Like all other types of hair, black hair is made up of many different parts.
A hair strand consists of a bulb, root and the hair shaft. The part that is visible to us is the hair shaft, the bulb and the root are found under the scalp. Follicles enclose each bulb and root. Surrounding the follicles are sebaceous glands which secrete sebum, coats the cuticle and gives it sheen.
Although black hair produces more sebum than other ethnic groups, in comparison to straight Caucasian hair follicles, the follicles in black hair are curved. These curves make it is harder for sebum to flow through the hair. That's why black hair can be very dry.
The hair shaft has 3 separate layers.Cuticle-This is the outer layer which protects the hair shaft. It is colourless and coated with sebaceous glands which gives hair its sheen.
Cortex- This gives hair its strength. Responsible for shape, texture and elasticity.
Medulla- This is the most inner part of the hair. No one is quite sure what the function of this layer is, but it is only present in large thick hairs.
Black hair, like all types of hair is made up of proteins, roughly 88%. These proteins are of a hard fibrous type known as keratin. Keratin protein is comprised of what is called "polypeptide chains." The word polypeptide comes from the Greek word "poly" which means many and "pepto" which means digested or broken down. In essence, if we break down protein, we have individual amino acids. Many (poly) amino acids joined together form a "polypeptide chain".
Black hair has two amino acids are joined together by a "peptide bond", and the correct number of amino acids are placed in their correct order will form a specific protein; ie Keratin, Insulin, Collagen etc.
The "alpha helix" is the descriptive term given to polypeptide chain that forms the keratin protein found in human hair. Its structure is a coiled coil. The amino acids link together to form the coil and there are approximately 3.6 amino acids per turn of the helix coil. Each amino acid is connected together by a "peptide bond". The peptide bond is located between the carbon atom of one amino acid extending to bond with the nitrogen atom of the next amino acid.
Within the keratin the hair contains 4 different bonds. Each bond is important in understanding hair growth and maintaining healthy hair.
The Hydrogen Bond- This bond is responsible for the hairs ability to be stretched and returned to its natural shape (elasticity). With the aid of water, the hydrogen bond allows the shape of the hair to change (i.e wet sets, twist outs and other curling methods done to wet hair. These bonds are responsibly for approximately 35% of the hairs strength and 50% of the hairs elasticity.
During a chemical process such as a relaxer, the hydrogen bond is broken down and reformed making the hair more prone to breakage.
The Salt Bond- This bond is an ionic (electrolytically controlled) bond formed by the electron transfer from the side chain of a basic amino group (an amino acid with an 00C-group) to the side chain of an amino acid, ie NH3+. This is two positive and negative charges attracting one another. This occurs in a position paralleled to axis line of the rotation of the helix of the hair. The salt bond is responsible for approximately 35% of the hair strength and 50% of the hairs strength
The Cystine Bond- This bond is perpendicular to the axis of the hair and between the polypeptide chains. Also known as the sulfur or disulfide bond, because of its position in the hair it is responsible for the hair's toughness or abrasion resistance. It holds the hair fibres together.
The Sugar Bond- This bond is formed between the side chain of an amino acid having an OH group and an acidic amino group. This bond is also formed perpendicular to the axis of the hair. Because of its position, it gives the hair toughness but little strength (5%).
Feel free to add to this if you have any more info.
References;
www.hairformula37.com
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