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Topic 3 Lecture Notes - Human Physiology 101...

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Human Physiology 101 – Topic 3 Notes

Integumentary System Introduction Cutaneous Membrane: skin Accessory structures: Hair, Nails, Exocrine glands (excretes) General Functions of the Skin -Protects underlying tissues and organs -Excretes salts, water, and organic wastes (glands) -Maintains body temperature (insulation and evaporation) -Synthesizes vitamin D3 -Stores lipids -Detects touch, pressure, pain, and temperature Skin Structure Epidermis -Outer, thinner layer -Composed of epithelium Dermis -Inner, thicker layer -Composed of connective tissue -Papillary and reticular layers Hypodermis layer -Fat store -Blood vessels -Pacinian corpuscles (sensitive to pressure) Organisation of the Epidermis

Layers of the Epidermis -Stratified Squamous Epithelium 4-5 layers thick Stratum corneum -Dead keratinocytes -Continuously shed and replaced by cells from deeper strata Stratum lucidum -Dead keratinocytes -Present in thick skin subjected to much friction Stratum granulosum -Keratin forms -Keratinocytes undergo apoptosis -Lamellar granules release waterproofing secretion Strata spinosum -Desmosomes hold cells together Stratum basale or stratum germinativum -Contains stem cells -Undergoes continuous cell division

Human Physiology 101 – Topic 3 Notes Cells of the Epidermis -Four principle cell types Keratinocytes -Produce keratin -Waterproofing sealant Melanocytes -Produce melanin (skin pigment)

Langerhans cells -Macrophages -Involved in immune response Merkel cells -Touch sense

Clinical Note - Callus (corn) -Abnormal thickening of the stratum corneum due to the constant exposure of skin to friction Fingerprints -Epidermal ridges of thick skin -Specific pattern of “whirls” -Unique for every individual Epidermal Pigmentation/Skin Colour -Pigments Carotene and Melanin -Circulation of Blood (red blood cells) Carotene -Orange-yellow pigment -Accumulates within epidermal cells and fatty tissues of the dermis -Can be converted to vitamin A (Retinal) Melanin -Yellow-black pigment -Produced by cells called melanocytes in stratum basale -Stored and transported within melanosomes -Transferred to keratinocytes -Protects skin from sun damage Clinical Note - Hermansky-Pudlak Syndrome -Deficiencies in the biogenesis of lysosome related organelles including melanosomes. Characterised by albinism and prolonged bleeding Clinical Note - Dermal Circulation/Blood Flow -Haemoglobin bound to oxygen is bright red, Dilated vessels causes skin to look red -Constricted vessels cause skin to become pale -Reduced supply of oxygen causes skin to become bluish-cyanosis Dermis Papillary Layer -Areolar tissue -Small capillaries, lymphatics, sensory neurons -Sensory receptors: tactile corpuscles (light touch) Reticular Layer -Dense irregular connective tissue -Larger blood vessels, lymph vessels, sensory neurons -Collagen, elastic fibres, connective tissue proper -Sensory receptors: lamellated corpuscles (pressure and vibration) -Skin turgor

Human Physiology 101 – Topic 3 Notes Clinical Note - Dermatitis -Inflammation of the papillary layer due to infection, radiation, mechanical irritation, or chemicals -Characterized by itch or pain Clinical Note - Sagging and wrinkles (reduced skin elasticity) -Dehydration -Age -Hormonal changes -UV exposure Clinical Note - Stretch marks -Thickened tissue resulting from excessive stretching of skin due to: -Pregnancy -Weight gain Dermis Cleavage Lines -Collagen and elastic fibres arranged in parallel bundles -Resist force in specific direction -Parallel cut remains shut and will heal well -A random cut will pull dermis open and scars Hypodermis/Subcutaneous Layer -Connects dermis to underlying tissue -Loose connective tissue with fat cells -Large blood vessels -Absence of vital organs Innervation of the Skin Nerve fibers in skin -Control blood flow -Regulate gland secretions -Sensory receptors

Innervation of the Skin (diagram)

Human Physiology 101 – Topic 3 Notes Accessory Structures -Hair -Hair follicles -Sebaceous glands -Derived from embryonic epidermis -Are located in dermis -Project through the skin surface

-Sweat glands

-Nails

Hair - What is hair? -Hairs (pili) composed of columns of dead, keratinised cells held together by extracellular proteins -Shaft – superficial portion -Root – penetrates skin -Surrounded by follicle -Dendrites of hair root plexuses surround each hair follicle -Generate nerve impulses if shaft of hair is move Hair - what does hair do? -Protects and insulates -Guards openings against particles and insects -Sensitive to very light touch Hair - why does hair vary in colour? -Result of amount and type of melanin in keratonised cells -Grey hair due to progressive decline in synthesis of tyrosinase enzyme Hair - what causes goose bumps? -The contraction of the arrector pilli muscle that is under control of the sympathetic nervous system Sebaceous (Oil) Glands -Majority connected to hair follicles -Secretory portion in the dermis -Absent in thick skin -Secrete sebum -moistens hairs, waterproofs, softens skin and inhibits bacterial growth

