Epithelial Tissue and Glands

Question 1

What are the 4 types of primary tissues?

Answer 1

1. epithelial 2. connective 3. neural 4. muscle

Question 2

Define epithelium?

Answer 2

avascular closely packed cells that line the external surface and internal closed cavities

Question 3

What are the 3 embryonic germ layers?

Answer 3

1. ectoderm 2. mesoderm 3. endoderm

Question 4

What are the functions of epithelium? PASSST

Answer 4

1. transportation - of substances across the epithelia 2. sensation & detection - olfactory mucosa, taste buds, retina and hair cells in ears 3. protection e.g. skin 4. selective permeability 5. secretion - mucus, hormones, enzymes 6. absorption - materials from lumen

Question 5

Types of epithelial tissue?

Answer 5

1. surface epithelium 2. glandular epithelium

Question 6

How is epithelia classified?

Answer 6

1. number of cell layers - simple and strattified 2. shape of cell - squamous, cuboidal, columnar, pseudostratified, transitional

Question 7

Describe classification of epithelia?

Answer 7

A. number of cells : 1. simple - single layer 2. stratified - multiple cell layers B. shape of cell : 1. squamous - flat 2. cuboidal - square/cube shaped 3. columnar - column shaped 4. psuedostratified - one cell layer but looks like multiple because nuclei are at different levels + not all cells reach the cell surface 5. transitional - have a round cap/umbrella shape

Question 8

Describe special features of epithelia?

Answer 8

1. goblet cells - secrete mucus 2. keratinized layer - layer of dead cells with no nuclei and filled with keratin 3. cilia - movement of substances across the epithelial surface 4. microvilli - increase surface area for absorption 5. stereocilia - specialized long immotile microvilli found in olfactory hair cells of the ear

Question 9

Describe specialized epithelial cells?

Answer 9

1. goblet cells - secrete mucus 2. myoepithelial cells - contractile, located between epithelia and basement membrane 3. neuroepithelial - auditory hair cells, taste buds, photoreceptors of retina, olfactory epithelia and chemo/osmotic receptor cells

Question 10

What are the 3 characteristic features of epithelium tissues?

Answer 10

1. cells are polarized 2. cells adhere to each other by cell to cell junctions 3. cells have a basement membrane

Question 11

What is a polarized cell?

Answer 11

cell divided morphologically/functionally to biochemical domains

Question 12

Name the surface domains?

Answer 12

1. apical 2. lateral 3. basal

Question 13

What is the apical domain?

Answer 13

the side of the cell that faces the external environment/lumen

Question 14

What is the surface of epithelial cells rich in? Transport + Recognition

Answer 14

1. ion channels and carrier proteins - for the transportation of substances across the epithelia 2. glycocalyx (glyoproteins and glycolipids) - for recognition of cells and substances

Question 15

Name and describe modifications of the top surface?

Answer 15

1. striated microvilli/brush border - increase surface area 2. keratinized layer - layer of dead cells with no nuclear filled with keratin 3. stereocilia - long immotile finger like extentions required for hearing and balance

Question 16

Name the cell to cell junctions?

Answer 16

1. zonulae occludens/occluding junctions (tight) 2. anchoring junctions (adhesion) 3. gap junctions (communicating)

Question 17

How are cells attached at the lateral domain?

Answer 17

cell to cell junctions

Question 18

What are these junction?

Answer 18

zonulae occludens/occluding (tight), anchoring (adhesion) and gap (communicating) junctions

Question 19

3 factors of tight junctions?

Answer 19

1. created by localized sealing of adjacent plasma membranes of epithelial cells 2. are concentrated towards the apical surface 3. they are a permeability barrier

Question 20

What do they use as the cytoskeletal component?

Answer 20

actin filaments

Question 21

What are they made of?

Answer 21

claudins, occludins, and JAM cell adhesion molecules

Question 22

What are the adapters?

Answer 22

ZO-1, ZO2, ZO3, cyngulin, sympleitin

Question 23

What do pathogenic agents cause?

Answer 23

act on ZO1 - causing junction to become permeable e.g. cholera toxins

Question 24

Mutation of Claudin - 16?

Answer 24

Claudin 16 is present in tight junctions of distal kidney tubule - its mutation will affect selective permeability & absorption of Mg2+ into blood stream

Question 25

Function of Claudin - 1?

Answer 25

Claudin 1 is present in epithelial junctions of skin responsible for water proofing/water barrier - keratin comes second in this regard

Question 26

What is the blood-brain barrier?

Answer 26

tight juctions protect neurons from toxins through the Blood-Air barrier

Question 27

What is function of gap junctions?

Answer 27

mediate electrical and chemical coupling between cells (ions, amino acids, etc)

Question 28

What is a gap junction made of and how many?

Answer 28

formed from 2 connexons (one on each cell)

Question 29

What is a connexon made of?

Answer 29

6 connexin proteins

Question 30

What is gap junction permeability regulated by?

Answer 30

by calcium, pH, and phosphorylation of connexins

Question 31

Mutations in Connexin 26 cause?

Answer 31

connexin 26 is highly exprssed in cells of the cochlea - causing deafness

Question 32

Mutations in Connexin 50 cause?

Answer 32

connexin 50 is associated with congenital cataracts - leading to blindness

Question 33

Function of Connexin 40?

Answer 33

spread impulses to the heart

Question 34

What are 4 examples of anchoring junctions?

Answer 34

1. macula adherens/desmosomes 2. zonula adherens 3. hemidesmosomes 4. focal adhesions

Question 35

What is the cytoskeletal component of zonulae adherens?

Answer 35

actin filament

Question 36

What is the function of actin filaments?

