Lecture 2: Epithelium Tissue Flashcards
what major tissue
- covers body surface
- lines hollow internal organs, cavities, ducts
- forms glands of body
epithelial tissue
x3 categories of function of the epithelium tissue?
Selective barriers = limit/aid transfer
secretory = onto a free surface
protective = from abrasion, external entry from exterior
x2 structural features of epithelium cells
(arrangement and held together)
- Arranged in continuous sheets: single or multi layered
- Held together by cell junctions: adherens, tight, gap, desmosomes, hemidesmosomes
What are the different surfaces of epithelial cells
Apical surface > environment exposure side
lateral surface
basal surface > internal exposure side
types of junctions in the lateral surface…
Tight junctions
Adherens junction
Gap junctions
Desmosomes
What junction is in the basal junction?
Hemidesomosomes
purpose of the cytoskeleton
provide cell skeleton to maintain structure + shape
x2 cytoskeleton components
- Microfilaments
- Intermediate filaments
x2 functions of the microfilaments
- link cells together
- generate force in cellular contraction and basic cell movements
Protein that makes up microfilaments?
Actin
Protein that makes up intermediate filaments?
many different proteins; Keratin
x3 functions of intermediate filaments
- cell cohesion and prevent acute fracture of cell sheet under tension
- structure
- path for material to move through cytoplasm (train track system)
are the intermediate filaments thicker/less flexible or thinner/flexible than microfilaments?
intermediate filaments thicker and less flexible
tight junctions are electrically tight… what does this mean?
ions can’t get down in between cells
- can keep x2 separate environments
what proteins in tight junctions “traverse membranes to weld + hold adjacent cells together”
Claudins
Occludins
function of the Claudia and Occluding proteins
- join cytoskeleton to actin
- maintain polarity of cell by preventing migration of proteins between apical and basal surfaces
Where are tight junctions found?
stomach
intestines
bladder
what type of junction contains “web-like transmembrane that fuse together surfaces of adjacent cells”
tight junctions
x2 main functions of tight junctions?
- inhibit passage of substance between cells
- prevent leakages
true or false
the adherens junctions are more apical located than tight junctions
FALSE
adherens junctions are more basal located
Why adherens junctions have a plaque layer of proteins inside cell
join actin (microfilaments) to cadherins (cytoskeleton)
glycoprotein that spans gap between adjacent cells in adherens junctions
cadherins
what is a type of cytoplasmic contractile protein
actin
What links cadherins to actin?
(cell cytoplasm to microfilaments)
Catenins
main function of the adherens junctions
- prevent cell separation from tension forces (contractions)
what is an adhesion belt
plaque layer on the inner cell membrane containing proteins
what this describes… “a collection or bump in the wall where proteins are aggregated together”
plaque
what type of junction carries out these functions
1. structural integrity to cells
2. cytoskeleton proteins of each cell welded to each other through plaques
3. RESIST SHEARING FORCES (cardiac)
Desmosomes
Function of the desmosome plaque?
attaches to keratin, intermediate filament of cytoskeleton for stability
Function of cadherin in desmosomes
Spans gap to bind to desmoplakin (protein) which then binds to keratin
true or false
the keratin is the linker and cadherin anchoring
FALSE
keratin anchoring and cadherin linker
appearance of the plaque on desmosomes
‘button’ shape
x2 main functions of gap junctions
- ion/molecule exchange in the connexON channels (cytosol of 1 cell to adjacent)
- rapid spread of nerve/muscle impulses along cell
what type of cell junction is used when things need coordinated movement (ie heart for contraction phase)
gap junctions
do gap junctions provide direct or indirect connection between cells
direct connection
process of how gap junctions are formed?
x6 connexIN form x1 connexON
> x2 connexON form x1 gap junction
how communication is carried out in gap junctions
junction formed
> change in their conformation so protein shape changes
» shape change opens tunnel
»> tunnel allows for messages to be transferred from x1 cell to another (messages = ions/RNA/atp)
Linker protein in hemidesomosomes?
integrin
What does Integrin protein bind to in hemidesmosomes?
