Epithelial Tissue

Question 1

Epithelial Tissues

Answer 1

• large sheets of cells covering all surfaces of the body exposed to the outside world and lining the outside of organs
• also forms much of the glandular tissue of the body
• skin, airways, urinary/reproductive system, hollow organs, and body cavities that don’t connect to the exterior of the body (blood vessels, serous membranes)
• nearly completely avascular (no blood vessels

Question 2

where do they derive from?

Answer 2

• all 3 major embryonic layers
• epithelia lining skin, parts of mouth and nose and anus develop from ectoderm
• cells lining airways and most of digestive system originate in endoderm
• epithelium that lines vessels in the lymphatic and cardiovascular systems derives from mesoderm –> called endothelium

Question 3

what structural and functional features do they share?

Answer 3

• tissues are highly cellular
• little or no extracellular material between cells
• adjoining cells form cell junction
• exhibit polarity with differences in structure/function between the exposed surface of the cellj

Question 4

cell junction

Answer 4

adjoining cells form specialized intercellular connection between cell membranes

Question 5

apical

Answer 5

surface of the cell and basal surface close to underlying body structures

Question 6

basal lamina

Answer 6

mixture of glycoproteins and collagen
- provides attachment site for epithelium, seperates it from underlying connective tissue
- attatches to reticular lamina to form basement membrane

Question 7

basement membrane

Answer 7

basal lamina attatched to reticular lamina
- holds everything together

Question 8

how do epithelial tissues get nutrients?

Answer 8

• nutrients come by diffusion or absorption from underlying tissues or the surface
• capable of rapidly replacing damaged and dead cells
  –> characteristic of surface epithelium that allows our airways and digestive tracts to rapidly replace damaged cells w new cells

Question 9

what is the body’s first line of protection from physical, chemical and biological wear and tear?

Answer 9

epithelial tissues
- act as gatekeepers of body to control permeability and allow selective transfer of materials across physical barrier

Question 10

functions of epithelium

Answer 10

• first line of protection
• gatekeepers
• selective transport
• capable of secretion and release of mucous
• releases digestive enzymes (in the small intestine)
• cells lining the respiratory system secrete mucous that traps incoming microorganisms and particles
• glandular epithelium contains many secretory cells

Question 11

Epithelial Cells

Answer 11

• characterized by polarized distribution of organelles and membrane-bound proteins between their basal and apical
• certain structures found in epithelial cells are an adaptation to specific functions: certain organelles are segregated to basal sides, other organelles and extensions (like cilia) are on apical surface

Question 12

cilia

Answer 12

• microscopic extensions of the apical cell membrane that are supported by microtubules
• they beat in unison and move fluids and trapped particles

Question 13

ciliated epithelium

Answer 13

• lines the ventricles of brain where it helps circulate the cerebrospinal fluid
• The ciliated epithelium of your airway forms a mucociliary escalator that sweeps particles of dust and pathogens trapped in secreted mucous toward the throat

Question 14

mucociliary escalator

Answer 14

• sweeps dust particles and pathogens trapped in mucous towards the throat
• called escalator bc it continuously pushes mucous with trapped particles upward

Question 15

nasal cilia

Answer 15

sweeps the mucous blanket down towards your throat

Question 16

common between nasal cilia and mucociliary escalator

Answer 16

• transported materials are usually swallowed
• end up in acidic environment of your stomach

Question 17

what are the 3 types of cell junctions

Answer 17

1. tight junctions
2. anchoring junctions
3. gap junctions

Question 18

what are tight junctions

Answer 18

• separates the cells into apical and basal compartments
• two adjacent epithelial cells form a tight junction
• no extracellular space between them
• movement of substances through the extracellular space between cells is blocked
• enables epithelia to act as selective barriers

Question 19

what are anchoring junctions

Answer 19

• several types of celljunctions that help stabilize epithelial tissues
• common on lateral and basal surfaces of cells where they provide strong and flexible connections
• 3 types: desmosomes, hemidesmosomes, adherens

Question 20

what are desmosomes?

