Additional images
Insertion of sebaceous glands into hair shaft
Cross-section of all skin layers
| Details | |
|---|---|
| Nerve | Sympathetic postganglionic nerve fibers |
| Identifiers | |
| TA98 | A16.0.00.024 |
| TA2 | 7051 |
| TH | H3.12.00.3.01041 |
| FMA | 67821 |
| Anatomical terms of muscle | |
The arrector pili muscles, also known as hair erector muscles, [1] are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end, [2] known colloquially as goose bumps (piloerection). [3]
Each arrector pili is composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit). [4] Each is innervated by the sympathetic division of the autonomic nervous system. [4] The muscle attaches to the follicular stem cell niche in the follicular bulge, [3] [4] [5] splitting at their deep end to encircle the follicle. [6]
The contraction of the muscle is involuntary. Stresses such as cold, fear etc. may stimulate the sympathetic nervous system, and thus cause muscle contraction. [4]
Contraction of arrector pili muscles have a principal function in the majority of mammals of providing thermal insulation. [4] Air becomes trapped between the erect hairs, helping the animal retain heat.
Erection of the porcupine's long, thick hairs causes the animal to become more intimidating, scaring predators.[ citation needed ]
Pressure exerted by the muscle may cause sebum to be forced along the hair follicle towards the surface, protecting the hair. [7]
Arrector pili muscles also stabilise the base of the hair follicle. [5] [6]
Skin conditions such as leprosy can damage arrector pili muscles, preventing their contraction. [8]
The term "arrector pili" comes from Latin. It translates to "hair erector". [1]
Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fine vellus hair. Most common interest in hair is focused on hair growth, hair types, and hair care, but hair is also an important biomaterial primarily composed of protein, notably alpha-keratin.
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between hormones, neuropeptides, and immune cells. This complex interaction induces the hair follicle to produce different types of hair as seen on different parts of the body. For example, terminal hairs grow on the scalp and lanugo hairs are seen covering the bodies of fetuses in the uterus and in some newborn babies. The process of hair growth occurs in distinct sequential stages: anagen is the active growth phase, catagen is the regression of the hair follicle phase, telogen is the resting stage, exogen is the active shedding of hair phase and kenogen is the phase between the empty hair follicle and the growth of new hair.
A sebaceous gland or oil gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number on the face and scalp, but also on all parts of the skin except the palms of the hands and soles of the feet. In the eyelids, meibomian glands, also called tarsal glands, are a type of sebaceous gland that secrete a special type of sebum into tears. Surrounding the female nipple, areolar glands are specialized sebaceous glands for lubricating the nipple. Fordyce spots are benign, visible, sebaceous glands found usually on the lips, gums and inner cheeks, and genitals.
A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, are sent to the central nervous system.
A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment.
Goose bumps, goosebumps or goose-pimples are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is tickled, cold or experiencing strong emotions such as fear, euphoria or sexual arousal.
Keratosis pilaris is a common, autosomal-dominant, genetic condition of the skin's hair follicles characterized by the appearance of possibly itchy, small, gooseflesh-like bumps, with varying degrees of reddening or inflammation. It most often appears on the outer sides of the upper arms, thighs, face, back, and buttocks; KP can also occur on the hands, and tops of legs, sides, or any body part except glabrous (hairless) skin. Often the lesions can appear on the face, which may be mistaken for acne or folliculitis.
The management of hair loss, includes prevention and treatment of alopecia, baldness, and hair thinning, and regrowth of hair.
A comedo is a clogged hair follicle (pore) in the skin. Keratin combines with oil to block the follicle. A comedo can be open (blackhead) or closed by skin (whitehead) and occur with or without acne. The word "comedo" comes from the Latin comedere, meaning "to eat up", and was historically used to describe parasitic worms; in modern medical terminology, it is used to suggest the worm-like appearance of the expressed material.
Protection from mechanical injury, chemical hazards, and bacterial invasion is provided by the skin because the epidermis is relatively thick and covered with keratin. Secretions from sebaceous glands and sweat glands also benefit this protective barrier. In the event of an injury that damages the skin's protective barrier, the body triggers a response called wound healing. After hemostasis, inflammation white blood cells, including phagocytic macrophages arrive at the injury site. Once the invading microorganisms have been brought under control, the skin proceeds to heal itself. The ability of the skin to heal even after considerable damage has occurred is due to the presence of stem cells in the dermis and cells in the stratum basale of the epidermis, all of which can generate new tissue.
An apocrine sweat gland is composed of a coiled secretory portion located at the junction of the dermis and subcutaneous fat, from which a straight portion inserts and secretes into the infundibular portion of the hair follicle. In humans, apocrine sweat glands are found only in certain locations of the body: the axillae (armpits), areola and nipples of the breast, ear canal, eyelids, wings of the nostril, perineal region, and some parts of the external genitalia. Modified apocrine glands include the ciliary glands in the eyelids; the ceruminous glands, which produce ear wax; and the mammary glands, which produce milk. The rest of the body is covered by eccrine sweat glands.
The lacrimal caruncle, or caruncula lacrimalis, is the small, pink, globular nodule at the inner corner of the eye. It consists of tissue types of neighbouring eye structures. It may suffer from lesions and allergic inflammation.
A trichilemmal cyst is a common cyst that forms from a hair follicle, most often on the scalp, and is smooth, mobile, and filled with keratin, a protein component found in hair, nails, skin, and horns. Trichilemmal cysts are clinically and histologically distinct from trichilemmal horns, hard tissue that is much rarer and not limited to the scalp. Rarely, these cysts may grow more extensively and form rapidly multiplying trichilemmal tumors, also called proliferating trichilemmal cysts, which are benign, but may grow aggressively at the cyst site. Very rarely, trichilemmal cysts can become cancerous.
Skin appendages are anatomical skin-associated structures that serve a particular function including sensation, contractility, lubrication and heat loss in animals. In humans, some of the more common skin appendages are hairs, arrector pilli, sebaceous glands, sweat glands, and nails (protection).
Madarosis is a condition that results in the loss of eyelashes, and sometimes eyebrows. The term "madarosis" is derived from the ancient Greek "madaros", meaning "bald". It originally was a disease of only losing eyelashes but it currently is the loss of both eyelashes and eyebrows. Eyebrows and eyelashes are both important in the prevention of bacteria and other foreign objects from entering the eye. A majority of patients with madarosis have leprosy, and it was reported that 76% of patients with varying types of leprosy had madarosis.
Alopecia mucinosa is a skin disorder that generally presents, but not exclusively, as erythematous plaques or flat patches without hair primarily on the scalp, neck and face. This can also be present on the body as a follicular mucinosis and may represent a systemic disease.
Hackles are the erectile plumage or hair in the neck area of some birds and mammals.
Valerie Horsley is an American cell and developmental biologist. She currently works as an associate professor at Yale University, where she has extensively researched the growth, restoration, and maintenance of skin cells. She is a currently a member of the Yale Cancer Center and Yale Stem Cell Center. She received a Presidential Early Career Award for Scientists and Engineers in 2012 and in 2013 she was the recipient of the Rosalind Franklin Young Investigator Award.
As in other mammals, thermoregulation in humans is an important aspect of homeostasis. In thermoregulation, body heat is generated mostly in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles. Humans have been able to adapt to a great diversity of climates, including hot humid and hot arid. High temperatures pose serious stress for the human body, placing it in great danger of injury or even death. For humans, adaptation to varying climatic conditions includes both physiological mechanisms resulting from evolution and behavioural mechanisms resulting from conscious cultural adaptations.
