Lecture 19 - Hair, Sweat And Nails Flashcards
Hair
AKA pili
Flexible strands of dead, keratinized cells produced by hair follicles.
Made of hard keratin
Functions of hair
Warning of parasites on skin
Insulating against heat loss
Protecting head against physical trauma
Shielding skin from sunlight
Main regions of hair
Shaft - projecting from the skin
Root- embedded in the skin
Hair structure (3 layers)
Inner core - medulla (not all hairs have medulla)
Middle layer - cortex
Outer layer - cuticle
Hair pigment
Melanins of different colours
Made by melanocytes at the base of the hair follicle and transferred to the cortical cells. Combinations of different melanins create all the hair colours
Red hair- additional pheomelanin in pigment
Gray/white- melanin production decreases and air huddles replace melanin
Structure of hair follicle
Hair follicles fold down from the epidermis into the dermis and occasionally into the hypodermis
Deep end of hair follicle is expanded forming a hair bulb, surrounded by sensory nerve endings called hair follicle receptor
Wall composed of dermal sheath, thicker basement membrane from the dermis and inner epithelial root sheath derived from the epidermis
Hair matrix, within hair bulb is a group of actively dividing cells that produce the hair.
Arrector pili muscle, when contraction occurs, hair stands upright
Hair papilla, dermal tissue containing knot of capillaries that’s up lies nutrients to growing hair
Types and growth of hair
Pale,fine vellum hairs
Long,coarse terminal hairs
Rate of hair growth varies, influence by factors such as nutrition and hormones
Grow in cycles, grow continuously for 2-7 years, then slow down for 2-3 weeks and rest for 2-4 months before growing begins again
Hair thinning and baldness
Follicles have limited number of cycles, and after age 40, hair is not replaced as quickly as it is lost, which leads to hair thinning and some degree of balding, or alopecia, in all humans
True baldness, such as male pattern baldness, is a genetically determined, sex influenced condition caused by a gene that changes the hair follicle in response to the hormone dihydrotestosterone
Factors that induce hair thinning
Acutely high fever
Surgery
Sever emotional trauma
Certain drugs ( such as antidepressants etc)
Protein deficient diets
Alopecia areata: immune system attacks follicles
Some hair loss is reversible, but others (burns or radiation) are permanent
Sebaceous (oil) glands
Secrete sebum, oily secretion, found all over the body except palms of hands and soles of feet
Function as holocrine glands, secreting their product into hair follicle or to a pore on the surface of the skin
Softens and lubricates hair and skin, slows water loss and is bactericidal
Eccrine sweat glands (merocrine)
Produce true sweat and are abundant on the palms of hands and soles of feet and forehead
Ducts connected to pores
Secretion of eccrine glands regulated by sympathetic nervous system and used to prevent the body from overheating
Apocrine sweat glands
Confined to axillary (armpit) and anogenital areas
Produce fat and protein rich true sweat
Larger than eccrine sweat glands and have ducts emptying into hair follicles
Begin functioning at puberty
Modified sweat glands
Ceruminous glands - modified appocrine sweat glands found in lining of the ear canal, secrete earwax aka cerumen
Mammary glands- modified apocrine sweat glands that secret milk
These glands do not produce true sweat
nails
Scale like modification of the epidermis, forms protective covering on the dorsal side of the distal finger or toe
Made of hard keratin, have free edge, nail body attached to skin, and root embedded in the skin
Nail matrix
located proximal part of nail bed, epithelium responsible for nail growth, contains dividing cells, which produce new nail cells
