Epithelia II Flashcards
What cell surface modification is commonly found on epithelia that are highly secretory or absorptive?
Microvilli. Many small folds/protrusions of the apical surface that dramatically increase surface area of the cell. They are highly organized and packed with cytoskeletal structures that assist in the transport of absorbed or secreted compounds.
What types of cell-cell interaction proteins are found between epithelial cells, other than tight junctions?
Desmosomes and adherence junctions mediate cell-cell contacts with cadherins. There are different types of cadherins, some specific to desmosomes and others specific to adherence junctions.
What is the structure of desmosome cadherins, what do they link to inside the cell, and what is their primary function?
Desmosome cadherins have extracellular domains that interact with other desmosome cadherins, and cytosolic domains that contact with intermediate filaments. Their primary function is the structural integrity of the skin, and mutation in these proteins cause diseases of skin integrity like lesions.
What do adherence junction cadherins interact with?
Adherence junction cadherins link to actin filaments. They act in signaling cascades that alter gene expression and secretory and translational machinery. They affect development, differentiation, and function of these cells.
What are the basal lamina?
Formerly called basement membranes (though they are not membranes but actually extracellular sheets). They are protein networks (not lipid based) that connect to integrins - transmembrane binding proteins on the basal surface of the epithelial cells. Different types of basal lamina are present around every cell structure (epithelia, endothelia, muscle, nerve, etc.)
What do integrins do?
Integrins are transmembrane proteins that have cytosolic domains and interact with proteins in the basal lamina to anchor the epithelial cells to the deeper connective tissue. There are different types of integrins (much like cadherins), some that connect to intermediate filaments (anchors), and others that connect to actin filaments (signaling). Those that connect to actin filaments convey signals that control cell development.
What are two critical functions that the basal lamina performs?
It forms the connections between the epithelial cells and the deeper connective tissue. It also forms a protective layer against invasion of the deeper tissues by other cells such as bacteria or cancer cells.
What is the function of the basal lamina in molecular gradients?
Because it is only a protein matrix, it is permeable to small molecules. However, in some locations like the glomerulus of the kidney, the basal lamina can provide molecular filtration.
What is the general structure of basal lamina and what does this structure do?
Basal lamina are generally constituted of fibrous proteins like collagen IV. They may also have specialized proteins present in specific areas that aid in the function of those cells, including growth factors or proteins that interact with integrins. They can control the development of epithelial sheets and control the stem cells within those sheets. They function in repair and modulation of function, and can direct motile cells to their destinations (such as neuronal axons).
What are epithelial glands?
Epithelial glands are collections of cells that are differentiated to become secretory machines that conduct large scale secretion of specific substances. Glands may consist of thousands of cells together producing many different substances down to individual cells in epithelial sheets secreting a specific substance.
Two kinds of glands
Exocrine - secrete materials onto surface of epithelium.
Endocrine - secrete material into the blood or interior of body.
What is the general structure of exocrine glands?
They invaginate from the lumen into deeper structures. Acini form at the deepest parts of the tubules, which are continuous with the epithelial layer and open to the lumen. Secretions from these cells exit through the apical surface into the lumen.
What is the general structure of endocrine glands?
They invaginate from the lumen into deeper structures, but eventually pinch off from the epithelial layer, forming structures that are isolated from the lumen and the epithelium that they originated from. Secretions from these cells must exit through the basolateral surface.
What is the pathway for hormones secreted by endocrine cells into the bloodstream?
They must cross the basolateral surface of the cell, through the basal lamina, connective tissue, basal lamina of the blood vessel, and both cell membranes across the endothelium cells into the blood.
What two types of secretions do exocrine glands produce?
Mucous - thick carbohydrate & protein rich secretions
Serous - watery secretions (ie, tears)
