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.
What is Simple Cuboidal Epithelium and its functions?
Simple Cuboidal Epithelium functions in secretion and absorption. It appears as cuboidal or hexagonal boxes, with the distance between adjacent nuclei approximately the height of the epithelium.
Where can Simple Cuboidal Epithelium be found?
It is located in pancreas ducts, parts of kidney tubules, smaller ducts of many glands, secretory chambers of the thyroid, anterior surface of the lens, pigmented epithelium at the posterior of the retina, and secretory parts of some glands like the thyroid.
What is Simple Columnar Epithelium and its appearance?
Simple Columnar Epithelium is rectangular and often hexagonal but taller and more slender than cuboidal. The nuclei are often elongated and near the base of the cell, with the height of the cell being several times the distance between adjacent nuclei.
What are the characteristics of Non-Ciliated Simple Columnar Epithelium?
Non-Ciliated Simple Columnar Epithelium is a single layer with microvilli on the apical surface and goblet cells interspersed. It increases surface area for absorption and is found in the gut mucosa from stomach to anus, ducts of many glands, and the gall bladder.
What is the function of Ciliated Simple Columnar Epithelium?
Ciliated Simple Columnar Epithelium assists in the motility of mucus and foreign objects or oocytes. It is found in bronchioles, fallopian tubes, sinuses, and the central canal of the spinal cord.
What is Stratified Squamous Epithelium and its appearance?
Stratified Squamous Epithelium consists of layers of cells that resemble plywood or pancakes in the upper layers, with lower layers appearing cuboidal or columnar. Cells furthest from nutrition are thinner and less active.
Where is Stratified Squamous Epithelium located?
Stratified Squamous Epithelium is located in areas where mechanical or chemical stresses are severe, providing protection against microbes.
What is Pseudostratified Columnar Epithelium and its appearance?
Pseudostratified Columnar Epithelium has nuclei at different levels, giving the appearance of several layers, but it is actually a simple epithelium where all cells contact the basement membrane, though not all reach the apical surface.
What are the specialized subtypes of Pseudostratified Columnar Epithelium?
Specialized subtypes include Pseudostratified Ciliated Columnar Epithelium, which has cilia and goblet cells, found in the upper airways, and Pseudostratified Non-Ciliated Columnar Epithelium, which lacks cilia and goblet cells, found in larger ducts of glands, epididymis, and part of the male urethra.
What is the function of Pseudostratified Ciliated Columnar Epithelium?
The function of Pseudostratified Ciliated Columnar Epithelium is to secrete mucus and move it, primarily found in the most upper airways.
What is Transitional Epithelium?
Transitional Epithelium is a stratified epithelium that changes shape and is found only in the urinary bladder.
What are Glandular Epithelia?
Glandular Epithelia consist of single cells or groups of cells that secrete substances into ducts, onto surfaces, or into the blood. Their primary function is secretion.
What are the two main types of glands in glandular epithelium?
Exocrine glands secrete into ducts that empty onto surfaces (e.g., goblet cells, sweat glands), while endocrine glands secrete hormones directly into the bloodstream.
What are examples of exocrine glands?
Examples of exocrine glands include sweat glands, salivary glands, oil glands, wax glands, and the pancreas.
What is a characteristic of endocrine glands?
Endocrine glands secrete hormones into the bloodstream via interstitial fluid, with generally distant strong effects. Examples include the pituitary, pineal, thyroid, and parathyroid glands.
What are the characteristics used to describe the structure of multicellular glands?
The structure of multicellular glands is described by the structure of the duct, the structure of the secretory area, and the relationship between the two.
What determines the subtype in stratified epithelium?
In stratified epithelium, the outer layer determines the subtype.
What are cell junctions?
Cell junctions are connection points between the plasma membranes of adjacent cells. There are namely 5 types: gap junction, adherens junction, desmosomes, hemidesmosomes, and tight junction.
What is the apical surface?
