Essentials of Human Anatomy & Physiology, 7 th ed. by Elaine N. Marieb Chapter 4 Skin and Body Membranes Physiology

Skin Functions 1. Protects deeper tissues 2. Aids in heat regulation 3. Aids in excretion of urea and uric acid 4. Synthesizes vitamin D Skin and Body Membranes: Integumentary System, Physiology

1. Protects deeper tissues from:  Mechanical damage (blisters, callouses)  Chemical damage (lipid-rich lamellar granules in the keratinocytes of the stratum granulosum)  Bacterial damage (Langerhan’s cells throughout epidermis, usually visible in the stratum spinosum) Skin and Body Membranes: Integumentary System, Physiology Popped blisters, with epidermis removed, revealing dermis

UV exposure stimulates melanin production. 1. Protects deeper tissues…  Thermal damage (hypodermis, edema)  Desiccation (keratinocytes produce keratin, as well as skin oil) Skin and Body Membranes: Integumentary System, Physiology  Ultraviolet radiation (melanocytes produce melanin)

 Melanin - yellow to brown to black pigments  Carotene - Orange-yellow pigment from some vegetables  Hemoglobin - Red coloring from blood cells in dermal capillaries (oxygen content determines the extent of red coloring) Normal Skin Color Determinants Skin and Body Membranes: Integumentary System, Physiology

1. Protects deeper tissues… Innervation = Nerves present in tissues which function to sense and/or instruct  Free nerve endings – detect pain, itch, and temperature (located in dermis)  Meissner’s corpuscles – structured nerve endings; detect touch (located in dermal papillae; most numerous on hands and feet)  Pacinian corpuscles – encapsulated nerve endings; detect pressure, vibration (located in reticular dermis and hypodermis; most numerous on hands and feet) Skin and Body Membranes: Integumentary System, Physiology

Meissner’s corpuscle Skin and Body Membranes: Integumentary System, Meissner’s corpuscle

Pacinian corpuscle

Pacinian corpuscles

1. Protects deeper tissues… Oil Glands = Sebaceous Glands  Produce sebum (oil) Lubricant for skin and hair Kills bacteria  Most with ducts that empty into hair follicles  Glands are activated at puberty Skin and Body Membranes: Integumentary System, Physiology

2. Aids in heat regulation  Small blood vessels in dermis Constrict in cold conditions Dilate in warm conditions  Sweat Glands = Sudoriferous Glands Glands are located in the reticular dermis, ducts open to the skin surface. Sweat is a hypotonic, watery solution containing some metabolic wastes, and sodium, potassium, and chloride ions. pH is neutral to slightly acid. Two types: eccrine & apocrine Skin and Body Membranes: Integumentary System, Physiology

 Eccrine More numerous; found all over body Open via duct to pore on skin surface  Apocrine Ducts empty into hair follicles Axillary and genital areas of the body, active after puberty Skin and Body Membranes: Integumentary System, Sweat Glands

Eccrine gland Apocrine gland Odor is from associated bacteria Skin and Body Membranes: Integumentary System, Sweat Glands

2. Aids in heat regulation Hot environments  Sweat absorbs body heat as it evaporates off of skin.  Blood vessels dilate, bringing blood closer to surface for more heat loss. Cold environments Blood vessels constrict, bringing blood away from surface for less heat loss. Subcutaneous fat* provides a layer of insulation. Skin and Body Membranes: Integumentary System, Physiology Goosebumps occur only where we have hair. They may have warmed our distant ancestors, but they don’t seem to do much for us today.

3. Aids in excretion of urea and uric acid Sweat is a hypotonic, watery solution containing some metabolic wastes, and sodium, potassium, and chloride ions. pH is neutral to slightly acid. Skin and Body Membranes: Integumentary System, Physiology

4. Synthesizes vitamin D

Skin and Body Membranes: Integumentary System, Physiology