skin & epithelial tissues

layers of the skin (superficial to deep)

1. epidermis

2. dermis

3. hypodermis

epidermis

outermost layer of the skin, stratified squamous keratinized epithelium

dermis tissue type

connective tissue

hypodermis tissue type

connective tissue

basement membrane

located between the epidermis and dermis

layers of the epidermis (deep to superficial)

1. stratum germinativum (stratum basale)

2. stratum spinosum

3. stratum granulosum

4. stratum corneum

stratum germinativum (stratum basale)

• first layer of cells in the epidermis, resting on the basement membrane

• cells actively divide (stem cells), are responsible for regenerating the epidermis

• cells are joined to the basement membrane by hemidesmosomes

stratum spinosum

• contains several layers of polygonal cells

• cells are joined together by desmosomes

• referred to as “spinosum” because the tonofibrils (fibers that insert into cellular junctions) look like spines on the cells

stratum granulosum

• 2-5 layers of cells

• cells are flattened and contain basophilic granules

keratohyalin granules

granules inside cells in the stratum granulosum, contain keratin

stratum corneum

• cells are non-nucleated, cytoplasm filled with keratin

• desmosomes break down and cells at the surface shed

de-squamation

process of cells at the surface of the stratum corneum being shed as desmosomes break down

basophilic structures

• high affinity for hematoxylin

• appear blue when stained with hematoxylin and eosin dye

• nuclei, area rich in RNA and DNA (negatively charged)

acidophilic / eosinophilic structures

• high affinity for eosin

• appear red/pink when stained with hematoxylin and eosin dye

• cytoplasm and regions rich in proteins

formalin

fixing agent used for light microscopy

ethanol

used to dehydrate and rehydrate samples for microscopy

xylene

clearing and infiltration agent used for light microscopy, also used to remove paraffin from sample

paraffin

what samples for light microscopy are embedded in

microtome

machine used to slice thin sections of sample for light microscopy

glass slide

what sample is mounted on for light microscopy

hematoxylin and eosin (H&E)

stain used for light microscopy

steps to prepare sample for light microscopy

1. chemical fixation

2. dehydration

3. clearing

4. infiltration

5. embedding

6. sectioning

7. mounting

8. removal of paraffin

9. rehydration

10. staining

11. light microscopy

fixing agent used in electron microscopy

gluteraldehyde and osmium tetroxide

propylene glycol

clearing and infiltration agent used for electron microscopy

plastic

what the sample is embedded in for electron microscopy

ultramicrotome

machine used to slice extremely thin samples for electron microscopy

copper grid

what sample is mounted on for electron microscopy

lead citrate

stain used for electron microscopy

electron dense structure

metal structure under an electron microscope that deflects electrons (grid or lead citrate stain)

electron lucent structure

structure under electron microscope through which electrons can pass through (plastic, gaps in sample)

primary functions of skin

• protection

  • resists abrasion and penetration

  • blocks the entry of foreign material

• containment

  • prevents loss of body fluid

• thermoregulation

  • controls the transfer of heat across the body’s surface

• immunological defense

• sensory abilities

• communication

  • releases visual and pheromonal signals

• appendages

  • hair, nails, sebaceous glands, sweat glands

• metabolism

  • produces vitamin D

covering epithelia

• simple

  • squamous

  • cuboidal

  • columnar

• stratified

  • squamous (keratinized and non-keratinized)

  • transitional

• pseudostratified columnar (ciliated)