Epithelial Transport

Question 1

What drives the process of epithelial renewal?

Answer 1

epithelial stem cells

Question 2

How do epithelial tissue get metabolite, gases, and secreted ligands?

Answer 2

• avascular

- they must diffuse through connective tissue and basal laminae to reach epithelia or blood

Question 3

What are some of the functions served by epithelial?

Answer 3

• barrier
• selective absorption and transport of various molecules from the environment
• selective secretion
• movement of particles, solutions, and cell elements through passageways
• large scale biochemical modification/conversion/metabolism
• communication to and from other tissues and organs
• reception of sensory stimuli

Question 4

What are endothelia?

Answer 4

line blood and lymphatic vessels (made of endothelial cells)

Question 5

What is mesothelium?

Answer 5

sheets of cells that line enclosed internal spaces of body cavities

Question 6

Embryonic epithelia often disassemble and move into the _______________, where they may migrate to other locations to form new __________ or may transform into distinct _____________ cell lineages that give rise to other tissues.

Answer 6

Embryonic epithelia often disassemble and move into the mesenchymal (connective) tissues, where 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 7

What are the two layers of mucosae?

Answer 7

• outer epithelium

- the connective tissue directly underneath called the lamina propria

Question 8

What does the lamina propria contain?

Answer 8

(connective tissue directly underneath the epithelial layer of mucosae)
- immune cells, small blood vessels

Question 9

What is submucosa?

Answer 9

• deeper connective tissue layer under the lamina propria

- contains bigger vessels and muscles, nerve axon bundles, etc.

Question 10

What are the general layers of epithelial sheets?

Answer 10

Space (lumen) - Epithelia - epithelial basal lamina - connective tissue - other connective embedded tissues (blood vessels, muscles, nerves - with their own basal laminae that connect them to the CT)

Question 11

What is simple epithelia?

Answer 11

all cells arranged in a single layer or sheet

Question 12

What is stratified epithelia?

Answer 12

more than one layer of cells in which the cells of the outer layers do not directly contact the basal lamina

Question 13

What is pseudostratified epithelia?

Answer 13

some cells do not reach the free surface but all directly rest on the basal lamina

Question 14

What is transitional epithelia?

Answer 14

(found in the bladder)

- epithelia are stratified but when stretched change shape from cuboidal to squamous

Question 15

What are tight junctions?

Answer 15

• highly selective barrier that limits or prevents diffusion of substances between epithelial cells

Question 16

What are the key core proteins of tight junctions?

Answer 16

occluding and claudins

Question 17

What are adherence junctions?

Answer 17

promote attachment, morphological organization, and stem cell behavior within the epithelial sheet

Question 18

What proteins do adherence junctions contain?

Answer 18

specific cadherins that link to actin filaments and other adapter/signaling proteins in the cytoplasm

Question 19

What are desmosomes?

Answer 19

promote mechanical strength and resist shearing forces and promote structural organization of the epithelial sheet

Question 20

What proteins do desomosomes contain?

Answer 20

different class of cadherins that link to intermediate filaments and other adapter proteins

Question 21

What are gap junctions?

Answer 21

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

Question 22

Why is the membrane surrounding the lateral and basal side of an epithelial cell called the basolateral membrane?

Answer 22

because the protein and lipid content is similar on both the lateral and basal sides

Question 23

What are the two key aspects of epithelial cell polarity?

Answer 23

• the plasma membrane composition is locally segregated into domains (apical and basal)
• the organelles and cytoplasm is polarized ( cytoskeleton, especially microtubules, is asymmetric or polar in orientation)

Question 24

What is transcytosis?

Answer 24

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

Question 25

Epithelial cell polarity is crucial to allow _____________ to or from one side of the epithelium.

Answer 25

unidirectional secretion and/or absorption of molecules

Question 26

What are two apical surface modifications?

Answer 26

microvilli and cilia

Question 27

What are microvilli?

Answer 27

cell surface extensions that contain actin bundles connected to cytoskeletal elements in the cell interior

Question 28

What is the primary function of microvilli?

Answer 28

to increase surface area, which greatly increases the rate/efficiency of membrane transport and secretion

Question 29

What is a basolateral surface modification?

Answer 29

infolds and outfolds of the basolateral membrane (lack structural organization of the apical microvilli and cilia)

Question 30

What is the basal lamina?

Answer 30

- thin sheet of extracellular material that underlies the basal surface of each epithelial tissue, blood vessels, muscle, and nerve tissue - made of collagen (esp. collagen IV) and extracellular glycoproteins (lamins and entactin)

Question 31

What are the functions of basal laminae?

Answer 31

- mediate attachment of epithelia to underlying connective tissue - contribute to selective filtration of substances diffusing to or from the epithelia - necessary for establishment and maintenance of epithelial polarity - serve as specific highways for migration of cells through connective tissue - barrier to movement of invading microbes or cancerous cell into other tissues - control the gene expression of cells to affect their proliferation or development - control development, organization, repair from injury or disease (tissue scaffolding)

Question 32

How do epithelial cells directly connect to the basal laminae?

Answer 32

by attachment of integrins (hemidesmosomes and focal adhesions) on the basal surface of the epithelial cell to components of the basal lamina

Question 33

What do focal adhesions connect to inside the epithelial cell?

Answer 33

actin filaments

Question 34

What are the three key properties of stem cells?

Answer 34

- they are competent for cell division - stem cells must self renew (at least one mother stem cell is regenerated with each division) - stem cells produce anywhere from one to many distinct, differentiated cell types specific to each tissue

Question 35

What are transit amplifying cells?

Answer 35

- daughters of stem cells that proliferate at faster rates - middle step - transitional intermediate - transit amplifying cells then produce differentiated cells

Question 36

What regulates cell division and differentiation in stem cells?

Answer 36

- in the stem cell niche, neighboring cells secrete regulatory factors that tightly control stem cell division and differentiation programs - signals from distant sources (hormones and endocrine glands)

Question 37

What is the typical cell signaling pathway for stem cells?

Answer 37

- extracellular ligand secreted by signaling cells - receptor in receiving cells binds and is activated/inactivated by the ligand - downstream effector proteins in the cytoplasm and nucleus - numerous modulator proteins that promote or suppress pathway components

Question 38

What are two key principles of stem cell signaling pathways?

Answer 38

- each pathway controls multiple, different stem cell systems (some are unique, but many are shared) - a single signaling pathway will have different development outcomes in different stem cell lineages

Question 39

What are exocrine glands?

Answer 39

secrete material onto epithelia lined surfaces or the outside world

Question 40

How do glands secrete their substances?

Answer 40

- exocytosis | - total cell disintegration (e.g. oily sebum onto hair and skin)

Question 41

What are the main components of multicellular exocrine glands?

Answer 41

- secretory units (clumps of secretory epithelial cells) | - ducts (tubular structures that emanate from the secretory units)

Question 42

What are the three general types of exocrine glands products?

Answer 42

- mucous (viscous glycoprotein-rich fluids) - serous (low viscosity watery fluids) - mised

Question 43

Do endocrine glands have ducts?

Answer 43

no

Question 44

How do endocrine glands secrete hormones when they're surrounded by basal lamina?

Answer 44

hormone molecules must cross the basal surface and basal lamina of the epithelium, so most endocrine cells secrete these molecules from the basolateral membrane

Question 45

What regulates secretions from the exocrine and endocrine glands?

Answer 45

autonomic nervous system and/or hormones from the blood

Question 46

What are adenocarcinomas derived from?

Answer 46

glandular epithelium