Hair (hair grows on the head):
Hair is not an organ, so it does not contain nerves and blood vessels, but contains cells. Soft and fluffy hair is elastic, can withstand lighter collisions, and can also help the sweat on the head evaporate. The average person has about 100,000 hairs. Among all hair types, the length of the hair is the longest, especially for women with long hair.
Hair color is generally determined by genes, and the common ones are black, golden yellow, brown and red. As humans age, their hair usually turns silvery white. Due to differences in race and region, hair is black, blonde, reddish brown, reddish brown, light yellow, gray, and even green and red. Black hair contains the same amount of copper, iron and melanin, and when the nickel content increases, it will become grayish white. Blond hair contains titanium, red-brown hair contains molybdenum, red-brown hair contains copper and iron, and cobalt, and green hair contains too much copper. In some countries in Africa, some children’s hair is red, which is caused by a severe lack of protein.
Physiological characteristics:
From bottom to top, hair can be divided into four parts: nipple, hair follicle, hair root and hair shaft. The physiological characteristics and functions of hair mainly depend on the nipples, hair follicles and sebaceous glands under the scalp.
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The hair follicle is a part of the hair root in the dermis, which is composed of inner root sheath, outer root sheath and hair bulb. The inner hair root sheath is the sheath directly adjacent to the hair at the later stage of hair growth. The inner hair root sheath is a hard thick-walled keratinized tube, which determines the cross-sectional shape of the hair as it grows. The lower part of the inner hair sheath is composed of three layers: the HUXLEY sheath, the HENLE sheath and the surface layer of the inner hair root sheath. Before hair keratinization, the inner hair root sheath grows together with the hair, and its source is the cells that multiply at the bottom of the hair follicle. Near the epidermis, the inner hair root sheath is separated from the epidermis and hair follicles.
The dermal papilla is the lowest end of the hair follicle and is connected to capillaries and nerve endings. At the bottom of the hair follicle, epidermal cells divide and differentiate continuously. These epidermal cells differentiate in different ways to form different components of the hair (such as cortex, epidermis, and medulla), and the outermost cells form the inner hair root sheath. At this stage, the cells are soft and non-keratinized.
The function of the sebaceous glands is to secrete sebum, which is squeezed out through the sebaceous tube. When the hair passes through the sebum tube, the sebum squeezed out by the sebum tube is taken away. Sebum provides natural protection to the hair, making it shiny and waterproof. The erector spinae is a small muscle organ connected to the epidermis. According to the external physiological environment, the erector spinae can be stretched or contracted. A drop in temperature or the action of adrenal hormones can pull the hair follicles to a higher position and make the hair stand upright.
Hair quality is the main component of hair and consists of elongated cells parallel to the long axis of the hair. There are approximately 10 mm of tension filaments and inter-fiber matrix in these cells. These components determine the main physiological characteristics of the hair. The filaments are composed of fibrin, 50% of which have a helical structure, and the matrix is composed of non-helical proteins rich in cystine. These proteins are synthesized at the lower end of hair follicles, and the cysteine in the final stage of synthesis is converted to cystine.
Soaking hair in water will swell quickly. The weight after swelling is about 40% higher than the dry weight before soaking. This phenomenon of swelling in water shows that the hair is almost pure protein, with very little lipid content. Hair has a strong duality, which is due to the arrangement of filaments in the cells parallel to the long axis of the hair.
Physical properties:
The root of the hair gets thicker and thinner as it goes to the tip, so the thickness of the hair is also different. It can be divided into normal hair, thick hair and fine hair.
Hair shapes can be divided into three types: straight hair, wavy curly hair and natural curly hair.
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