Epithelium, Glands, and Specialization Flashcards
Type of EPITHELIA
SIMPLE
STRATIFIED
PSEUDOSTRATIFIED
Types of SIMPLE EPITHELIA
Squamous
Cuboidal
Columnar
Types of STRATIFIED EPITHELIA
Squamous
Cuboidal
Columnar
Types of GLANDS
Unicellular
Multicellular (Simple, unbranched, and Compound, branched)
Exocrine
Endocrine
Types of secretion
Serous
Mucous
Mechanisms of secretion
Merocrine
Apocrine
Holocrine
Name the cell type
Endothelium cells
Simple Squamous
Endothelial nuclei are indicated by arrows
Important characteristics & functions of EPITHELIUM
1) covering/lining of all body surfaces – it is derived from all three germ layers
2) have specific apical, laterial, and basal domains
3) Basement membrane: Extracellular membrane attachment of cells to underlying connective tissue
4) Avascular
5) Majority of glands derived from epithelia
5) High regenerative capacity
6) Diversity of function (e.g. protections, secretion, absorbtion)
Name the cell type
Epithelium (gall bladder)
Simple columnar
Always look for the simplest form of an epithelium as it will usually be representative (plane of section artifacts can lead to mis-diagnosis)
Name the cell type
Epithelium (small intestine)
Simple Columnar
Always look for the simplest form of an epithelium as it will usually be representative (plane of section artifacts can lead to mis-diagnosis)
Transitional cells
Large surface cells [umbrella, dome cells], often binucleate. Unique to urinary system – thus also called UROTHELIUM
Cytokeratins
Intermediate filaments
All epithelia contain keratin intermediate filaments
Therefore, cytokeratins are diagnostic of epithelia
Terminal Bar: Junction Complex
Can be either Zonula Adherens or Zonula Occludens
(can’t distinguish between the two in that picture)
Zonula Occludens: Principal Functions
Selective permeability barrier
- seal intracellular space
- regulate paracellular transport
- facilitate/promote transcellular transport
Cell polarity influence
- separate apical from basolateral domains
- restrict movement within cell membrane
Tight junctions AKA zonula occludens
Zonula Occludens: Principal Components
Major integral membrane proteins
- Claudins
- Occludin
- Tricellulin
Peripheral membrane proteina (intracellular)
- Zonula occludens (ZO) ZO-1, ZO-2, ZO-3
- Others (eg. cingulin, spectrin)
Cytoskeleton proteins
- Actin
Tricellulin
regulation of paracellular flow
Zonula Adherens: Principal Functions
Important belt-like cell-cell adhesion units
(circumferential = zonary)
Functions:
- Thought to mediate folding and other 3D shapes of epithelia via actin and myosin
- Tranduce signals from adjacent cells
- resist mechanical stress
Zonula Adherens: Principal Components
Integral membrane proteins (E-cadherins: Ca++ binding, homotypic interactions)
•Peripheral membrane proteins (intracellular)
- Catenins (α-, β-, γ-)
- α-Actinin
- Vinculin
•Cytoskeleton proteins
- Actin (filamentous) – they are continuous with actin cytoskeleton
Gap junctions
A type of lateral surface specialization - Communicating junction
Important spot-like (punctate) cell-cell communication and resource-sharing unites
Channels formed as adjacent connexons align between cell membranes - 6 connexins make up one connexon
found in many tissues and function in electrical synapses
Appoximation to syncytium (multiple nuclei sharing cytoplasm)
(Basal Lamina cell)
a. Collagen III
b. Collagen IV, Lamina Densa
c. Lamina Lucida
d. Reticular Lamina
e. Basal Lamina
Basement Membrane
Made up of the basal lamina, retucular fibers, and anchoring fibrils (Collagen VII)
Provides physical support; trasmits forces to adjacent CT
Has selective permeability; filter for macromolecules and cell migration barrier
Basal Lamina
One component of basement membrane (along with reticular lamina)
Made up of Type IV collagen, laminin (both of which form chicken wire networks), and nidogen
Reticular Lamina
One component of the basement membrane (along with basal lamina)
Made up of reticular fibers; mostly collagen III
Describe and Identify
Repiratory tract epithelium
Pseudostratified
Ciliated
Columnar
with Goblet cells
(photo also contains wandering lymphocytes)
Pseudostratified
All cells rest on the basal lamina, but some don’t reach the free surface
