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Comparative Anatomy, Physiology, and Biochemistry of Mammalian Skin
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Each hair follicle (Figure 13) is usually associated with a capillary plexus, a collar of nerve fibers, an arrector pili muscle, and a sebaceous gland. All hairs, except for the sexual hairs found in the beard and pubic regions, have arrector pili muscles. This smooth muscle tends to be a fan-shaped structure and is forked in hooved animals. The broad end of the arrector pili (Figure 13) muscle originates in the elastic network of the superficial papillary dermis and inserts on the outer root sheath of the follicle immediately below the sebaceous gland. Since hair sits at an obtuse angle to the skin surface and the arrector pili is situated at the lower portion of the hair follicle, one can seen how its contraction will cause the hair to erect into a position vertical to the skin surface. This muscle is supplied by postganglionic adrenergic sympathetic nerve fibers.222
Autonomic Nervous System
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Most organs are innervated by both the sympathetic and parasympathetic divisions (dual innervation), where the postganglionic fibres supply different tissues (e.g. smooth muscle and secretory cells) or the same tissue (e.g. sinoatrial node of the heart). Other organs may be supplied by only one division (i.e. single innervation). The lacrimal gland is innervated only by parasympathetic division. The sweat glands, adipose tissue, arrector pili muscles, kidney and most blood vessels are only innervated by sympathetic nerves.
Biology of the Hair and Skin
Published in Randy Schueller, Perry Romanowski, Conditioning Agents for Hair and Skin, 2020
The hair grows from follicles which resemble stocking-like invaginations of the epithelium enclosing an area of dermis known as the dermal paillae (Figure 2). The area of active cell division, the living area of the hair, is formed around the dermal papillae and is known as the bulb, where cell division occurs every 23 to 72 hr (34). The follicles slope into the dermis at varying angles, depending on body location and individual variation, and reside at varying levels between the lower dermis and the subcutaneous fat. In general, larger hairs come from more deeply placed follicles than do finer hairs (35). An arrector piii muscle attaches to the midsection of the follicle wall and ends at the junction between the epidermis and the dermis. In some body areas, a sebaceous gland (oil gland) and an apocrine gland (scent gland) attach above the muscle and open into the follicle. The point at which the arrector pili muscle attaches is known as the hair "bulge" and is considered to be the site where new matrix cells are formed and the hair growth cycle initiated. It takes approximately 3 weeks for a newly formed hair to appear at the scalp surface (36).
Adnexal squamous cell carcinoma: incidence of eyelid margin involvement
Published in Orbit, 2023
Alison H. Watson, Sabah Akbani, Natalie Homer, Marie Somogyi, Vikram Durairaj
The eyelash follicle differs from other hair follicles in many ways. Notably, they are terminal hair follicles unlike the surrounding vellus follicles that are able to produce fully pigmented and medullated hair shafts.9 Unlike vellus hairs, they do not have arrector pili muscle and they are independent of sex hormones. Therefore, they are the darkest in the human body and the last to turn gray.9 There are limited identified studies of the lash follicle cycle in comparison to vellus hairs.9,13 One assessment postulated that the turnover cycle of these follicles is much longer than the vellus hairs.13 The predilection of SCC to develop along the marginal versus non-marginal eyelid may be a consequence of differences in the duration of the lash follicle life cycle, as this can influence the likelihood of malignant transformation.6,7
Injectable and adhesive hydrogels for dealing with wounds
Published in Expert Opinion on Biological Therapy, 2022
Parisa Ghandforoushan, Nasim Golafshan, Firoz Babu Kadumudi, Miguel Castilho, Alireza Dolatshahi-Pirouz, Gorka Orive
Human skin consists of a multilayered structure often categorized as epidermis, dermis, and hypodermis [17]. Each layer has distinctive features that are vital to its physiology. The epidermis, the outermost layer, contacts the environment directly and controls the release of water from the body. This layer also plays a protective role against UV radiation and pathogens. On the other side the dermis, consists of thick composite connective tissue of structural proteins and proteoglycans, and is located below the epidermis layer and exposed to the blood flow. The overall mechanical strength of the skin structure contributes to the dermis layer and provides an effective route to absorb drugs systemically. Besides these functions, dermis layer host many higher-order structures such as sebaceous and sweat glands, hair follicles, and arrector pili muscles, which together help to maintain essential cellular nutrition, by oxygen exchange and nerve signaling and ensures thermoregulation [18,19]. Finally, the hypodermis is the deepest layer (thickness of 10–20 µm) of the skin that ensures isolation and shock-adsorption. It is rich in collagen and fat, act as a reservoir of energy and connects the skin with the underlying muscles and bones [20].
A rare case of congenital piloleiomyoma of the eyelid
Published in Orbit, 2021
Shahid Alam, Prabrisha Banerjee, Subramanian Krishnakumar
Cutaneous leiomyomas (CLs) are rare benign smooth muscle neoplasm of the skin. Rudolf Virchow first identified this entity in 1854 and he termed it as “tuberculum dolorosum”.1 Based on the site of origin, CL is classified as a) piloleiomyoma which is the tumor of the arrector pili muscle of the hair follicles, b) angioleiomyoma originating from the tunica media of the small to medium-sized vessels and c) dartoic or genital leiomyoma arising from the smooth muscle of genital skin.1,2 Piloleiomyoma is the most common variant of cutaneous leiomyoma.3 It usually affects the adult population. Extensor surface of limbs and trunk are the sites involved more commonly.1 Head and neck is an extremely rare site for piloleiomyoma.4 While acquired piloleiomyomas are the most common variant of leiomyomas; their congenital variant is extremely rare.5 Congenital piloleiomyoma arising from the eyelid has never been reported in the literature and we for the first time are reporting a congenital piloleiomyoma of the eyelid. The child’s parents gave informed consent for the publication of the photograph for research purpose and the case report adhered to the tenets of Declaration of Helsinki.