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Skin Appendages

Neelam Maurya

Appendages of the Skin

Skin Appendages

SKIN APPENDAGES:

  • Cutaneous (relating to skin) glands Hair
  • Sebaceous glands
  • Sweat glands
  • Hair
  • Hair follicles
  • Nails

SWEAT (SUDORIFEROUS) GLANDS:

  • The ducts of Sweat gland consist of stratified cuboidal epithelium 
  • Mammary gland is a type of Modified sweat gland
  • Two main types-
  1.  Eccrine sweat glands – most numerous; very abundant in palms, soles of the feet, and forehead
  2. Apocrine sweat glands – found in axillary and anogenital areas
  3. Ceruminous glands – modified apocrine glands in external ear canal that secrete cerumen (earwax)
  4. Mammary glands – specialized sweat glands that secrete milk

SEBACEOUS GLANDS:

  • Simple alveolar glands found all over the body (except palms & soles)
  • Sebaceous gland is an example of  Holocrine gland
  • Secrete an oily secretion called sebum
  • Soften and lubricates hair and skin
  • Hair follicles, Sebaceous glands & Mammary gland are derived from ectoderm 
  • Fordyce spots are Ectopic sebaceous glands
  • Bactericidal action
  • Activated by hormones during puberty
  • Blocked gland=whiteheads & blackheads
  • Inflammed glands=acne, pimples

 STRUCTURE OF A NAIL:

  • Scale like modification of the epidermis on the distal, dorsal surface of fingers and toes

 

HAIR:

  • Filamentous strands of dead keratinized cells produced by hair follicles
  • Contains hard keratin which is tougher and more durable than soft keratin of the skin
  • Made up of the shaft projecting from the skin, and the root embedded in the skin
  • Rate of growth of beard hair is 0.4 mm/day
  • Consists of a core called the medulla, a cortex, and an outermost cuticle
  • In humans, cortex of hair is usually 4-10 times broader than the medulla
  • Pigmented by melanocytes at the base of the hair
  • DNA can be taken as sample from Hair roots

Hair Function and Distribution:

  • Functions of hair include:
  • Helping to maintain warmth
  • Alerting the body to presence of insects on the skin
  • Guarding the scalp against physical trauma, heat loss, and sunlight

Types of Hair:

  1. Vellus – pale, fine body hair found in children and the adult female
  2. Terminal – coarse, long hair of eyebrows, scalp, axillary, and pubic regions

 HAIR FOLLICLE:

  • Root sheath extending from the epidermal surface into the dermis
  • Deep end is expanded forming a hair bulb
  • A knot of sensory nerve endings (a root hair plexus) wraps around each hair bulb
  • Bending a hair stimulates these endings, hence our hairs act as sensitive touch receptors

 GROWTH PHASES OF HAIR:

  • The most important feature of hair follicle is that their activity is cyclic. Hair grows at 0.4 mm per day and as it reaches a definitive length, it is shed to be replaced by a new hair. Hair undergoes through 3 different phases of hair cycle :

1. Anagen phase (Phase of activity and growth)

  • This is the phase in which growth of hair takes place -4 Cells in the root of hair are dividing rapidly. 
  • Melanogenesis also occurs during anagen phase. 
  • This phase lasts for 3 years (2-6 years). Most of the hair (75-80%) are in anagen phase at a given time.

2. Catagen phase (Transition phase)

  • It is the transition phase between anagen and telogen. 3% of hair are in this phase. 
  • During this phase growth stops and outer root sheat shrinks and attaches to root of hair known as club hair.
  •  This phase lasts for 2-3 weeks.

3. Telogen phase (Resting or degenerative phase)

  • This phase is the resting phase and lasts for 100 days (3 months). 
  • About 25-100 telogen hair are shed normally each day. 10-15% of hair are in this phase.
  • After telogen phase the cycle is complete and the new hair, which starts growing in same follicle, pushes this old hair (who has completed the hair cycle) —> Old hair is lost and new hair starts growing.
  • This hair cycle of one hair is independent of the cycle of neighboring hair, i.e., the neighboring hair follicles are not synchronized in growth, this is called Mosaic. 
  • The proportion of hair in each phase can be estimated by looking at the plucked hair called as trichogra
Exam Question
 
  • Sebaceous gland is an example of  Holocrine gland
  • The ducts of Sweat gland consist of stratified cuboidal epithelium 
  • Halocrine secretion is seen in Sebaceous glands
  • Fordyce spots are Ectopic sebaceous glands
  • Apocrine gland are Modified sweat gland
  • Apocrine sweat glands are found in axillary and anogenital areas
  • Rate of growth of beard hair is 0.4 mm/day
  • DNA can be taken as sample from Hair roots
  • In humans, cortex of hair is usually 4-10 times broader than the medulla
  • Hair follicles, Sebaceous glands & Mammary gland are derived from ectoderm 
  • Telogen phase of hair growth lasts for  100 days
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