2A Hair Biology

Question 1

Composition of hair

Answer 1

Major -> cysteine-rich keratin

Minor -> Melanin, Lipids, Trace Elements, Water

Question 2

Amino acid structure

Answer 2

NH2-CH-COOH
|
R

Question 3

Melanin

Answer 3

Hair color

Question 4

Trace elements

Answer 4

Associated with hair loss

Copper - proper enzyme functions.
Iron - component of haemoglobin, transports oxygen around body
Selenium - concentration correlates to hair loss
Zinc - req. in DNA replication and RNA production.

Question 5

Lipids

Answer 5

Lubricate hair

Question 6

Water

Answer 6

Hair absorbs water through hydrogen bonding.

Question 7

Follicle Formation

Answer 7

1. Portion of epidermis grows downwards into dermis creating a deep canal (follicle)
2. Newly formed follicle canal wraps itself tightly around small amount of dermis tissue and surrounds itself with epidermis.
3. Dermal papilla - small, cone-shaped piece of dermal tissue that bulge up into the FC.
4. When dermal papilla fills into follicle, it forms a hair bulb.

Question 8

Arrector Pili Muscle

Answer 8

Thermoregulation

Question 9

APM (relaxed)

Answer 9

1. APM is relaxed.
2. Hair strand is flat.
3. Too hot -> heat can escape.
4. Sweat is secreted by sebaceous glands/
5. Cools down body by evaporation of sweat.
6. Increased blood flow in capillaries.

Question 10

APM (contracted)

Answer 10

1. APM is contracted.
2. Hair strand is upright.
3. Too cold -> traps a layer of air to minimize heat loss.
4. Decreased blood flow in capillaries.

Question 11

Sebaceous glands

Answer 11

Secretes sebum - lubricates and condition hair and skin.

Question 12

Structure of hair shaft

Answer 12

3. Medulla
4. Cortex
5. Cuticle

Question 13

Medulla (innermost layer)

Answer 13

Does not contain cysteine.

Question 14

Cortex (2nd layer)

Answer 14

90% of the total weight of hair.

Contributes to strength, flexibility, elasticity and color of hair.

Question 15

Cortex - types of melanin (range of hair colors)

Answer 15

Eumelanin

Pheomelanin

Question 16

Eumelanin

Answer 16

Brown to black (MOST COMMON TYPE OF MELANIN)

Question 17

Pheomelanin

Answer 17

Yellowish blonde and red colors

Question 18

Cortex - color of hair is determined by:

Answer 18

1. Ratio of Eumelanin and Pheomelanin
2. Thickness of hair
3. Total number & size of pigment granules

Question 19

1. Ratio of eumelanin and pheomelanin

Answer 19

Color - E - P
Black - Large # and size - Almost none
Dark brown - Quite large # and medium size - Very little
Blonde - Few in number and size - Some
Red - Almost none - Large # and size
Gray - Almost none - Almost none

Question 20

2. Thickness of hair

Answer 20

Diff. thickness = Diff. tones of similar colors.

Question 21

3. Total number & size of pigment granules

Answer 21

Granules - density

Black - large and more eumelanin granules (high density)
Blonde - fewer and smaller pheomelanin granules in cortex (low density)

Question 22

*Granules decreases naturally

Answer 22

Melanocytes slow down, produces lesser melanin according to age. Hence graying.

Question 23

Cuticle - consists of 4 layers

Answer 23

Responsible for shine of hair.

1. A-layer
2. Epicuticle
3. Exocuticle
4. Endocuticle

Question 24

1. A-layer

Answer 24

35% cysteine

Resistant to physical and chemical attacks.

Question 25

2. Epicuticle

Answer 25

Resistant to chemical attacks BUT susceptible to mechanical wear.

Question 26

3. Exocuticle

Answer 26

15% cysteine | Toughness to cuticle

Question 27

4. Endocuticle

Answer 27

3% cysteine | Soft later - swells in presence of water.

Question 28

Types of bonds

Answer 28

Peptide bonds Hydrogen bonds Salt linkages Disulfide bonds

Question 29

Peptide bonds

Answer 29

keratin made up of AA is joined together by peptide bonds to form long chain polypeptides which are then coiled and link together to form a helix

Question 30

Hydrogen bonds

Answer 30

formed between hydrogen & oxygen bonds of water molecules easily disrupted by water/heat breaks and reforms when hair wet/dry weak bond

Question 31

Salt linkages

Answer 31

formed by electrostatic attraction b/w cation of AA & anion of another AA. dependent on pH and pKa easily broken by strong acidic/alkaline solutions

Question 32

Disulfide bonds

Answer 32

formed when S atoms from 2 neighboring amino acids are joined together. fewer in # BUT stronger not easily broken by heat/water

Question 33

Hair growth stages

Answer 33

1, Anagen 2. Catagen 3. Telogen

Question 34

1, Anagen

Answer 34

growth phase - stem cells actively produce new keratinized cells in follicle LONGEST PHASE

Question 35

2. Catagen

Answer 35

"transition phase" FC starts to shrink away from DP hair bulb disappears to form rounded club cells stop making color pigment - root turns milky white DP starts to shrink

Question 36

3. Telogen

Answer 36

resting phase then pushed out by new growth

Question 37

Tensile strength

Answer 37

Force = weight*gravitational acceleration | TS (Pa) = Force (N) / CSA (m^2)