Biology 2404 A&P Basics

The Integumentary system is formed by the cutaneous membrane or skin, the subcutaneous region or hypodermis and the appendages or accessory structures such as hair and follicle sweat glands, sebaceous glands, and nails. As a system, the main function is to provide a protective covering for the body and provide secretions that aid in this function.

Additional functions are thermoregulation, somatic sensation, vitamin D production.

The skin or cutaneous membrane is formed by the epidermis and dermis. Together, they provide a protective barrier to prevent harmful substances from entering into the body.

The epidermis is a stratified squamous epithelium that is keratinized. There are several types of cells in the epidermis and the stratified layers are in five regions. The major cells of the epidermis are keratinocytes that secrete keratin, a water insoluble protein that fills the cells and replaces the normal organelles found in lower layers. Other cells include melanocytes that secrete a black-brown pigment called melanin, and Langerhans cells which are white blood cells that help provide defense.

The layers of the epidermis are named for their appearance. Starting at the bottom living layer and moving outward to the dead layers are:

Stratum Basale or Germinativum	single row of living cuboidal cells, regenerative	creates all other epidermal layers
Stratum Spinosum	several layers of keratinocytes producing RNA	Melanocytes are also found here
Stratum Granulosum	several layers of cells producing the protein keratin	Langerhans cells are found here
Stratum Lucidum	one-two layers of transparent dead cells	Present in thick skin of the palm and soles of feet
Stratum Corneum	5-20 layers of dead cells, filled with keratin	Cells are flat or squamous

Histo of Epidermis

Drawing of Epidermis

Epidermis Layers

DERMIS

The dermis of the skin is connective tissue and is divided into two regions: the papillary region and the reticular region.

Papillary dermis loose connective tissue that provides support for sensory nerve endings for pain, cold, heat, and light touch/pressure sensations. Provided the blood supply for Stratum Basale (Germinativum) of the Epidermis.
Reticular dermis dense irregular connective tissue that provides support for glands, hair and follicles, blood vessels, and sensory nerve endings for deep touch/ pressure and vibrations. Blood flow provides nutrients, heat regulation, and adds to the color of the skin

The subcutaneous region of the Integumentary system is also called the superficial fascia or hypodermis. It is primarily made of adipocytes (fat cells) that help connect the skin to the muscles below and also to provide cushioning, support, heat regulation, and energy. It also contains the larger blood vessels called arterioles and venules and nerve pathways for somatic (body) sensory information.

Drawing of Dermis and Hypodermis

Histology of Dermis

Histology of Hypodermis

Drug used to deaden skin for surgery

Electrocautery Unit used for surgery

Skin Staple gun used to close the skin after surgery

Accessory Organs of the Skin

All accessory organs of the skin come from the epidermal regions of the stratum basale and stratum spinosum. They are also known as appendages and are found in the dermis. All accessory appendages have specific functions.

Hair follicles and hair

Hair follicles create a sheath and protect the hair which grows from the base of the follicle known as the papilla. The region of the hair that grows from the papilla is called the bulb or root. New epidermal hair cells of the root produce hard keratin (verses the soft keratin of the epidermis) to create the shaft or body of the hair. Melanocytes provide color to the hair based on genetic factors that control the amount of pigment produced. The follicle and chemical cross-linking of keratin determines whether the hair will be straight, curly, or tightly curled.

Hair growth occurs in three phases: growth, resting, and loss. Duration of the growth cycle depends on the hair location. Scalp hair grows for about three years, rests for about 1-2 years and is then lost when new hair begins to grow. Hair growth is affected by hormones and diet. There are different types of hair such as eyelashes, eyebrows, facial hair, axillary hair, perineal hair, truncal hair, and even fur and whiskers for some mammals. Each type of hair and its location provide a unique function for the body.

Attached to the follicle is a smooth muscle called the arrector pili muscle and provides movement of the follicle and therefore the hair to raise or lower the shaft. This movement provides temperature regulation for most mammals and can even provide information about the emotional state of the individual.

Nail Follicles

At the ends of the fingers and toes there are nail follicles formed from stratum basale and stratum spinosum that produce nails by mitosis at the nail root. The new cells produce hard keratin for the nail body and then die. The function is to provide protection to the distal bones of the phalanges and to protect the ends of the digits from mechanical trauma.

The nail bed that supports the visible nail body is living tissue and contains blood supply and nerves. Nails grow approximately 1 mm per week unless damaged or diseased. The white lunula or half moon that is seen is due to air that is mixed in the keratin matrix and its size is determined by genetics. The cuticle or eponychium is stratum corneum that extends out over the proximal end of the nail body and marks the area where the nail follicle arises.

Regeneration of a lost nail can take several months to almost a year.

Glands

Exocrine glands are associated with the skin and produce secretions that are excreted through a duct system. The glandular appendages of the skin come from stratum basale and stratum spinosum. The cuboidal cells can produce a variety of secretions from watery clear solutions to opaque thick solutions.

Sweat Glands:

Eccrine or merocrine glands that produce a watery, thin, clear secretion that aids in cooling the body. Sweat glands are found throughout the body, but they are found in higher concentrations on the palms and soles of the feet and forehead.

Apocrine sweat glands produce a viscous, cloudy secretion that provides a unique body odor. Apocrine sweat glands are found on the scalp, perineal, and axillary regions of the body. Bacteria metabolize the chemicals in the sweat and their waste products can create unpleasant body odors.

Mammary glands are modified sweat glands and are under hormonal control to produce milk for a viable offspring.

Sebaceous Glands:

Sebaceous glands are found throughout the skin, except on the palms of the hand and soles of the feet. Their duct system can open into hair follicles or directly on the surface of the skin. The secretion is a thick, opaque product called sebum and it provides lubrication and protection to the stratum corneum. Sebaceous secretions are formed from entire cells dieing and secretions are controlled by hormones from the endocrine system.

Ceruminous glands are modified sebaceous glands found in the ear canal. Their secretion called ear wax or cerumen is thick and opaque and provides protection and lubrication to the outer ear canal.

Skin models

Skin wall mount

Skin poster

Hair and Hair follicle histology

Hair and hair follicle poster

Sweat Gland histology

Sebaceous gland poster

Sebaceous gland histology

Problems: Burns

Medical Terms

Derma- skin kerat/o- hard, cornea

Intra- beneath inter- between

-itis inflammation liga- bind together

melan/o- black pachy- thick

per- through sub- under

dactyl- finger, toe syn- together

trans- across trich- hair

cyano/o- blue onych/o- nail

follicul/o- follicle xer/o- dry

pil/o- hair hidr/o- sweat

pulp- flesh kerato/- hard, skin

pell- skin xanth- yellow

EXERCISES/ACTIVITIES

Models of skin

Wall mount of skin

Histology

Integumentary System Model

Magnifying glass for pores, nails

Experiment: pain, temperature, touch, pressure

Finger print analysis

Skin Lesion Research

Concept Map: Make a concept map of the integumentary system using the structures (gross and histological) anatomy, location, and physiological functions. Include this concept map in your LAR lab report (if selected) as a document insert or as an additional PDF scanned document of this map.

Case Study

Applications

Skin test for allergies

Skin patch

Injections

Sun screen

Skin diseases and conditions:

Impetigo

Eczema

Warts

Fever Blisters (cold sores)

Ringworm