- laminin in basement membrane
- intermediate filament keratin in cytoplasm
why keratin filaments are used on the side
tie down cytoskeleton onto BM so cells don’t slide
Function of hemidesmosomes?
connect epithelial cells/tissue to basement membrane
What types of junctions are in a junctional complex
combination of tight, adherens, and desmosomes
- close together with similar function
Where is the basement membrane found?
between epithelial and connective tissue
purpose of basement membrane
- protein structure = what cells sit on
- barrier between epithelium and CT underneath
x2 components of the basement membrane
- basal lamina
- Reticular lamina
Where is basal lamina secreted from?
epithelial cells
What does the basal lamina contain?
- collagen
- laminin
- glycoproteins
- proteoglycans
What is reticular lamina produced by?
fibroblast cells of connective tissue
What reticular lamina contains?
fibrous proteins
fibronectin
collagen
Why is epithelia avascular?
contains nerves but NO blood vessels
How are nutrients and wastes exchanged?
diffusion from vessels in connective tissue
Function of the basement membrane?
- support epithelium
- healing
- physical barrier
- filtration of kidney substances
how healing occurs on basement membrane
epithelial cell migrate along surface of injury
> cells secreting proteins to reconstitute BM
» growing BM for cell division to refill gap
»>forming platelet/fibrin clot
how malignant melanoma occurs
- malignancy of the melanocytes
barrier penetrated
= increased change of metastasis (spread)
x2 types of epithelial tissue + functions
- covering and lining epithelia = cover exposed surfaces + internal cavities (contain secretory cells)
- glandular epithelia = secretory portion of glands
Function of inner and outer covering and lining epithelia?
- outer covering > skin/internal organs
- inner lining > vessels/ducts/body cavities/system interiors
Function of exocrine and endocrine glandular epithelia
- exocrine > secrete onto surfaces + in passages/ducts
- endocrine > hormones or precursors into interstitial fluid
factors to classify covering and lining epithelia
- arrangement of cells in layers
- shapes of cells
Types of arrangement classification + function
- simple = single layer (secretion; absorption; filtration)
- stratified = 2 or more layers (protective)
- pseudo stratified = appears to have multiple layers as judged by positions of nuclei (secretion)
Types of shapes classification?
- squamous = flat/thin (diffusion)
- cuboidal = tall as are wide (secretion/absorption)
- columnar = more tall than wide (secretion/absorption)
- transitional = cells can change shape from cuboidal > flat
Types of simple covering and lining epithelia
- simple squamous
- simple cuboidal
- simple columnar (ciliated/non-ciliated)
Types of stratified covering and lining epithelia
- stratified squamous (keratinised/non-keratinised)
- stratified cuboidal
- stratified columnar
- transitional
Types of pseudostratified covering and lining epithelia
- pseudo stratified columnar (ciliated/non-ciliated)
simple squamous features
- delicate
- filtration (kidney); diffusion (lung); secretion (for slippery surface)
simple squamous appearance
- thin flat irregular
- like paving stones/”fried eggs”
simple squamous specialised subtypes
- Mesothelium = lines cavities (pericardial, pleural, peritoneal)
- Endothelium = lines heart interior, blood + lymphatic vessels
simple squamous location examples
- Bowman’s capsule kidney
- cardio. and lymph. system linings
- inside eye
- lung alveoli
- visceral cavity linings
- inside blood vessels + heart
simple cuboidal features
secretion and absorption
simple cuboidal appearance
cuboidal/hexagonal boxes
simple cuboidal location examples
- pancreas ducts
- part kidney tubules
- smaller ducts of glands
- secretory chambers of thyroid
- anterior surface of lens
- pigmented epithelium at posterior of retina
- secretory part of gland
types of columnar epithelium membrane modifications
- cilia
- microvilli
simple columnar features
