Intro Histology and Epithelia Flashcards
What is Histology?
•Histology is the study of the microscopic structure of tissues and organs
ie: microscopic anatomy.
- The shapes of individual cells and how they are arranged into tissues can tell us a lot about how they do their jobs (and whether they are doing their jobs)
- Light microscopy is used on regular basis to examine cells and tissues.
Processing a slide for Histology
(preparing samples- ex. kidney)
* kidney section has been fixed (1), processed(2), sectioned(3) , and stained (4)
- if you were to go without processing the tissue there are obvious problems: it is not permanent (decay), blob would appear, difficult to cut into thin and viewable slices, bad coloring
- This is solved by PROCESSING: a) fixation b) provision of support medium c)staining
Stains:
Why are they there?
What stains what?
- Stains are made to make the tissue visible
- Haematoxylin mainly stains nuclei blue/purple
- Eosin mainly stains cytoplasm pink (protein of the cytoplasm)
- all helps tell you the structure of the cell
- cellular protein vs. nuclei –> type of cell and tissue you may be looking at AND function
- or structure: rows vs. scattered
Directions of sectioning
(2)
•There are 2 ways to cut through a long organ
–Transverse = across the object, through its longest axis (embryo example with transverse sectioning)
–Longitudinal = Along the longest axis
Need to relate the anatomy to the histology–> know which section you are looking at and where it is located in relation to the organ of study
-where has this section come from?
Identifying what you are looking at on a histology section
(list)
1) Organisms are made of organs
2) Organs are made of tissues
3) Tissues are made of cells and matrix
•The best approach is to work down this list from the top
When looking at the entire slide
- Are you looking at an organism or several organs? If so, identify the organs and look at them one at a time
- This requires a knowledge of the anatomy of the organism
- Most slides will show a particular organ or part of an organ. They should be labelled so you know what you are starting with
Breaking up the Organ into Tissues
- In a section thorough an organ you will probably be able to see layers or regions which have a different appearance, by the naked eye or at low power
- This process gets harder if you zoom in too much
-look at slide even as a whole without microscope
•You can expect these different regions to be different tissues
- Organs consist of a variety of tissues acting together for functionality
Epithelia
•Epithelia form the boundaries and barriers - easiest to find when first looking at a slide
-tend to find at the interface between substances (glands, etc.)
- They are found at the edges of tissues and so have liquid or air on one side
- We characterise them mainly according to the shape of their cells and the number of layers of cells they have
A gland
(and its epithelia)
- Glands exist to secrete substances into the circulation. Secreting liquid into its lumen
- As they function as an interface they contain lots of epithelia.
- you can see rows of nuclei that indicate the epithelium
- Cells in this epithelium have a square shape
They are described as being in a “cuboidal” epithelium
-appear square in section and cuboidal in a 3D view of the tissue
Small Blood Vessels
(and their epithelia)
- In vessels, Can find Red Blood Cells by lack of Haematoxylin (RBCs not having nuclei)–> stained by cytoplasmic proteins
- These cells are flattened (epithelium) on edge
- boundary between flowing blood and solid tissue
- They are described as being in a “squamous” epithelium (flattened shape cell)
Lining of the Gut
(and its epithelium)
- The gut functions to absorb nutrients into the body. –> think about shape
- This makes them an interface where we can find a lot of epithelium.
- need a large interface for absorbtion
- microvillae give you even more surface area for absorbtion
- ignore round cells (immune cells), epithelium is in regards to long, oval cells
- Cells in this epithelium have an elongated shape
They are described as being in a “columnar” epithelium
What do the nuclei tell you about the cells?
(epithelium)
- shape of the nucleus does tend to mirror the shape of the cell
- flat looking nucleus, squamous cell of epithelia
Simple Epithelium
(3)
- “Simple” means that there is one layer of cells
1) Simple squamous epithelium
2) simple cuboidal epithelium (ex: gland, one job to secrete)
3) simple columnar epithelium (ex: gut, more complex)
1. –> 3. = Relatively passive barrier to relatively active barrier
An earlier part of the gut
(and epithelium)
- Organs vary depending on where they are sectioned!
- won’t always be a simple columnar epithelium
- now shows stratified epithelium
- Cells in this epithelium are in multiple layers
They are described as being in a “stratified” epithelium
Stratified Epithelium
*What is the function of this arrangement of cells?
PROTECTION
Multiple layers of cells provide protection to the tissue
-if top layer of cells are damaged then the newer layer of cells beneath will take its place
Dense Irregular Connective Tissue
- The positions and shapes of the cell nuclei are useful for seeing where the protein matrix is
- A lot of protein in it, but not very organized
- a lot of pink, with a few dark cells (nuclei) scattered around
- ex: a lot of collagen, but a few fibroblasts located randomly throughout
Dense Regular Connective Tissue
- The positions and shapes of the cell nuclei are useful for seeing where the protein matrix is
- nuclei (fibroblasts) are lying in rows –> giving away that there are parallel strands of collagen holding it together
- highly organized connective tissue
- Dense regular connective tissue will be stronger. (This is Achilles tendon.)-needs to carry a huge amount of force
