Anatomy and Physiology of Hair
Table Of Content
It is surrounded by the hair follicle (a sheath of skin and connective tissue), which is also connected to a sebaceous gland. Here, the outer root, inner root, connective tissue layer, hair bulb, and papilla are also identified in the labeled diagram. The arrector pili muscle is the band of smooth muscle fibers that attach to the dermis and connective tissue layer of the hair follicle. It passes obliquely from the lower part of the hair follicle to the junction of the dermis and epidermis. The root of each hair is surrounded by a tubular layer called the hair follicle. You will find different layers of cells in the hair follicles that derives from the different layer of skin.
Hair and Scalp Disorders
The amino acids are joined together in a chain, like beads on a string. Asyou can see, these two important components of the hair loss process(5-alpha reductase and androgen receptor sites) exist within various structures of the hair follicle. The significance of all this is that the mineral sulfur is known to be beneficial for hair growth. Clearly then, sulfur forms a very important component of hair structure. The bottom part of the follicle enlarges into anarea of actively growing cells.
Hair under microscope labeled
Men will classically present with receding temporal hairlines, described as hair thinning and loss in an “M” shape. Women will typically present with a widening part and thinning at the top of the scalp. A genetic predisposition to increased hair follicle sensitivity to circulating androgens causes this type of hair loss. Underneath the cuticle is the cortex, which is made up of long proteins that twist like the curly cord on a telephone. Try stretching a hair and you’ll find that it’s elastic—it stretches before it breaks. When you stretch a hair, you are straightening the coiled proteins in the cortex.
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The uppermost layer forms thesurface of the skin and is made from dead cells which are continuously beingshed and replaced from below. Zinc is important for hair growth because it supports DNA production. Without enough zinc, the protein structure of the hair follicle can deteriorate, causing hair shedding. The bulb is the rounded structure deep in the skin at the root of the hair that surrounds the papilla and germinal matrix.
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The uniserial and multi serial ladder medulla find in the rabbit hair. Again, the deer possess the lattice type of medulla in their hair. The amount of air bubbles in the cortex or medulla increases with the age of the animal. Again, the loss of pigmentation from the medulla and cortex is responsible for greying of the hair. The shape of your hair follicle determines the shape of your hair (i.e. whether it is straight, wavy or curly). The size, shape, and color of the hair shaft are highly variable.
At the bottom of the follicle, a piece of tissue called the papilla contains tiny blood vessels (capillaries). The follicle also contains the germinal matrix, where cells produce new hairs. By week 22 of pregnancy, babies already have all of their hair follicles, or openings in the skin where hair grows. This totals about five million hair follicles, with about one million on the head and 100,000 on the scalp.
Hair identifying characteristics in a microscope
At the lower tip of the hair bulb it consists of a single layer of cuboidal cells, becoming multilayered in the region of the upper hair bulb. In some follicles, there is a distinct single cell layer interposed between the outer and inner root sheaths, known as the companion layer [23]. The ORS of the hair follicle also contains melanocytes, Langerhans cells and Merkel cells. These cells take place in certain functions of the follicle such as acting as a sensory organ and serving as an immunologic sentinel for the skin [5]. In the catagen stage, mitosis in the hair matrix ceases and sheath cells below the bulge die. The follicle shrinks and the dermal papilla draws up toward the bulge.
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Medulla
Again, the medullary index of humans is generally less than 0.33. So, the medulla of an animal is much larger than it is in humans. The medullary index of a hair is determined by measuring the diameter of the medulla and dividing it by the diameter of the hair.
Someone who has thick,course hair will have more overlapping layers of cuticles than someonewith fine hair. It explains how it grows, what it’s made of, and how it changes. The color of the hair is determined by the amount of melanin in the hardened cells. This can vary a lot from person to person, and it changes over the course of a lifetime. The amount of melanin typically decreases as people get older, and more air gets trapped inside the hair – it then loses its color and turns white. Depending on someone’s original hair color and the number of white hairs that grow, the hair on their head then turns gray or white.
As already stated, hair cells are mostly made from keratin (up to 95%). This region is constantly growing anddividing into new cells, pushing the old cells up towards thesurface of the skin. To help understand the hair loss process, it makes sense then to learn about the structure of hair and how it grows. Niacin (vitamin B3) helps to repair the DNA in hair follicle cells.
A single layer of dead, keratinized cells at the outer surface of the hair overlap and form the cuticle that coats the hair. The portion of a hair above the skin is called the shaft, and all that beneath the surface is the root. The root penetrates deeply into the dermis or hypodermis and ends with a dilation called the hair bulb. The hair bulb grows around a bud of vascular connective tissue called the dermal papilla, which provides the hair with its sole source of nutrition. Immediately above the papilla is a region of mitotically active cells, the hair matrix, which is the hair’s growth center.
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