Hair Anatomy Overview

Study Notes

Hair Anatomy Overview

Hair is a filamentous outgrowth of the skin, primarily composed of keratinized cells.
It grows from a follicle located in the dermis, a layer of skin beneath the epidermis.
The follicle is a complex structure that plays a vital role in hair growth, structure, and maintenance.

Hair Follicle Components

Hair follicle: Encloses the hair root and associated structures.
Hair root: The part of the hair embedded within the follicle.
Hair shaft: The portion of the hair that projects above the skin's surface.
Hair bulb: The base of the follicle, containing the papilla and matrix.
Hair papilla: A connective tissue projection into the hair bulb that contains blood vessels and nerve endings, providing nutrients to the hair matrix.
Hair matrix: A layer of actively dividing cells that produce the keratin proteins forming the hair shaft.
Arrector pili muscle: Connects the follicle to the surrounding dermis, and controls hair follicle elevation, causing "goosebumps" when contracted.
Sebaceous glands: Associated with hair follicles, producing sebum, an oily substance that lubricates and protects the hair and skin.
Sensory nerves: Present in the follicle, contributing to touch perception related to hair movement.
Blood vessels: Within the papilla provide nutrition to the hair matrix.

Hair Shaft Structure

Cuticle: The outermost layer of the hair shaft, composed of overlapping scales, which, when correctly aligned, protects the hair. Damage to the cuticle can lead to split ends.
Cortex: The middle layer of the hair shaft, containing most of the hair’s pigment. This layer is responsible for the hair's color and strength.
Medulla: The innermost layer of the hair shaft, often less developed or absent in fine hair. This layer is primarily composed of loosely arranged keratin cells.

Hair Growth Cycle

Hair follicles go through alternating phases of growth (anagen), transition (catagen), and rest (telogen).
Anagen (growth phase): The active phase of hair growth. The hair matrix continuously produces new keratinized cells, pushing the hair shaft upwards. This phase varies in duration depending on factors.
Catagen (transition phase): The brief transition phase between active growth and rest. The follicle shrinks, and cell division slows.
Telogen (resting phase): The resting phase where hair is detached from the follicle. In this phase, the follicle is largely inactive and shedding of old hair occurs.

Hair Color

Hair color is determined primarily by melanin, a pigment produced by melanocytes within the hair matrix.
Eumelanin produces brown, black shades of hair.
Pheomelanin produces red and blonde shades of hair (or mixtures).
The interplay of these pigments dictates the final hair color.

Factors Affecting Hair Growth and Structure

Genetics: Predisposition to hair growth rate, color, and texture is largely determined by heredity.
Hormones: Hormonal factors, such as androgens, play a role in hair growth and distribution, particularly in males and during puberty.
Nutrition: Proper nutrition, particularly protein intake, supports hair growth.
Underlying health conditions: Certain medical conditions can affect hair growth and density.
External factors: Chemical treatments, harsh styling techniques and environmental factors can damage hair.

Clinical Considerations

Conditions affecting hair include:
- Alopecia (hair loss): Various forms of hair loss can occur relating to factors above.
- Trichotillomania (hair-pulling disorder): A mental health condition.
- Hair shaft disorders can affect hair health.

Description

This quiz explores the intricate structure of hair and its components. Learn about the hair follicle, hair root, hair shaft, hair bulb, and associated structures that play crucial roles in hair growth and maintenance. Test your knowledge of hair anatomy and its significance in skin biology.