Epithelium
Q: Epithelium consists largely of what?
A: Closely packed cells with little extracellular material.
Q: How are epithelial cells arranged?
A: In continuous sheets of either single (simple) or multiple (stratified) cells.
Q: Anything that enters or leaves the body must pass through what?
A: An epithelium.
Q: What surfaces do epithelia have?
A: A free surface (exposed) and a basal surface (attached to basal lamina).
Q: Are epithelia vascular?
A: No, they are avascular.
Q: Do epithelia have a nerve supply?
A: Yes.
Q: Do epithelia have renewal capacity?
A: Yes, they have a high capacity for renewal.
Q: List the functions of epithelia.
A: Mechanical protection, absorption, secretion, lubrication, surface for diffusion, transportation, excretion, sensory reception, reproduction.
Q: What forms the basement membrane?
A: Basal lamina and reticular lamina.
Q: What does the basal lamina do?
A: Binds epithelial cells to underlying connective tissue.
Q: What is the basal lamina composed of?
A: Type IV collagen, glycoproteins (laminin and entactin), proteoglycans.
Q: What does laminin bind?
A: Type IV collagen and integrins (hemidesmosomes).
Q: What synthesizes the reticular lamina?
A: Connective tissue of the lamina propria.
Q: What is the reticular lamina made of?
A: Type III collagen and connecting collagen.
Q: What are the specialized connections on lateral surfaces of epithelial cells called?
A: Intercellular junctions.
Q: What is the closest junction to the free surface?
A: Zonula occludens (tight junction).
Q: What proteins are involved in tight junctions?
A: Occludin and claudin.
Q: What are examples of adhering/anchoring junctions?
A: Zonula adherens, desmosome (macula adherens), hemidesmosomes.
Q: What do zonula adherens do?
A: Anchor cells together and connect actin filaments between cells.
Q: What do desmosomes do?
A: Provide strong spot links between cells.
Q: What do hemidesmosomes do?
A: Join epithelial cells to basal lamina, involve integrins.
Q: Name four cell adhesion molecules (CAMs).
A: Cadherins, integrins, selectins, immunoglobulin superfamily.
Q: What do cadherins do?
A: Anchor cells together in zonula adherens and suppress epithelial tumor cells.
Q: What do integrins interact with?
A: Basal lamina (laminin, Type IV collagen) and extracellular matrix.
Q: What do selectins do?
A: Involved in WBC and endothelial cell recognition.
Q: What family of molecules is involved in immune reactions?
A: Immunoglobulin superfamily.
Q: What is the function of gap junctions?
A: Form small diffusion channels (connexons) between cells.
Q: What are connexons made of?
A: Six integral proteins called connexins.
Q: What are the three specializations of the free surface of epithelia?
A: Cilia, microvilli, stereocilia.
Q: What do cilia do?
A: Move mucus and other substances.
Q: Where are microvilli found?
A: Brush border of kidney tubule cells and striated border of intestinal absorptive cells.
Q: What do microvilli do?
A: Increase surface area.
Q: Where are stereocilia found?
A: Epididymis and sensory (hair) cells of inner ear.
Q: What are the two main categories of epithelia?
A: Covering and glandular.
Q: What are the classifications of covering epithelium by layers?
A: Simple (single layer) and stratified (multiple layers).
Q: What are the classifications of covering epithelium by shape?
A: Squamous (flat), cuboidal (cube/hexagonal), columnar (tall).
Q: What is simple squamous epithelium specialized for?
A: Active and passive movement of substances.
Q: What are the special names for simple squamous epithelium?
A: Endothelium (lining of heart and blood vessels), mesothelium (lining of ventral body cavities).
Q: What is the shape of simple cuboidal epithelium?
A: Cube or hexagonal.
Q: What is the function of simple cuboidal epithelium?
A: Secretion and absorption.
Q: What are the types of simple columnar epithelium?
A: Ciliated, non-ciliated goblet cells, absorptive cells with microvilli.
Q: What are the types of stratified epithelium?
A: Squamous, cuboidal, columnar (rare), transitional.
Q: What are the types of stratified squamous epithelium?
A: Keratinized (dry, cornified) and non-keratinized (wet, non-cornified).
Q: What is pseudostratified columnar epithelium?
A: Appears multilayered, but all cells touch basement membrane.
Q: Where is transitional epithelium found?
A: Pelvis of kidney, ureters, urinary bladder, part of urethra.
Q: What is a characteristic of transitional epithelium?
A: Cells change shape according to degree of organ distension.
Q: What are the two classifications of glands?
A: Exocrine and endocrine.
Q: What are exocrine glands divided into?
A: Lobes and lobules.
Q: What are the secretion types of exocrine glands?
A: Serous, mucous, mixed.
Q: What is the only important unicellular gland?
A: Goblet cell.
Q: What are the two types of multicellular glands by duct?
A: Simple (unbranched) and compound (branched).
Q: What are the two types of multicellular glands by secretory part?
A: Tubular and acinar (alveolar).
Q: Give an example of a simple tubular gland.
A: Crypts of Lieberkühn (colon).
Q: Give an example of a simple coiled tubular gland.
A: Sweat gland.
Q: Give an example of a simple branched alveolar gland.
A: Sebaceous gland.
Q: Give an example of a compound gland.
A: Labial gland.