Sebaceous Glands Ebook
The skin of an adult weighs aii average of 4 kg and covers an area of 2 nr. It has Ihree layers (Fig. 2.15). The outer avascular epithelium, the epidermis, is firmly attached to, and supported by, a tough tibroelastic dermis. The dermis contains blood vessels, nerves, sweat and sebaceous glands and hair follicles. The third layer, the hypodermis, is of loose connective tissue, often containing abundant fat. which underlies the dermis.
The cornified epidermis protects the skin against water loss and against invasion by disease-causing organisms. Invaginations of the epithelium into the underlying connective tissue dermis create the exocrine glands of the skin. These include hair follicles (which produce the hair), sweat glands, and sebaceous glands. The secretion of sweat glands cools the body by evaporation and produces odors that, at least in lower animals, serve as sexual at-tractants. Sebaceous glands secrete oily sebum into hair follicles, which transport the sebum to the surface of the skin. Sebum lubricates the cornified surface of the skin, helping to prevent it from drying and cracking.
Yeasts of the genus Malassezia (Pityrosporum) are a normal part of the skin flora, and they are most often found in sebum-rich areas of the skin such as trunk, back, face and scalp. However, Malassezia is also thought to be connected to several common dermatologic conditions like pityriasis versicolor, Malassezia folliculitis and sebor-rheic dermatitis (SD) its role in atopic dermatitis and psoriasis is less well defined (Gupta et al. 2004). SD is a superficial fungal disease presenting clinically as scaling and inflammation on the areas of the body rich in sebaceous glands with patches of red, flaking greasy skin. The pathogenesis might involve an abnormal or inflammatory immune response to these yeasts, the presence of uncommon Malassezia species or toxin production by the fungus (Gupta et al. 2004) antifungal treatment reduces the number of yeasts on the skin, leading to an improvement in seborrheic dermatitis. Malassezia made up 46 of the microbial flora in normal subjects but 83...
Most of these four layers, the stratum corneum, consists of impermeable cellular layers composed of flattened, densely packed, anucleate cells embedded in a waxy lamellar matrix of complex intercellular lipids. The latter are derived from the lipid-filled membrane-coating granules of the cells of the next layer, the stratum granulosum. In addition, the lipid mixture sebum is secreted by the sebaceous glands. Typical compositions of sebum and epidermal lipids are shown in Table 6.18. Table 6.18 The main lipid classes of sebum and the skin's epidermis Table 6.18 The main lipid classes of sebum and the skin's epidermis Sebum lipids
An inflammatory disease of the sebaceous glands and hair follicles usually associated with excess secretion of sebum acne vulgaris A plug of sebum, often containing bacteria, in a hair follicle a black- tules, and overactivity of sebaceous glands, mainly on the face 5. sebum 53. discharge of sebum _
The sebaceous glands release an oily fluid, sebum, that lubricates the hair and skin and prevents drying. Hair is widely distributed over the body. Each hair develops within a sheath or hair follicle and grows from its base within the deep layers of the skin. Both hair and nails function in protection. Each nail develops from a growing region at its proximal end. Hair and nails are composed of nonliving material consisting mainly of keratin.
The globe is protected by the eyelids and lubrication of the ocular surface. The upper and lower eyelids are comprised of skin, subcutaneous connective tissue, and muscle. In addition, the tarsal plates in each lid consist of dense connective tissue and cartilage. They contain the meibomian glands - modified holocrine sebaceous glands - that are oriented vertically in two parallel rows through the tarsus. Movement of the eyelids assists lubrication of the surface of the globe, as well as protection from inadvertent trauma 9 . The surface of the cornea is protected by the tear film. It is a trilaminar layer consisting of an anterior lipid layer, a middle aqueous phase, and a posterior mucin layer 10 . The anterior layer of the tear film contains polar and non-polar lipids secreted primarily by the meibomian (tarsal) glands. The sebaceous glands in the lid margin are in close relation to the eyelashes and also secret lipids (fig. 3). The middle aqueous layer is secreted by the main and...
