Integumentary System

Hair comes from hair follicles located in the dermis of the skin. Keratin is the main component of hair strands as they extend from a bulb in the follicle. Adding insulation as well as UV ray protection are just two of the main components of hair function. Other functions include:

• Aesthetic

• Sensory functions

• Regulating temperature

• Protection from dust (nose hairs), sweat (eyelashes), and UV radiation (head hair)

Hair grows in phases. Starting at the anagen phase hair follicles divide and hair extends. About 90% of your scalp is in the anagen phase. Hair grows around 1 cm a month. The next phase is the catagen phase which lasts around 2-3 weeks. Hair growth stops at this phase because the hair follicle shrinks. Finally, in the telogen phase (3-4 months) hair begins to rest and eventually falls out. It is normal to shed around 50-100 hairs per day. 

Sweat glands produce and secrete sweat to regulate body temperature and excrete waste. 

The types of sweat glands are: 

Eccrine sweat glands: 

• Found all over the body

• In palms, forehead, and underarms

• Sweat produced primarily contains salt, water, and electrolytes

Apocrine sweat glands: 

• Found in hair follicles

• Armpits, groin, nipples

• Stimulated during stress as well

• When in contact with bacteria they produce an odor

Sebaceous glands: 

Secrete sebum, an oily substance that lubricates and protects the skin and hair. This maintains hydration and protects the skin from environmental damage. These can be found in everyone except the palms and soles of our hands and feet. They typically secrete the sebum through hair follicles.

Nails just like hair are composed of keratin. Their functions include protecting sensitive fingertips, aid in leverage and precision, and aesthetics. 

Nails are composed of: 

• Nail plate (hard, visible portion of the nail)

• Nail bed (skin beneath the nail plate)

• Cuticle (thin layer of skin where nail meets skin)

• Lanula (White crescent shape of nail at the base)

• Nail matrix (below cuticle and produces new nail cells)

Sensory receptors can be found in skin and other tissue to send signals to the brain. Allows us to perceive touch, pain, temperature, and more. 

The main types of sensory receptors: 

Mechanoreceptors: 

Respond to touch, pressure, and vibrations

Thermoreceptors:

Two forms cold and hot to respond to changes in temperature

Photoreceptors:

Located in eye to respond to light and allow vision

Nociceptors: 

Respond to pain such as tissue damage, extreme temperature, and pressure

The skin is composed of multiple layers: 

Epidermis is the outermost layer composed of various cells such as keratinocytes, melanocytes, and Langerhans cells. These protect the body from pathogens as well as water loss. In addition, they produce melanin to give the skin color and protect the body from UV radiation. 

The dermis is found underneath the epidermis. The collagens and elastin fibers provide strength and elasticity. Blood vessels can also be found in the dermis to supply nutrients to the skin. Hair follicles, glands, and nerve endings extend into the dermis.

The hypodermis is the innermost layer. It stores energy through fat and connective tissue. In addition, it absorbs shock and insulates the body.