The ceruminous glands of the ear are apocrine sweat glands.

B. Meissner corpuscles are encapsulated nerve endings present in dermal papillae, which are part of the papillary layer of the dermis. These corpuscles function as receptors for fine touch (see Chapter 14 III А).

The lunula is the half moon shaped white area on a nail. The anatomical term for the cuticle is the eponychium. The matrix is the region of the nails where there are dividing cells and nail growth. The nail plate rests on the nail bed. The nail root is the proximal portion of the nail that is underneath skin.

Macrophages are mononuclear phagocytes. Many tissues have resident (fixed) macrophages. Fixed macrophages are given a unique name, depending on the tissue that they are located in. Kupffer cells are the hepatic macrophages. Histiocytes are macrophages seen in connective tissue. Dust cells are alveolar macrophage found in the respiratory tract. Langerhans cells are macrophages seen in the skin. Microglia are the central nervous system macrophages.

A. Melanocytes are present in the stratum basale of the epidermis. They synthesize melanin pigment and transfer it to keratinocytes to protect against damage caused by UV radiation. Melanocytes sometimes give rise to a form of skin cancer called malignant melanoma. They derive from neural crest and migrate into the epidermis early during embryonic development (see Chapter 14 II C).

The skin is composed of two layers: the epidermis and the dermis. Underneath these layers lies the hypodermis. The epidermis is stratified squamous epithelium. The dermis is composed of a papillary layer and a reticular layer. The reticular layer of the dermis is made up of dense irregular connective tissue. The hypodermis is a layer of loose connective tissue.

Langerhans cells, keratinocytes, melanocytes, and Merkel cells are all found in the epidermis. The Langerhans cell is a phagocyte. The keratinocyte is the most abundant cell in the epidermis. The melanocyte produces melanin, which is responsible for skin pigmentation. The Merkel cell is a mechanoreceptor. Fibroblasts are found in the dermis. Fibroblasts produces collagen.

The epidermis is divided into five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
The stratum basale contains the dividing cells. This layer is also called the stratum germinativum. The stratum spinosum consists of a layer several cells deep. The cells have pointy or spiny processes on them. The cells in the stratum granulosum contain keratohyaline granules. The stratum lucidum is present only in thick skin. The stratum corneum is the outermost layer. The cells in this layer are essentially bags of keratin. They contain no nuclei or organelles.

B. Sebaceous glands produce sebum, an oily material, and release it into the upper shaft of the hair follicle by a mechanism called holocrine secretion (which means the product and cellular debris are both released from the gland) (see Chapter 14 IV C).

The lunula is the half moon shaped white area on a nail. The anatomical term for the cuticle is the eponychium. The matrix is the region of the nails where there are dividing cells and nail growth. The nail plate rests on the nail bed. The nail root is the proximal portion of the nail that is underneath skin.

D. In contrast to thick skin, which lacks hair follicles, thin skin contains many of them (see Chapter 14 II D).

3. D. Langerhans cells in the epidermis function as antigen-presenting cells by trapping antigens that penetrate the epidermis and transporting them to regional lymph nodes, where they are presented to T lymphocytes. In this way, these cells assist in the immune defense of the body. They originate in the bone marrow and do not arise from epithelium (see Chapter 14 II C

Hair is present over most of the body. It is not found on the palms of the hand, soles of the feet, urogenital openings, and lips.

D. Observations with an electron microscope show that intercellular bridges are associated with desmosomes (maculae adherentes), linking the processes of adjacent cells in the stratum spinosum. Desmosomes also link cells within the other epidermal layers, but these cells do not form processes characteristic of bridges. The keratinocytes of the stratum basale also contain hemidesmosomes, which attach the cells to the underlying basal lamina (see Chapter 14 II B).

Thick skin is found on the palms of the hand and the sole of the feet. Thin skin is found everywhere else.

The skin is composed of two layers: the epidermis and the dermis. Underneath these layers lies the hypodermis. The epidermis is stratified squamous epithelium. The dermis is composed of a papillary layer and a reticular layer. The reticular layer of the dermis is made up of dense irregular connective tissue. The hypodermis is a layer of loose connective tissue.

C. Eccrine sweat glands are simple, coiled tubular glands that have a duct lined by a stratified cuboidal epithelium. They are found in both thick and thin skin and are classified as merocrine glands, meaning they release only their secretory product, which does not include cells or portions of cells (see Chapter 14 IV A).

The skin is composed of two layers: the epidermis and the dermis. Underneath these layers lies the hypodermis. The epidermis is stratified squamous epithelium. The dermis is composed of a papillary layer and a reticular layer. The reticular layer of the dermis is made up of dense irregular connective tissue. The hypodermis is a layer of loose connective tissue.

D.The stratum granulosum contains a number of dense keratohyalin granules, but not melanosomes. It lies just deep to the stratum lucidum and is a relatively thin layer in the epidermis of thick skin. Only rarely would a cell undergo mitosis in this layer of the skin (see Chapter 14 II B).

The epidermis is divided into five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. The stratum basale contains the dividing cells. This layer is also called the stratum germinativum. The stratum spinosum consists of a layer several cells deep. The cells have pointy or spiny processes on them. The cells in the stratum granulosum contain keratohyaline granules. The stratum lucidum is present only in thick skin. The stratum corneum is the outermost layer. The cells in this layer are essentially bags of keratin. They contain no nuclei or organelles.

There are several different sensory receptors in the skin. The most abundant sensory receptor are the free nerve endings. Free nerve endings respond to pain and temperature. Ruffini's corpuscles respond to continuous pressure. Pacinian corpuscles respond to vibration and rapidly changing pressure. Krause's end bulbs are a receptor for fine touch which are located in mucous membranes and the tongue. Meissner's corpuscles are also a receptor for fine touch but they are located in the dermis.

B. Hair follicles are present only in thin skin. They are associated with sebaceous glands and arrector pili smooth muscle bundles (see Chapter 14 V).

Langerhans cells, keratinocytes, melanocytes, and Merkel cells are all found in the epidermis. The Langerhans cell is a phagocyte. The keratinocyte is the most abundant cell in the epidermis. The melanocyte produces melanin, which is responsible for skin pigmentation. The Merkel cell is a mechanoreceptor. Fibroblasts are found in the dermis. Fibroblasts produces collagen.

E. The nail is one appendage of the skin. Other skin appendages are hair follicles, sweat glands, and sebaceous glands (see Chapter 14 VI).