BIOL 1800 Lecture 7 Skin and thermoregulation 2024 PDF

Lecture 7: Skin Thermoregulation BIOL 1800 Dr Marie Conway Learning Outcomes At the end of this lecture you will be able to: Outline the functions of the skin Outline the Histology and Physiology of the Skin Explain the role of the Skin in: skin colour Vit D production The In...

Lecture 7: Skin Thermoregulation BIOL 1800 Dr Marie Conway Learning Outcomes At the end of this lecture you will be able to: Outline the functions of the skin Outline the Histology and Physiology of the Skin Explain the role of the Skin in: skin colour Vit D production The Integument The Integument system accounts for 16% of body weight Is composed of the cutaneous membrane and accessory structures Skin Psoriasis/ Dermatitis/ Hair Melanoma Sweat glands Accessory structures Nails Cutaneous membrane –Epidermis/Epithelium and Dermis/CT Functions of Skin Protection of underlying organs from dehydration, infection, abrasion, UV damage and cold/heat Maintenance of normal body temperature through insulation or evaporative cooling Synthesis of Vitamin D3 Excretion of water, salts and oils Production of melanin to protect underlying tissue from UV radiation Production of keratin which repels water and protects against abrasion Sensory Perception at the tactile receptors and free nerve endings Energy Storage (of lipid) in adipocytes in the dermis and in adipose tissue in the subcutaneous layer Coordination of immune response to pathogens and cancers in the skin The Integumentary System Skin Histology Cutaneous membrane Is skin, surface of the body Thick, relatively waterproof, and dry Epithelium in epidermis and CT in the Dermis CT connects epith to underlying structures Loose Aerolar first and then Dense irreg CT proper Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Skin Histology 3 Layers 1. Epidermis – keratinised stratified squamous epithelium, basement membrane (supported by areolar CT of dermis) 2. Dermis – composed of loose areolar CT and dense irregular CT proper with accessory structures 3. Hypodermis or subcutaneous layer (loose CT proper). (aka Cutaneous membrane includes the Epidermis and Dermis. superficial fascia) CT fibres are continuous between Dermis and Hypodermis and between the hypodermis and the deep fascia. Types of skin cells There are 3 main types of cells in the epidermis: Squamous cells: These are flat cells in the outer/superficial part of the epidermis that are constantly shed as new ones form Basal cells: These cells are in the lower/deeper part of the epidermis, called the basal cell layer Melanocytes: These cells make the brown pigment called melanin, which gives the skin its tan or brown colour. Melanin acts as the body’s natural sunscreen The epidermis is separated from the deeper layers of skin by the basement membrane When a skin cancer becomes more advanced, it generally grows through this barrier and into the deeper layers Epidermis may also have cells of the immune system and sensory nerve cells Thick or Thin Skin Skin is divided into: Thick skin on the palms of the hand and soles of the feet (5 epidermal layers) Thin skin on the rest of the body (4 epidermal layers) Thick/Thin skin refers to the thickness of the epidermal layer. Thin skin on most of body (0.08mm) Thick skin on soles of feet and hands (0.5mm) The Epidermis Stratified squamous epithelium (keratinised) Epithelial cells called Keratinocytes 4 or 5 layers Difficult to distinguish with light microscope Gives skin properties of water resistance; protection from microorganisms and abrasion; gland secretions; support some sensory cells Blister – water trapped between layers The fingerprint is a pattern of Epidermal ridges These ridges increase the surface area for contact between the epidermis and dermis and have a unique pattern Layers of the Epidermis The Epidermis has 4 (thin) or 5 (thick) layers: 1. Stratum Corneum has 15 – 30 rows of flat, dead cells completely filled with keratin. This layer is continually shed and replaced 2. Stratum Lucidu only found in thick skin of the palms and soles. They are flat densely packed cells Cover or Let’s 3. Stratum Granulosum Get has 3 – 5 rows of flattened cells with degenerating nuclei. Sun These cells produce keratin Burned 4. Stratum Spinosum has 8 – 10 rows of polyhedral cells tightly packed 5. Stratum Basale or stratum germinativum There are tight connections between the deepest layer; has stem cells that continually divide. Some the cells that leads to loss as sheets of cells move to the surface – squamous cells. Others give rise to skin. sweat or oil glands. Melanocytes may be found in this stratum Layers of the Epidermis The Dermis Between epidermis and subcutaneous layer A connective tissue layer containing collagen and elastin fibres to support: blood vessels nerves glands hair follicles adipocytes The dermis is subdivided into the outer Papillary region and the inner Reticular region