Integument Basics Lab

The Integumentary System

HASPI Medical Anatomy & Physiology 07a - Lab Activity

Background

The Integumentary System

The integumentary system is made up of the skin, hair, nails, sweat glands, and sebaceous glands.  The skin is the largest organ in the body.  It makes up 12-15% of body weight and has an entire surface area between 1-2 meters.  Our skin is our first barrier against infectious disease and prevents fluid loss from our organs, which allows our body to maintain homeostasis.  The skin is such an important organ that even moderate burns on more than 30% of the skin can be life-threatening due to fluid loss and infection. 

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The primary functions of the integumentary system include:

• Maintain internal temperature (sweating & shivering)
• Excrete excess fluids and waste
• Receive of pressure, pain, heat, and cold
• Produce and secrete melatonin & vitamin D
• Protect the body from infection
• Maintain fluid balance

The Layers of the Skin

The skin is separated into three main layers called the epidermis, dermis, and hypodermis.

The Epidermis

The epidermis is the outermost layer of the skin.  There are four types of cells that make up the epidermis:  melanocytes that produce melanin (influences skin color), keratinocytes that produce keratin, Merkel’s cells that function in touch, and Langerhans’ cells that function in immunity.  There are a few layers, called strata, that make up the epidermis.  The epidermis is avascular and all nutrients for the living cells of the epidermis diffuse from the basement membrane of the dermis below it. http://media.mercola.com/assets/images/healthy-skin/skin-cross-section.png

From the bottom layer to the outermost layer the strata include:

• Stratum basale – a layer of single cells that lays on the basement membrane of the dermis. These cells continuously divide and push up towards the surface of the skin.
• Stratum spinosum – These cells are “spiny” as the name denotes. They have been pushed out from the stratum basale and the spines interlock together to form a support layer.
• Stratum granulosum – The cells of this layer are still living, but none of the nutrients reach them. These cells begin producing keratin and the cells begin to die.  Eventually, the keratin protein produced will make up the majority of the dead cells in the next two layers.
• Stratum lucidum – This layer of dead keratinized cells is only found in areas where skin is thick, such as the soles of the feet, and is not found in thin skin areas, such as the forearm.
• Stratum corneum – This is the outer layer that we see and is made up of layers of dead keratinized cells. This layer is tightly bound together, and the keratin protects the underlying cells from fluid loss while keeping the skin elastic.  In a process called desquamation, cells of the stratum corneum are sloughed off.  Cells from the epidermis are completely shed every 35-45 days, so essentially you have completely new skin every month and a half!

The Dermis

The dermis is the layer below the epidermis.  The dermis is primarily made up of connective tissue layers and proteins including collagen, elastin, and reticular fibers.  The arrangement of these fibers allow for the dermis to be extremely elastic and flexible.  It also allows for blood vessels, glands, hair follicles, and nerves to be embedded in the dermis.  The two main glands embedded in the skin include the sweat and sebaceous glands.  The sweat glands assist the body in temperature control.  The sebaceous glands produce oils that keep the outer layer of skin and hair moisturized.  Hair and nail growth begin in the dermis.  Highly keratinized epithelial cells are arranged to make up hair and nails.    

The Hypodermis

The hypodermis is the bottommost layer of skin, located under the dermis.  This layer is primarily made up of adipose tissue and functions in insulation and protection.  The base of blood vessels, nerves, and some hair follicles also extend into the hypodermis.

Skin Disorders

There are more than 2,000 diseases and disorders that can affect the integumentary system.  The following table summarizes a few common skin disorders.  The prevalence is within the United States only for the year 2004.

Diagnostic Tests for Skin Disorders

The branch of medicine that focuses specifically on diseases of the integumentary system is called dermatology.  A dermatologist is a board certified medical doctor with additional training in skin, hair, and nail disorders.  There are many types of tests available to diagnose specific skin disorders.  Three of the most common tests that are performed when a skin disorder is suspected include:

• Skin Biopsy – When abnormal growths appear on the skin that may be indicative  of cancer, a skin biopsy may be performed.  The suspect area of skin is removed and a pathology lab will prepare and examine the tissue microscopically to determine whether the skin may be cancerous.

• Patch Test – These are used to detect whether an allergy may be causing the skin disorder.  A variety of allergens such as pollen, animal dander, milk proteins, etc. can be applied to the skin directly, or through subcutaneous injections.  The skin is observed for a period of time for any redness, swelling, or itching that would indicate an allergic reaction to that allergen.  The image to the right shows a common patch test.

http://fromyourdoctor.com/ext/skin_allergy_test.jpg

• Skin Culture – When a bacterial, fungal, or viral infection is suspected of causing a skin disorder, a skin culture can be taken.  The culture may include samples of tissue or fluids present in the affected portion of the skin.  The sample is then grown on different types of media in an attempt to identify the specific microorganism that may be causing the skin infection.

Levine, N.  2012.  Diagnosing Skin Problems, www.webmd.com.