anchor them.4. Desomglein and desmocollin both interact with each other to form the junction.
What is a use of desmosomes?
They help resist shearing forces?
How big of gaps are between desmosomes?
What are hemidesosomes?
Cell to ECM adhesion that are similar in appearance to desmosomes.
What are some components to hemidesmosomes?
1. Similar components as desmosomes.2. They also attach to intermediate filaments.3. They have integrin as the transmembrane protein.4. They attach the cell tightly to basal lamina by integrin-laminin and collagen XVII.
What is a use of hemidesmosomes?
They resist shearing forces like desmosomes. They also attach epithelium to CT.
What is a gap junction?
A cell to cell aqueous pore that allows the propagation of electrical signals.
How many connexins are in a connexon? Also what are connexins and connexons?
6 connexin=1 connexion. A connexon is an aqueous channel that is formed by 6 connexins. These are in gap junctions.
What are the size of the pores in a gap junction? What are the sizes of the gaps between the cells?
2 nm pores, 2-3 nm between cells.
What kinds of things can travel through a gap junction?
ions (electrical signals), and small water-soluble molecules can pass.
What things can not pass through a gap junction?
Nucleic acids, sugars, and proteins because they are too large.
What is another name for cell to cell adhesion junctions?
What is a junctional complex?
tight junctions, zonula adherent, desmosomes, and gap junctions
What is a terminal bar?
A group of junctional complexes which attach cells on their lateral surfaces. They appear as a sort of band under a light microscope.
How are epithelial cells renewed?
Mitosis of a progenitor cell (stem cell) occurs in the basal lamina. One of the daughter cells stays as a progenitor cell and the other becomes a transit amplifying cell, which can differentiate into the type of cell that it should as it moves up into the epithelium.
What regulates the renewal of epithelium?
How does epithelium provide protection?
1. provides a physical barrier due to junctions.2. They secrete various things. Mucous and cilia trap and move things along.3. provides a zone for antigen detection(EX of protective epithelium are skin, URT, oral mucosa, gut and urinary system)
How does epithelium provide transport?
1. lets stuff through in a selective way.2. Active and passive transport3. can secrete things4. Can absorb things5. Blood gases can passively diffuse across an epithelial barrier6. Most interactions with the outside world occur across an epithelial barrier.
What are the basic characteristics of CT?
1. separated by ECM2. They are not linked together3. Consist of cells, ECM fibers and ECM ground substance
What are the basic functions of CT?
1. Mechanical and protective support of other tissues. (often found as STROMA in organs. Also surrounds blood vessels lymphatics and nerves.)2. Early repair of damaged organs. If repairs are not complete will lead to scarring (fibrosis)3.Contains immune system cells and presents a physical barrier. i.e. It provides defense and protection.4. Stores interstitial fluid, water and electrolytes so as to provide shock absorbance.
What are the ways that CT is categorized?
Loose or dense and regular or irregular
What are permanent CT cell types? What does this mean?
1. fibroblasts2. adipocytes3. macrophages4. mast cellsThese are cells that are in a permanent location. i.e. subcutaneous
What are transient CT cell types. What does this mean?
1. plasma cells2. lymphocytes3. Neutrophils4. EosinophilsThey travel in various fluids. i.e. blood
What is a fibroblast?
1. A go-cell of CT.2. They are highly motile3. They are involved in ECM production and therefore tissue repair.4. They rarely have cell-cell connections except in the periodontal lig.5. Often have cytoskeletal connections from integrin to fibronectin in the ECM.6. There are many sub-types in different tissues. i.e. dental pulp7. They have incredible diversity in secretion of products.8. They may heal slower with age, causing things like wrinkles in the skin.
What is collagen?
1. The most abundant protein in the body (28 types in the body)2. A major synthetic product of cells derived from the mesenchyme.3. Can have triple helical assembly
What is collagen comprised of?
1. It is rich in proline and lysine.2. Five microfibrils with a 1/4 stagger align in a parallel fashion.
What types of collagen are in Dentin? Pulp? Cartilage?
dentin: type I and some type IIIpulp: mixture of type I and type IIIcartilage: type II, basement membrane
What is collagen IV look like?
What is elastin?
1. Made by fibroblasts into sheets or fibers with an elastin core supported by a glycoprotein scaffold.
What is elastin comprised of?
Glycoproteins fibrillar-1 and fibrillar-2. These form a microfiber scaffold onto which elastin fibers can accumulate.
What is Marfan's Syndrome?
A fibrillin-1 mutation
What are characteristics of adipocytes?
1. each adipocyte is surrounded by basal lamina.2. They are mostly comprised of a single lipid droplet, surrounded by a thin ring of cytoplasm and a flattened nucleus.
What are the functions of adipocytes?
1. store energy2. insulate3. cushion4. make hormones
What is CT ground substance and what is it comprised of?
1. Its the non fibrillar stuff that makes up CT ECM.2. It is highly hydrated and keeps things "squidgy"3. Its made up of all sorts of things, mostly proteoglycans and glycoproteins.4. Gives compressive strength to tissues like cartilage.
What are proteoglycans and what are they comprised of and used for?
1. A main component in ground substance.2. They have a protein core with glycosaminoglycan chains (GAGs)3. Have a relatively strong negative charge and are hydrophilic (water accumulates in them) However, there are many that are non-aggregating.4. Can serve to accumulate growth factors in the ECM and can help activate GF receptors.
What are glycoproteins and what are they comprised of and used for?
1. Proteins with carbohydrate side chains attached.2. They are found everywhere, but also in ground substance.3. Examples include fibronectin (wound healing), tenascin (directs migration), thrombospondin (attachment, migration and collagen alignment)
How do proteoglycans differ from glycoproteins?
Proteoglycans: technically are specialized glycoproteins and generally have a larger carbohydrate component than glycoproteins.
Can growth factors be stored?
Yes. They can either be excreted for immediate use or stored in the ECM for later use.
What are the 3 general types of CT?
1. Loose CT2. Dense Irregular CT3. Dense regular CT
What is loose CT and what is it used for?
1. Its the most abundant type of CT. 2. It contains more cells and ground substance with fewer fibers. 3. It contains most cell types.4. It provides support and form but not as much structure.
Where is loose CT found?
1. underlies epithelia2. forms stroma3. fills space between tissues and organs4. the sheath around lymphatic and blood vessels.
What is Dense irregular CT and what is it used for?
1. More fibers with fewer cells and ground substance.2. The fibers are arranged randomly3. It provides multi-directional structure
Where is dense irregular CT found?
1. deeper dermis2. organ capsules3. submucosa of intestine
What is dense regular CT and what is it used for?
1. Fibers arranged in the same direction.2. Few cells that are mostly fibroblasts3. Provides directional structure
Where is dense regular CT found?
ligaments and tendons
What is skin made of?
1. combined epithelium and CT2. Has epidermis, dermis and hypodermis