Introduction to Histology Flashcards
Why are tissues stained?
To see histological details
What is an electron microscope used for?
To see cells ultrastructure
e.g. nucleus, mitochondria etc
How are tissues preserved?
Why?
Placed in formalin (aqueous solution of gas formaldehyde).
Prevents tissue from rotting.
Method 1 - preparation of tissues for staining
- Prep thin slices of tissue
- Tissue is first preserved
- Samples of tissue to be examined are embedded in paraffin (process involves extraction of water and other substances from tissues).
- Fine slices of the tissues are made (4 microns thick)
- These are mounted on microscope slides and stained.
Method 2 - alternative methods of staining
Smear of tissue. Can be done by solid tissues also by fluids e.g. blood.
Looking at blood smears-see whole cells rather than thin slices through individual cell.
Why don’t some tissues go with either method of staining?
Too hard e.g. bones
Demineralise-can produce thin sections.
To see mineralised structure-grind down to produce thick slice.
Most commonly used dye
Combo of Haematoxylin and Eosin.
Water extra cellular jelly doesn’t stain
Appears as white spaces
Van Gieson’s trichrome stain
with haematoxylin counter-stain
Collagen - pink/red
Cytoplasm - yellow/olive green
Nuclei - black
Elastic tissue - dark brown
Haematoxylin
Nuclei - blue
RNA - blue
Eosin
Cytoplasm - pink
Collagen, Elastic - pink
Colloidal proteins, plasma - pink
Keratin - Orange/red
Alcian blue
GAG-rich structures - blue
Mucous goblet cells - blue
Mast cell granules - blue
Cartilage matrix - blue
Iron Haematoxylin
Nuclei - black
Elastic fibres - black
Periodic Acid Schiff (PAS)
Hexose sugars - Magenta (dark pink)
(especially those contained in complex carbohydrate containing structures including:
goblet cell mucins, cartilage matrix, glycogen, basement membranes, glycocalyx)
Perl’s stain
Ferric iron - Prussian blue
Romanovsky stains
e.g. Giemsa’s of Leishman’s stains for blood films
Chromatin, nuclei, azurophils - purple
Neutrophils granules - purple
Erythrocytes, Eosinophil granules - red/pink
Lymphocyte & Monocyte cytoplasm - pale blue
Basophil granules - dark blue/purple
Toluidine Blue
Nuclei, Ribosomes - dark blue
Cytoplasm - pale blue
Cartilage matrix , mast cell granules - bright purple
GAG-rich components - bright purple
Lymphocyte size
- Small = 10micrometres in diameter
- Little cytoplasm as dormant and not fully differentiated
- Metabolically inactive
- Minimal RER
Neuron size
- Large = 100micrometres in diameter
- Fully differentiated
- Metabolically active
- Can’t see all processes due to slide thickness
Rounded cell shape
e.g. RBC’s-biconcave disc shape
Polygonal cell shape
- Soft cells squashed together
- Get irregular shape
Fusiform cell shape
- Smooth muscle cells.
- Spindle shaped/elliptical
Squamous cell shape
- Flattened
- Appear as thin flattened plates
Cuboidal cell shape
-Square shaped e.g. thyroid, 2D
Columnar cell shape
- Taller than they are wide
- Rectangular, 3D
Globular cell shape
-Spherical, globe like
Difference between metabolically inactive/dormant and metabolically active cells
Inactive are smaller as only need little mitochondria whereas active needs an abundance of mitochondria
Lifespan of cells
- Days (4-5): lining of gut-small intestine
- Months: Skin and connective tissue. Cells of blood (RBCs-120 days before removed).
- Years: bones and tendons
- Nearly whole life: skeletal muscle-limited ability to regenerate
- Whole life: nerves, brain, heart & stem cells of germ cells.
Nucleus
- Brain of cell
- Collection of DNA that is surrounded by a double nuclear membrane where there are numerous small pores.
- Pores-allow passage of ribosomal RNA and chemical messengers.
- Doesn’t have uniform ultrastructure appearance.
- Contains chromatin
- Nucleolus(1-3microns diameter), site of ribosomal formation. Seen using light microscope.
Chromatin
- Nucleus contains different electron densities of chromatin.
- Darker areas called Heterochromatin.
- Lighter areas are called Euchromatin.
Mitochondria
-Powerhouses of cell
-Have their own DNA.
-Initially were bacteria that formed a symbiotic relationship with animal cells.
-Double membrane.
-Outer membrane is smooth- site of lipid synthesis and fatty acid metabolism.
-Inner membrane is highly folded, folds are called cristae. Site of respiratory chain (ETC), production of ATP and Oxidative phosphorylation.
-Between folds there is a mitochondrial matrix. Matrix is site of Krebs cycle
Space between inner and outer membranes- Intramembranous space- site of Nucleotide Phosphorylation (ADP to ATP).