Papillary Region Loose areolar CT (elastin) Loops of capillaries (thermoregulation), lymphatic vessels, sensory nerve fibres Meissner’s corpuscles (touch receptors) Is ridged The Dermis Reticular Region Dense irregular CT proper (collagen and elastin) Thickness varies Network of fibres Spaces occupied by adipose tissue, hair follicles, nerves and oil glands and ducts of sweat glands This reticular region enables the skin to be: Strong Extensible (stretchy in pregnancy, oedema and obesity) Elastic (return to original shape after stretch or contraction) The reticular region is attached to the underlying organs, such as bone and muscle, by the subcutaneous layer (superficial fascia) The Skin and Water Loss The outermost layer of skin is water-resistant (not waterproof) 0.5L of water migrate through the epidermis and is lost by evaporation  This is called insensible perspiration Sweating leads to additional fluid loss (and electrolyte loss). Sweating is varied as required for core temperature regulation called sensible perspiration. Daily Loss of H20 (ml) Normal Temp Hot weather Prolonged heavy exercise Skin 350 350 350 Lungs 350 250 650 Urine 1400 1200 500 Sweat 100 1400 5000 Faeces 100 100 100 Total 2300 3300 6600 Subcutaneous Layer Also called hypodermis – or superficial fascia Lies deep to the dermis Connects the skin to the underlying tissue The CT of the dermis and subcutaneous layers are interwoven Quite elastic, consists primarily of adipose tissue Functions to allow independent movement, as an energy store and to insulate the body Subcutaneous layer has sensory nerve endings called lamellated or Pacinian corpuscles that are sensitive to touch (pressure and vibration) Subcutaneous fat deposition NB in babies for insulation Hormone dependant (puberty) Varies in location; with: None on backs of hand and top of feet Pear or apple shape body Fat deposits in the body are: Subcutaneous Visceral Interscapular Adipose tissue may be white or brown AbdRaboh NR, Asif AM, Riaz S, Ahmed HA. Brown Adipose Tissue, Thermogenesis, and Obesity: A Review of Literature. Glob J Med Therap. 2020;2(1):1-9 Exocrine Gland structure Sweat (Sudoriferous) Glands Skin contains two types of sweat glands: Apocrine Sweat Glands Merocrine/eccrine Sweat Glands Simple branched tubular glands. Coiled tubular gland Only found in axilla, pubic region distributed widely in body (NB and areolae of breast. soles and palms) Secretary portion in dermis or Secretary portion in subcutaneous subcutaneous. layer Excretory duct opens into hair Excrete onto surface follicle. Functions include: Begin to function at puberty Cooling surface of skin; excreting Viscous secretion water and electrolytes; protection from environmental hazards Sweat (Sudoriferous) Glands Sebaceous (oil) glands Holocrine glands Discharge oily lipid secretion into hair follicles Produce sebum Other Integumentary Glands Ceruminous glands Modified sudoriferous (sweat) glands Simple, coiled tubular glands Present in the auditory canal (ear) Secretory portion in subcutaneous layer Excrete onto surface or into sebaceous glands. Combined secretions of sebaceous and ceruminous glands give rise to ear wax (cerumen) Function (along with hairs) to prevent entrance of foreign bodies, preventing them reaching the ear drum Mammary glands Anatomically related to Apocrine glands Development and secretion controlled by interaction between sex hormones and pituitary hormone Control of Secretion of Glands - Nervous control Sebaceous and Apocrine → collectively turned on/off by Autonomic Nervous System (e.g. in stressful situations) Merocrine → areas of the body selectively turned on (sweaty hands) or all activated by ANS During thermoregulation to cool the body all merocrine glands switched on Thermoregulation is the homeostatic process of maintaining temperature Skin Colour Skin colour is due to three factors: Melanin in the epidermis Carotene in the dermis and epidermis Capillaries in the dermis Melanin Produced by melanocytes Amount varies to give skin colour from pale yellow to black Found in basale and spinosum layers Synthesised in melanocytes of stratum basale Total absence of melanocyte activity results in Albinism Patchy absence of melanocyte activity results in Vitilgo Patchy production of melanocytes results in freckles Carotene Orange-yellow pigment that normally accumulates in epidermal cells Found in stratum corneum and fatty areas of the deep dermis and subcutaneous layer Together with melanin, carotene gives yellowish hue to their skin Carotene also found in vegetables Carotene → Vitamin A Essential for maintenance of epithelia Photoreceptor pigments in the eye Capillaries Caucasian Skin Colour Port wine stain – unusual dense Due to blood capillaries in the dermis collection of blood vessels in the dermis Redness not masked by pigments The Epidermis and Vitamin D3 Limited exposure to sunlight is very beneficial UV light on the