Hair Structure and Growth Cycle

Hair Structure and Growth Cycle

• Hair is found all over the body except on the palms of the hands, soles of the feet, lips, and external genitalia.
• There are three main types of hair:
  • Lanugo: Fills the womb, results from cellular activity in the skin, falls out before or after birth.
  • Vellus: Soft downy hair found on the cheeks and body, lacks pigmentation, grows shallowly, rarely longer than 2 cm, cannot become terminal without topical or systemic stimulation.
  • Terminal: Pigmented, coarse hair found on the scalp, eyebrows, eyelashes, pubic and underarm areas, legs, face, and chest in males.

Hair Layers

• Cuticle: Outermost layer of overlapping scale-like cells, translucent, protects.
• Cortex: Main layer, elongated keratinized cells cemented together, contains pigment granules (eumelanin/pheomelanin), determines strength, thickness and elasticity.
• Medulla: Innermost layer, soft, spongey, contains keratinized cells, may or may not be continuous, influences sheen and color tones through reflection of light; may be absent in fine terminal and vellus hairs.

Structure of Hair and its Follicle

• Hairs are dead keratin-based structures that protect the body.
• Hair comprises:
  • Shaft: Surrounds the skin surface.
  • Root: Lies underneath the skin, inside the follicle.
  • Bulb: Large base at the bottom of the root, encases the dermal papilla, and matrix is the lower region of the bulb where cells divide to produce new hair and follicles.
• Dermal Papilla: A loose mass of connective tissue surrounding the hair bulb with excellent blood supply crucial for hair growth.
• Hair follicle is a separate organ that serves the follicle but is not part of the hair; it is supplied by nutrients from capillary loops.

Hair Follicles

• Contains: Hair shaft, hair root, arrector pili muscle, sebaceous gland, apocrine sweat glands, hair bulb, hair matrix, hair papilla.
• Inner root sheath: Closest to the hair shaft, interlocks with the cuticle. Consists of cuticle, Henle's layer, and Huxley's layer
• Outer root sheath: The follicle wall, does not grow upwards, remains stationary.
• Connective tissue sheath: Surrounds the rest of the follicle and the sebaceous gland, an extension of the papillary layer of dermis. Provides sensory nerve and blood supply.

Hair Growth Cycle

• All hairs grow in cycles of varying speeds across the body.
• Hairs progress through cycles that lead to new hair growth following fall out.
• The speed of regrowth depends on the stage of hair growth when it was removed.
• Waxing/sugaring is most effective if carried out during anagen phase for slower regrowth

Stages of Hair Growth Cycle

• Anagen (Active): Hair receives nourishment via blood supply dermal papilla, hair cells divide to produce new hair which grows upwards and outwards.
• Catagen (Changing): Dermal papilla separates, but hair still receives nourishment for follicle walls, hair gradually dries and moves upwards until it easily falls out.
• Telogen (Tired/Resting): The dead hair rests in the follicle waiting to either fall out or new hair to replace it. Hair receives no nourishment. Follicle rests until stimulated to return to the anagen stage by hormones.

Recognizing Hair Stages

• Anagen: Dark bulb, clear jelly-like coating on inner root sheath .
• Catagen: Limp, slightly straggly end.
• Telogen: Straggly brush-like end, referred to as club-ended.

Factors Affecting Hair Growth

• Hormones
• Age
• Color
• Stress
• Medication
• Health (diet, conditions)
• Heredity
• Part of body
• Seasons
• Race/origin

Explore the fascinating world of hair in this quiz focusing on hair structure and its growth cycle. Learn about the different types of hair and their unique characteristics, as well as the layers that compose each strand. Perfect for students interested in biology and anatomy.