McCance 47 M10.3 - Anatomy and function of the skin

• The skin is the largest organ, making up roughly 20% of body weight.
• Combined with hair, nails, and glands, it forms the integumentary system.
• The main role is to shield the body from environmental factors like microorganisms, UV radiation, fluid loss, and mechanical stresses.
• It also regulates temperature, aids immune surveillance, and activates vitamin D.
• Touch and pressure receptors offer protective measures and pleasurable sensations.
• Commensal microorganisms (skin microbiota) defend against harmful bacteria.

Layers of the Skin

• The skin features three primary layers.
• Epidermis: Outermost layer.
• Dermis: Lies deeper.
• Subcutaneous layer (hypodermis): The deepest layer, mostly connective tissue, containing macrophages, fibroblasts, fat cells, nerves, blood vessels, lymphatics, and hair follicle roots.
• Each layer has cells showing different stages of skin cell specialization and function.

Epidermis

• The epidermis acts as a protective barrier that constantly renews by shedding the stratum corneum, its surface layer.
• Primarily made of keratinocytes in a lipid matrix, these cells create keratin, a scleroprotein providing protection from mechanical stress.
• The thickness varies from 0.05 mm on eyelids to 1.5 mm on palms/soles, averaging 0.12 mm.
• Keratinocytes, form in the basal layer (stratum basale), move upward, differentiate, and form the spinous layer (stratum spinosum).
• Together, they create the germinative layer (stratum germinativum), helping the skin renew constantly.
• Cornification, or keratinization, prevents deeper skin layer dehydration and body water loss, epidermis turnover averages about 30 days.
• Melanocytes: Near the base produce melanin upon UV light exposure by melanocyte-stimulating hormone (MSH). Melanin shields against UV radiation and determines skin color.
• Vitiligo is the autoimmune-related loss of melanocytes, depigmenting skin patches.
• Langerhans cells: Originating from bone marrow, these dendritic cells trigger immune response by presenting processed antigens to T cells, defending against environmental antigens.
• Merkel cells: Linked to touch receptors for slowly adapting mechanoreceptors, they respond to deformation.

Dermis

• Between 1 to 4 mm thick is composed of collagen, elastin, reticulin, and a gel-like ground substance.
• Irregularly arranged connective tissue enables skin mobility, stretching, and contraction with body movements.
• The dermis contains hair follicles, sebaceous glands, sweat glands, blood vessels, lymphatic vessels, and nerves.
• Cone-shaped projections of the papillary dermis connect with the epidermis, forming rete pegs for skin texture.
• Dermal cells include fibroblasts which secrete the connective tissue matrix and collagen.
• Mast cells release histamine, playing a role in hypersensitivity reactions.
• Macrophages are phagocytic, participating in immune responses, while histiocytes are macrophages residing in loose connective tissue to phagocytize pigments and debris from inflammation.

Subcutaneous Layer

• As the third skin layer, also known as the hypodermis, it consists of adipose tissue.
• Lobules are divided by fibrous walls (septa) of collagen and large blood vessels.
• Dermal collagen merges with collagen in the subcutaneous layer.

The Dermal Appendages

• Dermal appendages are inclusive of nails, hair, sebaceous glands, and sweat glands.
• Nails: Protective keratinized plates featuring the proxmial nail fold, eponychium, matrix, hyponychium, nail plate, and paronychium.
• Nail growth happens continuously a rate of 1 mm or less daily.
• Hair follicle and sebaceous glands form integrated units.
• Melanin-secreting follicular melanocytes determine hair color.
• Sebaceous glands secrete sebum, composed primarily of lipids to prevents skin/hair dryness, gland growth is propelled androgens with enlargement as an early puberty sign.
• Eccrine sweat glands: Play a thermoregulatory role in cooling the body through evaporation.
• Apocrine sweat glands: Have a limited function and located in the axillae, scalp, face, abdomen, and genital area.

Blood Supply and Innervation

• The skin's blood comes from the capillary loops that come from deeper horizontal cutaneous arterial plexus blood supply. Branches from the deep plexus supply hair follicles and sweat glands.
• Subpapillary network of veins then drain the capillary loops.
• The capillary loops connects with the arteriovenous Anastomoses in the dermis that helps with regulations for body temperature by opening and closing blood flow in conjunction with evaporative heat loss of sweat.
• The skin of hair is innervated with sympathetic a-adrenergic receptors and passive vasodilation.
• The skin of non-hair (Glabrous) is innervated solely by sympathetic vasoconstrictors with passive vasodilation.
• Lymph vessels originate in papillary dermis and are in larger subcutaneous trunks: For removing proteins cells and immunologic mediators.

