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-
- 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
Don’t Forget to Solve all the previous Year Question asked on Skin Appendages
