Transcript Histology - King George's Medical University

Histology
Study of cells, tissues
and organs as seen with
the help of microscope
Histology
• Often called
Microscopic Anatomy
• Greek word –
Histos= tissue
Logia=science/study
• Cells work together in
functionally related
groups called tissues
4 basic type of tissues:
• Epithelial – lining
and covering
• Connective –
support
• Muscle –
movement
• Nervous –
control
Epithelial Tissue or Epithelium
•
•
•
•
Consist of sheets of cells
Covers a external surface of the body
May line the internal cavities and the organs
Forms most organs & glands
Special Characteristics of Epithelia
• Cellularity
–cells are in close contact with each
other with little or no intercellular
space between them
• Specialized contacts: Junctional
Complexes
–may have junctions for both
attachment and communication
Special Characteristics of Epithelia
• Polarity
–epithelial tissues always have an apical
and basal surface
• Support by connective tissue
–at the basal surface, both the epithelial
tissue and the connective tissue
contribute to the basement membrane
• Avascular..No blood vessel, no
lymphatics
–nutrients must diffuse
Special Characteristics of Epit
• Innervated
• Regeneration
– epithelial tissues have a high capacity for
regeneration
• Invaginates and grows in the underlying
CT..specializing as glands
• Apical surface shows modification: presence of
cilia or microvilli
• Nuclear shape corresponds to the cell shape:
oval in columnar,round in cuboidal or polyhedral
and flat in squamous cells
Functions
• Functions of epithelium
– Protection
– Absorption,
– May secrete material and ion transport
– Filtration
– Forms slippery surfaces
– Function as sensory surfaces
Embryologically
• Epithelia are
layers:
• Ectoderm
• Endoderm
• Mesoderm
derived from all the 3 germ
Epithelium of skin
Epithelium of gut
Epithelium of pericardial,
peritoneal and pleural cavities
Basement Membrane
• All cells rest on it.
• Thin, non-cellular
• Separates epithelium from underlying connective
tissue
• Easily seen with light microscope
• Made up of:
Basal Lamina-Amorphous, product of epithelium
Reticular Lamina-Reticular fibres, product of CT
Basement Membrane
• The epithelial cells lie
on the reticular
lamina (collagen – CT)
• Reticular lamina is
bound to another CT
called areolar CT.
• Together this
structure is called the
"basement
membrane”
Basal Feature: The Basal Lamina
• Noncellular supporting sheet between the epithelium
and the connective tissue deep to it
• Consists of proteins secreted by the epithelial cells
• Functions:
– Acts as a selective filter, determining which molecules from
capillaries enter the epithelium
– Acts as scaffolding along which regenerating epithelial cells
can migrate
• Basal lamina and reticular layers of the underlying
connective tissue deep to it form the basement
membrane
Intercellular Junctions OR
Junctional Complexes
• Zonula occludens (Tight Junctions)
• Zonula adherens
• Macula adherens (Desmosome) and
hemidesmosome
• Gap junction (Nexus)
Lateral Surface Features
• Factors holding
epithelial cells together
– Adhesion proteins link
plasma membranes of
adjacent cells
– Contours of adjacent cell
membranes
– Special cell junctions
Tight junctions (zona occludens)
• – close off intercellular space
– Found at apical region of most epithelial types
– Some proteins in plasma membrane of adjacent
cells are fused
– Prevent molecules from passing between cells of
epithelial tissue…..Serves as a SELECTIVE BARRIER,
giving it a sealing effect.
– Example- Intestine and urinary bladder
Adherens junctions (zonula adherens)
– anchoring junction
– Transmembrane linker
proteins attach to actin
microfilaments of the
cytoskeleton and bind
adjacent cells
– Along with tight
junctions, form the tight
junctional complex
around apical lateral
borders of epithelial
tissues
• Present just below the
tight junctions
• Provides Rigidity to the
apex of the cell.