Aging and Skin Integrity

• Many changes with aging are generalized and related to Sun (UV Radiation) and tobacco Exposure by inflammatory responses.
• Skin becomes thinner, less elastic, drier, and wrinkled with a change in pigmentation.
• Adipose tissue volume is lost mainly in the face.
• There are is a flattening of the Dermoepidermal Junction with decreased capillary loops resulting in fewer melanocytes and reduced skin's immune response.
• The thickness of the Dermis decreases and accounts for the paper thin quality.
• There is decreased vascular compliance and loss of re-active Responses.
• Due to temperature regulation compromised there is risk for heatstroke and hypothermia.
• Less vasculature as well as lymphatic drainage results in less barrier protection with eccrine, apocrine, and sebaceous atrophy promoting dry skin.
• Elastin loss causes wrinkling collagen fibers become fragmented.
• Decreased cell proliferation, blood supply and Immune responses can impede healing, with changes in distribution and thinning do to loss of melanocytes and follicle stem cells.
• Epidermal cells alter shape and the Stratus Conium barrier function is reduced causing toxic oxidative substances to not be cleared and sensory.

Tests of Skin Function

• Diagnostic Skin evaluations require historical information along morphological structure identifications: critical because an understanding a thorough well Being is essential to understanding the pathophysiology.

Clinical Manifestations of Skin Dysfunction

• Identification of distribution: Is essential to identifying the pathophysiology with a complete health history in combination.

Pressure injury

• Pressure injury are caused by the shearing forces of the friction: With moisture pressure, Decubitus is in result time.
• Medical devices like endotracheal tubes also injure mucosa.

Pressure injuries

• Occur above bony, sacrum, heels, continuous tissue compression results capillaries distortion creating O2 supply occlusions with individuals that are darkly pigmented.
• Pressure relieved results in brief reactive Hyperemia with endothelial disrupt forming anoxic necrosis due to obstruction with pressure.
• Scales are available the braden scale is a common indicator.
• Stages and grades of injury include: Non-Blanchable Erythema and tissue loss involving epidermis without slough.
• Skin damage results in an abrasion or Blister that result in purple discoloration resulting bacterial infections localizing with necrotic tissue releasing debris enzymes and inflammation (pain fever leukocytosis with complications of debility).

Goal is prevention for pressure injury

• Early detections require caregiver education and frequent Assessments using strategies promotions and eliminations of drainage with Adequate nutrition (O2/fluid).
• Injuries can cause an abrasion or blister with pressure dressing and continued of Tissue requiring Relief.
• Proteolytic enzymes Bacteria and Microphages can cause necrotic tissue dissolve: Creating possible complications wound care (Debridement opening and repair).

Keloids and Hypertrophic Scars

• Occur as a result of improper abnormal healing with collagen, activity (genetic).
• With tension trauma introduction the provocative infection factors include shoulders lower legs occurring more often in ages of 10 to 30.
• The extreme scarring with difficult treatment requires surgeries, detection can be managed verapamil a calcium antagonist.

Pruritus

• Is itching a symptom in disorders, such as dermatitis or lice as well as xerosis, renal failure related to opiate drugs that are acute and chronic?
• Multiple stimuli create itching due to the Peripheral mediator such as histamine and opioids, unmyelinated Nerve Fibers send signals for sensations with cell interaction.
• Mechanisms modulate it being less sensory but the neuropathic Pathology happens along the Afferent pathway.

Disorders of the Skin

• Can be precipitated because disruptions create trauma.
• Cellular Functions may involve inflammation.

Inflammatory Disorders

• Cause itching lesions and indistinct borders with phases of irritation: Such as edema related.
• The location of disorder is related.

Allergic Contact Dermatitis

• The hypersensitivity T cell mediated response.
• From Microorganisms allergen cytokine, langerhans with genetics causing several allergen binding.
• With latex or sensitivity to latex.
• Sensitization comes from antigen.
• Re-Exposure causes symptoms and swelling due to the Pattern distribution by antigen of the Source with patch assistance for diagnosis.
• Removal can help along with steroids.

Irritant Contact Dermatitis

• Cause response related to properties concentration age etc...
• Skin lesions removed by removal.

Atopic Dermatitis

• (Eczema) more common at a young age.

Stasis Dermatitis

• Cause inflammation of blood cells which trap Leukocytes.
• Increase pressure of blood depositing inflammation with petechiae treated by lifting legs in fractions.