more cytoplasm = more organelles
simple columnar subtypes
- non-ciliated or ciliated
- microvilli
simple columnar appearance
- rectangular/hexagonal but taller, slender than cuboidal
- elongated nuclei near base of cell
non-ciliated simple columnar features
- single layer
- microvilli on apical surface
- goblet cells (modified columnar cell) interspersed
non-ciliated simple columnar function
- secretion + lubrication (mucus goblet cells)
- absorption
non-ciliated simple columnar location examples
- lines gut mucosa from stomach > anus
- ducts of glands
- gallbladder
ciliated simple columnar features
- single layer
- goblet cells
ciliated simple columnar function
synchronous movement assists mobility of mucus + foreign objects or oocytes
ciliated simple columnar location examples
- bronchioles
- uterine fallopian tubes
- sinuses
- central canal of spinal cord
- brain ventricles
stratified squamous features
- protect against microbes
- present in high mechanical/chemical stress areas
stratified squamous appearance
- layers like pancakes in upper layers
- lower layers cuboidal/columnar
- cells further from nutrition = thin less active
stratified squamous specialised subtypes
- keratinised (skin)
- non-keratinised (mouth/throat/tongue/oesophagus/ anus/vagina)
non-keratinised stratified squamous function
- abrasion protection
- microbe defence
- secretions from glands
pseudo-stratified columnar features
- cells contact basement membrane but won’t reach apical surface
pseudo-stratified columnar appearance
- nuclei all different levels
- appears to have several layers NOT the case
pseudo-stratified columnar subtypes
- ciliated (upper airways)
- non-ciliated (gland ducts, epididymis)
pseudo-stratified ciliated columnar appearance
- cilia on some cells
- secrete mucus from goblet cells
pseudo-stratified ciliated columnar function
secrete mucus and move it
pseudo-stratified non-ciliated columnar appearance
- no cilia
- lack goblet cells
pseudo-stratified non-ciliated columnar function
absorption + protection
stratified cuboidal features
- 2 or more layers of cells
- cells in apical layer
stratified cuboidal function
- protection
- limited secretion + absorption
stratified cuboidal location examples
- adult sweat gland ducts
- esophageal glands, part of male urethra
stratified columnar features
- short irregular cell shape
- apical layer
stratified columnar function
protection + secretion
stratified columnar location examples
- part of urethra
- large gland ducts (oesophageal glands)
- anal mucosal membrane (conjunctiva of eye)
stratified transitional features
- relaxed/unstretched state
- multiple layers of elasticity
stratified transitional function
- stretching of organs
- maintain protective lining will holding fluid without rupture
stratified transitional location examples
Bladder!
- ureter + urethra
Glandular epithelia function
secretion
What secretes substances into ducts, on surfaces, or in blood?
glands
- single/group of cells
Endocrine gland function
hormones regulate metabolic/physiological activity for homeostasis
Endocrine gland features
secrete directly into blood via traversing interstitial fluid
Endocrine gland location examples
pituitary, pineal, thyroid, parathyroid
Exocrine gland function
produce substances to lower body temp
Exocrine gland features
secrete into ducts that empty on surface of covering/lining epithelium
Exocrine gland location example
sweat + salivary glands
oil glands
wax glands
pancreas
What are mucous cells?
secretory cells in epithelia
- secrete mucin
characteristics used to describe multicellular gland structure
- Duct structure
- Secretory area structure
- Relationship between the two
Name the simple multicellular exocrine glands
- simple tubular
- simple branched tubular
- simple coiled tubular
- simple acinar
- simple branched acinar
name the compound multicellular exocrine glands
- compound tubular
- compound acinar
- compound tubuloacinar
purpose of basement membrane
- protein structure = what cells sit on
- barrier between epithelium and CT underneath
