Epithelia 2

Question 1

1. State the types and functions of the different cell surface modifications on epithelial cells.

Answer 1

Microvilli:

• Microvilli–> contain actin bundles connected to inner cytoskeleton.
• Increases surface area which increases the rate/efficiency of membrane transport/secretion.
• Sterocilia is a type of microvillus found in the epididymis. It is also found in sensory cells in ear.
• Sterocilia are long, actin-filled and are NOT cilia.

Cilia:

• Cilia = microtubule-containing extensions.
• Primary cilia organize and promote signal transduction systems that control cell division, fate, and function.
• Found in respiratory tract and oviduct.
• Sensory cilia involved in sensory reception (ear hair cells).
• Mutations in cilia = ciliopathies.
• On basolateral surface, have infolds and outfolds that increase surface area.

Question 2

2. Describe basal laminae by stating their basic components, their functions, the basis of their diversity, and their structural relationship to epithelia and other tissues.

Answer 2

Basal lamina:

• Extracellular material that underlies basal surface; also surrounds many other cell/tissues.
• Formed by collagen (IV) that forms sheets of fibers interwoven with glycoproteins (like laminins and entactin).
• BL structure is different in different tissues.
• Basal lamina:
• mediate attachment of epithelia to connective tissue
• contribute to selective filtration of things moving in and out of cells
• help establish cell polarity
• serve as highways for migration through connective tissue
• provide a barrier to movement of invaders
• control gene expression,
• control development/morphogenesis/organization,
• and provide tissue scaffolding.
• BL separate epithelial cells from underlying connective tissue and attach epithelial cells to ECM of connective tissue.
• Epithelial cells connect BL via hemidesmosomes/focal adhesions on basal surface of epithelial cells (integrins!).
• Specific integrins of hemidesmosomes connect to intermediate filaments; focal adhesions connect actin filaments (regulate polarity and signaling).

Question 3

3. Compare and contrast exocrine and endocrine glands in terms of their development, general structure, and functions. For both types of glands, trace the path that a secreted molecule must take from its synthesis to its destination, and describe all the barrries/structures the molecule must cross en route.

Answer 3

• Glands derived from epithelial tissue –> function is to:
• secrete specific bioactive molecules, complex fluids, or both.
• 2 major types of epithelial glands = exocrine and endocrine.
• Glands secrete substances via:
  1) exocytosis (aka merocrine/apocrine glands) or
  2) total cell disintegration (all cellular contents are part of secretion = holocrine).
• Exocrine glands secrete materials onto apical side of epithelial surfaces; multicellular.
• Some can be unicellular secreting glands –> goblet cell.
• secretory units can be alveolar glands or acinar glands, or tubular glands if organized into tubes.
• ducts emanate from secretory units –> their epithelia can modify secretion content and help them get to destination.
• Single duct glands = simple glands; multiple branched ducts = compound glands.
• glands can produce mucous, serous, or mixed fluids.
• secrete materials unidirectionally from apical surface

-Endocrine glands have no ducts (are ductless) and secrete substances directly into blood.
–hormones act over long distances
-glands are embedded with/surrounded by connective tissue containing capillary networks (each clump surrounded by basal lamina)
-hormones have to cross the basal surface, basal lamina of epithelium, and basal lamina and endothelial layer of capillary to reach blood stream
-Secretions from both types of glands regulated by ANS.