Skin
The skin is a very large organ system responsible for maintaining homeostasis for several activities. It maintains constant body temperature, protects the underlying tissues, helps prevent water loss, excretes waste, synthesizes certain chemicals, and is the location for many sensory receptors.
Structure: The skin is broken into two main layers: the outerepidermis and thedermis. The skin is connected to hypodermis (subcutaneous layer).
Epidermis
The epidermis is composed of stratified squamous epithelium. The actively reproducing cells lie at the base of the epidermis and are well nourished by blood vessels below in the dermal layer. Blood vessels do not extend into or through the epidermis. The actively replicating cell layer is referred to as stratum basale.
The cells are then pushed outward by new cells forming below. As the cells move further away from the stratum basale, they receive less nutrients and blood flow. These cells begin to dehydrate, dry out and keratinize. Keratinization is the process that creates the dryer, tougher protective cells on the outside of the skin.
The epidermal layers from the basement membrane extending outward are:
1. stratum basale
2. stratum spinosum
3. stratum granulosum
4. stratum corneum
The fifth layer, stratum lucidum, is found in the thicker palms and soles to provide additional protection.
The structure of the layered epidermis prevents against water loss and mechanical injury. But it also helps prevent outside chemicals or microorganisms from entering the body.
Melanocytes produce a pigment called melanin that protects against ultraviolet light. Melanocytes pass the melanin to nearby cells through a specialized process called cytocrine secretion. Variations in skin color results from a combination of genetic, environmental and physiological factors. Different amounts of melanin and the size of melanin granules can result from genetic differences between people. Exposure to UV or sunlight is a stimulus for increased melanin production. Blood circulation in the dermal blood vessels can also affect skin color in individuals.
Dermis
The second major layer of the skin is the dermis, which binds the epidermis to underlying tissues. Under the microscope it often appears in a wavelike fashion, which is the result of epidermal ridges and dermal papillae. As previously discussed, blood vessels from the dermal layer supply nutrients to the epidermis. These blood vessels are involved in temperature regulation and heat dispersion. The dermis is mostly made up of connective tissue with collagen and elastic fibers. It also contains nerve fibers, sensory fibers, hair follicles, sebaceous glands and sweat glands.
Hypodermis
This subcutaneous layer is composed of loose connective tissue and insulating adipose tissue. It helps bind the skin to the underlying organs and tissue. Unlike the epidermal – dermal boundary, there is not a distinct separation between the dermis and subcutaneous layer.
Skin’s Role in Regulation of Body Temperature
Heat can be lost to the environment through the skin by the process of radiation. Dilation of dermal blood vessels brings blood to the surface where heat from the blood is transferred to the skin layer. The skin then transfers this heat to the environment in conjunction with sweating. Our internal core produces a significant amount of heat through metabolically active systems and sells, especially the heart and skeletal muscle. Our body temperature is regulated by the hypothalamus, which is trying to maintain a stable temperature for metabolic reactions.
To maintain body heat the body constricts the dermal blood vessels to prevent heat loss. It shuts off the sweat glands to further reduce heat transfer to the environment. Shivering increases the amount of skeletal muscle contraction which releases heat as a byproduct of muscle contraction and energy utilization.
Superficial cuts are filled in by reproducing cells at the stratum basale. Deeper cuts require another process, utilizing clots, scabs and filling in the space with the help of fibroblasts. Blood vessels grow into the area to bring more nutrients and help the injured tissue repair and replace. With growth the scab will eventually fall off and reveal the newly formed tissue. Larger and deeper cuts may leave scars and the healing may also produce the formation of granulation.
Questions:
What would happen if you had a hole in your skin the size of a dime that extended all the way down to the dermis? _________________
What would happen if the hole extended into the subcutaneous? _________________________
Would it be an easy route for bacteria to enter the skin body? ____________________________
How would you try and protect yourself against bacteria entering that spot? ________________
What would happen if the injury was the size of your hand, would it be more problematic for your body? Please explain why? ________
What layer is the actively growing mitotic layer? _____________________________________
What happens as cells are pushed further from that layer? ______________________________
What is the process called of the dead cells hardening? _________________________________
Why are dried and harder cells more protective? ______________________________________
What would happen if the cells were not dry and hard, would they be as protective? __________
What layer is more prevalent in the soles of your feet and palms of your hand? ______________
What cell affects the color of your skin? _____________________________________________
Why does it produce the pigment? _________________________________________________
What is the stimulus for the cell to produce pigment? _________________________________
Why is the pigment protective? __________________________________________________
What would happen if you did not produce any pigment? _______________________________
What is this condition called? _____________________________________________________
What is the process of pigment creation and distribution called? _________________________
Please describe how it works? ____________________________________________________
What two things account for most of the pigment differences in people? ___________________
Why can very older people have a different color to their skin? ___________________________
What layer provides the nutrients to the epidermis? ____________________________________
How is the dermis involved in temperature regulation? _________________________________
What role does the dermis play to increase body temperature? ____________________________
What role does the dermis play to decrease body temperature? ___________________________
What important structures are in the dermis? _________________________________________
Is there a clear boundary line between the dermis and epidermis? _________________________
Is there a clear boundary line between the dermis and subcutaneous layer? _________________