Histology Flashcards
what is cell theory? (3)
- all living things are composed of one or more cells
- the cell is the basic unit of life
- new cells arise from pre-existing cells
what is the definition of a tissue? (2)
- groups of similar cells working together to carry out a common function
- made up of cells and an extracellular matrix
what are the 2 broad types of tissue?
- parenchyma - working tissue that directly carries out the function
- stroma - scaffold and nutrition tissue that surrounds the working tissue (eg. blood vessels)
what are the 4 sub-types of tissue and what are their functions?
- connective - protects and supports
- epithelial - covers and lines body surfaces
- muscle - cells contract to generate force
- nervous - generate electrical signals in response to environment
what is the definition of an organ? (3)
- made up of several tissue types
- morphologically recognisable structure
- performs a specific set of functions
what is the purpose of fixation in staining? (2)
- preserves the tissue
* kills off any bacteria
what are the 2 main types of fixation?
- freezing using dry ice or liquid nitrogen
* chemical fixation - aldehyde based (formaldehyde)
what is the purpose of embedding in staining?
provides support for the tissue when sectioning
what is the process of embedding a sample in paraffin wax? (3)
1 - dehydration: water in the sample is replaced with alcohol
2 - clearing: xylene replaces the alcohol as both alcohol and paraffin wax are soluble in it
3 - embedding: tissue is placed in warm paraffin wax - wax fills the spaces that used to have water in them
what is a side effect of using xylene as a solvent in tissue?
lipids are also dissolved -> areas appear clear on microscope
why do sections of samples need to be thin?
increase resolution
what tool is used for sectioning?
microtome
what extra step must be carried out in staining process if using an aqueous stain?
wax is dissolved in xylene, replaced with alcohol and then water (then mounted on slide)
what is the most common type of stain? what types of structures does it stain?
- H&E: haemotoxylin and eosin - purple and pink
- H is basic - stains acidic / basophilic structures
- E is acidic - stains basic / acidophilic structures
what stain is used for carbohydrates? what are organs rich in carbohydrates called?
- PAS - magenta
* PAS +
where is epithelial tissue found? (5)
- lining of internal cavities
- blood vessels
- lining of organs (respiratory, digestive, urinary and reproductive)
- glandular structures
- skin
what are the 5 functions of epithelial tissue?
- protective
- barrier (prevent water loss)
- permit absorption / diffusion
- sometimes involved in secretion from glands
- sometimes is combined with nervous tissue in special senses (smell, hearing etc)
how does epithelial tissue get it nourishment?
connective tissue (not BV)
what are the 2 types of glands?
- exocrine glands - retain continuity with surface and secrete via duct
- endocrine glands - lose contact with surface and secrete directly into blood stream
what is the structure simple squamous epithelium? (2)
- single later of flat / hexagonal cells
* flat nuclei
what is the function of simple squamous epithelium? (4)
- diffusion
- filtration
- some secretion
- some absorption
what is the structure of of simple cuboidal epithelium? (2)
- single layer of cube-shaped cells
* some have microvilli
what is the function of simple cuboidal epithelium? (3)
- diffusion
- secretion
- absorption
what is the structure of simple columnar epithelium? (2)
- single layer of tall narrow cells
* some have cilia or microvilli
what it’s he function of simple columnar epithelium? (4)
- movement of substances
- absorption
- secretion
- some protection (more than flatter cells)
what is the structure of stratified squamous epithelium? (2)
- multiple layers of cells that are cube-shaped in basal layer
- progressively flatten towards surface
what is the function of stratified squamous epithelium? (3)
- protection against abrasion
- barrier against infection
- reduction of water loss from the body
what is the difference between stratified and pseudostratified epithelium?
- stratified: multiple defined layers
* pseudostratified: appear to be different laters (nuclei in different places) but all cells touch the basement membrane
what is the structure of pseudostratified epithelium? (2)
- single layer of cells, but appear stratified
* almost always ciliates and associated with goblet cells (secrete mucus)
what is the function of pseudostratified epithelium? (2)
- synthesise and secrete mucus
* move mucus or fluid containing foreign particles over the surface (protective)
what is the structure of transitional epithelium? (3)
- cuboidal / columnar when not stretched
- squamous / flattened when stretched
- stratified layers - no. of layers fluctuated whether they are stretched or not
what is the function of transitional epithelium? (2)
- accommodate fluctuations in volume of liquid in organs or tubes
- protects against caustic effects of urine
