Chapter 7: Integumentary System & Body Temperature

I. Functions of the Integumentary System

The integumentary system consists of the skin, its accessory structures (hair, nails, glands), and the subcutaneous tissue.

  • Mechanical & Chemical Barrier: It keeps harmful substances out and keeps water and electrolytes in. The skin’s

  • surface has an acid pH, which serves as a protective chemical barrier.

  • Protection: It shields internal organs from cuts, sunlight, chemicals, and germs.

  • Immune Response: Specialized dendritic (Langerhans) cells in the skin alert the immune system if the skin is broken.

  • Excretion: It gets rid of small amounts of water, salt, and waste (urea).

  • Vitamin D Synthesis: When exposed to sunlight, the skin creates Vitamin D, which the body needs to absorb calcium.

  • Sensory Role: It houses receptors for touch, pressure, pain, and temperature.

  • Thermoregulation: It plays a major role in keeping the body at the right temperature.

II. Layers of the Skin

1. Epidermis (Outer Layer)

This is the thin, surface layer made of stratified squamous epithelium. It is avascular, meaning it has no blood supply of its own and must get nutrients from the layer below.

  • Stratum Germinativum: The "growth" layer at the bottom. These cells constantly divide and push older cells toward the surface.

  • Stratum Corneum: The surface layer made of about 30 layers of dead, flattened, keratinized (hardened) cells.

    • Example: Dander vs. Dandruff. Dead cells that flake off are "dander." When these cells clump together with oil on the scalp, it is called "dandruff".

2. Dermis (Inner Layer)

Located under the epidermis, this is the largest portion of the skin and is made of dense fibrous connective tissue.

  • Contains collagen and elastin fibers which make the skin strong and stretchable.

  • Contains blood vessels, nerves, and sensory receptors.

  • Fingerprints: Formed by the wavy boundary where the dermis and epidermis meet.

3. Subcutaneous Layer (Hypodermis)

This layer lies under the skin and is not technically part of the skin.

  • Roles: It anchors the skin to underlying structures and acts as insulation to protect the body from temperature changes.

  • Composition: Primarily loose connective and adipose (fat) tissue.

III. Skin Color and Health Indicators

Skin color is determined by genetics, physiology, and sometimes disease.

Condition

Appearance

Cause

Melanin

Darker tint

Pigment secreted by melanocytes. Everyone has the same number of melanocytes, but some secrete more melanin24.

Cyanosis

Blue tint

Low oxygen in the blood25.

Jaundice

Yellow tint

Liver disease causes a buildup of bilirubin26.

Pallor

Pale/Ashen

Constriction of blood vessels (often due to fear or shock)27.

Flushing

Red/Pink

Dilation of blood vessels (often due to embarrassment or heat)28.

Albinism

White skin/hair

Melanocytes fail to secrete any melanin29.

IV. Accessory Structures

Hair

  • Structure: The shaft is the visible part above the skin; the root is buried in the dermis.

  • Arrector Pili: Small muscles attached to hair follicles. When they contract (due to cold or fear), the hair stands up, causing goosebumps.

  • Alopecia: The medical term for hair loss.

Nails

  • Made of very hard keratin.

  • Lunula: The white half-moon shape at the base of the nail representing nail growth.

  • Diagnostic Clue: Clubbing (fingertips enlarge and nails curve) is a sign of chronic lung or heart disease where the body isn't getting enough oxygen.

Glands

  1. Sebaceous Glands (Oil Glands): Secrete sebum, which lubricates the skin and inhibits bacteria.

    • Pimple: Occurs when a sebaceous gland becomes blocked and infected.

    • Vernix Caseosa: The "cream cheese" coating on newborns produced by these glands to protect them in the womb.

  2. Sudoriferous Glands (Sweat Glands):

    • Eccrine Glands: Found all over the body; critical for temperature regulation through evaporation.

    • Apocrine Glands: Found in axillary (armpit) and genital areas; respond to emotional stress and cause body odor when broken down by bacteria.

V. Body Temperature (Thermoregulation)

Normal body temperature is approximately $98.6 Fahrenheit (37 Celsius), though it fluctuates slightly throughout the day.

Methods of Heat Loss

  • Radiation: Heat moves from the warm body to cooler surrounding air.

  • Conduction: Heat moves from the body to a cooler object it is touching (e.g., sitting on a cold bench).

  • Convection: Air currents move across the skin, taking heat away (e.g., a fan).

  • Evaporation: Liquid (sweat) turns into gas on the skin, which cools the body.

Abnormal Temperatures

  • Hypothermia: Excessive decrease in body temperature (below 95 Fahrenheit)

  • Hyperthermia: Excessive increase in body temperature (Heat stroke/Sunstroke).

VI. Burns

Burns are classified by their depth:

  1. First-degree: Partial thickness; only the epidermis is involved (e.g., a mild sunburn).

  2. Second-degree: Partial thickness; involves epidermis and dermis.

  3. Third-degree: Full thickness; destroys the epidermis, dermis, and sometimes underlying tissue.

  4. The Rule of Nines: A method used to quickly estimate the percentage of the body surface area that has been burned.