Rough Endoplasmic Reticulum (RER)
- Site of protein synthesis
- Series of highly folded flattened membrane sheets.
- Covered with ribosomes-gives rough appearance.
Smooth Endoplasmic Reticulum (SER)
- Site of membrane lipid synthesis
- Processes and synthesizes proteins.
- Series of highly folded flattened membrane sheets.
Golgi Apparatus
- Series of parallel stacks of membranes.
- Site at which macromolecules which have been synthesised in ER are processed and stored.
- Frequently not visible on light microscopy but plasma cells defy this as they have a very visible Golgi apparatus.
Plasma cells
- Plasma cells activated B lymphocytes - are the cells which produce antibodies.
- Nucleus is located at the edge of the cell and there is a prominent pattern of Heterochromatin and Euchromatin.
- Next to the nucleus is a pale area within cytoplasm known as a perinuclear hoff. This is the Golgi apparatus of the plasma cell.
Vesicles
-Very small spherical membrane-bound organelles used for transport, storage and exchanging cell membrane between compartments.
Several types:
- those derived from cell membranes are called pinocytotic/phagocytotic vesicles.
- Golgi-derived transport vesicles
- ER-derived transport vesicles
- Specialized vesicles called lysosomes and Peroxisomes.
Lysosomes
- Derived from Golgi apparatus
- Site at which proteins are degraded.
Why are lysosomes a danger to cells?
- Site at which proteins are degraded. Means lysosomes are dangerous to cells.
- To protect cells, there is special separation between enzymes which lower pH and enzymes which degrade proteins at a low pH.
Lysosome formation
- Formed by the fusion of 2 vesicles. Hydrolase vesicles (contain enzymes that degrade proteins at a low pH) and endosomes (bare hydrogen ATPase on their membrane).
- This energy dependent enzyme, pumps hydrogen ions into vesicle, lowering its internal pH.
- Fusion of these 2 vesicles produces an endolysosome in which there is both the ability to lower pH and enzymes which can degrade proteins at low pH.
Peroxisomes
- Very small vesicles (0.5-1.0 microns).
- Contain enzymes which oxidise long-chain fatty acids.
Cytoskeleton
- Supports the cells shape
- Comprised of different types of filaments.
- Smallest is microfilaments (5nm diameter). Made of actin.
Actin
- Globular G-actin protein that polymerises into filamentous F-actin.
- Actin forms a bracing mesh (cell cortex) on the inner surface of the cell membrane.
Microtubules
- When cells divide a mesh work of microtubules (tubulin proteins -25nm diameter) formed from tubulin develop.
- Acts as scaffold for chromosomes during mitosis and meiosis.
- Tubulin proteins are found in all cells except erythrocytes as they don’t divide.
- Microtubules-made of alpha and beta tubulin which arrange in groups of 13 to form hollow tubes.
Intermediate filaments
- 10nm diameter
- 6 types of protein.
- Anchored to transmembrane proteins.
- Spread tensile forces through tissues.
- Specific functions of the different types of intermediate filament are not known. But useful to tell one cell type from another by staining.
6 types of intermediate filaments
- Cytokeratin’s-found in Epithelial cells
- Desmin-Myocytes
- Glial fibrillary acidic protein-Astrocytic glial cells
- Neurofilament protein-Neurons
- Nuclear laminin-Nuclei of all cells
- Vimentin-Mesodermal cells
Storage products and inclusion-materials within cells
- Lipofuscin
- Lipid
- Glycogen
Lipofuscin
- Membrane bound orange-brown pigment, that is formed as a result of Peroxidation of lipids in older cells.
- Effectively a breakdown wear and tear pigment.
- Common in heart and liver of older patients.
Lipid
- Lipid accumulates in cells in non-membrane bound vacuoles.
- Because lipids are washed out of tissues during tissues processing (they dissolve) these accumulations of lipids appear as empty white spaces in cells.
- Find lipids accumulating normally in Adipocytes (fat cells) and liver.
Glycogen
- Carbohydrate polymer in cytoplasm
- Normally only seen on electron microscopy.
- Accumulates in some cells and diseases, becomes visible therefore can be seen with a light microscopy.
- Glycogen washed out of tissue during tissue processing, doesn’t stain, appears as white spaces.
Composition of tissues
- Cells interstitial fluid- water salts in solution and range of peptides and proteins, hormones etc.
- Extracellular material-fibrillar proteins (e.g. tendons). Glycosaminoglycan jelly. Inorganic salts as solids (calcium in bone).
Types of tissue
- Epithelial-protection, absorption, secretion
- Muscle- smooth, skeletal, heart
- Supporting tissues- cartilage, bone, tendon, blood
- Nerves-brain, peripheral, visceral
- Germ cells-ova, sperm
