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The integumentary system provides a variety of protections to the body beyond a physical barrier.



SKIN
The largest organ of the body







Skin is much more than a barrier against the external environment. In fact, it provides a variety of physical, chemical, and biological protections. The skin is indeed a complex multifunction organ







Provides a protective barrier against mechanical, thermal and physical injury and hazardous substances (stratified epidermis, keratinized cells, and collagen rich dermis)

Prevents loss of moisture (lipids disbursed throughout more superficial layers of the epidermis)


Reduces harmful effects of UV radiation (cellular action of melanocytes)


Acts as a sensory organ (touch, detects temperature—variety of nerve cells, presence of hair).


Helps regulate temperature (glandular production of sweat, vasomotor responses of dermal blood vessels)


An immune organ to detect infections etc.(presence of bone marrow derived immune cells)


Production of vitamin D (skin contains a chemical when exposed to ultraviolet energy converts to vitamin D)











The stratum basale is the deepest cellular layer of the epidermis. It is comprised of keratinocytes that act as stem cells supplying the tissue with its primary cells.


The keratinocytes in the basale are held tightly together by desmosomes.

Keratinocytes produce a durable protein called keratin.

As keratinocytes mature, keratin dominates the cell to the point that the cell becomes a non-living protein package.

Merkel cells exist at the epidermal-dermal junction.

Each cell is associated with with a nerve

(neuron).


A Merkel cell and associated neuron is known as a Merkel disc.


Merkel discs are touch receptors.

The melanocyte produces the protein pigment called melanin.

Melanin is a major protein responsible for skin color.

Ultraviolet energy stimulates melanin to produce melanin


Melanin is packaged by the Golgi apparatus into packets called melanosomes


Melanosomes leave the cells and are taken up by keratinocytes.

Melanosomes form a shield over the nucleus to protect the genetic material from UV damage.

Melanin is therefore responsible for skin tanning and tanning is protective.








Under the microscope, the keratinocytes n the stratum spinosum take on a spiny shape.
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The spinosum is the thickest of the epidermal layers.

Microtubules span the cytosol and attach to desmosomes reinforcing them.

Keratinaztion begins in the spinosum.

Dendritic or Langerhans cells are present in the spinosum.

Dendritic cells are bone marrow derived macrophages. They help mediate immune responses when microbes and infectious agents enter the skin.









The next superficial layer is called the stratum

granulosum


Comprised of keratinocytes now known as granular cells


Cells contain keratohyaline granules and lamellar granules.
The lamellar granules contain and release lipids that help waterproof the skin.

The Keratohyalin play a role in dehydrating the cell in preparation of its final role in the corneum.












When you carry a leather wallet or purse, you are carrying a portion of a processed and treated hide of an animal. The hide is the tough, collagen rich dermis.





PAPILLARY LAYER
20% of Dermis







RETICULAR LAYER
80% of Dermis









The glands, hair, and nails are considered accessory organs of the integumentary system. The sweat, sebaceous, and ceruminous glands are exocrine glands.

Glands are structures that intentionally synthesizes and then releases a substance. This release action is known as secretion (verb). And the substance is known as a secretion (noun).

There are two types of glands, exocrine and endocrine.

Endocrine glands secrete substances directly into the extra cellular space where it enters blood vessels and is carried throughout the body.

The glands of the integumentary system are exocrine glands.

Exocrine glands secrete substances into a duct that opens into a body cavity or onto the body surface.