Skin Integument

Skin Integument Objectives To gain a greater appreciation of the diversity of functions of skin To recognize the different cell types and structures of the skin which make possible this functional diversity Functions of Skin: Functional Diversity of Skin • Protects against injury and desiccation • Maintenance of water balance • Excretes/secretes various substances • Thermoregulation • Receives stimuli − Temperature − Pain − Pressure • Basis of recognition and yields clues to one’s well being • Fat metabolism in the subcutaneous layer Fat Metabolism in the Subcutaneous Layer Fat Metabolism in the Subcutaneous Layer Obesity = Too much fat in the Subcutaneous Layer BINARY ORIGIN OF SKIN EPIDERMIS – ECTODERM DERMIS MESODERM 31 Stratum Corneum Stratum Granulosum Stratum Spinosum Stratum Basale Layers of the Epidermis: palms and soles of feet Stratum Corneum – Keratinized flattened, denucleated, dead cells Stratum Granulosum – Keratohyalin granules Stratum Spinosum – Tonofibrils – desmosomes Stratum Basale – Continual renewal of epidermis Stratum Basale Stratum Spinosum Stratum Spinosum Stratum spinosum Slide 29: Thick Skin on finger cont. The epidermis of thick skin is subject to continuous friction and pressure so the abundant desmosomes (and tonofibrils) withstand this and hold the cell layers together. Keratohyalin granules Desmosomes Hemidesmosomes 1 Epidermis Stratum spinosum Dermis Stratum basale Stratum Corneum Stratum Granulosum Stratum Corneum Stratum Corneum Three Types of Granules in Keratinocytes Melanin – Skin pigment – Produced by melanocytes and passed by cytocrine secretion to keratinocytes Membrane coating granules (lamellated granules) – Water proofing function – Produced by keratinocytes Keratinohyalin granules Three Types of Granules in Keratinocytes Keratinohyalin granules – Chemical nature not clearly established – Rich in histodine forms – Matrix of cells in stratum corneum, stability due to disulfide bonds – Absent in hair and nails Slide 31: Thin Skin (scalp) Sun from NASA Stratum corneum Stratum granulosum Stratum spinosum 4 Stratum basale Melanin capping of nuclei Capping of Melanin Granules in Keratinocytes in Stratum Basale Capping 105 Melanin is produced by Melanocytes Melanin-producing enzymes in Melanocytes Space of removed dermis Epidermis Regional Variation of the Epidermis Thick skin - sole of foot (1.4 mm thick) Thin skin - eyelid and most of body (0.07 to 0.12 mm) Cornea of eye - transparent Appendages - hair follicles, nails, glands Regional Variation of the Epidermis Cells in Epidermis Stratified squamous - cell types include: • Keratinocytes - main cell = Renewal of skin by cell type – ectoderm division and differentiation • Melanocytes - pigmentation - neural crest • Langerhans cell immunologic role • Merkel cells - associated with nerve endings CYTOCRINE SECRETION - PASS MELANIN GRANULES FROM MELANOCYTES TO KERATINOCYTES Clinical Correlation Albinism can be caused by a hereditary defect in tyrosinase activity or the inability of cells to take up tyrosine. Patient with albinism would be more at risk for the development of basal and squamous cell carcinomas as albinism produces skin hypopigmentation so fewer melanin granules to protect nuclear DNA from the ionizing, mutagenic effects of UV radiation. Tyrosine amino acid figure Albino peacock - Melanocyte - pigment synthesis Freckles - melanin distributed in patches Melanocyte - pigment synthesis Freeze branding in cattle Melanocyte stimulating hormone secreted by the pars intermedia Melanocyte – disease states Albinism - failure to produce melanin Malignant melanomas - cancer Addison’s disease - pigment deposition in skin due to adrenocortical insufficiency Langerhans cells Bone marrow origin Located in stratum spinosum - gold chloride stain Clear cell - no desmosomes Dendritic cell Langerhans cells Dendritic cell Rod or racket shaped granules Function - immunologic role as an antigenpresenting cell Contact allergic responses and other cell mediated reaction of the skin Epidermal – dermal interface Epidermal – dermal interface Epidermis Rete pegs of epidermis Dermal papillae Dermis Epidermal – dermal interface Epidermal – dermal interface Epidermal – dermal interface Epidermis pulled off of dermis dermal view of epidermis Epidermal – dermal interface - finger pad PAPILLARY LAYER Dermis Two layers” Papillary layer sculptured layer of dermis Reticular layer - deeper main portion of dermis, rather dense irregular CT Melanin-producing enzymes in Melanocytes Dermal papilla removed Rete pegs of epidermis Dermis Elastic fibers - Network between collagen bundles muscle Smooth muscle - loose plexus in reticular layer in areolae, penis, perineum, and scrotum Epidermis Smooth muscle Dermis Muscle Skeletal muscle terminated in the dermis • Facial expression Dermis Muscle Skeletal muscle terminated in the dermis • Facial expression Cutaneous appendages Hair – Follicles – Pigmentation – Graying 108 Hair Graying with age Every hair follicle contains pigment cells called melanocytes. The melanocytes produce eumelanin, which is black or dark brown, and pheomelanin, which is reddish-yellow, and pass the melanin to the cells which produce keratin, the chief protein in hair. When the keratin-producing cells (keratinocytes) die, they retain the coloring from the melanin. When you first start to go gray, the melanocytes are still present, but they become