Download - 3. Fisiologi - Dr. S. Marunduh, MMed - SKIN
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The Skin: Anatomy & Physiology
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Introduction
Largest organ in the body
Varies in thickness at different parts (< 0.5 mm at eyelids to > 5 mm on middle of upper back)
Anatomy Of The Skin
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Skin
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Epidermis
Stratified squamous epithelium
No blood vessels
In palms of hand and soles of feet, epidermis is thicker
Composed of five layers:
[1] Stratum corneum
[2] Stratum lucidum
[3] Stratum granulosum
[4] Stratum spinosum
[5] Stratum basale
Frolich, Human Anatomy, Skin
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[1] Stratum Basale
Single layer of columnar or cuboidal cells
Lower surface of cells attached to dermis
Receives nutrients from blood in the dermal vessels
Mitosis occurs in this layer
Older cells expelled to outer layer
Melanin is produced in this layer
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Stratum Basale
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[2] Stratum Spinosum
Prickle cell layer
Several layers of polyhedral (many-sided) cells
Interlocking spine-like projections help binding of this layer
Active protein synthesis takes place (indicates cell growth and division)
Obtain nutrients through fine elements
Keratinization begins in this layer
Nuclei-containing cells change into flat cells composed of hard durable protein)
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Stratum Spinosum Contain Desmosome
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[3] Stratum Granulosum
Granular + 2 to 4 cells thick
Cells contain keratohyaline in granules
Final stages of keratinization occur
Loss of fluid, nucleus disintegrates
[4] Stratum Lucidum
Transparent layer
Flat + translucent dead cells
Protection against UV
Lucidum appears in palm of hands and soles of feet to protect against sun burn
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[5] Stratum Corneum (Horny Layer)
Thick layer of dead cells
Soft keratin (keep skin elastic)
Cells below contain fatty substrate keep skin waterproof + prevent skin cracking and allowing bacteria inside
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Epidermis
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Dermis
True skin
Highly elastic, tough and flexible tissue
Meshwork of collagenous, reticular and elastic fibres
Collagenous Fibres
Provide support for skin
Reticular Fibres
Thinner, yet still provide support
Elastic Fibres
Skin flexibility
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Cells Of The Dermis
a) Fibroblasts
b) Fat cells
c) Macrophages
Dermis subdivided into two main layers:
{1} Upper papillary layer
{2} Reticular layer
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[1] Upper Papillary Layer
Loose connective tissue
Contain protrusions into epidermis called “PAPILLAE”
Fine capillaries to carry waste away + provide nourishment and oxygen
Nerve endings for heat, pain, cold, pressure and touch (Meissner’s corpuscles)
Double row of papillae better gripping by hands and feet + distinctive fingerprint patterns
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[2] Reticular Layer
Elastic network of tough collagen fibres interwoven with elastic fibres
Collagenous fibres arranged in special pattern
Incisions made parallel to these lines during surgery wound heals faster
Contains sebaceous and sweat glands, arrector pili muscle and hair follicle
Pacinian corpuscles are distributed through the dermis and function as pressure receptors
Stretch marks and pregnancy due to breaks in collagen and elastic fibres
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Dermo-epidermal Junction
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Dermo-epidermal Junction
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Hypodermis
“Subcutaneous” layer
Thicker than dermis
Thicker in females
Ducts of sweat glands and bases of hair follicles
Area for formation and storage of fat due to:
@ Adipose tissue – containing fat cells
@ Areolar tissue – tissue elasticity
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Hypodermis
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Developmental Anatomy of the Skin
Dermis and epidermis are derived from different embryological tissues
Epidermis derived from “ECTODERM”
Dermis derived from “MESENCHYME”
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Glands Of The Skin
Two types: Eccrine and Apocrine
Eccrine Glands
Distributed almost all round the body
Secretory portion in hypodermis
Apocrine Glands
Arm pits and dark regions of nipple
