Histology Flashcards
What are the four basic tissues and function of each one?
1) Epithelia: cover and lines surfaces. I.e what lines intestines.
2) Connective tissue: packing, support, connecting.
3) Muscle: contractility.
4) Nerve: Irritability, conduction
Preparation steps of tissue for microscopy.
1) Fixation
2) Dehydration in alcohol.
3) Embedding
4)Trimming/sectioning
5)Removal of paraffin
6)Rehydration
7)Staining
8) Mounting sections on glass slide
9)Viewing the tissue (light microscope)
What preparation steps for microscopy affect the appearance of tissue?
1)Fixation: sample placed in a chemical solution that preserve the tissue by cross-linking proteins and inactivating degradative enzymes.
2) Dehydration in alcohol: removes water
3) Embedding: tissue placed in a small mold with melted paraffin (wax) and allowed to harden.
4)trimming/sectioning : paraffin block is trimmed to expose the tissue for sectioning (slicing) on microtome
7) staining: colors the cells that is completely colorless. Acid and basic dyes used to form salt linkages with molecules in tissues
Acid dye (most common )
Eosin. Binds with basic part of the cell
Stain blue!
Basic molecules bind with acidic dyes and stain red.
Basic dye (most common )
Hematoxylin. Binds with the acidic part of the cell
Stain red!
Acidic molecules bind with basic dyes and turn blue.
Basophilic
(Acidic molecules )Cell components such as nucleic acid with a negative charge (anionic), stain with basic dyes.
Acidophilic
(Basic molecules)Cell components that contain lots of basic molecules, such as protein with many ionized amino group, stain with acidic dyes.
What color is the cytoplasm stained? why?
Cytoplasm would be pink, bc it has lots of proteins which are basic molecules. Basic molecules love acidic dyes.
What color is the nucleus stained ?
Blue. It contains nucleic acid (acidic) and that loves basic dyes.
Luxol blue and hematoxylin
Luxol blue is a better dye to visualize nerve tissue
Trichrome
Visualize connective tissue better. Stains Ct in green and blue.
Why don’t fat and mucus stain well with H and E?
Bc they get washed out in preparation process.
Hydrophobic structures also tend to remain clear; these are usually rich in fats, e.g.adipocytes,myelinaround neuronaxons, andGolgi apparatusmembranes.
H&E staining dissolves fat out of the cell
Periodic Acid Schiff Reaction (PAS)
Best for staining mucus, microvilli, basement membrane and glycogen granules.
Sudan Black
Best for fat and myelin
What are the artifacts caused by preparation ?
Artificial space, wrinkles in tissues and precipitate of stains.
What causes artificial spaces in tissue ?
Shrinkage due to fixation, dehydration and embedding.
Loss of molecules( glycogen and lipids) that were not retained after fixation or removed during dehydration.
Electron Microscopy
Transmission electron microscope (TEM): shows inside of cell.
Scanning electron microscope (SEM): shows surface of cell.
Light grey: electron Lucent
Dark grey: electron dense.
Nucleus Structure
Membrane-limited.
Nucleus envelope: outer and inner membrane. outer membrane faces the cytoplasm, house ribosomes and is continuous with RER at certain sites.
The inner membrane faces the genetic material and is supported by nuclear lamina on its inner surface.
Nuclear pores on the surface of nucleus to aid with transport.
nucleolus in the center.
Nucleus functions
Cellular regulation: houses genetic material which direct cellular activities.
Production of ribosomal subunits that are exported into cytoplasm for ribosome assembly.
Function of nuclear lamina
Support of inner nuclear membrane
nucleus stability.
chromosome attach.
Mutation in nuclear lamina
Muscle dystrophy ( genetic defect condition)
WHAT HELPS SUPPORT THE NUCLEUS AND AIDS IN MAINTAINING ITS SHAPE?
Nuclear lamina
Nuclear envelope
The nuclear envelope, formed by two membranes with a perinuclear cisternal space between them, separates the nucleoplasm from the cytoplasm.
Nucleosome
DNA wrapped around histones. Forms chromatin.
Chromatin is the condensed to form chromosomes
Heterochromatin
condensed chromatin. No active transcription
Dense staining
Euchromatin
Open chromatin. Active gene transcription occurs.
Lightly staining.
Nucleolus
Spherical in shape.
Basophilic ( stains blue)
site of ribosomal RNA (rRNA) synthesis and initial ribosomal assembly
rRNA
Ribosomal RNAis the major structural component of the ribosome and has sequence complementarity to regions of mRNA with which it can interact
ER
Network of intercommunicating channels and sacs/cisternae formed by a continuous membrane
Ribosomes
Dark staining granules in EM.
