University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2020
Views:

101

Pages:

10
Author:

enflorarsja

Human Hair • Hair is composed of keratinocytes filled with keratin that is toughened by disulfide bridges between the keratin molecules – sulfur from the disulfide bridges is given off when hair is burned • Hair is found almost everywhere on the body – differences in the hair distribution of males and females is really a difference in texture and color of hair • 3 different body hair types: – lanugo is fine, unpigmented fetal hair – vellus is fine, unpigmented hair (peach fuzz) that covers much of the bodies of children and adults – its growth is not affected by hormones – terminal hair is coarse, long, pigmented hair – its growth can be affected by hormones Functions of Hair • Body Hair – enhances sense of touch (can alert us to an insect crawling on our skin) • Scalp Hair provides heat retention in cold weather and protection from sunburn. • Development of Facial, Pubic and Axillary Hair indicate gender and sexual maturity. • Nose Hairs, ear hairs and eyelashes prevent foreign objects from getting into nostrils, ear canals or eyes. • Eyebrows reinforce or exaggerate expression of emotions. Hair Follicle and Associates Structures Hair Follicle and Associates Structures • Hair Follicles are tubes of epidermis that a hair grows out of. • The hair shaft is composed of dead keratinocytes that emerge out of the skin – A hair shaft has three layers: Cuticle, Cortex and Medulla. • The hair root is composed of living cells below the surface of the skin within the hair follicle. • The hair bulb is a swelling in the base of the root where a hair originates • The dermal papilla is vascular tissue that provides nutrients to the hair bulb • Hair receptors are sensory nerves that wrap around each follicle Piloerector muscle (arrector pili) can lift up hairs and depress the skin around it (causing goose bumps). Hair shafts have 3 layers of dead keratinocytes: cuticle, cortex and medulla. Hair color is due to pigment deposited in cells of the cortex layer. Blond hair contains a mixture of a small amounts of black or brown eumelanin and red pheomelanin pigments. Straight hair has a round cross section Black and dark brown hair contains eumelanin pigment. Red hair contains some eumelanin, but mostly pheomelanin pigment. Wavy or curly hair is flattened in cross section. White hair lacks pigment, and the medulla may degrade into an air-filled space making the hair brittle. Gray hair is a mixture of white hairs and some pigmented hairs. Hair Growth • Scalp hairs take about 3 days to grow about 1mm • On average hair scalp hair grows about 4-7 inches per year • Scalp hairs grow for about 6-8 years and then the follicle rests for several months. • Each hair goes through a growth phase followed by a resting phase. Hairs across the body are in various, asynchronous phases.