Chapter 11 The Skin PDF 2024/2025

The Skin first semester 2024/2025 Introduction The skin forms a barrier between organs of the body and the external environment. It is a vital organ which play an important role maintaining homeostasis, provide protection, regulate body temperature and others. Skin layers Funct...

The Skin first semester 2024/2025 Introduction The skin forms a barrier between organs of the body and the external environment. It is a vital organ which play an important role maintaining homeostasis, provide protection, regulate body temperature and others. Skin layers Functions of the skin Protection Sensation Synthesis of vitamin D Excretion Absorption Regulation of body temperature Protection  The skin is considered as one of non-specific defense mechanism.  Langerhans cells found in the epidermis function with the helper T-lymphocytes, thus stimulation an immune reaction.  Protect the body from dehydration caused by loss of internal body fluid.  The melanin pigment protect the body from the harmful effect of continuous exposure to UV light.  The presence of the sensory nerve endings protect the body from further injury. Sensation Nerve impulses; generated by specialized sensory receptors in the dermis; are converted by sensory nerves to spinal cord then to the sensory area of the cerebrum in which sensations are perceived.  Synthesis of vitamin D After exposure to UV light, 7-dehydrocholesterol in the skin converted to cholicalciferol; vitamin D precursor. The pathway continued to the liver and kidney where the active vitamin D produced. Excretion Skinhas minor role in excretion which include: ◦ Sodium chloride in sweat. ◦ Excretion of urea, uric acid and ammonia when kidney function is impaired. ◦ Excretion aromatic substances e.g. spices. Absorption Limitedabsorption properties. Absorbed substances include: ◦ Fat soluble vitamins (K,E,D,A). ◦ Estrogen. ◦ Corticoid hormones. ◦ Nicotine. ◦ Some toxic chemicals such mercury. Regulation of body temperature Regulated by of altering blood flow to the skin. If temperature of the body raise Dermal blood vessels dilate (vasodilatation) Loss heat Regulation of body temperature If temperature of the body fall Dermal blood vessels constrict (vasoconstriction) Conserve heat  Body temperature regulation controlled by negative feed back mechanism as discussed previously. Wound healing Phases of wound healing: A. Inflammatory phase: initiate immediately after injury and last for 3-6 days and include:  Homeostasis  Phagocytosis B. Proliferation phase: extend for days; include collagen formation. C. Maturation phase: extended from 21day to 2-3 years after injury; include:  Continue collagen formation  Wound remodeled and contracted End of Chapter  Good Luck