Histology

Question 1

what is cell theory? (3)

Answer 1

• 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

Question 2

what is the definition of a tissue? (2)

Answer 2

• groups of similar cells working together to carry out a common function
• made up of cells and an extracellular matrix

Question 3

what are the 2 broad types of tissue?

Answer 3

• parenchyma - working tissue that directly carries out the function
• stroma - scaffold and nutrition tissue that surrounds the working tissue (eg. blood vessels)

Question 4

what are the 4 sub-types of tissue and what are their functions?

Answer 4

• connective - protects and supports
• epithelial - covers and lines body surfaces
• muscle - cells contract to generate force
• nervous - generate electrical signals in response to environment

Question 5

what is the definition of an organ? (3)

Answer 5

• made up of several tissue types
• morphologically recognisable structure
• performs a specific set of functions

Question 6

what is the purpose of fixation in staining? (2)

Answer 6

• preserves the tissue

* kills off any bacteria

Question 7

what are the 2 main types of fixation?

Answer 7

• freezing using dry ice or liquid nitrogen

* chemical fixation - aldehyde based (formaldehyde)

Question 8

what is the purpose of embedding in staining?

Answer 8

provides support for the tissue when sectioning

Question 9

what is the process of embedding a sample in paraffin wax? (3)

Answer 9

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

Question 10

what is a side effect of using xylene as a solvent in tissue?

Answer 10

lipids are also dissolved -> areas appear clear on microscope

Question 11

why do sections of samples need to be thin?

Answer 11

increase resolution

Question 12

what tool is used for sectioning?

Answer 12

microtome

Question 13

what extra step must be carried out in staining process if using an aqueous stain?

Answer 13

wax is dissolved in xylene, replaced with alcohol and then water (then mounted on slide)

Question 14

what is the most common type of stain? what types of structures does it stain?

Answer 14

• H&E: haemotoxylin and eosin - purple and pink
• H is basic - stains acidic / basophilic structures
• E is acidic - stains basic / acidophilic structures

Question 15

what stain is used for carbohydrates? what are organs rich in carbohydrates called?

Answer 15

• PAS - magenta

* PAS +

Question 16

where is epithelial tissue found? (5)

Answer 16

• lining of internal cavities
• blood vessels
• lining of organs (respiratory, digestive, urinary and reproductive)
• glandular structures
• skin

Question 17

what are the 5 functions of epithelial tissue?

Answer 17

• 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)

Question 18

how does epithelial tissue get it nourishment?

Answer 18

connective tissue (not BV)

Question 19

what are the 2 types of glands?

Answer 19

• exocrine glands - retain continuity with surface and secrete via duct
• endocrine glands - lose contact with surface and secrete directly into blood stream

Question 20

what is the structure simple squamous epithelium? (2)

Answer 20

• single later of flat / hexagonal cells

* flat nuclei

Question 21

what is the function of simple squamous epithelium? (4)

Answer 21

• diffusion
• filtration
• some secretion
• some absorption

Question 22

what is the structure of of simple cuboidal epithelium? (2)

Answer 22

• single layer of cube-shaped cells

* some have microvilli

Question 23

what is the function of simple cuboidal epithelium? (3)

Answer 23

• diffusion
• secretion
• absorption

Question 24

what is the structure of simple columnar epithelium? (2)

Answer 24

• single layer of tall narrow cells

* some have cilia or microvilli

Question 25

what it’s he function of simple columnar epithelium? (4)

Answer 25

• movement of substances
• absorption
• secretion
• some protection (more than flatter cells)

Question 26

what is the structure of stratified squamous epithelium? (2)

Answer 26

• multiple layers of cells that are cube-shaped in basal layer
• progressively flatten towards surface

Question 27

what is the function of stratified squamous epithelium? (3)

Answer 27

• protection against abrasion
• barrier against infection
• reduction of water loss from the body

Question 28

what is the difference between stratified and pseudostratified epithelium?

Answer 28

• stratified: multiple defined layers

* pseudostratified: appear to be different laters (nuclei in different places) but all cells touch the basement membrane

Question 29

what is the structure of pseudostratified epithelium? (2)

Answer 29

• single layer of cells, but appear stratified

* almost always ciliates and associated with goblet cells (secrete mucus)

Question 30

what is the function of pseudostratified epithelium? (2)

Answer 30

• synthesise and secrete mucus

* move mucus or fluid containing foreign particles over the surface (protective)

Question 31

what is the structure of transitional epithelium? (3)

Answer 31

• cuboidal / columnar when not stretched
• squamous / flattened when stretched
• stratified layers - no. of layers fluctuated whether they are stretched or not

Question 32

what is the function of transitional epithelium? (2)

Answer 32

• accommodate fluctuations in volume of liquid in organs or tubes
• protects against caustic effects of urine