stratum spinosum and basale result in Vit D3 production 7-dehydrocholesterol is converted to Vit D3 or cholecalciferol in the skin In the Liver this is converted to 25-hydroxy-D3 This then is converted to calcitriol, the active form of the vitamin, in the kidney Calcitriol is essential for Ca++ and PO4- absorption from the GIT Deficiency in Vit D result in abnormal bone development in children (Rickets) and (Osteomalacia) in adults Thermoregulation Learning Outcomes At the end of this lecture you will be able to: Give an account of vascular and nervous supply of the skin Explain the physiology and importance of thermoregulation: Mechanism of heat gain Mechanism of heat loss Outline the physiology and importance of Pyrexia Dermal Circulation and Innervation 2 major functions of blood in skin: Nutrition of the skin tissues Heat loss Dermal circulation: Cutaneous plexus A network of capillaries Located between subcutaneous layer and dermis Supplies adipocytes, hair follicles and sweat glands Papillary plexus Formed from branches of the cutaneous plexus Gives rise to papillary loops Skin Vascularity Arteriovenous Shunts Shunts blood between arteries and veins to conserve heat Have muscular walls innervated by the sympathetic division of the ANS Activation of sympathetic division results in blood flow to plexus and heat loss. Blood Flow to Skin and Metabolism is influenced by To of surroundings. Nervous Control Vasodilator control Vasoconstrictor control https://www.science20.com/news_articles/fibromyalgia_not_all_head _its_skin_paper_concludes-114985 Innervation and Skin Epidermis contains sensory nerve endings that provide sensations of pain and temperature Sensory Nerves From pain, temp, and touch receptors Free nerve endings (dendrites of sensory nerve) or sensory receptors: Merkel Discs Messiners Corpuscles – sensitive to light touch (in dermal papillae) Pacinian corpuscles - sensitive to deep pressure and vibration (in reticular layer) Motor Nerves To sweat glands To erector pili muscle To blood vessels Nerves in Thermoregulation Epidermis contains sensory nerve endings that provide sensations of pain and temperature Sensory Nerves Detect increase or decrease in skin temperature Carry the information to the hypothalamus of the brain for thermoregulation Motor nerves Activation of Sweat glands and pili muscle Contraction of skeletal muscle - shivering Shunting of blood in skin and limbs Metabolic Rate and Heat production Metabolic rate is the sum of all the catabolic and anabolic processes Rate at which heat is produced in the body The heat is produced as food is oxidised Energy from food = ATP + Heat Significant amount of energy used to synthesise ATP, but much of it is lost to environment as heat The heat produced is carried in H2O (plasma) throughout the body For body temperature to remain constant, heat must be lost to the environment at same rate it is generated Factors that Affect Metabolic Rate Exercise may increase BMR x15% (20% in well trained athlete) Nervous system, in stress ANS releases noradrenaline which increases BMR Hormones; adrenaline, noradrenaline, hGH, testosterone and thyroid hormones increase BMR Body To; a 1oC rise in body To increases BMR X 10% (fever) Digestion of food increases MR X 10-20% (diet induced thermogenesis) Age; MR is higher in children Other factors: Sex (female MR is lower except in pregnancy) Climate (↓ if hot) malnutrition (↓ if malnourished) Homeostasis of Body To Regulation Core To is the body To below the skin Shell To is the surface To Usually the core To is higher If the heat loosing mechanisms give off more heat than is produced the core To ↓ If heat producing mechanisms generate more heat than is lost the core To ↑ Importance of temperature: Too high core To kills by denaturing protein (it also causes convulsions) Too low core To causes arrhythmias (it also causes disorientation) Core Temperature kept between 36.7oC and 37.2oC by homeostatic control  Physics of Heat Loss Four processes of heat exchange with environment: Evaporation Radiation Absorbs energy and cools surface where Objects warmer than environment lose evaporation occurs heat as radiation Insensible water loss – each hour 20- Heat from sun is radiant heat 25ml of water crosses epithelia and More than 50% of heat you lose indoors is evaporates from alveolar surfaces and lost through radiation surface of skin (accounts for 20% of boy’s average indoor heat loss). Sensible heat loss – evaporation of sweat Convection Heat loss to cooler air that moves Conduction across the surface of your body. As Direct transfer of heat through body loses heat to air next to skin, physical contact e.g. sitting on a the air warms and rises away from cold chair skin surface, and is replaced by Not effective way of gaining or cooler air which is then warmed losing heat – impact depends on the Accounts for roughly 15% of temperature of the object and the body’s heat