Integumentary system

Anatomy

1. Prepared by: Maryam Fida (o-1827) INTEGUMENTARY SYSTEM

2. Integumentary system Skin Appendages (specialized derivatives of skin) Hairs Nails Sebaceous glands Sweat glands

3. THE SKIN Largest organ of the body  forms the external covering of the body Consist of two layers of completely different types of tissues Superficial layer known as Epidermis , is stratified squamous keratinized epithelium  five layers/strata

4. Deeper layer known as Dermis , composed of Dense connective tissue Below dermis is hypodermis (superficial fascia or subcutaneous tissue) is loose connective tissue This loose connective tissue attaches skin to underlying structures (loosely)  allows the skin to move over structures

5. Skin thickness  0.5 to 4 mm (varies in thickness) Total weight  3 – 5 kg Skin serves as Protective barrier against injury, infectious pathogens, ultraviolet radiation) Temperature regulation Vitamin D synthesis Sensory reception

6. Epidermis It is a continuously self-replacing stratified squamous keratinized epithelium Five layers/strata Stratum basale , Stratum spinosum , Stratum granulosum , stratum lucidum & stratum corneum Contains four types of cells: Keratinocytes Melanocytes Langerhans cells Merkel cells

7. KERATINOCYTES Primary cells of epidermis  90% of cell population Constant renewal throughout life  constant mitotic division of the cells in the basal layer The newly produced keratinocytes constantly move outward into the more superficial layers

8. As they move outward from basement membrane  undergo progressive changes : the number of keratin filaments increases Secrete certain substances which act as Water Barrier Transformation from cuboidal living cells to dead flat cells  cytoplasm is full of keratin Constantly shedding off from skin surface

9. MELANOCYTES Oval shape cells Synthesize melanin (brownish black pigment) Protects the skin from the harmful effects of electromagnetic radiations

10. LANGERHANS CELLS Part of mononuclear phagocyte system Located mainly in stratum spinosum Phagocytosis of foreign anigen MERKEL CELLS Found scattered along stratum basale of epidermis Generally occur as single cell Serves as mechanoreceptors for sensory reception

11. LAYERS OF THE EPIDERMIS Layers of the epidermis reflects successive stages in the life of a keratinocyte It involves  Proliferation growth, outward displacement & differentiation, followed by death and desquamation STRATUM BASALE STRATUM SPINOSUM STRATUM GRANULOSUM STRATUM LUCIDUM STRATUM CORNEUM

12. STRATUM BASALE Also called stratum germinativum Consist of a single layer of cuboidal or low columnar keratinocytes  resting on a basement membrane Deep to basement membrane is dermis Constant mitosis and production of new keratinocytes  therefore called stratum germinativum Keratinocytes from this layer constantly displacing into the layer above Also contains Merkel cells & Melanocytes

13. STRATUM SPINOSUM Consist of several layers of irregular polyhedral keratinocytes Toward the surface, the cells become flattened Presence of numerous fine cytoplasmic processes  named as spines  stratum spinosum Its deeper part exhibit mitosis Stratum basale & stratum spinosum are collectively known as Malpighian layer

14. STRATUM GRANULOSUM 3 – 5 layers of flattened rhomboid keratinocytes Cytoplasm contain large number of granules In its outer layer  keratinization becomes more pronounced Nuclei shows degenerative changes Cell organelle are lost, as a result of autophagy by lysosomal enzymes Consequently, the cells become dead before moving into more superficial layers

15. STRATUM LUCIDUM Apparent only in skin of palm and soles (thick skin) Three to five layers of closely packed and flattened cells Nuclei & organelles are absent Cytoplasm consist of densely packed keratin filaments

16. STRATUM CORNEUM Consist of many layers of flattened keratinized cells Some histologists called these keratinocytes as Corneocytes (due to appearance) Cells are devoid of nuclei and organelles Cytoplasm filled with keratin filaments Keratinized cells become more and more flattened as the surface is approached In most superficial layer, the cells called squames (extremely thin and flat)  desquamation

17. DERMIS A sheet of connective tissue that supports the epidermis & binds it to subcutaneous tissue Two layers Papillary layer (outer layer) Reticular layer (deeper layer)

18. PAPILLARY LAYER Thinner than the reticular layer Named so because it bears projections called papillae These projections protrude into the overlying epidermis and interdigitate with projections of epidermal epithelium (epidermal ridges) Consist of loose connective tissue (collagen fibers, reticular fibers, elastic fibers, fibroblasts, macrophages & mast cells)

19. Rich blood supply, numerous capillary loops Capillaries regulate body temperature & nourishes overlying epidermis Sensory nerves Sensory receptors  meissner’s corpuscles (located in dermal papillae)

20. RETICULAR LAYER Thicker than papillary layer Dense irregular connective tissue Less cellular than papillary layer Consist of collagen fibers, elastic fibers, fibroblasts, mast cells, macrophages, T lymphocytes and fat cells Two types of sensory receptors Pacinian corpuscles Ruffini’s corpuscles

21. THICK SKIN THIN SKIN EPIDERMIS THICK THIN STRATUM LUCIDUM PRESENT ABSENT STRATUM CORNEUM THICK THIN HAIRS ABSENT PRESENT SEBACEOUS GLANDS ABSENT PRESENT