In the respiratory tract, they are specialized for propelling mucus + debris towards the oral cavity
Goblet cells
Unicellular epithelial gland
pseudostratified eg. trachea
simply columnar eg. ntestine
Respiratory Tract Epithelial characteristics
Pseudostratified, ciliated columnar with goblet cells
Identify and describe
Myoepithelial cells AKA Basket cells
Pseudostratified
Cells sitting on basal lamina are highly eosinophilic, because there are lots of mitochondria and lots of actin/myosin protein
ID type of cells and where it is from
Stratified squamous keratinizing epithelium (SSKE) from the skin
Gland formation
All begin as an epithelial ingrowth and all retain keratin expression
Exocrine Glands
Maintain contact with surface epithelium, secrete into a lumen
Endocrine gland
Lose contact with surface epithelium, secrete into interstitial space
Merocrine secretion
Secretions by exocytosis; only the product is released
Typical secretions include:
- zymogens
- sweat
- mucous
- lysozyme
Subcategory: eccrine, referring to sweat secretion from eccrine sweat glands
Sebum
Released by holocrin secretion: the entire cell and its contents become the secretory product
Note: the phenotypic progression of cells from base to duct
- cell borders disappear
- nucleus degenerates
- cytoplasmic droplets coalesce
Holocrin secretion
the entire cell and its contents (sebum) become the secretory product
Mechanism of secretion: apoptosis
Note phenotypic progression of cells from base to duct:
- cell borders disappear
- nucleus degenerates
- cytoplasmic droplets coalesce
What type of gland is this?
Mixed seromucous, a combination of serous and mucous common in a lot of glands
Serous
- watery secretion
- abundant RER
- round nucleus
- cells well stained
Mucous
- thick secretion
- clear cytoplasm
- flat nucleus (an artifact of preparation)
- cells poory stained
Apocrine secretion
aka decapitation secretion; a portion of the apical cytoplasm is released along with the product.
Identify type of secretion
This mammary gland exibits both apocrine secretion (large round form) and merocrine secretion (small black circles floating away to the sides of the apocrine secretion)
Describe cell type
Simple cuboidal
Pseudostratified
Stratified Cuboidal
Simple columnar
Transitional
SSNKE
Stratified Columnar
Simple squamous
SSKE
Epithelia are derived from…
Ecotoderm - external eg. epidermis
Mesoderm - internal eg. pericardial cavity
Endoderm - “internal” eg. GI, respiratory tract
Epithelia display what kind of intermediate filaments
Keratin
Epithelia express keratin intermediate filaments (diagnostic for all epithelia)
Two general classes of epithelia
Lining or glandular
All epithelia are vascular or avascular?
Avascular
Epithelia Functions
Protection (epidermis provides waterproofing, and insulation
stomach lining protects from acid, etc.)
Surface transport (cilia in respiratory epithelium propel particles upward; oviduct cilia move the ovum)
Absorption (microvilli in intestinal epithelium & kidney tubules absorb nutrients)
Secretion (both unicellular & multicellular glands)
Trans-epithelial transport
- apical to basal: kidney tubules transport nutrients from the lumen to basal connective tissue
- basal to apical: lymph resorption into lymphatics
Reproductive (seminiferous tubule generates sperm)
Special sensory (taste buds, hair cells in cochlea)
Contraction (myoepithelium)
Simple squamous cells of a small vein
Simple cuboidal cells of renal tubule
Simple columnar cells of intestine
Stratified columnar cells of large ducts, conjuntiva
stratified squamous keratinizing epithelium (SSKE)
eg. skin epidermis
stratified squamous non-keratinizing epithelium (SSNKE)
e.g. esophagus, anal canal, vagina
Pseudostratified, columnar, ciliated with goblet cells in the trachea (aka respiratory epithelium)
Pseudostratified: All cells contact basal lamina, not all reach free surface. Typically has cilia except in parts of male reproductive system. (True stratified epithelia NEVER have cilia).
Transitional AKA urothelium cells of the urinary system
(technically pseudostratified)
Large surface cells [umbrella cells], often binucleate. Unique to urinary system – thus also called urothelium
Myoepithelial cells
AKA basket cells
help to expel the secretory products
