Lecture 2: Epithelia Flashcards
What is a Junctional Complex?
A Junctional Complex is a combination of tight junctions, adherens junctions, and desmosomes that strengthens cellular attachment.
What are Tight Junctions and their key proteins? Where are they found?
Tight Junctions, also known as “sewing,” are composed of individual sealing strands (transmembrane proteins)
Key proteins include Claudins and Occludins.
They are found in the stomach, intestines, and bladder, maintaining cell polarity and preventing leakage of contents into the blood or surrounding tissue.
What is the purpose of Tight Junctions?
The purpose of Tight Junctions is to maintain cell polarity by preventing protein migration between apical and basal surfaces and to prevent the contents of organs from leaking into the blood or surrounding tissue.
What are Adherens Junctions and their function?
Adherens Junctions, also known as “bridge” or “belt desmosomes,” connect actin filaments to cadherins through a plaque layer of proteins. They prevent cell separation from tension forces, such as muscle contractions.
What is the structure of Gap Junctions?
Gap Junctions are formed by 6 Connexin proteins that create a Connexon (hemichannel). Two hemichannels combine to form a gap junction, allowing direct cell-to-cell connections and the passage of molecules up to 1 kDa.
What are Desmosomes and their role?
Desmosomes, similar to adherens junctions, have a plaque and resist shearing forces. They use cadherins to span the gap and bind to Desmoplakin, linking the cell surface to Keratin, providing structural integrity, especially in skin epithelium and cardiac cells.
Name and picture the different shapes of multicellular ducts 8 total
Simple tubular - tear shaped
Simple branched tubular -3 tears branching from single duct
Simple coiled tubular - tube that is coiled
Simple acinar (alveolar) - a single sac-like shape
Simple branched acinar (alveolar) - 3 sacs from one duct
Compound tubular (multiple branched tubular secretory portions)
Compound acinar (multiple branched acinar secretory portions)
Compound tubuloacinar (multiple branched mix of acinar and tubular secretory portions)
What are the 3 characteristics of multicellular ducts to be considered?
1) structure of the duct
2) structure of secretory area
3) relationship between the two
What is a single cell gland?
In epithelia that have independent, scattered gland cells, the individual secretory cells are called mucous cells, and they secrete mucin. The apical cytoplasm is filled with large secretory vesicles that look clear or foamy in a light micrograph.
What are the general features of epithelium?
Epithelium covers body surfaces, lines hollow organs, and forms glands. It functions as a selective barrier, secretory surface, and protective layer. It is arranged in a continuous sheet, either as a single layer or multiple layers, and has distinct surfaces: apical (free) surface, basal (attached) surface, and lateral surface (sides of the cell).
What are the two main types of epithelium?
The two main types of epithelium are Covering Epithelia, which cover exposed surfaces and internal cavities, and Glandular Epithelia, where secretory cells predominate.
What is the function of Covering Epithelia?
Covering Epithelia cover exposed surfaces and internal cavities, often containing scattered secretory cells. They make up the outer covering of the skin, some internal organs, and the inner lining of blood vessels, ducts, and body cavities, as well as the interior of the respiratory, digestive, urinary, and reproductive systems.
What is the function of Glandular Epithelia?
Glandular Epithelia are composed of secretory cells that can be classified into exocrine glands, which secrete onto external surfaces and into passages (ducts), and endocrine glands, which secrete hormones or precursors into interstitial fluid.
What are the cytoskeletal components of epithelial cells?
The cytoskeletal components include microfilaments, which provide strength and alter cell shape, and intermediate filaments, which are thicker and stronger, providing structural integrity.
What is the structure of the Basement Membrane?
The Basement Membrane is composed of two layers: the Basal Lamina (secreted by epithelial cells) containing collagen, laminin, proteoglycans, and glycoproteins, and the Reticular Lamina (produced by underlying fibroblasts) containing fibronectin and collagen. It separates epithelial tissue from connective tissue and is avascular but has nerves.
Do epithelia contain blood vessels?
No, epithelia are avascular, meaning they do not contain blood vessels.
How do epithelia exchange nutrients and wastes?
The exchange of nutrients and wastes in epithelia takes place by diffusion from vessels in the underlying connective tissue.
What are the functions of the Basement Membrane?
The functions of the Basement Membrane include supporting the overlying epithelium, providing a migration surface for epithelial cell growth and wound healing, acting as a physical barrier, and filtering substances in the kidneys.
How is epithelial tissue classified based on layers?
Epithelial tissue is classified based on layers into simple epithelium (one layer), stratified epithelium (two or more layers), and pseudostratified epithelium, which appears multilayered but all cells touch the basement membrane.
What is Simple Squamous Epithelium and its functions?
Simple Squamous Epithelium is the most delicate type of epithelium, functioning in filtration, diffusion, and secretion. It is found in areas requiring filtration (kidneys), diffusion (lungs), and secretion (e.g., outer layer of serous membranes).
How is epithelial tissue classified based on shape?
Epithelial tissue is classified based on shape into squamous (flat and thin), cuboidal (about as tall as they are wide), columnar (more tall than wide), and transitional (can change shape depending on organ shape, e.g., urinary bladder).
What is the appearance of Simple Squamous Epithelium?
Simple Squamous Epithelium appears thin, flat, and somewhat irregular, resembling jigsaw pieces or “fried eggs” or paving stones.
What are the subtypes of Simple Squamous Epithelium?
Subtypes include Mesothelium (lines pericardial, pleural, peritoneal cavities), Endothelium (lines blood & lymphatic vessels, heart), and Serosa (mesothelium + underlying connective tissue).
Where can Simple Squamous Epithelium be found?
It can be found in Bowman’s capsule of the kidney, lining cardiovascular and lymphatic systems, inside the eye, alveoli of lungs, visceral cavity linings, inside blood vessels, and inside the heart.
