Histology of Integument

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Skin facts

• Skin is composed of epidermis & dermis.

• Largest organ 1.5-2.3 square meters.

• ~15% of total body weight.

Hypodermis

Also known as subcutis is not a part of skin, superficial fascia of gross anatomy, mostly adipose.

Functions of skin

1. Mechanical protection from abrasions, bacterial invasions (suit of armor).

2. Prevents desiccation and keep fluids from entering (wetsuit or raincoat).

3. Maintain body temperature by regulating blood flow to vessels in skin, sweating & fat deposition (AC or fan).

4. Sunlight stimulates synthesis of vitamin D which helps in absorption of calcium (drug store).

5. Immunity is enhanced by antigen presenting cells of Langerhans that present to T-helper cells & Grunstein cells that present to T-suppressor cells (paramedic).

6. Reception of stimuli such as temperature, pressure, vibrations & pain, keeps us aware of the environment (TV ).

7. Protection from UV radiation via melanin (beach umbrella).

8. Organ of rapid communication of clinical significance (e-mail) localize nerve damage via dermatomes homeostasis via color, jaundice cardiovascular, cyanotic, blue texture, vitamin deficiencies age, wrinkles emotional state, blushing.

Layers of Skin:

Dermis

• Papillary layer of dermis - fairly thin, loose CT that holds dermis to epidermis. Forms conical papillae, hence the name.

• Reticular layer of dermis - fairly thick DICT that resists stress in all directions.

Basale

• Present in thick skin only.

• Stratum basale or germinitivum - single layer of cells with desmosomes, hemidesmosomes and basal lamina.

• One basal cell undergoes mitosis to produce 10-11 cells that move up to desquamate as a unit, an epidermal proliferation unit (EPU).

• Psoriasis is excessive epidermal proliferation.

• Cells normally desquamate in 4 weeks but it psoriasis it takes 1 week.

• Malpighian layer is composite of s. basale & s. spinosum.

Granulosum

• Diamond shaped cells with keratohyalin granules (function unknown) that coat tonofilaments.

• Cells begin to die.

• Lamellated granules with hydrophobic lipid material are thought to act as a sealant and penetration barrier.

• This layer first appeared in reptiles and was an important step in evolution of terrestrial life.

Lucidum

• Not present on thin hairy skin.

• Cells are dead yet are full of keratin fibers.

• Characteristic of thick skin.

• Stratum corneum Arranged in vertical stacks.

• Each cell transforms into a scale or squame with no nucleus.

Keratins

• There are 19 different keratins, each the product of a different gene.

• Cells in the s. basale have tonofilaments of prekeratin & as they undergo differentiation they synthesize progressively different types of keratin.

Melanocytes

• Melanocytes are derived from neural crest.

• Not attached to adjacent keratinocytes by desmosomes, but hemidesmosomes occur.

• Synthesize melanin & tyrosinase plays an important part.

• Tyrosinase is packaged in premelanosomes with no tyrosinase activity.

• Enzyme converts tyrosine to DOPA (3,4-dihydroxyphenalalanine).

• Eventually melanin is produced and stored in melanosomes.

• Melanocytes stain clear.

Melanin

• Melanocytes pinch off cell processes that are taken up by adjacent keratinocytes.

• A melanocyte & its group of keratinocytes are called an epidermal melanin unit.

• Melanin protects DNA from solar radiation & prevent vessel damage.Different races have different rates of synthesis & degeneration of melanin, NOT different numbers of melanocytes.

• Melanocyte numbers are constant at 1,000-2,000 per mm3 Blacks have higher rate of synthesis & lower rate of degeneration.

• They suntan like any skin.

Albinos

Albinos lack tyrosinase. Overall skin color is due to: melanin foods like ones containing carotene blood.

Immunity cells

• Present within the s. spinosum and are thought to be derived from monocytes.

• Langerhans cells present to T-helper cells.

• Grunstein cells present to T-suppressor cells.

Types of Skin:

Thick Skin

• Thick has all 6 layers.

• Glabrous (smooth, no hair) Palms, soles back & shoulders.

• Contain secondary interpapillary ridges.

• Back is thickest at 3-4 mm.

Thin Skin

• Thin skin lacks stratum lucidum.

• Found everywhere else on body.

• Hairy.

• Contains only primary dermal ridges.

• Eyelid is 0.5 mm - thinnest skin in the body.

Fingerprints:

Dermatoglyphic pattern of surface ridges are fingerprints.

Stratum Sapillare

• Stratum papillare of thick skin creates primary epidermal ridges & corresponding primary dermal ridges.

