Anatomy & Physiology I and II

Anatomy & Physiology Study Guide Several diseases can produce secondary effects on skin color and pigmentation: • In jaundice, a yellowish pigment builds up in body fluids. This occurs because the liver is unable to properly excrete bile. The skin andwhites of the eyes turn yellow in advanced stages. • Some tumors affecting the pituitary gland cause the secretion of large amounts of melanocyte- stimulating hormone (MSH). This hormone causes a darkening of the skin, similar to a deep bronze tan. • In Addison disease, the pituitary secretes adrenocorticotropic hormone (ACTH) in large quantities. ACTH is structurally like MSH. Thus, its effect on skin color mirrors MSH. • In vitiligo, individuals lose their melanocytes. About one percent of the population develops this disease, and its incidence increases among individuals with certain endocrine disorders. It is suspected that vitiligo develops when antibodies attack normal melanocytes due to a malfunctioning immune system. The primary problem with vitiligo is cosmetic, especially for individuals with darker pigmentation. 6.2 Accessory Structures Sebaceous (Oil) Glands Sebaceous glands, or oil glands, are holocrine glands that discharge an oily lipid secretion into hair follicles. Sebaceous glands that communicate with a single follicle share a duct and are classified as simple branched alveolar glands. The lipids released from gland cells enter the lumen (open passageway) of the gland. The arrector pili muscles erect the hair then contract, squeezing the sebaceous gland and forcing the lipids into the hair follicle and onto the surface of the skin. The secreted lipid product, called sebum, is a mixture of triacylglycerides, cholesterol, proteins, and electrolytes. Sebaceous follicles are large sebaceous glands that are not associated with hair follicles; their ducts discharge sebum directly onto the epidermis. Sebaceous follicles are located on the face, back, chest, nipples, and external genitalia. Sweat Glands The skin contains two types of sweat glands, or sudoriferous glands : apocrine sweat glands and merocrine sweat glands. • Apocrine sweat glands secrete their products into hair follicles in the armpits, around the nipples, and in the pubic region. A sticky, cloudy, and potentially odorous secretion is produced in these coiled tubular glands. Puberty stimulates the maturation and secretion of these apocrine sweat glands. The sweat produced is a nutrient source for bacteria, which intensifies its odor. • Merocrine sweat glands are also known as eccrine sweat glands. These are coiled, tubular glands that discharge their secretions directly onto the surface of the skin. Eccrine sweat glands are far more numerous and widely distributed than apocrine sweat glands. The adult integument contains 2–5 million merocrine sweat glands, which are smaller than apocrine sweat glands and do not extend as deeply into the dermis. The palms and soles have the ©2018 Achieve Test Prep Page 66 of 367