Thick skin, thin skin- discussion, viva

Skin:

1. What are the two regions/layers of skin?
• Superficial nonvascular epidermis
• Deep vascular dermis
2. What are the derivatives/ appendages of the skin?
• Nail
• Hair
• Sweat gland
• Sebaceous gland
• Arrector pili muscle
3. What are the two types of skin?
• Thick skin
• Thin skin
4. Where do you find Thick skin?
• Palm, sole
5. Where do you find thin skin?
• Whole body except palms and soles is covered by thin skin
6. What are the functions of the skin?
• Protection from mechanical abrasion, forms physical barrier to pathogens or foreign microorganisms
• Prevents the loss of body fluids
• Temperature regulation
• Acts as sensory organ responding to external stimuli like temperature, touch, pain and pressure
• Acts as excretory organ by producing sweat through which water, sodium salts, urea and nitrogenous wastes are excreted
• Vitamin D necessary for calcium absorption is synthesized in the skin

Thick skin:

1. Give examples of thick skin?
• Palm and sole
2.  Is there any difference in the structure between thick and thin skin?
• There is no difference in the structure, except in the thickness of the epidermis and the appendages. In thick skin only sweat glands are present
3. What are sweat glands?
• Sweat glands are exocrine glands which are simple tubular highly coiled glands.
• coiled secretory portion is lined by simple columnar epithelium
• Ductal excretory portion is lined by stratified cuboidal epithelium
4. Why is epidermis in palm and sole very thick?
• These regions are constantly exposed to wear, tear and abrasion
5. What are the types of cells present in epidermis?
• Keratinocytes
• Melanocytes
• Langerhan's cells
• Merkel's cells
6. What are dermal papillae?
• The numerous raised projections in the superficial layer of dermis which interdigitate with evaginations of epidermis is called dermal papillae
7. What are epidermal ridges?
• The evaginations of epidermis which interdigitate with the dermal papillae are called epidermal ridges
8. What are the two layers of dermis?
• Superficial papillary layer
• Deep reticular layer
9. What is papillary layer made up of?
• It is made up of loose irregular connective tissue with cells and fibers, capillaries, blood vessels, fibroblasts, macrophages, nerves, Meissner's corpuscles
10. What is reticular layer made up of?
• It is made up of dense irregular connective tissue with less number of cells, Pacinian corpuscles
11. What are the layers of epidermis?
• From deep to superficial- Stratum basale (germinativum), stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum
12. Why is stratum basale also called as germinativum?
• The single layer of cuboidal or columnar cells are capable of cell division which increases the number of cells and differentiate into other layers. They act as stem cells and also produce intermediate keratin filaments
13. Explain stratum spinosum?
• It consists of 4 to 6 rows of cells. During routine histologic preparations the cell membranes shrink except near the desmosomes which appear as spines. The keratin filaments are arranged in the form bundles called tonofilaments.
14. Why is third layer given the name stratum granulosum?
• The cells in the third layer are filled with dense basophilic keratohyalin granules which lack membrane and are associated with bundles of keratin filaments, together form keratin. Because of the keratohyalin granules the third layer is called stratum granulosum
15. What is stratum lucidum?
• It is a translucent layer present superficial to stratum granulosum. The cells lack nuclei or orgenelles
16. What is stratum corneum?
• It is the superficial layer of cells without nuclei and organelles, filled with keratin filaments. They are continuously shed or desquamated
17. Where are melanocytes derived from?
• Melanocytes are derived from Neural crest cells
18. Where are melanocytes located?
• They are located between stratum basale and stratum spinosum. The function is to synthesize melanin pigment which protects the skin from damaging effects of ultraviolet radiation

Thin skin:

1. What are the layers present in thin skin?
• Four layers from deep to superficial- stratum basale, stratum spinosum, stratum granulosum, stratum corneum. Stratum lucidum is absent.
• Except the thickness and the absence of stratum lucidum the rest of the features are same as in thick skin
2. Name the appendages of thin skin
• Hair, sebaceous glands, arrector pili muscle, sweat glands
3. What is dermal papillae?
• The papillary layer indents the base of the epidermis to form the dermal papillae
4. What are sebaceous glands?
• Sebaceous glands are exocrine and holocrine glands with aggregates of clear cells connected to duct opening into hair follicle
• It secretes oily or wax material to lubricate and water proof the skin
5. What is holocrine secretion?
• The whole is cell is destroyed during the secretion which is poured into the lumen
6. What are arrector pili muscles?
• Arrector pili muscles are smooth muscles aligned at oblique angle from papillary layer of dermis to the hair follicle
• Contraction of the muscle moves hair shaft into vertical position