• Each dermal ridge has 2 secondary dermal ridges called, the interpapillary pegs.

• Projecting from the tops are conical dermal papillae.

• During development dermis determines the fate of epidermis.

• Dermis (mesoderm) is instructive on epidermis (ectoderm).

Stratum Reticulare

• Stratum reticulare has collagen runs in a predominant direction creating Langer lines, paths of least resistance.

• In surgery, parallel incisions make for less scarring.

• Tattoo ink is primarily in papillary & reticular layers in macrophages & fibroblasts, not the interstitium.

• Lasers (thermal mediated injury) can remove them, tattoos of different colors require different lasers.

Hair

Hair is a skin appendage formed from an epidermal downgrowth forming the hair follicle.

Hair Bulb

• Hair bulb is dilation of follicle in dermis.

• Matrix is inside the bulb where mitosis occurs.

• Hair follicle has a hair root.

Hair Root

• Hair root has medulla (moderately keratinized), cortex (heavily) keratinized & cuticle (scale-like) that interlocks with IRS.

• IRS has inner cuticle, Huxley's granular layer in middle and Henle's layer adjacent to ERS.

• These layers are constantly desquamated and replaced.

• External root sheath has characteristics of s. basale & s. spinosum.

• It becomes thinner toward the bulb.

• At the base it consists only of s. basale & is continuous with the epidermis.

• Dermal sheath of CT surrounds ERS.

• Dermal papilla indents bulb & contains vessels.

Arrector Pili

• Arrector pili muscles & sebaceous glands.

• All hairs except pubic & beard have arrector pili.

Hair Color

• Hair color is due to a mix of pigments brown, black & yellow.

• Gray is due to lack of melanin production.

• White is due to air trapped in cortex.

Sebaceous Glands

• Sebaceous glands - holocrine, sebum, the greaseys.

• Acne is an over production of sebum along with blockage associated with puberty.

Sudiferous Glands

• Sudiferous glands - sweat glands.

• Eccrine - coiled tubular with duct going through the epidermis.

• Small lumen & stain dark.

• The 3rd kidney, widely distributed and cools the body.

Apocrine Duct

• Apocrine Duct does not go to surface but empties along hair shaft.

• In axilla, prepuce, labia minora, nipple & perianal region.

• Give distinct odors of recognition.

• Secretions are odorless but surface bacteria break them down producing a musky odor.

• Produce phermones in other vertebrates.

Nails

• Nail plate = s. corneum.

• Nail bed is underneath & attached to periosteum (torture chambers pull out fingernails, also insert bamboo slivers under nails).

• Nail groove on side.

• Nail matrix is the proliferation site.

• Lunula white crescent.

• Eponychium is cuticle, s. corneum.

• Hyponychium is thick layer layer at side.

Skin Nerve Endings

Free nerve endings:

Thermoreceotors:

• Hot & cold

Nociceptors:

• Itch & pain.

Encapsulated mechanoreceptors:

• Merkel's endings in palms.

Meissner's corpuscle:

• For light touch.

Pacinian corpuscle:

• Senses pressure, touch & vibrations.

Ruffini corpuscle:

• Pressure.

Krause end bulb:

• Senses pressure.

Skin Cancer

Melanoma:

• Is very malignant and metastasizes early with 90% fatality once it reaches the lymph nodes.

Carcinoma:

• Malignant neoplasm derived from epithelium of skin, large intestine, bronchi, stomach, prostate, breasts or cervix.

Basal cell carcinoma:

• From s. basale most common skin cancer.

• Develops slowly and metastasizes late.

Squamous cell carcinoma

• Develops from stratified epithelium.

Additional Reading:

Basic Histology

1. Introduction to Histology
2. Basic Cell Physiology
3. Actin, Microtubules, and Intermediate Filaments
4. Mitochondria, Nucleus, Endoplasmic Reticulum, Golgi
5. Epithelium (Epithelial Tissue)
6. Connective and Adipose Tissue
7. Types of Cartilage
8. Osteogenesis
9. Nervous Tissue
10. Muscle Tissue
11. Cardiovascular System
12. Blood and Hematopoiesis
13. Lymphoid Tissue
14. Digestive Tract I: Oral Cavity
15. Digestive Tract II: Esophagus through Intestines
16. Liver, Pancreas, and Gall Bladder
17. Respiratory System
18. Integument
19. Urinary System
20. Endocrine System
21. Male Reproductive System
22. Female Reproductive System
23. Eye and Ear

Medical Images

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