loss indoors amount of skin surface area involved Heat loss Hypothalamic Thermostat Tries to keep heat production and heat loss in balance – i.e. maintain Figure 14–10a The Hypothalamus in Sagittal Section Temp range Sensory thermoreceptors (in skin, mucous membrane and in hypothalamus) bring information to hypothalamus of the brain Hypothalamus has a special region called the Preoptic area output that has: heat losing centre heat production centre Copyright © 2014 Pearson Education, Inc. Preoptic area - regulates body temperature Heat Loss Centre (Heat loss) Heat loss centre stimulated when temperature at pre-optic area rises above its set point Mechanisms for heat loss: 1. Vasodilation, inhibition of the ANS vasomotor output. This increases blood flow to the skin, warms the skin and increases heat transfer 2. Perspiration, activation of the sweat glands and evaporation of H2O cools the skin 3. Decreased Metabolic Rate and Decreased Shivering, mediated through hypothalamic reflexes 4. Increased Respiration, depth of breathing increased and breathing through the mouth will increase evaporation 5. Behavioural change – seek shade or remove clothing Heat Promoting Centre (Heat gain) Function of heat-promoting centre is to prevent hypothermia, or below-normal body temperature When temperature at pre-optic area drops below acceptable level, heat-loss centre inhibited, and heat-gain centre activated Mechanisms of heat gain: 1. Vasoconstriction → increase vasomotor output (decrease blood flow to skin surface) 2. Skeletal muscle by shivering increases muscle tone and increases heat production. 3. Sympathetic release from adrenal gland (adrenaline and noradrenaline stimulate cellular metabolism, i.e. chemical thermogenesis) 4. Thyroxine increases cellular metabolism by increasing catabolic reaction 5. Behavioural responses – put on more clothing or move to a heated area Thermogenesis Shivering Thermogenesis muscle metabolism in contraction/relaxation Gradual increase in muscle tone increases energy consumption of skeletal muscle tissue  more energy used the more heat produced Heat produced warms deep vessels where blood has been shunted Shivering can increase rate of heat generation as much as 400% Non Shivering Thermogenesis increased metabolism (by liver) and BAT adipose breakdown Involves release of hormones that increase tissue metabolic activity Adrenal medulla – releases epinephrine, increasing glycogenolysis Thyroid gland – releases thyroxine, increasing nutrient catabolism Heat loss and heat gain Abnormal Body Temperature - Pyrexia Fever Usually bacterial or virus stimulated Other causes are heart attack, tumour, surgery or trauma Mechanism: Phagocyte ingests bacteria ↓ Interleukin-1 secreted and circulated in the blood ↓ Prostaglandin production in the hypothalamus ↓ Resetting of To thermostat Fever Stages of fever Core To thermostat ↑ 39.4oC, → activation of the heat production mechanism resulting in vasoconstriction, increased metabolic rate and shivering → Chill When skin To is increased to 39oC the chill disappears When stress is removed the thermostat is reset → the heat losing mechanism goes into operation. Resulting in Vasodilation and sweating. Crisis → To is falling Why is To increased? Complications of fever The high To is beneficial: Dehydration Inhibits growth of bacteria Acidosis – Blood pH WBC delivered to site of infection faster Permanent brain damage Increases Ab production Increases rate of repair Death of To rises to 44.5 – 45.5°C Heat Cramp Result of profuse sweating that removes NaCl from the body Salt loss causes painful muscle contraction called heat cramp Cramp in muscles used in working only felt when relaxed Salted liquid relieves cramp. Heat Exhaustion Difficulty in maintaining blood volume Normal or slightly low To. Cool clammy skin due to loss of fluid and electrolytes as sweat. Muscle cramps, dizziness, vomiting, fainting, low blood pressure and low blood volume. Body cannot compensate for low blood pressure. Relieved by rest and salt tablets. Heat Stroke (sunstroke) Occurs when To and relative humidity are high. Body heat cannot be lost by evaporation and radiation Decreased blood flow to skin and decreased sweating → Core To rises. May destroy brain cells. Relieved by immersion of the body in cool water (increased conduction) and rehydration.  Response to Heat Gain: how to Response to Heat Loss: how to raise lower body temp body temp Vasomotor Center inhibited Vasomotor Center stimulated Vasodilation occurs Vasoconstriction occurs Skin Colour changes Skin cools Heat lost through radiation and Heat not lost because blood shunted convection away from skins surface Sweat production increases Sweat production decreases Heat lost through evaporation Shivering thermogenesis Increased respiration and metabolism Generates heat dec Non-shivering thermogenesis Behaviour changes Generates heat = Overall Loss of Heat = Overall Gain of Heat