< Skin >
Skin is the only organ in the integumentary system.
The skin has two layers: epidermis and dermis. The epidermis is a stratified squamous epithelium to bear mechanical stress (Fig. 16-17) (Fig. 16-19) (Fig. 16-21), while the dermis is a dense irregular connective tissue (Fig. 16-26).
Due to the dead epidermis cells (keratin), the epithelium is specifically called “keratinized stratified squamous epithelium.”
A pigment, melanin is generated by exposure to ultraviolet radiation, causing skin tanning. The generates melanin protects skin from ultraviolet damage, reducing risk of skin cancer.
Another pigment, carotene exists in the epidermis and dermis. Capillary resides only in the dermis because blood vessel is not in the epithelium by nature. The skin color is decided by melanin (brown), carotene (yellow), and blood (red). The main determining factor between races and ethnic groups is the melanin.
Literally, the subcutaneous tissue underneath the skin does not belong to the skin; however, the subcutaneous tissue is usually mentioned together with the skin.
The subcutaneous tissue is a loose connective tissue containing few fibers (Fig. 16-25) and lots of fat. Fat acts as energy reserve, padding for shock absorption, and insulation for thermoregulation. Simultaneously, too much fat (obesity) increases possibility of the heart disease, diabetes, and so on.
In the subcutaneous tissue of the head and neck, the facial muscles reside (Fig. 3-6). In case of the scalp covering the calvaria (Fig. 13-43), there is an intermediate aponeurosis between the two facial muscles: frontalis (Fig. 3-9) and occipitalis. This aponeurosis divides the subcutaneous tissue into the connective tissue and loose connective tissue (Fig. 15-8) (Fig. 16-25).
Fig. 15-8. Scalp, calvaria.
Consequently, five layers of SCALP are Skin, Connective tissue, Aponeurosis, Loose connective tissue, and Periosteum (Fig. 1-4) of calvaria. However, it is only by coincidence that these first letters comprise the word SCALP.
Loose connective tissue in the scalp enables the skin, connective tissue, and aponeurosis to slide above the periosteum (Fig. 15-8).
Skin of sole and palm is thick, which makes it possible to protect muscle, nerves, and blood vessels inside. This is reasonable since remote ancestors of human beings crawled. In case of the sole, the longitudinal and transverse arches of foot also contribute to the protection (Fig. 1-52).
The fingerprints are the skin ridges to enhance friction. The fingerprints are unique, difficult to alter, and durable over the life of an individual.
The sole crease is also present, but it is not prominent like the palm crease because toes are not as free as fingers.
Sweat gland secretes sweat to cool the body.
Hair is one of the defining characteristics of mammals.
The eyebrow is also important to human communication and facial expression.
Hair is a protein filament that grows from the hair follicle.
Hair follicle growth occurs in cycles. At the end of a cycle, a hair falls out and a new hair grows in the follicle, beginning another cycle. A disruption of the cycle causes abnormal loss of hairs.
Another structure near the hair follicle is the sebaceous gland to produce oil (sebum) which lubricates the hair.
Fig. 15-18. Cutaneous nerve and vein.
The subcutaneous tissue holds larger cutaneous nerve and cutaneous vein (Fig. 10-69) than those found in the dermis. The main component of cutaneous nerve is somatic sensory nerve attached to the receptor in the skin and subcutaneous tissue (Fig. 13-54). The somatic sensory nerve accounts for the dermatome (Fig. 13-98).
< Breast >
In mammals, the skin and subcutaneous tissue are modified to form the female breast.
Fig. 15-20. Location of breast.
Level of the breast is R2–R6; level of the nipple that is center of the breast is R4.
Fig. 15-21. Breast (sagittal plane).
R2–R6 are an origin of the pectoralis major (Fig. 3-46). As a result, the breast is placed on the pectoralis major. In the breast, the subcutaneous tissue and less than 20 mammary glands are contained.
The size of breast is dependent on the subcutaneous tissue (Fig. 15-5) that supports the mammary glands.
Each mammary gland produces milk that flows through the corresponding lactiferous duct. The milk is stored in lactiferous sinus and then secreted (Fig. 15-21).
Oil produced from the areolar gland makes the skin soft.