Isf A Lecture 25: Skin

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integument

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the skin and its appendages

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epidermis

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surface layer of epithelium that makes up one of the two main layers of skin

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dermis

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the second layer of skin composed of dense connective tissue and underlays the epidermis

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hypodermis

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is an adipose-rich layer beneath the dermis

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Functions of the skin:

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1. maintains temp
2. protection from physical insults
3. receives stimuli from environment4.thermoregulation by sweat glands, fat deposits and blood vessels
4. excretory and photochemical functions

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Embryonic origin of skin

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- epidermis - extoderm
- dermis - underlying mesoderm
- accessory structures (hair, sweat glands, and mammary glands) - derivatives of epidermal cells
-nural crest cells migrate to the dermo-epidermal junction and differentiate into melanocytes

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epidermis: classify

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kerantinized, stratified squamous epithelium. Composed of keratinocytes and melanocytes

minor cells: langerhans and merkel cells

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Keratinization

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1. proliferation
2. maturation and outward displacement
3 shedding

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pacinian corpuscles

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encapsulated, ovoid sensory receptors. Sensitive to deep pressure together with meissner's corpuscles they are responsible for vibratory sensation. Found in subcutaneous tissue

- appears as concentric lamellae

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Stratum spinosum

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above the stratum basale of the epidermis and have spinous processes on their surface there processes are attached to spinous processes of neighboring cells by desomosomes

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Langerhan cells

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clear cells in LM. EM contain rod or racquet shaped organelles

- antigen presenting cells (dendritic cells) in the epidermis
-endocytose foreign molecules

- have a characteristically indented nucleus - EM

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melanocytes

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pigment cell beneath or between the epithelial cells of the stratum basale

-synthesize melanin granules

- a cell with tenticles coming off in teh stratum basale. Contains melanosomes which synthesize melanin.

-melanin granuales, made in melanocytes are injucteed into keratinocytes

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melanin

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made from tyrosine by tyrosinase
-syn. on fibrous lattice within specialized granule called melanosome.

pigmentation based on melanocyte size, distribution and density of pigment (not number)

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eccrine sweat glands

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most sweat glands
- uses merocine secretion

-increase in hot climates. People can adapt to reduce salt loss.

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apocrine sweat glands

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odoriferous glands that secrete a product that is rich in protein: sweat glands of axilla, mammary areola, labia majora, and circum-anal regions

- use merocine secretion

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Merkel cells

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cells resemble the cells fo teh stratum spinosum
- dense core neurosecretory granules
-form flattened structure called Merkel's disc.

Makes contact with peripheral terminal of a neuron

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medulla

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forms central axis of hair after it emerges from follicle

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cortex

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mmultilayered structure that contain pigment granules of the hair after it emerges from the follicle

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cuticle

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thin protective covering of the hair after it emerges from follicle

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Keratinocyte

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pigment cell in teh epidermis.
- undergoes a progression of maturation and keratinization
-like other epithelia lacks blood vessels and is dependent on the dermis for its nutritional needs

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tonofilament

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epithelial-specific intermediate filament.

- found in keratinocytes

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keratohyalin granules

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found in the stratum granulosum. They are not membrane bound. Do not confuse with melanin granules (found in basal layers of epidermis)

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membrane coating granules

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lamellar bodies - contain a lipid-rich secretory product