Secretes fatty substances
These react to air YOU STINK
Sweat Glands
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Sebaceous Glands
Located in the dermis
Lubrication and protection
Cluster of cells
Breakdown of inner cells in the cluster sebum formation
Connected to hair follicles
Sebum fight bacteria and fungi
Blackheads due to blocked glands
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Hair
Shaft = protrudes from skin
Root = embedded in skin
Follicle surrounds hair
Arrector pili muscle = bundle of smooth muscle
Arrector pili causes:
a) Hair erection
b) Sebum release from the sebaceous glands
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Anatomy Of The Skin
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Anatomy Of The Skin
Frolich, Human Anatomy, Skin
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Functions Of The Skin
Non-specific immunity
[1] Protection
Anatomical barrier against infection
Melanin = screen out excess UV rays
When melanin is darkened by the tan transferred to outer skin layers (suntan) skin less sensitive to sunrays
Dark skin due to wider distribution of melanin beyond stratum basale into higher levels of epidermis
[2] Thermoregulation
Control of heat production
Shivering
Skeletal m uscle
Motor neurons
Control of heat loss
Skin vasocontriction and vasodilation
Skin blood vessels
Sym pathetic nervous system
Control of heat loss
Sw eating
Sw eat glands
Sym pathetic nervous system
Hypothalam ic therm oregulatory integrating centre
Peripheral Therm oreceptors (Skin)
Skin tem perature
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[3] Sensory Perception
Millions of nerve endings
Receptor for pain, heat and pressure
Therefore, maintain homeostasis
[4] Excretion
Excretion of lactic acid and sodium chloride
Urea (1 g nitrogenous waste eliminated through skin per hour)
[5] Vitamin D Synthesis
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P ro m o tes ab sorp tion o f ca lc iu m a nd ph o sp h ate th ro ug h in tes tine
A c tive v ita m in D
M o d if ica tio n b y live r a nd k id ne y e nzym es
V ita m in D 3 (C h o leca lc ife ro l)
Vitam in D precursor (in skin)
Defining PruritisAn unpleasant localized or generalized
sensation on the skin, mucus membranes or conjunctivae which the patient instinctively attempts to relieve by scratching or rubbing
Diversity of Causes and Presentation
Many Causes, Many Treatments
Trivial to to Life threatening
(mosquito bite) (malignancy)
10-50% of cases with generalized itching have systemic disease
Diseases & ItchingInfectionsInfestations
(scabies)Inflammatory skin
conditions (eczema, contact derm, psoriasis)
Chronic Renal Failure
Cholestatic liver disease
Depression/anxiety
Poorly Understood & ManagedRelies on similar components of the pain
system: receptors, neurotransmitters, spinal pathways and centers in the brain
Stimulating pain can relief itchingTreating pain with some analgesics relieves
itching, others trigger itchingPruritis is a common side-effect of opioid
administration, sometimes worse than the pain
Pruritogenic StimuliPressureLow-intensity electrical or punctate stimuli Histamine: acts directly on free nerve
endings in skin
Pain vs Itch NervesItch transmitted from specialized pain
receptors: a subclass of C-nociceptorsMechano-insensitiveHistamine sensitive
Nerve endings cluster around “itch points” which correspond to areas very sensitive to pruritogenic stimuli
Itch pathwaysFibers originate @ dermal/epidermal jxn Thin unmyelinated axons, lots of branching Ipsilateral dorsal horn of spinal cord Synapse with itch-specific secondary neuronsCross to opposite anterolateral spinothalamic
tract to thalamus Somatosensory cortex of postcentral gyrusSLOW transmission and BROAD receptor field
Itch MediatorsHistamineProstaglandinsLeukotrienesSerotoninAcetylcholine
Substance PProteasesPeptidesEnzymesCytokines
Why do you scratch?Histamine activates both the anterior
cingulate cortex (sensory, emotions) and the supplemental motor area
Lateral Inhibition: “Gate Theory”Noxious stimuli of skin adjacent to pruritic
trigger attenuates initial itch sensationScratching stimulates large fast-conducting
A-fibers adjacent to slow unmyelinated C fibers
A-fibers synapse with inhibitory interneurons and inhibit C-fibers
Pain & ItchPainful stimuli (thermal, mechanical,
chemical) can inhibit itchingInhibition of pain (opioids) may enhance
itching
How to Treat an Itch(Understand the Cause!)Inhibit mediators of itch: histamine,
prostaglandins, substance P, serotonin, cytokinesBlock chemicals that induce pruritis: opioids,
antimicrobialsTreat effects of diseases which induce
itching: eczema, CRF, LF, heme, neuro, endo