1. Chapter 11 skin General structure of the skin
(Epidermis/Dermis/Hypodermis)
Nonkeratinocyte
melanocyte/Langerhans &Merkel cell
Epidermal derivatives :hairs, nails, sebaceous and sweat glands.

2. 1. General description Function: epidermis :
keratinized stratified squamous epithelium
dermis:
Epidermal derivatives :
hairs, nails, and sebaceous and sweat glands.
Function:
1. Protection from injuries
or microorganisms.
2. Sensitive organ (feeling pain, temperature, touch & pressure ).
3. Regulation the balance of water, electrolyte & temperature of body.
HYPODERMIS (Subcutaneous tissue). It is NOT the part of skin

3. 2. Epidermis (1) Construction
Keratinized stratified squamous epithelium
Stratum basale
keratinized Stratum spinosum
cell (5 layers) Stratum granulosum
Stratum lucidum
Stratum corneum
non- Keratinized Melanocytes
cell Langerhans cells
Merkel cells

4. ①keratinised cell:
---from basal to surface, reflect changes :keratinization ↑;
Mitotic action ↓

5. Stratum basale / stratum germinativum
Single layer of Columnar or Cuboidal cells Rests on the basement membrane by hemidesmosomes ;
Cytoplasm is BASOPHILIC (Ribosomes—synthesis of keratin) , Desmosomes (lateral surface), mitotic activity( stem cells ) which diferentiate daughters and migrates upward to replace dead cells
Scatter MELANOCYTES & MERKEL CELLS

6. Stratum spinosum 4 – 10 layers of Polygonal cells with large nuclei
desmosomes ("spines"), tonofilaments development well Cytoplasm is BASOPHILIC (Many ribosomes)
Thick (thick skin,high friction areas), Contains langerhans cells

7. keratohyalin + tonofilament = keratin
Stratum granulosum 
LM: 3-5 layers, spindle
degenerating nu. & organells
coarse & basophilic granules( no surrounded by membrane) --keratohyalin (phosphate groups)
EM:lamellated granules--fused with cell membrane,produce a “cement” ----seals the skin to foreign objects & water
keratohyalin + tonofilament = keratin

8. Stratum lucidum 3-4 layers and transparent no nucleus and organella
eosinophilic-keratohyalin
More in thick skin

9. Stratum corneum
 Cells of the cornified layer are dead, eventually sloughed
15 – 20 layers in Thick skin,3 – 4 layers in Thin skin
EM: full of keratin, thickened membrane, degenerated desmosomes (surface layers).

10. CONCLUSION
The changes of the keratinized cells from basal layer to cornified layer show the process of the keratinization:
①Morphology: Columner
→polygonal→ flattened;
basophilic→acidophilic
② Nu./ Organelle:↓
③ keratin: ↑ Filaments: ↑
scattered→bundle;
④ desmosomes:↓
⑤ Mitotic action ↓

11. thin skin (eyelids): Stratum granulosum
Thickness of epidermis
thick skin (palms and soles):well-developed stratum corneum. lacks hair follicles and sebaceous glands.
thin skin (eyelids): Stratum granulosum
and lucidum less-developed ;but hair follicles and sebaceous glands well-developed.

12. NON KERATINIZED CELLS MELANOCYTES
Originates:neural crest
Located: stratum basale & hair follicles
LM: Irregular extension branches
into the epidermis
melanosomes containing tyrosinase.
Melanin protects the body against the
harmful sun’s ultraviolet rays.
Skin Colour depends upon activity of these cells rather than number
Deficiency of Tyrosinase  ALBINISM
(白化病)
most pigment-containing cells in the epidermis are normally keratinocytes rather than melanocytes.

14. On exposure to sunlight, the enzyme TYROSINASE is activated  Increased melanin formation
tyrosin melanosome(tyrosinase) →↓
↓ melanin
melanin granules

15. antigen presenting cell in skin involve in immune reaction
LANGERHANS CELLS
derived Monocyte
Present in all layers but predominant
in stratum spinosum
pale cytoplasm
Contains BIRBECK GRANULES
---function:
antigen presenting cell in skin
involve in immune reaction

17. Merkel’s cell
---structure:
Seen in stratum basale
near the hair follicles
short processes, dense-core granules
chemical synapse: between Merkel’s cell and afferent nerve
---function: not very clear, may be sensory epithelial (perception of stimulation / induce and regulate the growth of nerve fiber in skin?)

18. Structure related dermal protective function
1. Cornified layer--dried dead cell, full of wear-resisting keratin.
2. lamellated granules(Stratum granulosum )-fused with cell membrane,seals the skin to foreign objects & water
3. Melanocyte---- melanin, prevent ultraviolet radiation from damaging skin
4. Langerhans cells immune defence

19. DERMIS Papillary layer: LCT, tactile corpuscles are found
Papillary layer+Reticular layer
Papillary layer:
LCT, tactile corpuscles are found
strengthening (more found friction is more)
touch feeling; nourishment.

20. thin in the eyelid thick over the back. Reticular layer: Irregular DCT
More elastic & collagen fibres (elasticity & toughness of skin)
Hair follicles, sweat & sebaceous
glands are found
thin in the eyelid
thick over the back.

21. HYPODERMIS loose connective tissue Contains FAT TISSUE
Excessive fat gets deposited in the hypodermis

22. SKIN APPENDAGES Hairs sebaceous sweat glands Nails
important in recovery scrapes and burns (epidermis removed a fairly large area,--- grow quickly from the epithelial cells in hair follicles and/or sweat glands.  
Third-degree burns :tissue damage extends deep enough into the dermis and destroy sources of replacement cells.
Hairs
sebaceous
sweat glands
Nails

23. a strip of cornified cells hair root hair follicle
1. Hair hair shaft
a strip of cornified cells hair root
hair follicle
hair
Sebaceous
gland
sweat gland
papilla
hair bulb

24. hair shaft
hair root
epithelial root
sheath
ct sheath
hair papilla

25. arrector pilli muscle SHAFT: outside the epidermis
cornified cells filled with Keratin
ROOT: Implanted in the skin
- Surrounded by a hair follicle ,
Hair bulb---stem cell
Hair papilla(CT) – Nourishes
HAIR MUSCLE (arrector pili):
smooth muscle connecting dermal papilla and hair follicle Its contraction causes hair to become erect & the surrounding skin to rise (goose pimples)

26. 2. Sebaceous gland periphery– smaller, immature cell ;
secretory portion:
periphery– smaller, immature cell ;
centeral -- full of lipid droplet, excrete sebum
by holocrine.
Duct: shorter, open at the superior segment of hair follicle.
Function: soften skin and kill bacteria.

27. arrector pili

28. 3、 SWEAT GLANDS
ECCRINE SWEAT GLANDS
secretory portion : simple cuboidal epithelium interspersed myoepithelial cells.
conducting portion: two-layered stratified cuboidal epithelium,  stained intensely.
APOCRINE SWEAT GLANDS
Distribute at armpit, areola of breast ，duct in secretory portion is thicker, open at hair follicle
Secretion is mainly protein controlled by sex hormones when acted upon by bacteria, give a characteristic odour of sweat

30. 汗腺导管 canal of sweat gland

31. NAIL
Horny plates on the distal parts of the dorsal surfaces of fingers & toes, keratinized epidermal cells
Stratum corneum forms the Eponychium (指甲上皮 )
Nail plate rests on a Nail bed made up of stratum basale & stratum spinosum
Nail root is embedded proximally in between the fold of skin on itself

32. THE END