• Presence of dense
plaque – like material
on the cytoplasmic
surface of the plasma
membranes of the
junction.
Desmosomes (Macula Adherens)
Hemidesmosomes
• Gap of 30nm
• Transmembrane
Proteins
• Electron dense
plaque
• Attachment to
Intermediate
Filaments
FIRM ADHESION between cells
Subjected to friction,
Epidermis of skin.
Desmosomes
• Desmosomes – two
disc-like plaques
connected across
intercellular space
– Plaques of adjoining cells
are joined by proteins
called cadherins
– Proteins interdigitate
into extracellular space
– Intermediate filaments
insert into plaques from
cytoplasmic side
Desmosomes
Gap junctions (Nexus)
• passageway between
two adjacent cells
– Let small molecules
move directly between
neighboring cells
– Cells are connected by
hollow cylinders of
protein
– Passage of inorganic ions
– Exchange of chemical
messengers in cell
recognition and
differentiation.
Gap Junction
Tight Junctions
• In the apical
• Band or belt
• Barrier device
Surface Modifications
• Glycocalyx-rich in
polysaccharides
• Concentrates ions prior to
absorption
• Act as receptor sites for
hormones and enzymes.
• Microvilli- minute
finger like projections
• Increase absorptive
surface
• Stereocilia – Long
thick Microvilli, Non
motile, may show
branching, Increase
surface area(
Epididimis), helps
perception of stimuli
(Internal Ear)
• Cilia- long, hair like
projections of plasma
membrane
Microvilli and Cilia
•
•
•
•
Nonmotile
Contain Microfilaments
Function-Absorption
Intestinal epithelium,
proximal convoluted
tubules of the kidney
• Motile
• Contain 9+2 pattern of
microtubules
• Driving the entangled
particles, transport in
one dcirection
• Examples: Respirastory
tract,uterine tube and
ependyma
Epithelial Tissues
Classifications & Naming of Epithelia
• According to the number of cell layers
• First name of tissue indicates number of layers
– Simple – one layer of cells
– Stratified – more than one
layer of cells
Classification & Naming of Epithelia
• Last name of tissue describes shape of cells
– Squamous – cells wider
than tall (plate or “scale” like)
– Cuboidal – cells are as wide
as tall, as in cubes
Columnar – cells are taller than
they are wide, like columns
Naming Epithelia
• Naming the epithelia includes both the layers (first)
and the shape of the cells (second)
– i.e. stratified cuboidal epithelium
• The name may also include any accessory structures
– Goblet cells
– Cilia
– Keratin
• Special epithelial tissues (don’t follow naming
convention)
– Psuedostratified
– Transitional
Simple Squamous Epithelium
• Description
– single layer of flat cells with disc-shaped nuclei
• Special types
– Endothelium (inner covering)
• slick lining of hollow organs
– Mesothelium (middle covering)
• Lines peritoneal, pleural, and pericardial cavities
• Covers visceral organs of those cavities
Simple Squamous Epithelium
• Function
– Passage of materials by passive diffusion and
filtration
– Secretes lubricating substances in serosae
• Location
– Renal corpuscles
– Alveoli of lungs
– Lining of heart, blood and lymphatic vessels
– Lining of ventral body cavity (serosae)
Simple Squamous Epithelium
Simple squamous
lining the walls of
the capillary
Simple Cuboidal Epithelium
• Description
– single layer of cube-like cells with large, spherical central
nuclei
• Function
– secretion and absorption
• Location
– kidney tubules, secretory
portions of small glands,
ovary & thyroid follicles
Simple Columnar Epithelium
• Description
– single layer of column-shaped (rectangular) cells
with oval nuclei
• Some bear cilia at their apical surface
• May contain goblet cells
• Function
– Absorption; secretion of mucus, enzymes, and
other substances
– Ciliated type propels mucus or reproductive cells