Clinical Note: Zits - Opening of sebaceous gland blocked: “Whitehead’ -Pustule – superficial layers -Papule – deeper layers -Cyst – deepest layers

Human Physiology 101 – Topic 3 Notes Sweat (sudoriferous) Glands - Apocrine Sweat Glands -Limited in distribution to the skin of the axilla (arm pit), areolae (around nipples), pubis (groin) and beard for males -Ducts into hair follicles -Sticky, cloudy secretions which sometimes produce an odor. -Do not begin to function until puberty Sweat Glands - Merocrine (Eccrine) Sweat Glands -Widely distributed on body surface, especially palms and soles -Discharge directly onto skin surface -Excretes water and electrolytes -Main function is heat loss Temperature Homeostasis Regulating cutaneous blood flow -Increased dilation of skin blood vessels as core temperature increases -During intense exercise skin blood vessels constrict - rapid increase in core temperature results Perspiration/Sweating -Sympathetic response Cutaneous Blood Flow -Blood flow from inside the body affects the skin’s temperature -lost by radiation and conduction and convection -Dilation/constriction of skin blood vessels Sweating/Perspiration Insensible perspiration: Interstitial fluid lost by evaporation through the stratum corneum Sensible perspiration: Water excreted by sweat glands Thermoregulation

Human Physiology 101 – Topic 3 Notes Other Integumentary Glands Ceruminous glands -Modified sudoriferous glands -Located in external auditory canal -Produce waxy substance called cerumen (ear wax) -Impedes entrance of foreign bodies Mammary glands -Specialised sweat glands Nails – What are nails? -Plates of tightly packed, hard, keratinised epidermal cells -Consists of: nail body, free edge and nail root Lunula -Area of thickened stratum basale Hyponychium (nail bed): -Area of thickened stratum corneum -Secures nail to tip of digit Eponychium (cuticle) -Narrow band of epithelium occupying proximal border of nail Nail Growth – Nail Matrix -Epithelium deep to nail root -Cells divide by mitosis -Superficial cells of matrix converted to nail cells -Average growth 1 mm per week Clubbing- Lung/CV disease

Dark lines- Melanoma

Blue: Cyanosis

Epidermal Wound Healing -Basal cells of epidermis break contact with basement membrane -Enlarge and migrate across wound – stimulated by Epidermal Growth Factor (EGF) -Stop migration due to contact inhibition -Relocated cells divide to build new epidermal layers and thicken epidermis

Human Physiology 101 – Topic 3 Notes Deep Wound Healing - Injury extends to dermis and/or subcutaneous layer: 4 phases 1. Inflammatory phase -Blood clot forms loosely binding wound edges -Inflammation 2. Migratory Phase -Clot becomes a scab -Epithelial cells migrate beneath scab to bridge wound -Fibroblasts migrate and form collagen 3. Proliferative phase -Extensive growth of epithelial cells beneath scab -Random deposition of collagen fibres -Blood vessel growth 4. Maturation phase -Collagen fibres become organised -Epithelium restored to normal thickness and scab sloughs off -Blood vessels restored Clinical Note – Lines of cleavage -Collagen and elastic fibers in the dermis: -Are arranged in parallel bundles -Resist force in a specific direction Lines of cleavage establish important patterns: -A parallel cut remains shut, heals well -A cut across (right angle) pulls open and scars Photodamage - UVA, UVB, UVC UVA: Long-term damage UVB: Main cause of skin tanning and sunburn DNA damage in epidermal cells Clinical Note: Skin Cancer -Accounts for > 80 % of all cancer diagnosed in Australia (1600 deaths/year) -UVB rays can damage DNA in epidermal cells -Disable tumour suppressor gene -Cells multiply uncontrollably = tumour Types: -Basal cell carcinoma -Squamous cell carcinoma -Melanoma

Human Physiology 101 – Topic 3 Notes

Burns – Extent of Injury

Burns -Estimating percentage affected surface area -Burns to > 20% can be life threatening -Any partial or full thickness burn that involves the genitals, eyes, ears, hands, feet, or burns over major joints regardless of size = medical care Effects of Ageing -Increased skin injuries and infections -Immune system is reduced -Muscles become weaker -Decrease in bone strength -Increased sensitivity to the sun -Skin dries and becomes scaly -Hair changes -Reduced ability to lose heat -Skin repair slows...