Answer 20

• type of anchoring junctions
• occurs in patches on membranes of cells
• patches are structural proteins on inner surface of cells membrane
• the adhesion molecule (cadherin) is embedded in patches and projects through cell membrane to link with cadherin molecules of adjacent cells
• these connections are especially important in holding cells together

Question 21

hemidesmosomes

Answer 21

• type of anchoring junction
• look like half a desmosome
• link cells to extracellular matrix (like basal lamina)
• similar in appearance but they include adhesion proteins called integrins instead of cadherins
• use either cadherins or integrins depending on contractile protein actin located on cytoplasmic surface of cell membrane
• actin can connect isolated patches or form belt-like structure inside the cell
• these junctions influence the shape and folding of epithelial tissue

Question 22

gap junction

Answer 22

• not the same as tight and anchoring junctions
• forms intercellular passageway between membranes of adjacent cells to facilitate the movement of small molecules and ions between cytoplasm of adjacent cells
• junctions allow electrical and metabolic coupling of adjacent cells, which coordinates function in large group cells

Question 23

how are epithelial tissues classified?

Answer 23

according to shape of cells and number of cell layers formed

Question 24

what are the different cell shapes?

Answer 24

• squamous (flattened and thin)
• cuboidal (boxy, as wide as it is tall)
• columnar (rectangular, taller than it is wide)

Question 25

what is it called when it has more than one layer

Answer 25

stratified

Question 26

pesudostratified

Answer 26

- pseudo: false - tissue with single layer of irregularly shaped cells that give appearance of more than one layer

Question 27

transitional

Answer 27

- form of specialized stratified epithelium in which the shape of cells can vary

Question 28

true or false: shape of cells in single cell layer of single epithelium reflects the function

Answer 28

true

Question 29

what does squamous cell nuclei look like

Answer 29

flat, horizontal, elliptical (mirrors form of cell)

Question 30

endothelium

Answer 30

- epithelial tissue that lines vessels of lymphatic and cardiovascular system - made up of a single layer of squamous cells

Question 31

simple squamous epithelium

Answer 31

- thin scale like cell - present where rapid passage of chemical compounds is observed ex: alveoli of lungs, segments of kidney tubules, lining of capillaries

Question 32

mesothelium

Answer 32

- simple squamous epithelium that forms surface layer of serous membrane that lines body cavities and internal organs - function: provide smooth and protective surface

Question 33

mesothelial cells

Answer 33

- squamous epithelial cells that secrete fluid that lubricates mesothelium

Question 34

what does simple cuboidal epithelium

Answer 34

- nucleus of box-like cells appears round - located near center of cell - epithelia are active in secretion and absorptions of molecules EX: observed in lining of kidney tubules and ducts of glands

Question 35

simple columnar epithelium

Answer 35

- nucleus of tall column-like cells tends to be elongated and located in basal end of cells - epithelium is active in absorption and secretion of molecules - forms the lining of some secretions of the digestive system and parts of the female reproductive tract

Question 36

ciliated columnar epithelium

Answer 36

- simple columnar epithelial cells with cilia on apical surfaces - found in lining of fallopian tubes and parts of respiratory system - function: beating of cilia helps remove particulate matter

Question 37

pseudostratified columnar epithelium

Answer 37

- appears stratified but instead consists of single layer of irregularly shaped and differently sized columnar cells - nuclei of neighboring cells appear at different levels rather than clustered in basal end - all cells are in contact w basal lamina (even tho it doesnt look like it), some dont reach apical surface EX: respiratory tract (some have cilia)

Question 38

true or false: simple and pseudostratified cuboidal epithelia are heterogeneous bc they include additional types of cells interspersed among epithelial cells

Answer 38

false -- simple and pseudostratified columnar epithelia

Question 39

goblet cell

Answer 39

- mucous-secreting unicellular 'gland' interspersed between columnar epithelial cells of mucous membranes

Question 40

stratified epithelium

Answer 40

- several stacked layers of cells - protects against physical and chemical wear and tear - named by shape of most apical layer of cells (closest to free space)

Question 41

stratified squamous epithelium

Answer 41

- most common tpype of stratified epithelium in human body - apical cells are squamous - basal layer mgiht be columnar or cuboidal - top layer: covered with dead cells filled with keratin EX: mammalian skin

