Skin Structure and Function PDF

Skin structure and functions By Dr. Sahla Mohammed Ahmed Department of physiology By the end of this lecture you will be able to:  Describe anatomical functions of the skin.  Discuss the functions of skin.  Describe the skin Appendages.  skin It’s...

Skin structure and functions By Dr. Sahla Mohammed Ahmed Department of physiology By the end of this lecture you will be able to:  Describe anatomical functions of the skin.  Discuss the functions of skin.  Describe the skin Appendages.  skin It’s the largest organ of the body Skin structure Primarily composed of :- The epidermis (outer layer) Derived from ectoderm -keratinized stratified squamous epithelium - 5 main layers: 1-Stratum basales Deep layer 10%-15% of the cell are melanocytes 2-Stratum spinosum -Thickest layer of epidermis 3-Stratum granulosum -Thin layer 4-6 cells -Cells flatten 4-Stratum lucidum -Seen only in thick skin Made up of 2-3 layers of keratinocytes 5-Stratum corneum -20-30 layers of flattened cells Have 4 types of cells -Keratinocytes -Melanocytes -Merkel cells -Langerhans cell 2- Dermis -Derived from mesoderm Components:- 1-Strong flexible connective tissue (primarily collagen) 2-Fibroblsts, macrophages, mast cells and WBCs 3-Elastic fiber 4-Sebaceous glands maintain elasticity and strength Supplies the epidermis with nutrients and moisture Contains rich supply of blood , lymphatic vessels and nerve ending Layers:- Papillary layer :- -Thin superficial layer -Made up of elastin and collagen fiber and contains phagocyte and adipose tissue -have projections into the epidermis are called papillae this form (finger prints) -Free nerve ending and Meissner corpuscles are located in the dermal papillae Reticular layer:- -80% of thickness of the dermis -Irregular dense connective tissue -Well-vascularized cutaneous plexus -Gives skin its elasticity -Contains sweat glands and hair follicles Cells of the skin:- 1-keratinocytes -Primary cell -Produce keratin through fibrous protein 2-Melanocytes:- -Spider shaped epithelial cells -Produce melanin (UV protection) -Melanin granules accumulate on surface of keratinocytes 3- Dendritic cells (Langerhans cells) - Macrophages of the skin -Activate the immune system 4- mechanoreceptors A- Merkel cells:- -Slowly adapting light-touch receptors -In contact with a sensory ending B-Ruffini corpuscles:- -Slowly adapting receptors -Located in deep dermis C- Meissner corpuscles -Rapidly adapting light-touch receptors -Located in superficial dermis D- Pacinian corpuscles:- -Detect deep pressure and vibration -Located in deep dermis  Skin Appendages Hair -Growth being in the hair papilla of the dermis -Composed of keratinized cells -Each hair follicle has an associated sebaceous gland -Terminal hairs coarse hair on scalp, eyebrows, ect -Vellus hair very fine hair covering a newborn Nails Made up of dense keratinized cells of the epidermis protect Finger tips and toes against injuries Structure of nail Nail palate :- actual fingernail composed of keratin Nail bed :-below nail palate and continuous with strata basale and spinosum Nail matrix (nail root):- deep to skin responsible for new nail formation Function of skin 1-Protection -Prevents dehydration -Prevents infection -Physical barrier to injury -Protects against ultraviolet light injury 2-Thermoregulation -Insulation (hair and adipose tissue) -Heat dissipation. Sweat evaporation.Increase blood flow Sensory function -Free nerves ending are sensitive to pain touch heat and cold Metabolic function -Synthesis of Vit D3 with UV absorption – for Ca metabolism -Excess electrolytes can be removed in sweat -Adipose in subcutaneous is major storage of triglycerides energy Aesthetic -Provides prettiness and appearance