General Histology Lec 8: The Dermis PDF

General histology lec _8_ the dermis The dermis The dermis is the thick layer of connective tissue which is attached to the epidermis. Its deepest part continues into the subcutaneous. Made of fibrous connective tissue that contains arterioles for supply...

General histology lec _8_ the dermis The dermis The dermis is the thick layer of connective tissue which is attached to the epidermis. Its deepest part continues into the subcutaneous. Made of fibrous connective tissue that contains arterioles for supplying nutrients (i.e. oxygen , glucose , water , and ions ) to its structures and to the epidermis. Also contains hair follicles to develop the hair , pili arrector muscles to wrinkle the skin and erect the hairs. And sebaceous gland to secrete sebum onto skin surface, and sudoriferous glands to secrete sweat. contains nerves and nerve receptors to detect the sensations of heat, cold, pressure, touch, and pain. The dermis divided into two sublayers ( without a sharp boundary): 1- The papillary layer consists of loose connective tissue, which fills the hollows at the deep surface (dermal papillae) of the epidermis. Capillaries are frequent. Collagen fibers appear finer than in the reticular layer. 2- The reticular layer appears denser and contains fewer cells. Thick collagen fibers (5- 10 µm) often aggregate into bundles (up to 100 µm thick). The fibers form an interlacing network, although their predominant direction is parallel to the surface of the skin. A preferred orientation of the collagen fibers is not visible in the sections, but the main orientation of the fibers differs in skin from different parts of the body. General histology lec _8_ the dermis Usually, their main orientation will follow the "lines of greatest tension" in the skin (Kraissl lines). This is of some surgical importance since incisions parallel to these lines will heal faster and with less formation of scar tissue. Hypodermis layer (also called subcutaneous layer or superficial fascia), layer directly below dermis, serving to connect skin to the underlying fascia (fibrous tissue) of the bones and muscles. although border between hypodermis and dermis can be difficult to distinguish: consists of well vascularized, loose, areolar connective tissue and adipose tissue, which functions as a mode of fat storage and provides insulation and cushioning for integument. Skin repair (cutaneous wound healing) Skin has a good capacity for repair, which is important in this exposed and easily damaged organ. The process of cutaneous wound healing, whether initiated surgically or accidentally, involves several overlapping stages that vary in duration with the size of the wound. 1- In the first phase blood from cut vessels coagulates in the wound, releasing polypeptide growth factors and chemokines from the disintegrating platelets. Neutrophils and macrophages undergo diapedesis locally and remove bacteria and debris from the wound. 2- These are major events of inflammation that typically lasts 2-3 days. Before this phase is completed, epithelialization begins as cells of the epidermal basal layer remove their desmosomes and hemidesmosomes and migrate laterally beneath the blood clot that becomes an increasingly desiccated eschar, or scab. If much epidermis has been lost, new cells may migrate from the bulge region of surviving hair follicles. Growth of epidermal cells and fibroblasts is stimulated by several different growth factors released from macrophages and other cells and from their binding sites ECM proteoglycans. Matrix metalloproteinases and other proteases from the migrating cells and macrophages facilitate cell migration. 3- Proliferating fibroblasts and newly sprouted capillaries produce new collagen-rich, well vascularized tissue in the dermis called granulation tissue, which gradually replaces the blood clot. 4- In the final stage the epidermis reestablishes continuity but has lost the ability to form new hair or glands. The granulation tissue undergoes remodeling and a more normal vasculature is reestablished. Collagen bundles General histology lec _8_ the dermis and fibroblasts in this new connective tissue are at least initially much more abundant and disorganized than in uninjured skin, producing scar tissue at the wound site Summary Integumentary System Skin and derivatives form the integumentary system Consists of superficial epidermis and deeper dermis Nonvascular epidermis is covered by keratinized stratified squamous epithelium Vascular dermis consists of irregular connective tissue Epidermis: Thick Versus Thin Skin Palms and soles, because of wear and tear, are covered by thick skin Thick skin contains sweat glands, but lacks hair, sebaceous glands, and smooth muscle Thin skin contains sebaceous glands, hair, sweat glands, and arrector pili smooth muscle Keratinocytes are predominant cell type in the epidermis Lessnumerousepidermalcells are themelanocytes,Langerhans cells, andMerkel’s cells Basement membrane separates dermis from epidermis Dermis Papillary Layer Is the superficial layer in dermis and contains loose irregular connective tissue Dermal papillae and epidermal ridges form evaginations and interdigitations Connective tissue filled with fibers, cells, and blood vessels Sensory receptors Meissner’s corpuscles are present in dermal papillae Reticular Layer Is the deeper and thicker layer in dermis, filled with dense irregular connective tissue Few cells present and collagen is type I No distinct boundary between papillary and reticular layers Blends inferiorly with hypodermis or subcutaneous layer (hypodermis) of superficial fascia Contains arteriovenous anastomoses and sensory receptors Pacinian corpuscles Concentric lamellae of collagen fibers surround myelinated axons in Pacinian corpuscles Epidermal Cell Layers Stratum Basale (Germinativum) General histology lec _8_ the dermis Deepest or basal single layer of cells that rests on the basement membrane Cells attached by desmosomes and by hemidesmosomes to basement membrane Cells serve as stem cells for epidermis and show increased mitosis Cells migrate upward in epidermis and produce intermediate keratin filaments Stratum Spinosum Is the second layer above stratum basale that consists of four Summary Integumentary System Skin and derivatives form the integumentary system Consists of superficial epidermis and deeper dermis Nonvascular epidermis is covered by keratinized stratified squamous epithelium Vascular dermis consists of irregular connective tissue Epidermis: Thick Versus Thin Skin Palms and soles, because of wear and tear, are covered by thick skin Thick skin contains sweat glands, but lacks hair, sebaceous glands, and smooth muscle Thin skin contains sebaceous glands, hair, sweat glands, and arrector pili smooth muscle Keratinocytes are predominant cell type in the epidermis Lessnumerousepidermalcells are themelanocytes,Langerhans cells, andMerkel’s cells Basement membrane separates dermis from epidermis Dermis Papillary Layer Is the superficial layer in dermis and contains loose irregular connective tissue Dermal papillae and epidermal ridges form evaginations and interdigitations Connective tissue filled with fibers, cells, and blood vessels Sensory receptors Meissner’s corpuscles are present in dermal papillae General histology lec _8_ the dermis Reticular Layer Is the deeper and thicker layer in dermis, filled with dense irregular connective tissue Few cells present and collagen is type I No distinct boundary between papillary and reticular layers Blends inferiorly with hypodermis or subcutaneous layer (hypodermis) of superficial fascia Contains arteriovenous anastomoses and sensory receptors Pacinian corpuscles Concentric lamellae of collagen fibers surround myelinated axons in Pacinian corpuscles