Histology Flashcards
(44 cards)
What are the 7 steps for preparing a slide for light miscropy?
- ) Fixation
- )Dehydration
- ) Infiltration
- )Embedding
- ) Sectioning
- ) Staining
- ) Mounting
Describe fixation of a sample, the purpose and possible issues associated with this step.
Immobilize and cross link proteins to preserve sample using formalin, alcohol or freezing temperatures. Risks breakage or possible shrinking/swelling
Describe dehydration of a sample, the purpose and possible issues associated with this step.
Increase alcohol content of sample to avoid shrinkage. Risks breakage, possible shrinkage/swelling, possible removal of proteins/lipids
Describe infiltration of a sample, the purpose and possible issues associated with this step.
Volatile solvent (such as xylene) replaces alcohol b/c alcohol doesn’t mix with paraffin wax. Risks possible shrinkage/swelling or removal of proteins/lipids.
Describe embedding of a sample, the purpose and possible issues associated with this step.
Sample is EMBEDDED into molten paraffin wax to provide support to sample and allow for sectioning. Heat involved in this step could result in space b/t tissues
Describe sectioning of a sample, the purpose and possible issues associated with this step.
Sample is cut into 3-10 micrometer thick slices using microtome to allow for view of different layers of sample.Risks possible folds/scratches within the slices
Describe staining of a sample, the purpose and possible issues associated with this step.
Sample is exposed to dye (commonly use H&E) to create contrast amongst components. Risks over/under staining and false precipitates.
Describe mounting of a sample, the purpose and possible issues associated with this step.
Sample is fixated to a glass slide with a coverslip to allow viewing of sample in LM. Risks breakage of tissue or creating folds.
What are two other quick methods of preparing tissues and their use?
- Frozen sections-tissue immediately frozen and sectioned using a cryostat (cold microtome) allowing prep in minutes rather than days with other method, used for time critical instances (biopsy of an open operation pt)
- Smears-isolated cells are smeared directly onto slide and stained. Examples include blood, bone marrow and cervical cells (pap smear)
What is the most common stain used for tissues (for our purposes), what are its components and what color do those components stain/what structures?
H&E which is composed of Hematoxylin and Eosin
- Hematoxylin stains blue and basophilic. It will stain organelles with lots of DNA/RNA [nucleus (heterochromatin, chromosomes, nucleoli), ribosomes in cytoplasm] and some secretory vesicles
- Eosin stains red and acidophilic. Stains cytoplasm, mitochondria, some secretory/lysosomal cells, RBCs
What is the relationship between acidophilicity and basophilicity of a tissue slide and the living tissue?
There is no relationship, the trends that we recognize with prepared slides are based off a sampled that has gone through many steps of preparation and doesn’t reflect the acidophilicity/basophilicity of the living structure in biochemical surrounding
What are the three main components of the nucleus and descriptions of each?
Nuclear membrane-2 unit membrane containing nuclear pores (holes in membrane), continuous with RER of cytoplasm
Nucleolus-dense, central portion, the site of rRNA syn and initial ribosomal assembly
Chromatin-long tangled threads of DNA, RNA, assoc. proteins, become distinct entities during mitosis/meiosis (CHROMOSOMES)
What are the two interchangeable states of chromatin and the description of each?
Heterochromatin-tightly coiled and condensed, contains genomic info that is NOT transcriptionally nor metabolically active
Euchromatin- dispersed, extended; it is transcriptionally AND metabolically active
What is the importance of nuclear staining and the meaning/implications of a “light staining” or “dark staining” nucleus?
Size, shape, staining of nucleus helps in cell identification and functional activity
- Light staining=euchromatic nucleus; it is large, well developed and transcriptionally/metabolically ACTIVE
- Dark staining=heterochromatic nucleus; small, poorly developed nucleus and nucleolus, transcriptionally/metabolically INACTIVE (dead/dying cell will be intensely heterochromatic/pyknotic
What is the importance of the S phase?
Chromosomes are duplicated in preparation for mitosis; begins w 2 centrioles ends w 4 centrioles
What is karyotyping? What stage of mitosis are the cells suspended in for ideal results?
Visualization of the # and morphology of an individual’s chromosomes to screen for abnormalities. Colchicine is added to suspend the cells in metaphase (ideal for karyotyping)
What is a Barr body?
An inactivated X chromosome, used to sex type, XX (girl,), XY (boy). Girl will have Barr body. Remains condensed and transcriptionally inactive thru interphase
What are the divisions of the cell cycle?
Mitosis and interphase (G1, S, G2)
G1=most variable part of cycle, protein and RNA synthesis; grow and preform specialized Fox
S= DNA syn and proteins assoc. w chromatin
G2= synthesis of mitotic apparatus
What is Go?
Outside of cell cycle can be cells that are temporarily non-dividing or terminal cells that will not divide
What are the three cell categories and examples of each?
- Constantly dividing labile cells (move rapidly thru the cell cycle) ex. Embryonic, skin, bone marrow
- Quiescent stable Go, extended G1 that can re-enter cycle ex. Liver cells
- Permanently non-dividing/permanent Go = postmiotic (heavily specialized/differentiated that can no longer replicate) ex. Neurons, cardiac and skeletal muscle
What is the characterization and function of the cell membrane?
Semi-permeable phospholipid belayer b/t 7-10 nm thick, contains integral and peripheral proteins, allows for transport of material into and out of cell, maintain cell’s inner compositionn
What is the function of cytoskeleton?
Support framework of cell, variety of proteins assembled into minute rods/filaments/tubules
What are the two main cytoskeletal structure categories?
Filaments, Microtubules
What are the different size categories of filaments?
- Microfilaments/Thin/Actin filaments(~7nm)
- Myosin Filaments (~12-16nm)
- Intermediate filaments (~8-12nm)
