Epithelial tissue

Question 1

Is epithelial tissue vascularized?

Answer 1

no, it’s avascular

Question 2

What are the functions of epithelia?

Answer 2

• barrier that protects internal tissue
• selective absorption and transport of various molecules from the environment
• selective secretion of various molecules and fluids
• movement of particles, solutions and cell elements
• large scale biochemical modification/conversion/metabolism (e.g. liver, kidney, intestine)
• communication
• reception of sensory stimuli

Question 3

What is endothelia?

Answer 3

linings blood and lymphatic vessels that face blood and lymph

Question 4

What are the sheets of cells that line enclosed internal spaces of body cavities?

Answer 4

mesothelium

Question 5

What is the epithelial to mesenchymal transition?

Answer 5

• embryonic epithelia disassemble and move into the mesenchymal (connective) tissues
• then they may migrate to other locations to form new epithelia or may transform into distinct non-epithelial cell lineages that give rise to other tissues

Question 6

Where is connective tissue?

Answer 6

under the basal lamina

Question 7

What runs through the connective tissue?

Answer 7

blood vessels, nerves, lymph, muscles

- each is surrounded by its own basal laminae that attach to their own neighboring connective tissue

Question 8

What are the two layers of mucosa?

Answer 8

• outer epithelium
• the connective tissue directly underneath called lamina propria (beneath is submucosa that has bigger vessels and muscles)

Question 9

What is the general relationship with the layers of epithelia tissue?

Answer 9

space(lumen)-epithelia-epithelial basal lamina-CT-other CT embedded tissues (blood vessels, muscles, nerves, each with their own basal laminae that connects them with CT)

Question 10

What are tight junctions?

Answer 10

• provide highly selective barrier that limits or prevents diffusion of substances between epithelial cells
• key proteins - occluding and Claudine
• ensure substances must pass through the epithelial cell by specific transport pathways

Question 11

What are adherence junctions?

Answer 11

• contain specific cadherins that link to actin filaments and other adapter/signaling proteins in the cytoplasm
• cadherins extracellular domains interact with each other (cytoplasmic tails that bind to adapters and actin filaments)
• some cadherin proteins control various aspects of epithelial polarity, development and function

Question 12

What are desmosomes?

Answer 12

• promote mechanical strength and resist shearing forces and promote structural organization of the epithelial sheet
• different class of cadherins that link to intermediate filaments and other adapter proteins

Question 13

What are gap junctions?

Answer 13

promote rapid communication between epithelial cells through diffusion of ions and small molecules

Question 14

Is the cytoskeleton asymmetric or polar in orientation?

Answer 14

yes, particularly microtubules

Question 15

Why is epithelial cell polarity crucial?

Answer 15

to allow unidirectional secretion and/or absorption of molecules to or from one side of the epithelium

Question 16

What is transcytosis?

Answer 16

• endocytosis of substances from one membrane region, followed by trans-cellular transport of the vesicles and their exocytosis from another membrane region

Question 17

What does basal laminae do?

Answer 17

• lines basal surface of epithelial tissue

- surrounds blood vessels, muscle and nerve tissue

Question 18

What is basal laminae made of?

Answer 18

network forming collagen interwoven with a variety of glycoproteins (laminin and enactins)

Question 19

What are the functions of basal laminae?

Answer 19

• mediate attachment of epithelia to underlying connective tissue
• contribute to selective filtration of substances diffusing to or from the epithelia
• necessary for the establishment and maintenance of epithelial cell polarity
• serve as highways for the migration of cells through connective tissue
• provide barrier to movement of invading microbes or cancer cells
• control the gene expression of cells to affect their proliferation or development
• critical to repair of epithelial tissue following injury (control development, morphogenesis and organization of epithelial cells)

Question 20

How do epithelial cells directly connect to the basal laminae?

Answer 20

• key class is integrins

- attachment of hemidesmosomes and focal adhesions

Question 21

What do focal adhesions regulate?

Answer 21

• integrins of focal adhesions connect to actin filaments inside the epithelial cell
• regulate epithelial polarity and function through signaling mechanisms

Question 22

What are the key properties of all stem cells?

Answer 22

• competent for cell division
• must self renew (one mother stem cell is regenerated with each division)
• produce anywhere from one to many distinct, differentiated cell types specific to each tissue

Question 23

What are transit amplifying cells?

Answer 23

daughter stem cells that proliferate at faster rates

- transitional intermediates

Question 24

Where do most stem cells reside in vivo?

Answer 24

stem cell niche - a specific tissue subcompartment

Question 25

What are two important principles to understand about stem cell signaling?

Answer 25

- each pathway controls multiple, different stem cell systems - a single signaling pathway will have different developmental outcomes in different stem cell lineages

Question 26

How do epithelial glands secrete their substances?

Answer 26

- exocytosis | - total cell disintegration (secretion of sebum)

Question 27

Where do exocrine glands secrete their materials?

Answer 27

apical side of epithelial surfaces

Question 28

What are secretory units (in relation to exocrine glands)?

Answer 28

- clumps of secretory epithelial cells that produce the bulk of the exocrine secretion - can be organized into alveoli or acini (bowl shaped lobules) or tubular glands (tubes)

Question 29

What are ducts (in relation to exocrine glands)?

Answer 29

- tubular structures that emanate from the secretory units - passageways to conduct secretions to their destination - simple glands - one duct - compound ducts - multiple, branched ducts

Question 30

What are the three types of exocrine glands of the body tubes (alimentary canal, respiratory, and urogenital system)?

Answer 30

- mucous - produces viscous glycoprotein rich fluids - serous - produces low viscosity watery fluids carrying specific enzymes - mixed - both kinds, typically from different cell types within the gland's secretory units

Question 31

Where do endocrine glands secrete substances?

Answer 31

- directly into the blood stream (have no ducts) - hormones must cross the basal surface and basal lamina of the epithelium - most endocrine cells secrete these molecules from the basolateral membrane

Question 32

What generally regulates secretions from both exocrine and endocrine glands?

Answer 32

autonomic nervous system, hormones, or both

Question 33

What are adenocarcinomas?

Answer 33

cancers derived from glandular epithelium