2.Skin Derivatives NOTES.pdf

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Anatomy and Cell Biology
Anatomy and Cell Biology 3309
Ron Podesta

Skin Appendages 1) hair follicles and hair/nails 2) sebaceous glands and sebum 3) eccrine sweat glands and sweat 4) apocrine sweat glands – serous secretions Hair: - composed of keratinized cells: develop from hair follicles - all thin skin, with minor exceptions, has hair - influenced by hormones: facial and pubic hair, male pattern baldness - two kinds of hair: terminal hair (thick), and vellus hair (difficult to see) - colour comes from melanin - Structure: i. Bulb at base ii. Dermal papilla – vascularized iii. Outside of hair: down growth of epithelium called external root sheath - surrounded by basement membrane called “glassy membrane” iv. Rest of bulb called matrix which consists of 1. basal layer of stem cells (keratinocytes) 2. melanocytes, which impart colour to the hair v. Bulb gives rise to the 1. internal root sheath (which is discontinued after the hair leaves the epidermis). Contains keratinocytes which form soft keratin 2. the hair itself, which is divided into three layers. Hair is composed of hard keratin a. the outer cuticle b. the middle cortex c. the central medulla (may not be present in fine hairs) - arrector pili muscle associated with hair follicle. Smooth muscle under autonomic nervous system control Sebaceous glands: - develop as a growth off the side of the hair follicle. - Secrete sebum: holocrine secretion. Basal cells renew, and cells fill up with lipid secretion until the cell dies and all is secreted into the hair follicle. - Process takes approximately 8 days - Well developed SER for production of lipids. - No myoepithelial cells – arrangement of arrector pili muscle can help expel contents. Sweat glands: consist of simple coiled tubular glands (apocrine may be compound) - two types: i. Eccrine: 1. Found in all skin except lips and certain regions of external genitalia 2. secretory portion in deep dermis or hypodermis
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