Seborrheic Dermatitis

• Scalp eyebrows and back.
• With Malassezia by immunosuppression causing hyper proliferation.
• Treated by coal tar shampoos for inflammation due to the steroid.

Papulosquamous

• Disorders which include Scale Erythema as well with psoriasis.
• Which involves world population.

Psoriasis

• The genetics include the immunity by Interleukin.
• Both thick epidermis because high vascularity results that takes several angiogenic.
• Triggers involve Beta blockers that are mild to severe by Distribution with Plaque and rare inverse erythrodermic forms affecting immune T lymphocyte.

Pityriasis Rosea

• Is a self-limiting inflammatory more often than youngsters after strep infection that is single-lesion followed symmetrical oval patterns.
• UV light is a treatment.

Lichen Planus

• Is an auto immune with various presentations stimulated with T cells caused by various skin disorders on limbs forming hypertrophic ulcers by thinning or splitting with nail damage (Treated steroids).

Acne vulgaris

• Can be caused in adolescence.

Hidradenitis

• A chronic disorder scarring.

Acne Rosacea

• Is a condition with inflammatory damage trigger resulting edema on middleface with rosacea sun damage causing sebaceous swelling controlled with steroids with antiandrogen treatment/ surgery.

Lupus Erythematosus

• Autoimmune causing rash (localized UV).

Pemphigus

• Autoimmune blistering due to the IgG binding a junction to break cell to cause blistering causing infection and varying lesions with variants.
• Diagnosed because epithelial auto anti bodies can managed via cortical.

Bullous Pemphigoid

• A autoimmune Blister benign autoimmune
• with localized plaques (edematous) after 60s
• can treat using Clobetasol as well as Antihistamines.

Erythema Multiforme

• Has a skin involvement and the skin surfaces have a Target that has inflammation or rings around vessels.

SJS/Ten

• Lesions form for a Ten SJS in relation to necrosis blisters and blisters and mucosal in a response T Cell cytotoxin to specific prodome that requires fluid
• The treatment involves supportive care with antibiotic to a SSSS.

Infections

• From pathogenic bacterial
• Folliculitis: Microbacterial infections such as staph and moisture with antibiotics.
• Furuncles: From Folliculitis spread (staph aureus) in the skin treated by draining with antibiotics if from the nares
• Carbuncles: Infections through the dermis can spreads requiring incisions with chills
• Cellulitis: Due to wounds from sores, treat with Burow treatment antibiotics by identifying the illness
• Erysipelas : Superficial that causes spots by Streptococcus from streptococci with an antibiotic treat, cold compression can be use as a symptom by symptoms relief
• Impetigo can be streptococci.
• Lyme Disease occurs through Lyme bacteria causes tick and 3 stages (can develop carditis), the erythema T cell can be recognized or the Lyme test will have to be done, requires higher Doxy for test and Doxycyline.
• Herpes simplex virus include with spread, the pain has symptoms to vesicles lasting within (weeks. with antiviral treatment, vertical infections from spread during shedding by mothers with high spread.
• Varicella Zoster have symptom for dermato and dorsal treat using compresses
• Warts occur due to the Hvp various types of verrucae (transmission with touch).
• Tinea occurs with surface scale identified by examination.
• Treat infection is caused the Candidasis can be triggered with wetness (infection will occur )

Vascular

• Vasculitis : blood cells or vasculitis from vessel for bleeding.
• With localized lower legs vessel leading
• To immune reaction which be systemic through Biopsy identify.
• Urticaria hives from Edema and is from allergies by contraction

Autoimmune

• Scleroderma: Can result system sclerosis caused stiffness.
• By immune system that involve high collagen tissue with hands becoming shiny and require clothing due to pulmonary and failure

Noncacerous tumors can occur.

• Seborrheic Keratosis: Are seen in elder the broad mass requires liquid treatment.
• Keratoacanthoma result 1_4 months resolution
• Actinic damage needs sunscreen protection.
• Nevi require evaluation for a melanoma ( ABCDE: asymmetrical check)

Cancer to review

• Risk for skin which increases with age.
• Basal cell caused by radiation exposure the tumors start a surface with a Bcc
• squar cells and 90 of which are in early
• Actinic damage can lead to malignancy a tumor needs treatment and analysis
• It can affect the extremities and be a high risk through exam

Kaposis

• Are vascular and a low aids can make
• Multiple and spread causing lung issues.

Cell Damage

• Radiation and and in with (lymph with skin ) stem.

Problems with hair

• Alopecia: Resulting loss in scalp
• The hair is a reversible issue

Nails

• Infections cause and pain.