重温棕色脂肪组织变白:生理机制和病理生理后果

The body's temperature, measured in degrees, is determined by the balance between heat production and dissipation to the surrounding environment. For instance, if exercising vigorously, the body will produce more heat, causing sweat and dissipating that heat. Despite extreme environmental conditions and physical exertion, the human temperature-control system maintains a constant core body temperature (the temperature of deep tissues, which are the tissues located beneath the skin and other...

The human body has a sophisticated thermoregulation system that employs negative feedback mechanisms to maintain an optimal core temperature. When the core temperature drops, peripheral and central thermoreceptors send signals to the hypothalamus, activating the heat-promoting center. This center triggers several responses aimed at increasing the core temperature. First, vasoconstriction reduces the flow of warm blood from internal organs to the skin so that the heat is not lost from the skin,...

The hypodermis (the subcutaneous layer or superficial fascia) is present directly below the dermis. It connects the skin to the underlying fascia (fibrous tissue) of the bones and muscles. It is not strictly a part of the skin, although the border between the hypodermis and dermis can be difficult to distinguish. The hypodermis consists of well-vascularized, loose, areolar connective tissue and adipose tissue, which functions as a mode of fat storage and provides insulation and cushioning for...

The first thing a clinician sees is the skin, so the examination of the skin should be part of any thorough physical examination. Most skin disorders are relatively benign, but a few, including melanomas, can be fatal if untreated. A couple of the more noticeable disorders, albinism and vitiligo, affect the appearance of the skin and its accessory organs.
Albinism
Albinism is a genetic disorder that affects (completely or partially) the coloring of skin, hair, and eyes. The defect is primarily...

The color of the skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Recall that melanin is produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The melanin is transferred to the keratinocytes via melanosomes.
Melanin occurs in two primary forms: eumelanin that provides black and brown pigment and pheomelanin that provides red color. Dark-skinned individuals produce more melanin than those with pale...

Understanding heat transfer mechanisms is essential for understanding how our bodies maintain balance in different environmental conditions. When the environment is thermoneutral, the body is in a state of balance, neither using nor releasing energy to maintain its core temperature. However, when the environment is not thermoneutral, the body employs four heat transfer mechanisms to maintain homeostasis: conduction, convection, evaporation, and radiation. These mechanisms facilitate heat...