The Integumentary (Dermatologic) System and Its Disorders
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss in Understanding Medical Terms, 2020
The epidermis is composed of up to five layers called strata. There are no blood vessels in these epithelial tissues, and the epidermis contains the melanocytes that produce the pigment melanin and dead cells containing the fibrous protein keratin. Skin pigmentation results from the presence of melanin (mela = black), the yellow pigment carotene (the yellow pigment in carrots), and the color of blood reflected through the epidermis. The main function of melanin is to screen out excessive ultraviolet radiation. The thickness and number of these layers of the epidermis varies throughout the body.
Cellular and Molecular Basis of Human Biology
Lawrence S. Chan, William C. Tang in Engineering-Medicine, 2019
Many cells in the human body are stationary in nature, that means that they stay in certain body location all their lives. Major stationary cells include the followings: Epithelial cells (of the skin, mucous membranes, hair follicles, cornea, retina, and lining of esophagus, intestines, and bladders).Fibroblasts (cells that produce many extracellular matrices like collagens).Melanocytes (pigment-producing cells of skin, mucous membrane, retina, and iris).Endothelial cells (of the lining of blood or lymphatic vessels).Neurons (of the nerve and brain).Muscle cells (cells that constitute the muscle mass).Bone-building cells (osteoblasts).Bone-breakdown cells (osteoclasts), and many more.
The Injured Cell
Jeremy R. Jass in Understanding Pathology, 2020
Melanin is the dark brown or black pigment produced by the melanocytes of the skin and passed into adjacent epithelial cells. Melanin absorbs ultraviolet light and therefore protects the skin from damage. The amount of melanin produced by organelles called melanosomes is responsible for skin colour. Inflammatory skin lesions resulting in apoptosis are marked by the presence of melanophages (macrophages that have engulfed apoptotic bodies containing melanin). Regression of malignant melanoma is also associated with the presence of melanophages. ‘Melanosis coli’ in which the colonic musosal lining accumulates brown pigment is a misnomer. The pigment is related to lipfuscin and the condition results from chronic injury to the epithelium of the large bowel caused by purgative abuse.
Nanocrystal: a novel approach to overcome skin barriers for improved topical drug delivery
Published in Expert Opinion on Drug Delivery, 2018
Viral Patel, Om Prakash Sharma, Tejal Mehta
Apart from keratinocytes, melanocytes, Langerhans, and Merkel cells are also present in the epidermis. Melanocytes are the cells that have a potential to secrete a pigment known as melanin. They originate from the neural crest and are dopa-positive cells. Melanin is stored in the special cell organelle known as melanosome and is transported by structures called dendrites to keratinocytes [36]. Similar to the melanocytes, few cells are also present which lack pigment secretion and are dopa negative, known as the Langerhans cells. They were first identified, by a scientist named Langerhans, by staining the human epidermis with gold chloride [37]. This epidermal Langerhans cells originate in the bone marrow and migrate toward the skin epidermis via blood vessel walls of the dermis [38]. In epidermis, the Langerhans cells perform the function of antigen-presenting cells. They uptake the antigens from the skin and migrate toward the regional lymph nodes and activate the T cells, which help in fighting the skin infections. Merkel cells are positioned on the basal epidermal layer in touch-sensitive areas; thus, they are also called as touch cells or Tastzellen [39,39].
An overview of nanosomes delivery mechanisms: trafficking, orders, barriers and cellular effects
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Gamaleldin I. Harisa, Mohamed M. Badran, Fars K. Alanazi, Sabry M. Attia
Specific checkpoints are present in particular organs, e.g. the mucociliary escalator is present in the upper airways of respiratory system. It is contains fluids composed of phospholipids and proteins that caused nanosomes wetting and facilitate their movement towards the epithelium of bronchi [4]. The bronchial epithelial cells cilia move particles into the gastrointestinal tract (GIT) to be eliminated into the faeces. The mucociliary escalator is a predominant barrier for pulmonary trafficking of nanosomes [4]. Meanwhile, the main barriers in the GIT are the gastric and intestinal environment, mucus barrier, tight junctions, epithelial cells and subepithelial tissue [30]. Dermal barriers include keratinocytes and tight junctions that impermeable to most drug cargoes. Furthermore, melanocytes provide melanin which absorbs ultraviolet radiation and protects DNA from damage. Also, Langerhans cells, macrophages and dermal dendritic cells act as checkpoints for xenobiotics [31]. The blood–brain barrier (BBB) is surrounded by the endothelium, astrocytes and pericytes. These cells contribute to the induction tight junctions [28]. Moreover, the BBB is a transport barrier having specific transport proteins and transcytosis mechanisms that mediate the uptake and efflux of molecules [28]. Table 2 represents the checkpoints that face artificial nanosomes during their journey from the first level to the final destination.
Prader-Willi syndrome and Angelman syndrome: Visualisation of the molecular pathways for two chromosomal disorders
Published in The World Journal of Biological Psychiatry, 2019
Friederike Ehrhart, Kelly J. M. Janssen, Susan L. Coort, Chris T. Evelo, Leopold M. G. Curfs
GABRB3 therefore appears to play a role in the hypopigmentation that is seen in PWS as well as AS. It plays a role in the differentiation of melanocytes (Delahanty et al. 2016). This was concluded due to the fact that wild-type mice had far more melanocytes in the last two out of four maturation stages than mice lacking one or two copies of GABRB3. GABRB3 also influences pigmentation via OCA2. Deletion of GABRB3 causes the expression of OCA2 to drop significantly. In PWS and AS, both genes are deleted, resulting in an impaired melanin synthesis pathway. However, one non-imprinted copy remains, preventing the affected individuals from having no pigment at all. As GABRB3 encodes a subunit of the GABA(A) receptor, and stimulates transcription of two other subunits (GABRA5 and GABRG3), loss of it will interfere with the function of this receptor. This was found to cause several disorders in mice, including epilepsy, cleft palate and hyperactive behaviour. It is plausible that this mechanism also plays a role in the development of these disorders in humans. Epilepsy features might be related to the seizures that are seen in AS, yet they are not reported in PWS. The relation of the cleft palate and hyperactive behaviour to these two syndromes remains open to debate. However, it is an effect caused by GABRB3, a PWS/AS related gene, and therefore it is depicted here.
Related Knowledge Centers
- Epidermis
- Eye
- Inner Ear
- Meninges
- Neural Crest
- Stratum Basale
- Uvea
- Melanin
- Cell
- Vaginal Epithelium