Skin Anatomy & Physiology PDF

The skin Louise Ainscough [email protected] 1  Lecture outline Structure & function of skin Epidermis Dermis Hypodermis Epidermal derivatives – Hair – Exocrine glands Martini & Na...

The skin Louise Ainscough [email protected] 1  Lecture outline Structure & function of skin Epidermis Dermis Hypodermis Epidermal derivatives – Hair – Exocrine glands Martini & Nath: Chapter 5 Chapter sections: 5.1, 5.2, 5.5 - 5.8 2  Integumentary system Skin (cutaneous membrane) Epidermal derivatives Epidermis Hair Dermis Nails Hypodermis Glands 3 Martini & Nath: Fig 5.1  Skin is “thick” or “thin” Thickness of the epidermis Thin – Most of the body – Usually has hairs Thick epidermis – Soles of feet, palms of hands – hairless epidermis Thin skin x154 Thick skin x154 Martini & Nath: Fig 5.3 4  Epidermis Multi-layered epithelium consisting primarily of keratinocytes – Provides a protective barrier McKinley: Fig 6.2 5  The epidermis has distinct layers that represent different stages of cell maturation Stratum basale – Deepest layer – Single layer of cells – Contains stem cells for regeneration of the epidermis Stratum spinosum – Prickly layer – Daughter cells from basale Stratum granulosum – Granular layer – Contains granules → keratin formation and water resistance Tortora: Fig 5.3 6  The epidermis has distinct layers that represent different stages of cell maturation Stratum lucidum (thick skin only) – Clear layer – Sub-division of the stratum corneum Stratum corneum – Cells lack a nucleus or organelles – Cell membrane becomes thickened – Filled with keratin filaments – Deepest layer coated with lipids to form a water resistant barrier Tortora: Fig 5.3 7  Keratinocytes mature over time Stem cells divide in stratum basale – Daughter cells pushed up 2 weeks (superficially) over time Dead, keratinized cells lost from surface 7-10 days McKinley: Fig 6.2 8  Melanocytes Produce pigment (melanin) – Brown, yellow-brown, black – Packaged in vesicles (melanosomes) – Transferred to keratinocytes Melanin – Protects DNA from UV radiation – Degrades & must be replaced Martini & Nath: Fig 5.8 9  The dermis Connective tissue supporting the epidermis – Mostly fibres (collagen & elastic fibres) Two layers – Papillary layer Closest to epidermis Loose connective tissue – Reticular layer Closest to hypodermis Papillary layer Dense irregular connective tissue Reticular layer Martini & Nath: Fig 5.6 10 Fibres in the papillary layer have a smaller diameter than the reticular layer 11  Papillary layer of the dermis Forms dermal papillae that interlock with epidermal ridges – Strengthens attachment between epidermis and dermis Contains sensory nerve endings Contains capillaries – Epidermis is avascular – Nutrient & gas exchange Epidermal ridges Dermal papillae McKinley: Fig 6.6 12  Reticular layer of the dermis Meshwork of thick collagen and elastic fibres Contains – Blood vessels – Nerves – Hair follicles Epidermal ridge – Glands Papillary layer Dermal papilla Arrector pili muscle Sebaceous (oil) gland Reticular Sweat gland duct layer Merocrine sweat gland Vein Artery Hair Tactile (sensory) McKinley: Fig 6.1 follicle receptors 13  Hypodermis Holds integument to underlying tissue & permits movement of skin Location of subcutaneous fat – Protection/padding – Energy reservoir – Insulation Marieb, Wilhelm & Mallatt: Fig 5.2 14  Hair Located everywhere except – Palms, soles, lips & portions of external genitalia Non-living structure produced in hair follicles – Surrounded by connective tissue sheath Martini & Nath: Fig 5.12 15  Hair production Hair growth starts at the hair bulb – Base of hair follicle Hair papilla is connective tissue containing blood vessels – Nutrients and chemical signals for epithelial (hair) cell growth Epithelial cells divide & push upward – Become keratinized (hard & dead!) Hair follicle Hair Dividing cells Hair papilla Marieb: Fig 5.6 16  Hair Hair follicle Hair Hair bulb Hair papilla Hair follicle 17  Hair is also associated with: – Arrector pili Smooth muscle “Goose bumps” – Root hair plexus Sensory nerves Sense hair movement – Certain glands Martini & Nath: Fig 5.12 18  Different types of glands are found in the skin Exocrine glands Different modes of secretion Ross & Pawlina: Fig 5.38 19  Sebaceous glands Usually associated with hair follicles Holocrine glands – Cells burst to release secretions Produce sebum – Oily secretion into hair follicles – Lubricates hair and skin – Increased activity during puberty Oily skin/hair Acne! Ross & Pawlina: Fig 5.38 20  Sebaceous glands have a pale stain in H&E Sebaceous gland McKinley: Fig 6.10 21  Merocrine sweat glands Secrete directly onto skin surface Merocrine secretion – Secretion released by exocytosis Distributed all over the body Produce sweat – 99% water – 1% electrolytes (NaCl), metabolites & waste products Important for temp regulation Ross & Pawlina: Fig 5.38 22  Martini & Nath: Fig 5.14 Myoepithelial cells cause the contraction of sweat glands 23  Apocrine sweat glands Merocrine secretion, not apocrine! Axilla, nipples, pubic & anal region Secrete into hair follicles Secretion attract bacteria - odour Ross & Pawlina: Fig 5.38 24 Martini & Nath: Fig 5.14 25  Essential terminology Do you know the definition of these terms? – Epidermis – Dermis – Hypodermis – Sebaceous glands – Merocrine glands – Apocrine glands 26  Key points Can you answer the following questions? – What are the defining characteristics of each layer of the epidermis? – Compare and contrast the two layers of the dermis. – Describe the structure of hair. – Explain the three different types of glands found in the skin. Compare and contrast these glands. 27  References Marieb EN & Hoehn K (2019). Human Anatomy & Physiology (11th Ed). Marieb EN, Wilhelm PB & Mallatt J (2011). Human Anatomy (6th Ed). Martini FH, Nath JL & Bartholomew EF (2018). Fundamentals of Anatomy & Physiology (11th Ed). McKinley MP, O’Loughlin VD & Bidle TS (2013). Anatomy & Physiology: An Integrative Approach (1st Ed). Ross MH & Pawlina W (2016). Histology: A Text and Atlas (7th Ed). Saladin KS (2010). Anatomy & Physiology: The Unity of Form and Function (5th Ed). Tortora GJ & Derrickson B (2012). Principles of Anatomy & Physiology (13th Ed). 28