Integumentary System

DEVELOPMENT OF SKIN:
  • Epidermis & its appendages, pilo sebaceous unit, nail & sweat glands: Surface ectoderm
  • Melanocyte Et Merkel cells: Neural crest
  • Langerhan's cells: Bone marrow
  • Dermis in limbs & trunks: Somatopleuric mesenchyme
  • Dermis in face, Head Et neck: Neural crest
  • Skin and facia of great toe drains into Vertical group of superficial inguinal lymph nodes
  • It has been calculated that a human adult has about 1012 bacteria on the skin
  • Density of bacterial population at most sites is between 100-1000 per square cm.
LAYERS OF SKIN: 
  • Skin is the largest organ in the body.
  • Total surface area: 1.7m2.
  • The layers of the skin are
  • Epidermis
  • Dermis
  • Subcutaneous fat/ hypodermis 

EPIDERMIS 
  • 0.4 -1.6 mm in thickness
  • Layers of epidermis: 
Stratum corneum (Horny cell layer) Outermost layer
Made of flat, anucleated cells
No cell organelles
Dead layer of epidermis
Underdeveloped in preterm infants for 2-3 weeks
The stratum corneum of the palms and soles is about 0.5 mm thick and much thicker than that on the trunk and limbs
Stratum corneum is permeable in preterm infants and becomes
similar to the adult and full term infant after 2-3 weeks, postnatal maturation.
Stratum lucidum Transparent layerSeen only in palm & sole
Stratum granulosum Made of intracellular basophilic kerato hyaline granules
Forms a water impermeable layer
Contains abundant Odland bodies.
Layer absent in nail bed & matrix
Stratum spinosum orPrickle cells layer [Malphigian layer] Provides mechanical strength to the skinLangerhan cells present.
Stratum basale orStratum germinatum Single layer of columnar/ cuboidal cells
Contains mitotically active keratinocytes & melanocytes
Melanoblast cells appear in basal layer of epidermis during 3rd month of intrauterine life

Cells in the epidermis:
  1. keratinoytes
  2. melanocytes
  3. Merkel cells
  4. Langerhans’ cells
  • Langerhans cells – antigen-presenting cells, derived from bone-marrow and found in the prickle cell layer.
  • Langerhans cells are found scattered evenly throughout the epidermis.
  • Merkel cells are normally located in the basal layer
  • slow adapting mechanoreceptors found in prickle cell layer.
  • Keratinization: conversion of keratinocyte into keratin (4 weeks)
  1. Keratin filaments are hallmark of keratinocyte
  2. Adamson's fringe: beginning of Keratinization
  3. Keratin expressed in basal layer: K5, K14
Development:
  1. 1 epidermal melanocyte unit: 36 keratinocytes
  2. Skin doubling time: 4 weeks
  3. Epidermal turn over time: 1 month
  4. Accelerated cell turnover: psoriasis and ichthyosiform erythroderma [2 to 4 days]
  5. Nail first develops at: 3 months of intra uterine life
  6. Finger nail growth: 0.1mm/day
  7. Scalp hair growth: 0.35 mm/day
  8. Number of hair normally lost pev day:50-100
  9. Factors stimulating skin development (Epidermopoiesis): EGF, TGF-a, IL-II & fibroblast growth factor.
  10. Factors inhibiting skin development: Chalones, TGF-B, a and y interferons, TNF
  • Grenz zone: narrow clear zone B/W epidermis & dermis.
  • Racial variations in pigmentation are due to differences in melanocyte morphology and activity rather than to differences in frequency or distribution
  • Function of the epidermis layer of the skin provides a waterproof barrier and creates our skin tone.
DERMIS: 
  •  Flexible and strong connective tissue
  • Elastic, reticular and collagen fibers
  • Cells: fibroblasts, macrophages (WBC), mast cells (histamine).
  • Nerves, blood and lymphatic vessels Oil and sweat glands originate
Two layers: Papillary layer:
  1. Loose connective tissue with nipple like surface projection called dermal papilla.
  2. Capillaries
  3. Contain pain receptors
  4. Contain touch receptors (Meissner’s corpuscles)
  5. Dermal ridges- epidermal ridges- pattern called fingerprints
Reticular layer:
  1. Dense irregular c.t.
  2. Collagen fibers offer strength
  3. Holds water
  4. Dermal tearing causes stretch marks.
  5. Striae
Hair (pili)
  1. Main function is protection
  2. Hair root nerve plexus for touch
  3. Normal hair loss in adult 70-100 hairs/day
Nerve endings:
  1. Exteroceptors (stimulus outside of body)
  2. Pacinian (lamellated) corpuscles: deep pressure and stretch
  3. Meissner’s (tactile) corpuscles: light touch, vibration and discriminative touch.
  4. Hair root plexus
  5. Free (naked) nerve endings: nociceptors (pain) and thermoreceptors ( hot – deep and cold- surface)
  6. Ruffini’s corpuscles: deep pressure
  7. Haascheiben cells in epidermis are responsible for Touch
HYPODERMIS:
  • Called subcutaneous, Sub- or superficial fascia
  • Anchors skin to underlying structures
  • Contains adipose tissue and blood vessels
  • Common site for injection
Exam Question
  • The portion of the skin that serves as a barrier to water loss is the Epidermis
  • Melanoblast cells appear in basal layer of epidermis during 3rd month of intrauterine life
  • Lymphatics are found in Dermis of skin
  • Stratum corneum is underdeveloped in the VLBW infants in the initial 7 days
  • Normal turnover time of epidermis (skin doubling time) is 4 weeks
  • Function of the epidermis layer of the skin provides a waterproof barrier and creates our skin tone.
  • Haascheiben cells in epidermis are responsible for Touch
  • Dead layer of epidermis is Stratum corneum
  • Skin and facia of great toe drains into Vertical group of superficial inguinal lymph nodes
  • It has been calculated that a human adult has about 1012 bacteria on the skin
  • Density of bacterial population at most sites is between 100-1000 per square cm.
Don't Forget to Solve all the previous Year Question asked on Integumentary System