Answer 36

connects the cytoskeleton of one cell to the cytoskeleton of another cell - making the adhesion belt

Question 37

Name the adhesiosn molecules and adapters of the adhesion belt?

Answer 37

adapter = E-cadherins and adhesion molecules = Ca2+

Question 38

How is cadherin linked to actin?

Answer 38

via catenin and vinculin

Question 39

What are these junctions used in the formation of?

Answer 39

neural tube, branching morphogenesis of mammary, salivary glands

Question 40

What anchoring junction is used for tensil strength?

Answer 40

macula adherens/desmosomes

Question 41

What is the cytoskeletal component for desmosomes?

Answer 41

intermediate filament

Question 42

How does it do this?

Answer 42

by using cadherins (desmoglein and desmocollin)

Question 43

What do cadherins use?

Answer 43

desmoplakins and plakoglobins adapter proteins

Question 44

What are 2 examples of intermediate filaments of desmosomes?

Answer 44

1. keratin filaments (epithelial cells) 2. desmin filaments (heart muscle)

Question 45

What is pemphigus vulgaris?

Answer 45

is an auto-immune disease in which the body produces auto-antibodies against desmosome proteins, binding of the auto-antibodies disrupts cell adhesion - skin integrity is compromised leading to widespread blistering and loss of extracellular fluids

Question 46

What are the cell-to-extracellular matrix junctions?

Answer 46

1. hemidesmosomes 2. focal adhesions

Question 47

What is the function of hemidesmosomes?

Answer 47

connect intermediate filaments in the cell to the basal lamina (ECM)

Question 48

What is the function of focal adhesions?

Answer 48

create a link between the actin cytoskeleton and extracellular matrix proteins

Question 49

What do they consist of ?

Answer 49

1. cytoplasmic face : where actin binds - vinculin & talin 2. transmebrane region - integrins 3. extracellular face : where extracellular proteins bind e.g. fibronectin, collagen, ephrins, laminin

Question 50

Where are the basal surface located?

Answer 50

unberlying epithelial cells

Question 51

What is the basal surface characterised by?

Answer 51

1. basement membrane 2. cell to extracellular matrix junctions 3. plasma membrne

Question 52

What does the basement membrane consist of?

Answer 52

1.Basal lamina - secreted by epithelial cells 2. Reticular lamina (lamina reticularis)- secreted by connective tissue cells (collagen type I and type III)

Question 53

What are the functions of basal laminas?

Answer 53

1. support - for overlying epithelium 2. differentiation - via signaling by integrins 3. cell migration 4. filter - for large particles 5. wound response - clotting 6. has a role in cancer metastasis - cells break this barrier to spread

Question 54

What is the reticular lamina?

Answer 54

a layer of reticular fibers that underlies the basal lamina secreted by CT cells

Question 55

What are the Structures responsible for attachment of basal lamina to the underlying CT ?

Answer 55

1. anchoring fibrils (type VII collagen) 2. fibrillin microfibrils

Question 56

Definition of glandular epithelium?

Answer 56

type of epithelial tissue which cover the glands of the body

Question 57

What are glands?

Answer 57

organized arrangements of secretory cells

Question 58

What are the major types of glands?

Answer 58

1. exocrine - glands that secrete their products via ducts or tubes 2. endocrine - glands that release their products basally into the underlying connective tissue and enter the vascular system (no duct systems) 3. paracrine - secretions reach target cells by diffusion through the extracellular space or immediately subjacent connective tissue

Question 59

Classification of glandular epithelia according to the number of secretory cells?

Answer 59

1. unicellular glands - have one cell e.g. goblet cells that secrete mucus 2. multicellular glands - glands have many cells

Question 60

Classification of glandular epithelia according to their nature of secretion?

Answer 60

1. serous - cell-type that produces a thin watery, protein-rich secretion 2. mucous - cell type that secretes viscous hydrophilic glycoproteins called mucins (that have a lubricating or protective function) 3. mixed - these glands have both serous and mucous cells

Question 61

Classification of glandular epithelia according to their mechanism of secretion?

Answer 61

1. merocrine secretion 2. holocrine 3. apocrine

Question 62

Merocrine secretion?

Answer 62

1. the membrane bound secretory granules fuse with the apical membrane 2. the contents of the granule are opened and released by exocytosis 3. the secretory granules leave the cell with no loss of other cellular material. e.g. Pancreatic acinar cells

Question 63

Apocrine secretion?

Answer 63

1. secretory granules gather at the apical region of the cell 2. a portion of the cytoplasm of the cell simply pinches off enclosing the granules 3. within the lumen, secretory vesicle breaks down and releases the gland’s products e.g. lactating mammary glands

Question 64

Holocrine secretion?

Answer 64

1. granules fill the cell until the entire cell becomes “bloated” with secretory products 2. cell undergoes apoptosis 3. secretory product constitutes entire cell and its product e.g. in sebaceous glands of the skin

Question 65

Classification of glandular epithelia according to the shape of secretory units?

Answer 65

1. tubular - elongated group of secretory cells with a tube-shaped lumen e.g gastric glands 2. acinar (or alveolar) - a small grape-like (acinus means “grape”) or sac-like (alveolus means “sac”) group of secretory cells arranged about a small lumen 3. tubulo-alveolar – lumen of secretory units have both of the above listed shapes

Question 66

Classification of glandular epithelia according to arrangement and occurrence of duct system?

Answer 66

1. simple glands - have an unbranched duct into which the cells secrete 2. compound glands - have branched duct system

Question 67

Describe types of exocrine glands?

Answer 67

1 simple tubular glands 2. simple alveolar (acinar) 3. simple branched alveolar 4. simple alveolar glands 5. compund tubular 6. compund alveolar 7. compund tubulo-alveolar