Support & movement · Topic 4 of 18

Integumentary System

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Anatomy · integumentary system

Skin is epidermis over dermis, with the hypodermis beneath; with hair, nails and glands it protects, cools, senses and makes vitamin D.

01 · Layers, outside inEpidermis → dermis → hypodermis

02 · Four jobsProtect · cool · sense · make vitamin D

03 · Vitamin DSunlight on skin → vitamin D

Integumentary = skin + hair, nails, sweat and oil glands must know

Skin jobs: protect, regulate temperature, sense, make vitamin D must know

Keratin = the tough, water-resistant protein of skin, hair, nails

Melanocytes make melanin: skin color and UV protection

Outside in: epidermis → dermis → hypodermis (subcutaneous) must know

Epidermis = stratified squamous epithelium with no blood vessels must know

Dermis holds the vessels, nerves, follicles and glands must know

Hypodermis = fat layer that insulates, cushions and anchors the skin

Stratum basale = deepest epidermal layer, where new cells are made

Stratum corneum = surface layer of dead keratinized cells

Sebaceous glands secrete sebum, an oil that lubricates skin and hair

Eccrine glands: watery sweat everywhere that cools the body

Apocrine glands: armpit and groin, thicker sweat, body odor

Hair = dead keratin cells from a follicle; arrector pili lifts it

Nails = keratin plates that protect fingertips and toe tips

Hot: dermal vessels dilate + sweat; cold: vessels constrict

UV light on skin → vitamin D → calcium absorption for bone

Commonly confused

	Eccrine	Apocrine
Where	All over the skin; most on palms, soles, forehead	Armpits and groin
Duct opens onto	A pore on the skin surface	A hair follicle
Sweat	Watery (mostly water and salt)	Thicker, with organic compounds
Main job / result	Cooling by evaporation	Body odor once bacteria break it down

Show 5 more facts

Strata, deep → top: basale, spinosum, granulosum, lucidum (thick skin only), corneum

Dermis = papillary layer (fingerprint ridges) over the reticular layer

Meissner corpuscles = light touch; Pacinian corpuscles = vibration

Skin makes vitamin D; liver then kidneys activate it (calcitriol)

Lunula = pale crescent at nail base; cuticle = eponychium

Pearl

Epi- means upon and hypo- means below: epidermis on top, dermis in the middle, hypodermis underneath.

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