A&P Lecture: Integumentary System

Skin

Largest organ in human body

• Protection

• Immunity

• Sensation

• Vitamin D production

• Body temperature

• Excretion

Function of Integumentary system

Keratin layer helps protect against

Water loss, friction, and pathogens

Keratosis pilaris

occurs when excess keratin accumulates and plugs hair follicles, producing small rough bumps on the skin

Melanocytes

Spider-shaped epithelial cells that synthesize the pigment melanin

Produce pigment for hair and skin color. Found in basal layer

Melanocytes purpose

Albinism

Caused by reduced or absent melanin production. May be melanocytes but they may not be functional at producing melanin

Eumelanin

usually means more natural UV protection

Pheomelanin

yellow to reddish natural pigment that contributes to human pigmentation, particularly in people with red hair, freckles, and fair skin

Tanning

Melanins response to UV exposure

Stem Cells

• Mitotically active

• Replace superficial epidermal cells

Stem cells in the basal layer continuously divide to replace old or damaged epidermal cells, allowing the skin to renew and repair itself.

Thick skin purpose

Protect against abrasions and friction

Thin skin purpose

Cover the muscles and grow hair

Cyanosis, jaundice, and albinism

Skin variations

Epidermis function

Protection, First line of defense

• Physical & chemical

• Innate

Nonspecific

• Physical barrier

Langerhans cells

Help detect potential threats

Vitiligo

occurs when melanocytes are lost or destroyed in certain areas of the skin, causing patches with little or no pigment.

1. Type of melanin produced

2. How much the melanosomes are filled with melanin granules prior to transfer

3. Number and size of melanosomes produced

4. How long the melanosomes persist in the keratinocytes

5. Degree of transfer within the dermis

Factors affecting pigmentation

Melanocytes produce melanin from tyrosine in specialized organelles (melanosomes)

THEN

Melanosomes are transferred to keratinocytes upon stimulation

THEN

Melanosomes in keratinocytes contribute to skin’s pigmentation

UV Rays

Tactile (merkel) discs

• Associated with fine touch and pressure

• Adapt slowly

• Small receptive field

• Basal layer

FEEL WHAT SOMETHING IS LIKE

Meissner’s (tactile) corpuscles

• Within Papillary dermis (on the border)

• Light touch, pressure, and vibration

• Adapt quickly

FEEL SOMETHING THAT HAS MOVED ACROSS YOUR SKIN

Vitamin D production

• Cells of the epidermis convert 7-dehydrocholesterol to cholecalciferol (Vitamin D3)

• Eventually this is converted to calcitriol in the kidneys

• Calcitriol increases calcium absorption (small intestine) and bone mineralization

can impair calcium absorption and bone mineralization in children, leading to rickets. Risk increases when sunlight exposure, dietary vitamin D, or calcium intake is low.

Low vitamin D

Papillary and reticular layer

Dermis layer consists of

• Hair

• Glands

• Blood vessels

• Nerves

• Smooth muscle

Dermis structure

Maintain steady internal temp

Dermis functions

Blood vessels do

• Vasoconstriction/dilation

• Radiation & convection

Sweat glands

Evaporation

Lines of cleavage

The orientation of skin tension lines (Langer’s lines) affects how incisions heal and how scars form.

Stretch

Elastic fibers in skin

Stretch marks

Extent of stretch is limited. They are usually pink; white scar as they heal.

Hypodermis

• Collagen and elastic fibers, fibroblasts and adipocytes

• Connects skin to underlying tissue

• Energy reserve

• Larger blood vessels

• Protection

• Foreign substances

• UV radiation

• Cushion

• Sensory

• Identification

• Location

• Keratinized cells form slender filament

Hair functions

• Hair Bulb

• Root

• Shaft

Parts of hair

Hair follicle

integumentary structure that surrounds and produces the hair.

Hair papilla

Connective tissue, blood vessels, and nerves

Hair matrix

Produces new hair

surgeons move the living follicle, not just the hair shaft. The transplanted hair bulb/matrix cells can survive in the new location and produce a new hair shaft.

Why does hair transplant work?

Medulla

• Cells contain soft keratin

• Formed by cells closest to the hair matrix

Cortex

• Cells contain hard keratin

• Formed by cells near the edge of the hair matrix

Cuticle

• Cells contain hard keratin

• Outermost layer

Hair color

• Generated by melanocytes residing in hair papilla

• Color depends on the amount and type of melanin

• As we age, these melanocytes stop producing as much melanin

Pheomelanin color

Red

Eumelanin color

Brown or black

Vellus hair

fine, short, lightly pigmented “peach fuzz,

Terminal Hair

thicker, longer, darker, and more deeply rooted.

Anlagen

active growth phase, when matrix cells in the hair bulb produce the hair shaft

• The longer the phase, the longer the hair can grow.

Catagen

short transition phase when hair growth stops and the follicle begins to shrink.

Telogen

the resting phase, when the follicle is inactive and the old hair remains in place temporarily.

• Cuticle

• Nail plate

• Nail bed

• Nail matrix

Pairs of nail

Sebaceous glands

• Secretes sebum

• Helps protect the surface of the skin

• Prevents water loss and bacteria growth

• Play a role in thermoregulation

• Holocrine glands

Apocrine sweat glands

• Armpits and pubic regions

• Secrete into hair follicles

• Product secreted used by bacteria, contributing to odor

Merocrine/Eccrine Sweat glands

• More numerous

• Secrete directly onto skin surface

• Thermoregulation, secretion, and protection (odorless)

• Skin thickness

• Elastic fibers

• Melanin production

• UV exposure

Age related changes to integumentary system