View
215
Download
1
Category
Tags:
Preview:
Citation preview
Histology
Study of cells, tissues and organs as seen with the help of microscope
Histology
• Often called Microscopic Anatomy
• Greek word – Histos= tissueLogia=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 derived from all the 3 germ layers:
• Ectoderm Epithelium of skin• Endoderm Epithelium of gut• MesodermEpithelium 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 epitheliumReticular 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 ORJunctional 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 cellsSubjected 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
• 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
Classifications & Naming of Epithelia
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 dome-
shaped or squamous
• Function– stretches and permits
distension of urinary bladder
• Location – Lines ureters, urinary
bladder and part of urethra
Introduction • Histology
• 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
Basement Membrane
Apical
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 in1. Uterus2. Ureter3. Gall bladder 4. vagina
MCQ
• Stomach is lined by1. Simple columnar epithelium2. Straified squamous epithelium3. Simple cuboidal epithelium4. Pseudostratified columnar epithelium
MCQ
• Simple Squamous epithelium is seen in1. Alveoli of lungs2. Stomach3. Urinary bladder 4. Tongue
MCG
• Glycocalyx coat present in the absorptive surface of small intestine
1.Increases the surface area2.Transports the absorbed material3.Concentrates ions prior to absorption4.Participates in the digestion of carbohydrates
MCQ
• Pseudostratified Epithelium is seen in1. Ureter2.Skin3.Trachea4.Kidney
• Simple squamous epithelium lining of serous membrane is called………..
• Basement membrane is made up of how many layers….
• What are Microvilli?• Desmosomes?
Recommended