The edge surface of epithelial tissue facing the body surface, body cavity, lumen of an internal organ, or a tubular duct that receives cell secretions. They may contain cilia or microvilli
What is the lateral surface?
The surface of an epithelial cells which face the adjacent cells on either side - these surfaces contain junctions (gap, desomosome, tight, adherens)
What is the basal surface?
The deepest layer of epithelial cells facing the basement membrane - these may contain hemidesmosome junctions.
How are epithelial cells arranged?
Epithelial cells are arranged into flat, continuous sheets and can be comprised of single or multiple layers
What is the cytoskeleton?
A structure that helps cells maintain their shape and internal organization, and it also provides mechanical support that enables cells to carry out essential functions like division and movement.
What are the components of the cytoskeleton?
Microfilaments - such as actin
Intermediate filaments - such as keratin
What is ACTIN?
A type of microfilament - protein bundles beneath cell membrane and cytoplasm that determine cell shape and structure and allow for muscle contraction.
What is KERATIN?
A type of intermediate filament - structural roles in the cytoplasm of cells, also allow movement of material within cytoplasm
Describe the structure of tight junctions
Located near the apical surface
Strands of transmembrane proteins (claudins and occludins) link adjacent plasma membranes in a ‘sewing-like’ appearance
No gap is left
What is the function of tight junctions?
Joins adjacent plasma membranes tightly together keeping cell polarity (ie electrically tight) by preventing migration of proteins between apical and basal surfaces
Where are tight junctions found?
Epithelial tissue lining stomach, intestines, and bladder
What are claudins and occludins?
Transmembrane proteins that form the tight junction
Describe the structure of a single cell gland.
A single cell gland consists of independent, scattered gland cells, such as mucous cells, which secrete mucus. The cytoplasm contains large secretory vesicles.
Explain the function of goblet cells.
Goblet cells are a type of mucous single cell exocrine gland that secrete mucus to lubricate and protect epithelial surfaces.
Define what a mucous cell is.
A mucous cell is a type of glandular cell that produces and secretes mucus, often found in epithelial tissues.
How do secretory vesicles appear in the cytoplasm of a single cell gland?
The secretory vesicles in the cytoplasm of a single cell gland appear large and can look clear or foamy when viewed under a microscope.
What is the significance of the Golgi apparatus in single cell glands?
The Golgi apparatus is involved in modifying, sorting, and packaging proteins and lipids for secretion, playing a crucial role in the function of single cell glands.
What is the relationship between goblet cells and mucous cells?
Goblet cells are a specific type of mucous cell, but not all mucous cells are shaped like goblet cells.
Describe the structure of simple tubular exocrine glands.
Simple tubular exocrine glands consist of a single, straight tube that opens directly onto the surface.
Explain the characteristics of branched tubular exocrine glands.
Branched tubular exocrine glands have multiple tubular branches that extend from a single duct.
Define the structure of coiled tubular exocrine glands.
Coiled tubular exocrine glands are characterized by a tube that is coiled, allowing for a compact structure.
How do simple acinar exocrine glands differ from simple tubular glands?
Simple acinar exocrine glands have a sac-like structure at the end of the duct, while simple tubular glands have a straight tube.
Describe the features of compound tubular exocrine glands.
Compound tubular exocrine glands consist of multiple tubular units that branch and connect to a larger duct.
Explain the structure of compound acinar exocrine glands.
Compound acinar exocrine glands have multiple sac-like structures that connect to a larger duct, resembling clusters.
How do multicellular exocrine glands differ from unicellular exocrine glands?
Multicellular exocrine glands consist of multiple cells organized into a structure, while unicellular glands are single cells that secrete directly.
Describe the three characteristics used to describe the structure of multicellular glands.
- Structure of duct 2. Structure of secretory area 3. Relationship between the two.
Define the structure of duct in multicellular glands.
The structure of the duct refers to the configuration and branching pattern of the duct system that transports secretions from the gland.
