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Medulla (hair)
The medulla is the innermost layer of the hair shaft. This nearly invisible layer is the most soft and fragile, and serves as the pith or marrow of the hair. Some mammals don't have a medulla in their hair. The presence or absence of this layer and the characteristics of the medulla can aid taxonomists in identifying what taxa a hair comes from. Characteristics include whether the medulla contains air pockets as well as the histology of the medulla. Scientists are still uncertain about the exact role A role (also rôle or social role) is a set of connected behaviors, rights, moral obligation, obligations, beliefs, and social norm, norms as conceptualized by people in a social situation. It is an expected or free or continuously changing behavi ... of the medulla, but they speculate that it is primarily an extension that is more prominent in depigmented (grey or white) hair .James, William; Berger, Timothy; Elston, Dirk (2005) ''Andrews' Diseases of the Skin: Clinical Dermatolog ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hair Shaft Diagram
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. Attitudes towards different forms of hair, such as hairstyles and hair removal, vary widely across different cultures and historical periods, but it is often used to indicate a person's personal beliefs or social position, such as their age, sex, or religion. Overview The word "hair" usually refers to two distinct structures: #the part beneath the skin, called the hair follicle, or, when pulled from the skin, the bulb or root. This organ is located in the dermis and maintains stem cells, which not only re-grow the hair after it falls out, but also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hair Shaft
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. Attitudes towards different forms of hair, such as hairstyles and hair removal, vary widely across different cultures and historical periods, but it is often used to indicate a person's personal beliefs or social position, such as their age, sex, or religion. Overview The word "hair" usually refers to two distinct structures: #the part beneath the skin, called the hair follicle, or, when pulled from the skin, the bulb or root. This organ is located in the dermis and maintains stem cells, which not only re-grow the hair after it falls out, but also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles (including birds) from which they diverged in the Carboniferous, over 300 million years ago. Around 6,400 extant species of mammals have been described divided into 29 orders. The largest orders, in terms of number of species, are the rodents, bats, and Eulipotyphla (hedgehogs, moles, shrews, and others). The next three are the Primates (including humans, apes, monkeys, and others), the Artiodactyla ( cetaceans and even-toed ungulates), and the Carnivora (cats, dogs, seals, and others). In terms of cladistics, which reflects evolutionary history, mammals are the only living members of the Synapsida (synapsids); this clade, together with Saur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Histology
Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures visible without a microscope. Although one may divide microscopic anatomy into ''organology'', the study of organs, ''histology'', the study of tissues, and ''cytology'', the study of cells, modern usage places all of these topics under the field of histology. In medicine, histopathology is the branch of histology that includes the microscopic identification and study of diseased tissue. In the field of paleontology, the term paleohistology refers to the histology of fossil organisms. Biological tissues Animal tissue classification There are four basic types of animal tissues: muscle tissue, nervous tissue, connective tissue, and epithelial tissue. All animal tissues are considered to be subtypes of these four principal tissue types ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Function (biology)
In evolutionary biology, function is the reason some object or process occurred in a system that evolved through natural selection. That reason is typically that it achieves some result, such as that chlorophyll helps to capture the energy of sunlight in photosynthesis. Hence, the organism that contains it is more likely to survive and reproduce, in other words the function increases the organism's fitness. A characteristic that assists in evolution is called an adaptation; other characteristics may be non-functional spandrels, though these in turn may later be co-opted by evolution to serve new functions. In biology, function has been defined in many ways. In physiology, it is simply what an organ, tissue, cell or molecule does. In the philosophy of biology, talk of function inevitably suggests some kind of teleological purpose, even though natural selection operates without any goal for the future. All the same, biologists often use teleological language as a shorthand for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Human Hair Color
Human hair color is the pigmentation of human hair follicles due to two types of melanin: eumelanin and pheomelanin. Generally, if more melanin is present, the color of the hair is darker; if less melanin is present, the hair is lighter. The tone of the hair is dependent on the ratio of black or brown eumelanin to yellow or red pheomelanin. Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of more than one color on the same person. Some hair colors are associated with some ethnic groups due to observed higher frequency of particular hair color within their geographical region, e.g. straight dark hair amongst East Asians, a large variety of dark, fair, curly, wavy and bushy hair amongst Europeans, curly, dark, and uniquely helical hair with Africans, whilst gray, white or "silver" hair is often associated with age and wisdom. Genetics and biochemistry of hair color The full genetic basis of hair color is co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