Question 42

stratified cuboidal epithelium and stratified columnar epithelium

Answer 42

- found in certain glands and ducts - uncommon in human body

Question 43

transitional epithelium

Answer 43

- another kind of stratified epithelium - gradual changes in shapes of apical cells as bladder fills with urine - only found in urinary system: ureters and urinary bladder - when bladder is empty: epithelium is convoluted and has cuboidal apical cells w convex umbrella-shaped apical surfaces - bladder filled: epithelium loses its convolutions and apical transition from cuboidal and squamous, more stretched out and less stratified

Question 44

Gland

Answer 44

structure made up of one or more cells modified to synthesize and secrete chemical substances - consist of groups of epithelial cells - can be classified as endocrine or exocrine glands

Question 45

endocrine gland

Answer 45

- ductless gland that releases secretions directly into surrounding tissues and fluids - secretions of endocrine glands are hormones --> released into interstitial fluid, diffused into bloodstream and dleivered to targets (cells that have receptors to bind the hormones) - part of major regulartory system coordinating the regulation and integration of body responses ex: anterior pituitary, thymus, adrenal cortex, gonads

Question 46

exocrine glands

Answer 46

- secretions that leave through duct that opens directly/indirectly to external environment - release contents through duct that leads to epithelial surface EX of secretions: mucous, sweat, saliva, and breast milk - all discharged through tubular ducts - secretions into lumen of the gastrointestinal tract (technically outside the body)

Question 47

glandular structure

Answer 47

- exocrine are either unicellular or multicellular

Question 48

unicellular glands

Answer 48

- scattered single cells - such as goblet cells (found in mucous membranes of small and large intestine

Question 49

multicellular exocrine glands

Answer 49

- aka serous glands - develop from simple epithelium to form a secretory surface that secretes directly into an inner cavity - glands line the internal cavities of the abdomen and chest and release their secretions directly into the cavities - other multicellular exocrine glands release their contents through a tubular duct (duct is single in a simple gland but in compound glands, is divided into one or more glands) - tubular glands --> ducts can be straight or coiled - alveolar (acinar) --> tubes that form pockets (an exocrine portion of the pancreas) - combination of tubes and pockets are known as tubuloalveolar (tubuloacinar) compound glands - branched gland: duct connected to more than one secretory group of cells

Question 50

what do the exocrine glands mode of secretion and nature of released substances look like?

Answer 50

- merocrine secretion - apocrine secretion - holocrine secretion

Question 51

merocrine secretion

Answer 51

merocrine secretion: most common type of exocrine secretion - secretions are enclosed in vesicles that move to the apical surface of cell where ocontents are released by exocytosis EX: watery mucous containing the glycoprotein mucin is a lubricant that offers some pathogen protection is a merocrine secretion - eccrine glands that produce and secrete sweat are another example

Question 52

apocrine secretion

Answer 52

- accumulates near the apical portion of the cell - that portion of the cell and its secretory contents pinch off from the cell and are released - apocrine sweat glands in the axillary and genital areas release fatty secretions that local bacteria break down (causes body odor)

Question 53

what happens in both merocrine and apocrine glands

Answer 53

both continue to produce and secrete their contents with little damage caused to the cell because the nucleus and gogi regions remain intact after secretion

Question 54

holocrine secretion

Answer 54

- involves the rupture and destruction of the entire gland cell - cell accumulates its secretory products and releases them only when it bursts - new gland cells differentiate from cells in the surrounding tissue to replace those lost by secretion - the sebaceous glands that produce the oils on the skin and hair are holocrine glands/cells

Question 55

Serous Gland

Answer 55

- produces watery, blood-plasma-like secretions rich in enzymes such as alpha amylase - common in salivary glands of mouth - mixed exocrine glands have both serous and mucous glands and release both types of secretions

Question 56

Mucous Gland

Answer 56

- releases watery to viscous products rich in the glycoprotein mucin - common in salivary glands of the mouth - mixed exocrine glands have both serous and mucous glands and release both types of secretions