��Skin Appendages�Structure and Function of Hair �

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BY: DR.NABIHA IQBAL

Hair

• Hair are keratinous filaments derived from invaginations of the germinative layer of epidermis into the dermis.
• Hair are distributed all over the body, except for the palms, soles, dorsal surface of distal phalanges, umbilicus, glans penis, inner surface of prepuce, the labia minora, and inner surface of labia majora.
• The length, thickness and colour of the hair vary in different part of the body and in different individuals.

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Types of Hair

Lanugo

• The foetal skin is covered by fine hair called lanugo (primary hair).

Vellus

• These are mostly shed by birth, and are replaced during infancy by another set of fine hair called vellus (secondary hair).

Terminal hair

• These are retained in most parts of the body, but are replaced by the thick and dark terminal hair of the scalp and eyebrows, and other hairy areas of the adult skin.

Hair growth

• The hair grow at the rate of about 1.5-2.2 mm per week; their growth is controlled by hormones.
• The life span of the hair varies from 4 months (eyelashes, axillary hair) to 4 years (scalp hair).

The follicular life cycle can be divided into 3 phases

• Anagen phase is the phase of active growth, lasts approximately 3-4 years
• Catagen phase marks follicular regression, lasts about 2-3 weeks
• Telogen phase represents a resting period, lasts approximately 3 months
• Approximately 84% of scalp hairs are in the anagen phase, 1-2% are in the catagen phase, and 10-15% are in the telogen phase

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Function

• The Main Functions and role of the hair
• •Thermo regulation – helps retains body heat
• •Physical protection – acts as a buffer to knocks and abrasions •Provides a good environment for micro organisms – increased warmth, moisture and sebum under hair

Structure of Hair

• Each hair has an implanted part called the root, and a projecting part called the shaft
• 2. Layers of the Hair The hair shaft consists of 3 layers
• 1. MEDULLA
• 2. CORTEX
• 3. CUTICLE

Hair Follicle

 The Follicle is a pocket of skin and grows deep into the dermis and consists of the following:

1. Papilla

2. Germinal Matrix

3. Hair Bulb

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Papilla

•Found below the follicle in the dermis

•Is located at the base of the follicle

•Is where the CAPILLARIES pass nutrients through to dividing cells in the germinal matrix

•Where the waste products from the cell are passed back through to the capillaries and taken away.

Germinal Matrix

 Germinal Matrix Inside the follicle above the PAPILLA Were the cells divide ( Mitosis) Each cell already knows if it is a cortex, cuticle or medulla

Melanin is produced in the cells within the germinal matrix.

Cells are being pushed upwards as new cells are produced Once the cell leaves the germinal matrix its supply of nutrients is cut off so the cells stop dividing and dies

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Hair Bulb �

•Bulb shape located at the lower end of the follicle

•The germinal matrix is found in the hair bulb

•Keratinisation occurs here.

• Sebaceous Gland
• Attached to the side of the follicle

• Secretes oil (sebum)

• Helps hair stay supple and shiny

• Sebum forms part of the acid mantle that helps protect the skin from harmful bacteria and chemical attack

• Arrector Pili Muscle
• Attached to the follicle and the base of the epidermis
• Involuntary muscle – cannot control it •Contracts due to cold or fright creating goose bumps.
• The arrectores pilorum muscles (smooth muscles supplied by sympathetic nerves) connect the undersurface of the follicles to the superficial part of the dermis.
• Contraction of these muscles leads to erection of hair, squeezes out the sebum, and produces 'goose skin'

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� Nails

Structure of Nail

• Nails are hardened keratin plates (cornified zone) on the dorsal surface of the tips of fingers and toes, acting as a rigid support for the digital pads of terminal phalanges.
• Each nail has the following parts.
• Root is the proximal hidden part which is burried into the nail groove and is overlapped by the nail fold of the skin.
• (b) Free border is the distal part free from the skin.
• (c) Body is the exposed part of the nail which is adherent to the underlying skin. The proximal part of the body presents a white opaque crescent called lunule.

• Each lateral border of the nail body is overlapped by a fold of a skin, termed the nail wall.
• The skin (germinative zone + corium) beneath the root and body of the nail is called nail bed. The germinative zone of the nail bed beneath the root and lunule is thick and proliferative (germinal matrix), and is responsible for the growth of the nail. T
• he rest of the nail bed is thin (sterile matrix) over which the growing nail glides. Under the translucent body (except lunule) of the nail, the corium is very vascular.
• This accounts for their pink colour

Functions of Skin

1. Protection

• Skin protects the body from mechanical injuries, bacterial infections, heat and cold, wet and drought, acid and alkali, and the actinic rays of the sun.

2. Sensory

• Skin is sensory to touch, pain and temperature.

3. Regulation of body temperature

• Heat is lost through evaporation of sweat; and heat is conserved by the fat and hair.

4. Absorption

• Oily substances are freely absorbed by the skin.

5. Secretion

• Skin secretes sweat and sebum.

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6. Excretion

• The excess of water, salts and waste products are excreted through the sweat

7. Regulation of PH

• A good amount of acid is excreted through the sweat.

8. Synthesis

• In the skin, vitamin D is synthesized from ergosterol by the action of ultraviolet rays of the sun.

9. Storage

• Skin stores chlorides.

10. Reparative.

• The cuts and wounds of the skin are quickly heale