by ciliary action
Simple Columnar Epithelium
• Location
– Non-ciliated form
• Lines digestive tract,
gallbladder, ducts of
some glands
– Ciliated form
• Lines small bronchi,
uterine tubes, uterus
Pseudostratified Columnar Epithelium
• Description
–
–
–
–
All cells originate at basement membrane
Only tall cells reach the apical surface
May contain goblet cells and bear cilia
Nuclei lie at varying heights within cells
• Gives false impression of stratification
• Function
– secretion of mucus; propulsion of mucus by cilia
Pseudostratified Columnar Epithelium
• Locations
– Non-ciliated type
• Ducts of male
reproductive tubes
• Ducts of large glands
– Ciliated variety
• Lines trachea and most of
upper respiratory tract
Stratified Epithelia
•
•
•
•
Contain two or more layers of cells
Regenerate from below
Major role is protection
Are named according to the shape of cells at
apical layer
Stratified Squamous Epithelium
• Description
– Many layers of cells – squamous in shape
– Deeper layers of cells appear cuboidal or
columnar
– Thickest epithelial tissue – adapted for protection
Stratified Squamous Epithelium
• Specific types
– Keratinized – contain the protective protein keratin
• Surface cells are dead and full of keratin
– Non-keratinized – forms moist lining of body openings
• Function
– Protects underlying tissues in
areas subject to abrasion
• Location
– Keratinized – forms epidermis
– Non-keratinized – forms lining of
esophagus, mouth, and vagina
Transitional Epithelium
• Description
– Basal cells usually cuboidal
or columnar
– Superficial cells domeshaped or squamous
• Function
– stretches and permits
distension of urinary bladder
• Location
– Lines ureters, urinary
bladder and part of urethra
• Histology
Introduction
• There are (4) types of tissue:
–
–
–
–
1. Epithelial
2. Connective
3. Muscle
4. Nervous
• Similarities between tissue
types:
– 1. All contain cells
– 2. Cells that make up tissues
have similar functions
Epithelial Structure
Apical
Apical
Basement
Membrane
Basement Membrane
• The epithelial cells lie
on the reticular
lamina (collagen – CT)
• Reticular lamina is
bound to another CT
called areolar CT.
• Together this
structure is called the
"basement
membrane”
Classification and Examples
1. Simple Epithelium
– Single layer
– All cells anchored
to basement
membrane
2. Simple Squamous
– Kidney – filtration
3. Simple Cuboidal
– Kidney tubules
– Filtration;
secretion,
absorption
Simple Epithelia
4. Simple Columnar
– Tall, thin cells
– Absorptive cells (small
intestine)
– Goblet Cells
5. Pseudostratified
‘Ciliated’ Columnar
Epithelium
– “Pseudostratified” ?
– Trachea
– Goblet Cells and Mucus
Stratified Epithelium
1. Characteristics
– 2+ layers
2. Stratified Squamous
– Skin – outer layer
hardened by ‘keratin’
– 4 to 5 layers thick
3. Stratified Cuboidal
– Ducts of sweat glands
– This type + stratified
columnar are rare!
MCQ
• Transitional epithelium is found in
1. Uterus
2. Ureter
3. Gall bladder
4. vagina
MCQ
• Stomach is lined by
1. Simple columnar epithelium
2. Straified squamous epithelium
3. Simple cuboidal epithelium
4. Pseudostratified columnar epithelium
MCQ
• Simple Squamous epithelium is seen in
1. Alveoli of lungs
2. Stomach
3. Urinary bladder
4. Tongue
MCG
• Glycocalyx coat present in the absorptive
surface of small intestine
1.Increases the surface area
2.Transports the absorbed material
3.Concentrates ions prior to absorption
4.Participates in the digestion of carbohydrates
MCQ
• Pseudostratified Epithelium is seen in
1. Ureter
2.Skin
3.Trachea
4.Kidney
• Simple squamous epithelium lining of serous
membrane is called………..
• Basement membrane is made up of how many
layers….
• What are Microvilli?
• Desmosomes?