Introduction to Histology and Epithelium Flashcards
Define Tissue
Group of similar cells working together to carry out a common function + the extracelluar matrix surrounding them
Cytosol
Intracellular fluid
Simple vs Complex tissue
Simple contains all the same cell type, Complex contains several different cell types
Parenchyma vs Stroma
Parenchyma is working tissue, Stroma is supporting tissue which also supplies nutrition (via blood vessels or ducts)
Define Organ
Several tissues grouped into a morphologically recognisable structure, performing a set of functions.
List 4 types of tissue and briefly describe their function
Connective (protects and supports), Epithelial (covers and lines body surfaces), Muscle (cells contract to generate force), Nervous (generate electrical signals in response to environment)
Extracellular Matrix (ECM)
the material between cells
How are cells joined to one another or other structures? List the types:
Cell juntions: GAP, Tight, Adherens, Desmosome, Focal adhesions, Hemidesmosomes
GAP junctions: function, component, example
Metabolic and electric coupling
Connexins
e.g. cardiac tissue
TIght junctions: function, component, cytoskeleton, example
Barrier, selective permeability and cells polarity;
Claudings;
Actin;
e.g. epidermis
Adherens junctions: function, component, cytoskeleton, example
Tissue integrity, contractility, motility;
Cadherins;
Actin;
e.g. morphogenesis
Desmosomes: functions, components, cytoskeleton, example
Strong adhesions and resist mechanical strength;
Desmosomal cadherins;
IF;
e.g. epidermis (keratins)
Focal adhesions: function, component, cytoskeleton, example
Cell anchorage, mechanical and biochemical signalling;
Integrins,
Actin,
e.g. cell migration
Hemidesmosomes: function, component, cytoskeleton, example
Cell anchorage;
Integrins;
IF;
e.g. Dermal-epidermal junction
5 stages of tissue processing for histology
Fixation, embedding, sectioning, staining, mounting
What is the role of fixation?
preserves tissue, prevents degridation, kills bacteria, enhances tissue staining
Methods of tissue fixation:
Freezing (dry ice or liquid nitrogen), Chemical fixation (inactivated enzymes and hardens tissue, often aldehyde based chemical used)
What is the role of embedding?
Provides support for tissue when sectioning
Two ways of embedding a sample:
Paraffin wax - most common, can alter apperance, water in tissues needs to be replaced, can’t see lipids or fats, can use water based alternatives (these dissolve sugars)
Frozen samples - less common
What is the role of sectioning?
Cutting cells into very thin slices so there is a higher resolution
Method of sectioning:
Using a microtone
What is the role of staining?
Colours tissue as most cells are transparent, features visable under microscope
Two types of staining:
Non-specific staining, specific staining
3 Types of Microscopy
Light (most common - limited detail), Electron (for finer detail, beam of electrons instead of light),
Magnification vs resolution
Magnification = measure of how large a microscope causes an object to appear
Resolution = smallest distance by which two points can be separated and still distinguishable as separate objects
What does H&E stand for? Explain each letter:
Haemotoxylin and Eosin
H = Basic, stains acidic/basophilic structures purplish blue
E = Acidic, stains basic/ acidophilic structures red/ pink
What does PAS stand for? Why is it used?
Periodic acid staining - for staining complex carbohydrates and glycogen, stains mucus, BM and brush borders
What does a PAS+ tissue look like?
deep red/ magenta
When is Masson Trichrome used?
to demonstrate supporting tissue elements, mainly collagen
What colours does Masson trichome stain various things?
nuclei and other basic structures = blue; collagen = green or blue depending on technique; cytoplasm, muscle, erythrocytes and keratin = bright red
Structure of Epithelial Tissue
- Continuous sheet of cells (1+ layers thick)
- cells in close contact with each other,
- cells bound togther by cell to cell junctions
- gap junctions allow things through
- sit on BM
- no blood vessels
- cell polarity (base is different to apex - apex faces outwards)
Function of Epithelial Tissue
Cover and protect surfaces inside and out of body
Form glandular structures (produces secretions that are discharged onto surface or into blood)
Form barriers (against abrasion, prevents water loss, prevents entrance of toxic molecules),
Combine with nervous tissue to make special senses
Can have specialised structure and function
Types of Epithelial tissue
Covering Epithelia, glandular epithelia
What are glandular epithelia?
Secretory epithelium arranged glands, invagination of epithelium, glandular organs - composed of mainly epithelium cells with connective tissue
Exocrine vs Endocrine glands
Exocrine - retain continuity with surface, secrete via a duct
Endocrine - lose contact with surface, pass substance into blood
2 ways to categorise Epithelia:
By number of layers, by shape of cells
Simple epithelia
1 layer of cells, good for adsportion, fragile
Stratified epithelia
2+ layers, good for protection
Pseudostratified epithelia
1 layer with mixture of cell shapes (looks stratified), not all cells reach surface but all in contact with BM
4 types of shapes of cells:
Squamous (flat), Cuboidal, Columnar (tall cylindrical), Transitional (readily change shape, accomodate stretching)
Structure, Function and Location: Simple Squamous Epithelium
Structure:single layer of flat, hexagonal cells, nuclei appear v flat
Function:diffusion, filtration, some secretion and absorption, few provide barrier as are delicate so can’t protect against friction
Location: alveoli
Structure, Function and Location: Simple Cuboidal Epithelium
Structure: single layer of cube shape cells, some with microvilli
Function: good for diffusion, secretion and absorption
Location:kidney tubules, glands and ducts, lining bronchioles of lungs, ovary surfaces
Structure, Function and Location: Simple Columnal Epithleium
Structure: single layer of tall & narrow cells, some have cilia or microvilli
Function: movement of substances, absorption and secretion, more protection than flatter cells
Location: glands and some ducts, bronchioles of the lungs, auditory tubes, uterus & uterine tubes, stomach, intestines
Structure, Function and Location: Stratified Squamous Epithelium
Structure:multiple layers of cells that are cube-shaped in basal layer, increasingly flat towards surface
- can be non keratinized (moist) or keratinised
Function: protect against abrasion, barrier against infection, reduction of water loss from body
Location
- Keratinized = skin
- Nonkeratinized = mouth, throat, larynx, anus, cornea of eye
Keratinised Epithelium: cytoplasm of cells replaced by keratin so cells are dead, living cells beneath the keratinized layer, thicker keratinized layer in certain areas, dry durable and moisture resistant characteristics
Structure, Function and Location: Pseudostratified Epithelium
Structure: technically single layer, almost always ciliated and associated with goblet cells (secreting mucus)
Function: synthesize and secrete mucus and move mucus containing foreign bodiesLocation: lining of nasal cavity, nasal sinuses, auditory tubes, bronchi of lungs
Structure, Function and Location: Transitional Epithelium
Structure: cuboidal/ columnar when not stretched, squamous when stretched, number of layers decrease when stretched (5-6 cells to 2-3 layered)
Function: accommodate fluctuations in volume of fluid in organs/ tubes, protects against effect of urine
Location: lining of urinary bladder, ureters, superior urethra, pelvis of kidney - this is where considerable expansion occurs