Free or bound to ER.
Polyribosomes
Ribosomes associated with mRNA. Occur in the cytosol or RER membranes
RER
continuous with outer nuclear envelope and the SER.
has ribosomes= rough
Functions of ER
Protein synthesis: hormones, receptors etcc.. proteins either remain in the cell , incorporated into membranes, enter nucleus and/ore are secreted/exported from the cell.
Glycosylation (N-linked glycosylation): adding sugar molecule to nitrogen molecule of amino acid
Constitutive secretion and name a cell that carrys it
Always happening. proteins required by cell to carry out necessary function.
Hepatocytes
Regulated secretion
waits for signal. In granules
SER
Hard to identify bc shape varies.
What are membrane bound organelles?
Mitochondria
ER
Lysosome
Peroxisome
Gogi
Cells with extensive RER and a well-developed Golgi apparatus show few secretory granules because the proteins undergo exocytosis immediately after Golgi processing is complete.
SER functions
-Synthesis and breakdown of glycogen
-Synthesis of cholesterol, bile salts and lipoproteins.
-Synthesis of steroid hormones
-Detoxification.
-Uptake and release of calcium in muscle cells.
The enzymes involved in making steroid hormones, and those that synthesize and breakdown glycogen in liver cells are located in SER membrane
Golgi apparatus
Membrane bound disc shaped envelopes (cisternae)
has receiving surface (cisface)( from rough ER) for transport vesicles and exporting surface (trans face)
Closely packed cisternae is how we identify it.
Functions of Golgi apparatus
-Post- translational modification of proteins. Proteins produced by ER that are properly folded move, via small vesicles, to Golgi complex.
- O-linked glycosylation: glycan attached to oxygen molecule of an amino acid. (less common than N-glycosylation)
- Synthesis of lipoproteins
Glycosylation and effects if failed
Adding glycans.
when attached to proteins they form glycoproteins; when attached to lipids they form glycolipids.
If failed we get Dandy-walker malformation : where the cerebellum does not develop normally
Mitochondria characteristics and function.
Double membrane
Cristae (not cisternae pay attention!) internally.
Matrix where mito DNA is
Functions:
-Beta oxidation of fatty acids chains in the matrix
-Energy production (ATP)
-Steroid hormone synthesis( at the site at which side chain on cholesterol is removed. This is termed side chain cleavage. The enzyme involved in side chain cleavage is located the inner membrane of mito.
-Storage and release of calcium
- Regulates apoptosis.
Lysosomes
Membrane bound organelles.
Contains hydrolytic enzymes
Acidic contents (proton pump in membrane to maintain acidic environment)
Electron dense contents.
For microscopy we only need to identify secondary lysosome.
secondary lysosome is primary lysosome fused with things the cell eats.
Lysosome functions
Digest ingested material and aged or damaged organelles.
1) heterophagy, e.g phagocytosis and degradation of bacteria by ( neutrophils)
2) break down of bone during bone remodeling (by osteoclasts)
3) Autophagy, destruction of worn out organelles.
Lysosome storage diseases
mutation in in the gene that encodes for proteins in lysosomes. i.e don’t have normal enzymes in lysosomes to breakdown things.
results in accumulation of substates for lysosomal digestion.
Peroxisomes/ Microbodies.
Membrane bound organelles containing oxidative enzymes.
The matrix consists of fibrils or a crystalloid structure containing enzymes.
Crystalloid core is dark, the enzymes are lighter grey area.
Functions:
Beta oxidation
Cholesterol synthesis
Degrade hydrogen peroxide.
Zellweger’s cerebrohepatorenal syndrome
Fatal disease due to the absence of peroxisomal enzymes.
-Reduced degradation of hydrogen peroxide and abnormal accumulation of fatty acid chains causes neuronal membrane injury and demyelination which leads to…..
- …skeletal muscle weakness . inability to nurse properly. seizures, enlarged liver, kidney cysts etc..
under microscope you se peroxisomal membrane but no enzymes inside. the membrane is dark grey but inside is very very light grey.
Cytoskeleton
-unique to eukaryotic cells,
-not covered by membrane.
- compromised of microfilaments, micortubules, and intermediate filaments.
Secretory granules
much bigger than lysosome. can be seen by light microscopy.
lysosome can’t be seen by light microscopy
Organelles that participate in beta oxidation
Mitochondria and Peroxisome
Organelles that participate in steroid hormone synthesis
Mitochondria and SER, peroxisom
Organelles that participate in Ca uptake
Mitochondria and SER
