SKIN APPENDAGES

SKIN APPENDAGES:
  • Cutaneous (relating to skin) glandsHair
  • 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:
  • Eccrine sweat glands – most numerous; very abundant in palms, soles of the feet, and forehead
  • Apocrine sweat glands – found in axillary and anogenital areas
  • Ceruminous glands – modified apocrine glands in external ear canal that secrete cerumen (earwax)
  • 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:
  • Vellus – pale, fine body hair found in children and the adult female
  • 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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