Histology Flashcards
What is the sequence of preparing histological sections?
- Tissue collection
- Fixation
- Dehydration (alcohol)
- Paraffin embedding
- Sectioning with microtome
- Straightening with water bath
- Transfer section to slide
- Stain and cover slip
Why is fixation needed?
- to prevent it rotting
Why does it need to be embedded in paraffin?
- to make it solid so it can be sectioned
Haematoxylin (stain)
- blue
- stains mainly genetic material (DNA/RNA)
Eosin (stain)
- pink
- stains mainly proteins (mainly cytoplasm)
What is epithelium?
- tissue that covers all external and internal surfaces of the body
- polar orientation - one side facing lumen/ free space other side attached t another tissue
Epithelium key characteristics
- forms basement membrane (anchors epithelial cells)
- little extracellular space between cells (form sheets)
- contains no blood vessels
- can have apical modifications
How can epithelium be classified?
- Morphology - cell shape, arrangement of cells
2. Function - glandular or non glandular
What is the function of simple squamous epithelium?
- passive transport of substances across cytoplasm - short diffusion distance
- provide little protection
Where is simple squamous epithelium found?
- alveoli, vessels (endothelium), body cavities (mesothelium)
What is the function of simple cuboidal/ columnar epithelium?
- secretion and absoption
Where is simple cuboidal epithelium found?
- thyroid, kidney, lungs, ovary, ducts
Where is simple columnar found?
- intestine, female reproductive tract, many exocrine glands
What is the function of pseudo stratified epithelium?
- secretion and movement of particles along tubular organs (respiratory epithelium)
Where is pseudo stratified epithelium found?
- trachea, bronchi, epididymis
What is the function of stratified squamous epithelium?
- protects underlying tissues by acting as a barrier and stops it drying out
- undergoes keratinisation but not in areas that remain moist in small animals
Where is stratified squamous epithelium found?
- most external and some internal body parts
Where is stratified cuboidal and columnar found epithelium?
- covers areas of transition between simple and stratified epithelia
- respiratory tracts, duct of exocrine glandes
What is transitional epithelium?
- only in urogenital system
- AKA urothelium
- changes shape depending of internal pressure
e. g bladder stretches out into thin layer when full
How can epithelial glands be classified?
- Method of secretion (ego/endo)
- Type of secretion
- Shape
- Cell numbers
What are endocrine glands?
- ductless
- secrete hormones
- near blood vessels
- high diversity in morphology
What are exocrine glands?
- secrete product into lumen or free surface (directly into organ or duct)
- normally secrete enzymes
How are exocrine glands classified?
- shape:
1. secretory component = tubular or acinar
2. tubular shape = simple or compound (branched tubules) - no. of cells:
1. unicellular e.g goblet cell
2. multicellular e.g sebaceous - secretory product:
1. serous = clear, watery fluid
2. mucous = more viscous fluid
3. mixed = mixture of the 2 - type of secretion:
1. merocrine = exocytosis (cell membrane in tact)
2. apocrine = decapitation (top pinches off - top of cell secreted)
3. holocrine = cell membrane rupture - cell death
What are the adaptations of epithelia?
- basal membrane
- apical modifications
- cell junctions
What are apical modifications?
- cilia: motile long cell processes
e. g respiratory tract - microvilli: non-motile, minute projections used to increase S.A
e. g kidney and intestine - stereocilia: long microvilli
e. g epididymis
What are cell junctions and their functions?
- Adherent junctions:
(anchoring) cells must bind to each other and to CT to assure tissue cohesion - Tight junctions:
(occluding) cells controls what enters the body - Gap junctions:
(communicating) cells must communicate with each other
What are adherent junctions?
- provides the stiffness of a tissue
- cells join to each other with desmosomes
- cells anchored to basement membrane with hemidesmosomes
What are tight junctions?
- limit paracellular (between cell) movement of water and other molecules
- control what can enter and leave
What are gap junctions?
- aqueous channels allowing small molecules to pass between 2 adjacent cells
- allow communication
