The Integumentary System Explained
- Thermoregulation - By regulating the amount of blood flow to the dermis and the evaporation of sweat, this system is able to regulate body temperature.
- Protection – The skin acts as a protective barrier to internal structures preventing pathogenic infections, dehydration, sunburns and abrupt changes in temperature.
- Excretion – Thanks to the vast amount of exocrine glands found in this system, the body can eliminate waste products
- Sensory Activation – Due to the presence of sensory organs, this system is able to perceive changes in the environment (cold, hot, pressure, etc)
- Nutrition – Thanks to the UV rays, the skin can produce vitamin D, also is able to storage fats, carbohydrates (glucose) and water.
The surface of the skin is composed of three layers:
EPIDERMIS – Outer most layer of the skin consisting of keratinized stratified squamous epithelium that provides strength and elasticity. This layer is completely avascular and is formed by four types of cells:
Type of Cell
Produce keratin, a protein that hardens and waterproofs the skin
Produce melanin, a substance that protect us from the UV rays and give the skin its color
Phagocytic macrophages that, during an immune response, will work with white blood cell to fight the pathogens
They form the Merkel discs which are mechanoreceptors sensitive to tissue displacement
- The stratum corneum - Outermost layer.
- The stratum lucidum – Found only in the palm of the hand and the sole of the foot.
- The stratum granulosum - Contribute to the keratin formation.
- The stratum spinosum - Form by eight to ten layers of cells connected by desmosomes which are moderately active in mitosis.
The stratum basale (stratum germinativum) - Single layer of columnar cells actively dividing by mitosis so that the new cells can migrate to the upper epidermal layers
Though a genetic factor, there are three pigment responsible for the color of the skin:
- Melanin - Responsible for the darker colors of the skin, it is produced in the melanocytes migrating later to the keratinocytes.
- Carotene - Most obvious in the palm of the hands and the sole of the feet, carotene is responsible for the yellow to orange colors of the skin.
- Hemoglobin - Most obvious on the cheek, hemoglobin is responsible for the pinkish color of the skin.
Dermal-Epidermal Junction – Composed of two layers, a thin lamina lucida and a thicker lamina densa, this undulating membrane glues the dermis to the epidermis. Main functions are:
- Epidermal-Dermal Adherence – Thanks to this junction, the normal process of keratinization occurs, allowing the cells to move upward but always leaving the deepest layer “glued” to the dermis.
- Support - Mechanical support is provided to the outer protective layers of the epidermis
- Barrier – This junctions acts as a barrier to the exchange nutrients and to the movement of large particles between the two layers
DERMIS - Located directly below the Epidermis it is also known as the True Skin. The Dermis is composed of different types of connective tissues that provide strength, elasticity and extensibility. Here we find many lymphatic and blood capillaries, nerve ending relaying sensory information (pressure, heat, cold, and tact) and glands.
- The papillary layer - Outermost layer composed of areolar connective tissue with projections named dermal papillae.
- The reticular layer – Making most of the dermis, it is a thick layer of dense irregular connective tissue.
SUBCUTANEOUS (hypodermis or superficial fascia) – It lies directly below the dermis and is composed of fibrous tissues with adipose deposits. It provides thermal insulation and acts as a protecting padding to the internal organs. During an intense effort (ex: exercising) some of the fat accumulated there can be converted into energy in order to sustain it for longer periods of time. it is composed of three basic cells:
Type of Cell
Produce collagen, glycoglycosaminoglycans, reticular and elastic fibers, glycoproteins found in the extracellular matrix, and cytokine TSLP
Specialized in fat storege
Rid the body of cellular debris and dying cells. Also plays a role in immune responses, muscle regeneration and wound healing.
Skin Accessory Organs
The accessory organs found in the integumentary system are a number of embedded structures that help the skin accomplish its functions. It consist of:
- Sebaceous (oil) Glands - They secrete an oily substance that inhibits bacterial growth and keeps the skin and hair looking healthy.
- Sudoriferous (sweat) Glands – Helping maintain body temperature, they secrete sweat, which consists of mainly water with various salts. There are four kinds:
- Merocrine Glands – Located throughout the skin, they secrete a watery solution through the pores to cool down the skin.
- Apocrine Glands – Located under the skin surface of the armpits and pubic regions, they secrete a solution in response to stress or sexual excitement that is thicker and more odorous than sweat itself.
- Ceruminous Glands – Located in the external auditory canal, they secrete pigmented earwax to prevent the entrance of foreign bodies into the body.
- Mammary Glands – Located in the women breasts, they produce milk that is secreted through the nipples.
- Hair – Filaments of keratinized epithelial cells emerging from the dermis. Its primary functions include heat insulation and UV rays protection. Its composed of:
- Hair Follicle – Sheath that surrounds the hair inside the skin.
- Hair Bulb – Base of the hair follicle.
- Matrix – Located within the bulb, here the cells actively divide to form new cells.
- Hair Root – Portion of hair that inserts into the skin deep into the dermis.
- Erector Pili – Muscle attached to the hair follicle that when contracted, in response to cold or fear, erects the hair thus producing “goose bumps”.
- Hair Shaft – Portion of the hair that is visible. Its composition consist of:
- Cuticle - Protective outer layer form by overlapping transparent keratin cells.
- Cortex - Provides moisture and color (melanin)
- Medulla - Center or core of the hair. It may be absent in some.
- Nails – Keratinized epithelial cells emerging from the skin which main function is to protect the ends of fingers and toes. Fingernails grow about a milimeter a week while a toenail grows about a milimeter every two weeks. Its composed of:
- Nail Plate – made of translucent keratin, this portion is known as the fingernail.
- Lunula – Area where the nail grows.
- Matrix – Located behind the lunula, this is the area where the cells actively divide to form new cells.
- Nail Bed – Skin located below the nail plate.
- Cuticle – Overlaping the nail plate at the base of the nail, this tissue fuses these structures together while providing a waterproof barrier