Exam I | Epithelia Flashcards
What are the 4 tissue types?
- epithelial
- connective
- muscle
- nervous
Where is epithelium found?
- internal cavities
- GI, GU, and reproductive tract
- exocrine glands
What are the 3 functions of epithelium?
1) protective barrier against pathogens, toxins
2) limits or regulates fluid loss in some regions
3) secretion, absorption, and excretion
6 characteristics of epithelium
- contains little, if any, matrix (ground substance)
- linked by cell junctions
- typically have apical (lumenal) and basolateral surfaces
- largely avascular
- highly mitotic
- may be derived from all 3 germ layers
What is the basal lamina, and what is it made up of?
- is the “bed” for overlying epithelial cells and is part of anchoring membrane
- superficial portion of basement membrane
- made up of lamina lucida and lamina densa
What is endothelium?
a type of epithelium that lines blood vessels, serous membranes, etc.
What makes up basement membrane?
- basal lamina (lamina lucida and lamia densa)
- reticular lamina
What are the three main types of cell junctions?
- tight junctions
- gap junctions
- anchoring junctions
What are the 3 types of anchoring junctions?
- desmosomes
- hemidesmosomes
- adherens junctions
What 4 important proteins make up tight junctions?
1) e-cadherins
2) occludin
3) catenins
4) caludin-1
What are the functions of tight junctions?
- separate cell into apical and basalolateral compartments
- prevent passage of substances between adjacent cells
what cytoskeletal components are associated with tight junctions?
actin filaments
What are two other names for tight junctions?
- zonula occludens
- blocking zones
What are two other names for gap junctions?
- connexons
- electrical junctions
What are gap junctions made up of?
connexins
What is the function of gap junctions?
- facilitate rapid cell-to-cell communication. Can transmit action potentials (depolarization)
- allow small proteins, sugars, and ions to pass from one cell to another
Name 5 areas where gap junctions can be found.
- epithelia
- cardiac muscle
- some types of smooth muscle
- certain types of neuron
- osteocytes
What is the difference between desmosomes and hemidesmosomes?
- desmosomes tie together 2 epithelial cells
- hemidesmosomes bind epithelial cells to basement membrane
what are CAMs? Give 3 examples
- cell adhesion molecules
- cadherins and catenins
What are desmosomes made up of?
cadherins
How do desmosomes function?
link intermediate filaments of adjacent cells
which cell junctions aggregate into “plaques” along the cell membrane?
desmosomes
What do hemidesmosomes do?
link cells to extracellular matrix (basal lamina)
What are hemidesmosomes made up of?
integrins
where are tight junctions found?
proximal to apical membrane
What cytoskeletal filaments are hemidesmosomes associated with?
Intermediate filaments
what are the functions of adherens junctions?
- use cadherins or integrins to link actin filaments
- provide points linking cytoskeletons of adjacent cells
- strengthens and stabilized nearby tight junctions
what are adherens junctions essential to?
cell morphology
Name 3 ways epithelia can be classified by shape.
- squamous (flat, thin)
- cuboidal (square)
- columnar (rectangular)
Name 3 ways epithelia can be classified by number of layers.
- simple (one layer)
- stratified (multiple layers)
- pseudostratified (appearance of multiple layers)
What are 3 ways, besides number of layers and shape, that epithelia can be classified?
- function
- appearance
- presence of cilia
structure of simple squamous epithelia
- single, thin layer of flat cells
- little or no intracellular matrix
simple squamous epithelia function
- gas exchange
- diffusion
- filtration
What 3 places can simple squamous epithelia be found?
- alveoli
- endothelia of capillaries
- renal corpuscle
Where can you find stratified squamous epithelium?
- epidermis
- cornea of eye
What is the function of stratified squamous epithelium?
protection
simple cuboidal epithelium is usually involved in what?
- glandular secretion
- absorption
What 4 places can simple cuboidal epithelium found?
- ovary
- kidney tubules
- glandular tissue of thyroid (thyroid follicles)
- pancreas
Where are 3 places stratified cuboidal can be found?
- uncommon
- mamillary glands
- salivary glands
- some sweat glands
What are the functions of simple columnar epithelia?
- secretion and absorption
- some protection
what 2 places can simple columnar be found?
- GI tract (villi)
- reproductive tract
what are 2 places pseudostratified epithelium can be found?
- respiratory tract
- portions of reproductive tract
describe the structure of pseudostratified epithelium.
- typically ciliated
- simple, but appears stratified
- columnar cells extend to basement membrane, but not all cells reach lumen. Cells are of different heights
- heterogeneous arrangement of nuclei
What is the function of Goblet cells, and where are they found?
- secrete mucus
- in stratified squamous, columnar epithelia, and pseudostratified epithelia
- in GI and GU tract epithelium
What are the three types of epithelial secretion?
- merocrine
- apocrine
- holocrine
What is merocrine secretion and where does it occur?
- relatively common (e.g. some sweat glands)
- vesicles leave Golgi, merge with plasma membrane (EXOCYTOSIS), and secrete contents
What is apocrine secretion, and where does it occur?
- apical portion of cell is pinched off and released during secretion (blebbing)
- occurs in sweat glands of axillary and pubic region
What is holocrine secretion, and where does it occur?
- cell undergoes lysis and disintegrates
- sebaceous glands
Where is glycocalyx found?
- slime on fish and eels
- ubiquitous in all human tissues
- respiratory tract
- protective lining in blood vessels
- lining of skeletal muscle
Glycocalyx functions (the proven ones)
- mediates interactions between epithelium and underlying connective tissue
- mediates interactions between lumen of a tract and what flows through it
- mediates flow of blood through vessels
- protective lining of blood vessels
what is the composition of the glycocalyx?
gel-like matrix of glycolipids, glycoproteins, and negatively charged molecules