less active. Less pigment is deposited into the hair so it appears lighter. As graying progresses, the melanocytes die off until there aren't any cells left to produce the color. Http://chemistry.About.Com/od/howthingsworkfaqs/f/why -does-hair-turn-gray.Htm Regeneration of epidermis Glands of epidermal origin Sweat glands – Eccrine: common sweat gland - local cooling – Apocrine axillary region: function in animals Sweat Gland Secretions Human Skin, scalp 108 Skin, scalp Mode of secretion of the sebaceous glands is holocrine where by the sebum is released when cells burst. sebaceous glands Eccrine sweat glands Sweat Glands Slide 29: Thick Skin (ventral surface of finger) Myoepithelial cells are eosinophilic because of the presence of muscle contractile proteins, which contract to expel sweat when needed. Ducts of eccrine sweat glands with stratified cuboidal epithelium Myoepithelial cells Eccrine sweat glands Slide 66: Recto-anal junction skin Anal opening Sebaceous gland Hair follicle Apocrine sweat gland Slide 66: Recto-anal junction hair Sebaceous gland Apocrine sweat gland Other Glands of Epidermal Origin Cerumenous glands - produce wax (cerumen) in the ear for waterproofing and discourage entry of insects Tarsal lacrimal glands - tears of the eye Other Glands of Epidermal Origin Cerumenous glands - produce wax (cerumen) in the ear for waterproofing and discourage entry of insects Tarsal lacrimal glands - tears of the eye Tarsal gland of meibomian – wax-like secretion that holds in tears Other Glands of Epidermal Origin – mammary gland Other Glands of Epidermal Origin – Mammary Gland Gland for which our class, mammalia, was named. Mammals are characterized by hair on skin, special ear bones, and milk-producing mammary glands in females for nourishment of young. Variations in the Microvasculature Common Arteriole  Capillary  Venule Shunts Arteriole  Metarteriole  Venule arteries  av shunt  venules Circulation of Blood Through Skin: Blushing? Circulation of Blood Through Skin Function and structure Nutrition capillaries Heat conduction from body Subcutaneous venous plexus (holds large quantities of blood to heat skin) Arterio-venous anastomoses Circulation of Blood Through Skin Circulation of Blood Through Skin Blood volume capacity of skin is 4.5% of total blood volume Circulation of Blood Through Skin Blood flow through skin in an average adult – Normal conditions 400 mL/min. – Hot conditions - 2.8 liters/min (Volume 5-6 L = 12-13 pints/person) Circulation of Blood Through Skin Blood vessels in different layers Of skin to accommodate variation in flow rate. 109 Skin hand monkey Eccrine sweat glands Adipocytes Hypodermis Pacinian corpuscles Papillary layer Dermal papillae Epidermal peg Epidermal and dermal – nerve interfaces The End bulb of Krause is a thermoreceptor that picks up on the sensation of cold temperatures. Pain receptors are found on free nerve endings located in many tissues throughout the body. This includes skin, muscles, joints, connective tissues, and internal organs. Pain receptors are activated in response to a painful stimulus, usually involving tissue damage. Epidermal and dermal– nerve interfaces Merkel cells or Merkel-Ranvier cells are oval receptor cells found in the skin of vertebrates that have synaptic contacts with somatosensory afferents. They are associated with the sense of light touch discrimination of shapes and textures. Genetic knockout mice have recently shown that Merkel cells are essential for the specialized coding by which afferent nerves resolve fine spatial details. Meissner's corpuscles (or tactile corpuscles) are a type of nerve ending in the skin that is responsible for sensitivity to light touch. In particular, they have highest sensitivity (lowest threshold) when sensing vibrations lower than 50 Hertz. They are rapidly adaptive receptors. Any physical deformation in the corpuscle will cause an action potential in the nerve. Since they are rapidly adapting or phasic, the action potentials generated quickly decrease and eventually cease (this is the reason one stops "feeling" one's clothes). Epidermal and dermal – nerve interfaces Meissner's Corpuscles (or tactile corpuscles) • The number of Meissner’s corpuscles per square millimeter of human skin on the fingertips drops four fold between the ages of 12 and 50. The rate at which they are lost correlates well with the age-related loss in touch sensitivity for small probes (Thornbury and Mistretta, 1981). Histo 029 Epidermal and Dermal – Nerve Interfaces A Pacinian corpuscle is a type of touch receptor located in the skin. It is classed as a mechanoreceptor, meaning it is part of the group of sensory receptors that respond to touch and pressure. Pacinian corpuscles are especially suited to feeling rough surfaces and detecting vibration. They respond to transient touches rather than sustained pressure. This is because a Pacinian corpuscle is able to quickly adapt to pressure so that it no longer acts as a stimulus. 105 Epidermal and Dermal – nerve Interfaces Mucocutaneous Junctions Lips, Nares, Eyelids, Vulva or Prepuce Anal Canal Functional Diversity of Skin • Protects against injury and desiccation • Maintenance of water balance • Excretes/secretes various substances • Thermoregulation • Receives stimuli − Temperature − Pain − Pressure • Basis of recognition and yields clues to one’s well being • Fat metabolism in the subcutaneous layer