histology - kamil espiritu - med 1b 2012 Lecture 14 INTEGUMENTARY SYSTEM INTEGUMENT → skin + specialized appendages SKIN - largest single organ of the body - comprising 16% of total body weight function: - protection - thermoregulation - sensation / sensory perception - metabolic functions -- adipose cells in hypodermis is a major storage of energy (triglycerides) -- vitamin D synthesis -- enzymes from epidermal cells (carboxylase, phosphatase, sulfatase) - principal organ for sexual attraction layers: EPIDERMIS - stratified squamous keratinizing epithelium - derived from the ectoderm DERMIS ( corium / cutis vera ) - dense irregular CT - derived from the mesoderm - provides mechanical support and a vascular bed HYPODERMIS ( subcutaneous tissue / subcutis ) - not considered to be part of the skin - layer of varying thickness of adipose tissue beneath the dermis EPIDERMO-DERMAL JUNCTION - uneven and irregular lines because of alternating ⋅ downward projections epidermal ridges / rete pegs ⋅ upward projections dermal papillae Cells of the Epidermis KERATINOCYTES - most numerous cell of the epidermis -- 90% - produces keratin stratum characteristics Basale or Germinativum or Cylindricum ⋅ single layer of basophilic tall columnar cells with mitotic figures to replace desquamated cells Spinosum or Prickle Cell Layer ⋅ several layers of polyhedral cells with intercellular ridges spiny projections that interconnect the cells ⋅ presence of desmosomes Granulosum ⋅ intensely basophilic diamond-shaped cells with keratohyalin granules Lucidum ⋅ consists of non-nucleated cells with clear or eleidin droplets Corneum or Horny Layer ⋅ superficial layer of dead cornified cells Stratum Malphigii = Stratum Basale + Stratum Spinosum MELANOCYTES - scattered between keratinocytes of the stratum basale and stratum spinosum - differentiate from melanoblasts from the neural crest - synthesizes melanin is formed on a specific cell particle mature melanosome - in routine preparations: body is clear and cannot be identified but is made visible with “DOPA” reagent (dihydroxyphenylalanine) which colors them black - tyrosinase is responsible for synthesis of melanin from tyrosine - activity of melanocytes increases with exposure to X-rays and UV light
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histology - kamil espiritu - med 1b 2012 Lecture 14
INTEGUMENTARY SYSTEM
INTEGUMENT → skin + specialized appendages
SKIN - largest single organ of the body- comprising 16% of total body weight
MELANOCYTES- scattered between keratinocytes of the stratum basale
and stratum spinosum
- differentiate from melanoblasts from the neural crest
- synthesizes melanin is formed on a specific cell particle mature melanosome
- in routine preparations: body is clear and cannot be identified but is made visible with “DOPA” reagent (dihydroxyphenylalanine) which colors them black
- tyrosinase is responsible for synthesis of melanin from tyrosine
- activity of melanocytes increases with exposure to X-rays and UV light
histology - kamil espiritu - med 1b 2012 LANGERHAN'S CELLS- star-shaped cells with numerous dendritic processes
- found principally in the stratum spinosum
- appear as clear cells but sharply delineated by impregnation with gold chloride
- EM: indented nucleus, well-developed Golgi complex and RER, clear cytoplasm with rod-like inclusion called Birbeck granules
- with immunological function
- responsible for contact dermatitis
MERKEL'S CELLS- found in the stratum germinativum, often in assoc
with intraepithelial nerve endings
- irregularly-shaped nuclei with less electron-dense cytoplasm containing tonofilaments
- function as mechanoreceptors
Layers of the Dermis
Thin PAPILLARY or SUB-EPITHELIAL Layer- typical loose CT composed of a meshwork of thin
collagenous and elastic fibers thrown into the papillae
- contains vascular and nervous papilla
- rich capillary bed in the dermis acts as thermoregulators and nourishment for the epidermis
Thick RETICULAR Layer- main fibrous bed of the dermis
- with coarse collagenous and bundles of elastic fibers
- direction of the fibers form the “Langer’s line” wherein surgical incision are made for less scar formation
additional info…
Hypodermis- constitute the superficial fascia- with fat cells : panniculus adiposus on the abdomen- devoid of fat : eyelids, penis, scrotum
Thick Skin Thin Skin
⋅ palms of hands, fingers, soles, toes
⋅ thickness of epidermis & prominent strat corneum
⋅ abundant sweat glands
⋅ no pilosebaceous follicles
⋅ prominent grooves and ridges because of tall dermal papillae
⋅ numerous arterio-venous anastomosis
⋅ all regions of the skin except palms, soles, fingers, toes
⋅ thin epidermal layer & less prominent strat corneum
⋅ few sweat glands
⋅ presence of pilosebaceous follicles
⋅ lacks ridges and grooves with checkered network of lines
⋅ absent or few arterio-venous anastomosis
SKIN APPENDAGES
SEBACEOUS GLANDS
- assoc with a hair follicle pilosebaceous unit
- simple or branched alveolar
(saccules) in
histology - kamil espiritu - med 1b 2012 morphology appearing like a bunch of grapes
- holocrine gland-- total disintegration of
secretory cells with sebum (destruction!)
- ↑ activity during puberty
- becomes plugged with sebum, debris and
bacteria resulting in blackheads and acne
HAIR FOLLICLE
- invagination of the epidermis consisting of
medulla:int epidermal root sheath
-- root sheath cuticle Huxley’s layer
Henle’s layer
cortex:ext dermal root sheath
-- derived from the dermis-- direct continuation of
the malphigian layer
- expands into a hair bulb at its deep end
ARRECTORES PILORUM MUSCLE- oblique bands of smooth muscle inserted into middle
of hair follicle creating a triangle with surface
- contraction cause hair to stand on its end"goose flesh appearance"
ORDINARY SWEAT GLANDS- found in palms, soles and foreheads
- simple coiled tubular in morphology made up of clear and dark cells
- merocrine / eccrine in type-- secretion discharged by exocytosis
- stimulus is heat, under control of hypothalamicthermostat (thermoregulation)
- duct -- opens into epidermis as sweat pore -- re-absorb sodium without water -- sweat becomes hypotonic
APOCRINE / ODORIFEROUS SWEAT GLANDS- found in axilla, mammary areola, labia majora and
circumanal region
- less coiledwider lumenmore numerous myoepithelial cellssecretion is thick milky fluid with lipid dropletsopens into a hair follicle
- stimulus: emotional stresssympathetic discharge
- responsible for the production of body odor
NAILS- found on dorsal surfaces of terminal phalanges- consists of clear cells with shrunken degenerated nuclei- contain hard keratin
- made up of
⋅ nail root - nail beneath a fold of skin with whitish lunula
⋅ nail body - attached on a covered portion w/c is
pink due to vascular tissue
⋅ free edge - anterior unattached extension
- nail growth occurs in matrix of nail plate, a semilunar area of proliferative cells on proximal ventral surface of nail groove
- protection and tactile
Blood Vessels of the Skin
blood supply comes from the large arteries in thesubcutaneous layer
Rete Cutaneum- vessels in the superficial part from a horizontally
oriented network at its junction between the dermis and hypodermis
Rete Subpapillare- network of blood vessels between the papillary and
reticular layers of dermis
Arterio Venous Anastomosis - common in deeper layers of dermis
Glomus Body- special type of AV anastomosis for temperature
regulation in the fingers, toes and beneath the nails