Lecture 7: The Integumentary System PDF

Lecture #7 The Integumentary System  The Integumentary System The integumentary system includes: Skin Glands Hair Nails Nerves (sensory receptors) The skin consists of: 1. The epidermis Epithelial tissue derived from the ectoderm...

Lecture #7 The Integumentary System  The Integumentary System The integumentary system includes: Skin Glands Hair Nails Nerves (sensory receptors) The skin consists of: 1. The epidermis Epithelial tissue derived from the ectoderm Stratified squamous epithelium Avascular 2. The dermis Connective tissue derived from the mesoderm Vascular Also contains nerves, glands and hair follicles  The Epidermis Layers of the epidermis: 1. Stratum basale: Single layer of cells The basal layer (bottommost, deepest layer, furthest from the outside) 90% of cells within this layer are keratinocytes 8% of cells within this layer are melanocytes Mitotically active 2. Stratum spinosum: Several cell layers thick Limited cell division occurring here Melanin granules are scattered throughout Many keratinocytes layered atop one another  The Epidermis Layers of the epidermis: 3. Stratum granulosum: Dark granules are seen within this layer ~3-5 cell layers thick All cells above this layer (closer to the surface of the body) are too far above the blood supply to maintain life 4. Stratum lucidum: Very apparent in thick skin (soles of the feet and the palms of the hands) Flat, dead cells 2-3 cell layers thick Appears as a clear band of cells with indistinct boundaries under the microscope  The Epidermis Layers of the epidermis: 5. Stratum corneum: The outermost layer of the skin Functions in protection and moisture retention ~30 layers of dead cells Flat and keratin-filled Keratin provides strength These cells are shed from the skin surface Replaced by cells produced from mitosis below Waterproof glycolipid secreted onto the skin surface Prevents against water loss  The Epidermis Thin skin vs thick skin: Differences exist within the epidermal structure The stratum lucidum is present in some areas and absent in others 1. Thin skin: The stratum lucidum is not visible Thin skin has hair follicles, sweat glands and sebaceous glands 2. Thick skin: The stratum lucidum is visible Appears under the microscope as a clear layer of cells No hair follicles, no hair or sebaceous glands Sweat glands are found here Includes the palms of the hands and the soles of the feet  The Dermis The dermis is formed from connective tissue proper Consists of fibroblasts, fibrocytes and matrix Composed of two layers: 1. The papillary layer 2. The reticular layer  The Dermis 1. The papillary layer: Located immediately under the epidermis Composed of loose, areolar connective tissue Dermal papillae are upward projections from this layer into the epidermis Vascular allowing nutrients to reach living cells Dermal ridges are found below the dermal papillae Dermal ridges cause the epidermis to form epidermal ridges which we know as finger prints Sweat pores open along the crests of the dermal ridges leaving behind finger prints on surfaces that have been touched  The Dermis 2. The Reticular Layer: The deepest layer of the dermis Furthest away from the surface of the skin Accounts for 80% of the dermis Composed of dense irregular connective tissue Lots of collagen fibers running in many different directions Stretching of the skin can tear the dermis Results in white scars called striaeà commonly known as stretch marks  The Dermis Structures that are located in the dermis include: Hair follicles Glandsà sebaceous glands and sudoriferous glands Sensory receptors Arrector pili muscles Contraction causes goosebumps Your hairs stand on end  The Hypodermis Also called the subcutaneous layer This is not part of the dermis Found immediately below the dermis Connective tissue that is located below the skin Superficial fascia: binds the skin to the muscle that lies underneath ~ One half of the bodies adipose tissue lies in the hypodermis Insulates the body  Skin Color Melanin is found within the stratum basale and the stratum spinosum of the epidermis Formed by melanocytes Provides variation in skin color seen in different people Found in two different forms that range in color from yellow to tan to reddish brown to black Albinos are unable to make melanin Sun exposure stimulates melanin productionà suntan The pinkish tinge seen in fair skinned people comes from hemoglobin found within the vascular dermal layer of the skin  Epidermal Derivatives Structures that are derived from the epidermis include: 1. Hairà hair follicle 2. Nails 3. Exocrine glands Sebaceous glands produce oil Sudoriferous glands produce sweat Ceruminous glands produce ear wax Mammary glands produce milk  Epidermal Derivatives 1a. Hair: Composed of dead keratinized cells The shaft projects above the skin surface Keratinization is complete here The root is found below the skin surface Keratinization is still ongoing Found deep within the follicle  Epidermal Derivatives 1b. Hair follicle: Folds down from the epidermal surface into the dermis The expanded region at the deepest point is called the hair bulb Hair papilla is a small piece of dermal tissue that protrudes into the hair bulb Contains a knot of capillaries that supplies nutrients to the growing hair and signals it to grow The hair matrix is the actively dividing area of the hair bulb: produces the hair The hair follicle is also associated with a(n): Root hair plexusà nerve ending Sebaceous gland which opens into the hair follicle Arrector pili muscle  Epidermal Derivatives 2. Nails: These are made of heavily keratinized epidermal cells found within the stratum corneum Other epidermal layers form the nail bed The nail matrix is responsible for nail growth Each nail is composed of a: Free edge Nail body (visible portion of the nail) Proximal root (embedded in the root)  Epidermal Derivatives 3a. Sebaceous glands: Produce sebum which is composed of fats, salts and proteins Connected to the hair follicle Functions to lubricate both the hair and the skin preventing desiccation and softening the hair Also has an antibiotic function 3b. Ceruminous glands: Modified sweat glands located in the inner ear canal Function to produce ear wax 3c. Mammary glands: Modified sweat glands Produce milk  Epidermal Derivatives 3d. Sudoriferous glands: Produce sweat which functions to cool the body Sweat evaporates from the skinà heat from the body is used to break hydrogen bonds between water molecules in sweat This heat is no longer available to warm the body Water molecules evaporate when hydrogen bonds no longer hold them on the skin surface Sweat also contains antibiotic function Contains lysozyme, an enzyme that breaks apart bacterial structures Sweat also functions to remove wastes such as urea  Cutaneous Sense Receptors Nerve endings form from the end of sensory neurons Found in the skin Respond to stimuli such as touch Four varieties: 1. Touch receptors 2. Pressure receptors 3. Thermoreceptors 4. Nociceptors 1. Touch receptors: The root hair plexus which wraps around the hair follicle Free nerve endings are found in the epidermis Meissner’s corpuscles are touch receptors found in the dermal papillae  Cutaneous Sense Receptors 2. Pressure receptors: Free nerve endings that are able to respond to changes in pressure Pacinian corpuscles are pressure receptors located within the deep dermis or the hypodermis 3. Thermoreceptors: Temperature receptors Free nerve endings that detect hot and cold More nerve endings to detect cold than to detect hot 4. Nociceptors: Receptors that detect pain Free nerve endings Function in protectionà make you aware Example: put your hand on a hot stove element