# Human Physiology (The Integumentary System)



## medicRob (Feb 3, 2011)

Last week's physiology thread outlined the basic structures and functions of the cell, the smallest unit of life. This week, I will focus on the integumentary system, also known as your "Skin".

Your skin is the largest organ in your body, it has many functions, not the least of which is acting as the first line of defense against foreign invaders.. 

The skin consists of two reasons the *epidermis* and the *dermis.* 

*The Epidermis*







The epidermis consisting of epithelial cells is the outermost protective shield of the body. The cells populating the epidermis are, "Keratinocytes", "Melanocytes", "Merkel cells", and "Langerhans' cells" 

Keratinocytes: The primary cell type found in the epidermis, produces keratin.

Melanocytes: Cells which produce the pigment melanin that protects the DNA contained within the nucleus of a cell from harmful UV Radiation by acting as somewhat of an umbrella.  

Merkel Cells: Specialized receptor cells 

Langerhans' cells: participate in inflammatory response. 


The purpose of the Keratinocyte is to produce keratin, a fibrous protein that aids the epidermis in its protective properties. These cells are tightly connected to each other by structures known as *desmosomes*, the structural units responsible for adhesion between cells to form an overall tissue via specialized contact with other cells. 

*The Epidermal Strata*






The epidermis can be subdivided into 5 layers consisting of cells in various stages of life including the outermost layer which consists of dead cells.  (Listed in order from the deepest to the most superficial) 

The *Stratum Basale (aka Stratum Germinativum)* is the deepest of the 5 strata. This layer consists of fresh cells constantly undergoing mitosis. As new cells are created in this layer, earlier cells are pushed upward eventually ending up as dead cells on the *stratum corneum*, the outermost layer of the epidermis.

The *Stratum Spinosum* is several cell layers thick and consists of a web-like system of intermediate filaments. As you will note in the diagram above, the cells in this layer appear irregular "Spiny" in shape.. These actual spines depicted are only noted in prepared slides and are the result of tissue preparation causing the cells to shrink while their desmosomes hold tight.. Within this layer, one will note the presence of melanin granules and Langerhan's cells. 

[Was interrupted by work duties in the middle of this post so here are some vids:]

EDIT:
Posted by accident, it is unfinished... will finish later.


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