Human Scalp with Hair Follicle Follicle root, with sheath embedded in pale adipose tissue, has sebaceous glands surrounding it near surface. (X10) Human Scalp with Hair Follicle Follicle root, with sheath embedded in pale adipose tissue, has sebaceous glands surrounding it near surface. (X10) Detail of Sebaceous Gland Nucleated germinative cells at base of gland mature and accumulate lipid. At duct, they degenerate and lyse to release their oily product, sebum. (X 100) Detail of Sebaceous Gland Nucleated germinative cells at base of gland mature and accumulate lipid. At duct, they degenerate and lyse to release their oily product, sebum. (X 100)
During the last 2 months, the fetus obtains well-rounded contours as the result of deposition of subcutaneous fat (Fig. 6.6). By the end of intrauterine life, the skin is covered by a whitish, fatty substance (vernix caseosa) composed of secretory products from sebaceous glands.
The growth and secretory activity of the sebaceous glands on the face, upper back, and chest are stimulated by androgens, primarily DHT, and inhibited by estrogens. Increased sensitivity of target cells to androgenic action, especially during puberty, is the cause of acne vulgaris in both males and females. Skin derived from the urogenital ridge (e.g., the prepuce, scrotum, clitoris, and labia majora) remains sensitive to androgens throughout life and contains an active 5a-reductase. Growth of the larynx and thickening of the vocal cords are also androgen-dependent. Eunuchs maintain the high-pitched voice typical of prepuber-tal boys because they were castrated prior to puberty.
A carbuncle is a coalescent mass of deeply infected follicles or sebaceous glands with multiple interconnecting sinus tracts and cutaneous openings that drain pus ineffectively. Carbuncles usually occur in the thick skin on the back of the neck and the upper back. The lesions steadily worsen, with increasing pain, erythema, swelling, purulent drainage, and lateral enlargement. These lesions range from 3 to 10 cm in diameter. Fever and other systemic symptoms and signs are common.
T, the primary androgen secreted by the testis, has a direct stimulatory effect on androgen-dependent activities in skeletal muscle, in the brain, and in testicular seminiferous tubules. However, DHT is the primary androgen present in the prostate gland (10). T is converted to DHT by 5a-reductase (Fig. 1). Two isozymes for 5a-reductase exist type I and type II. Type I 5a-reductase is present in the liver and in the skin (sebaceous glands), and in small amounts in the prostate. Type II 5a-reductase is present in the prostate, liver, chest skin, beard, and scalp (hair follicles). Within the prostate gland, 90 of androgens are in the form of DHT. In 1970, Siiteri et al. postulated that DHT secretion might be associated with the development of BPH (11). Although T and DHT both bind to the same androgen receptor, DHT binds with greater affinity and forms a more stable complex than T. Additionally, the DHT-receptor complex stimulates a greater increase in androgen-receptor concentration....
The skin is an effective barrier to microbes. It consists of an impenetrable dead layer (the stratum corneum) and the living epidermis. Below the epidermis is the dermis containing blood vessels and connective tissue. Interspersed in the dermis are hair follicles and sebaceous glands. The sebaceous glands also contribute to the innate skin immunity. These glands produce sebum, which lowers the skin pH to 3-5. The low pH prevents most bacteria from colonizing the skin. However, this pH range provides a suitable environment for fungal growth that often results in skin infections.
The insulating ability of blubber may explain why whales living in warm waters have much thinner blubber layers than those living in cold waters. In addition, a whale's soft rubbery skin lacks pores, sweat glands, and sebaceous glands. It is hairless, except for small patches on areas near the chin and atop the head. These hair patches support the theory that baleen whales evolved from animals having hair or fur.
Reports of such cases have been few (133). In addition to the epidermal elements present in epidermoid cysts, dermoid cysts have the additional features of hair follicles, sweat glands, and sebaceous glands. These lesions typically have a firm fibrous capsule that is often densely adherent to surrounding structures.
Hordeola are infections of the lid margin sebaceous glands and manifest in two clinical forms external (stye) and internal. These two forms are differentiated by the particular group of sebaceous glands infected. An external hordeolum (stye) is an infection of the glands of Zeis, which extend along the base of the eyelash hair follicle. It is by far the most common type of hordeolum, and Staphylococcus aureus is the predominant microbial pathogen.
Menarche (first menstrual flow) Axillary (underarm) hair Eccrine sweat glands and sebaceous glands acne (from blocked sebaceous glands) Growth of testes Pubic hair Body growth Growth of penis Growth of larynx (voice lowers) Facial and axillary (underarm) hair Eccrine sweat glands and sebaceous glands acne (from blocked sebaceous glands)
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