Structure and Function of Hair

Structure Hair is an appendage of the skin that grows out of an organ known as the hair follicle. A hair is made up of three general parts: Follicle Root Shaft

Structure 1. Follicle – tube like organ in the under layer of the dermis and is linked to the body’s blood supply 1. Papilla – indentation of follicle where blood vessels, nerves enter and exit 2. Matrix – area of cell division and hair growth 2. Root – portion of hair below the skin, embedded in the follicle

Structure 3. Shaft – portion of hair above the surface of the skin, made up of three layers 1. Cuticle – clear outside covering of the shaft, made up of overlapping scales. There are three basic scale structures that make up the cuticle. Combinations and variations of these types are possible. Corona-crown-like, found in small rodents and bats, rarely in humans Spinous- petal-like, found in seals, cats, & some animals never humans Imbricate-flattened, found in humans and animals

Cat

Structure of the Hair Shaft (cont.) 2. Cortex – made up of keratin molecules, the pigment that gives hair its color. 3. Medulla – row of cells running along the center of the cortex which may appear dark or translucent depending on the presence of air, liquid, or pigment. Can be fragmentary, interrupted, continuous, or stacked. May not be visible in human hair. **In animals, it is at least 1/3 of the diameter of the hair.

Medulla Patterns

Medullary Index is the quickest way to determine a hairs origin in terms of human or non-human. Hair is 3-D & of a circular nature A circumference is the distance across a circle If the circumference of the medulla is less than 1/3 (33%) the circumference of the entire shaft, then it is most likely of human origin. If the circumference of the medulla is greater than 1/3 (33%) of the circumference of the entire shaft, then it is most likely of animal origin.

Medualla diameter vs. total diameter = medullary index

Moose hair: medullary index is > 1/3

Pigment granules

GENERAL BIOLOGICAL MAKE-UP OF HAIR A. Shapes of hair 1. Round - Straight Hair 2. Oval - curly hair 3. Crescent - kinky hair B. Growth- there are 3 stages: Anagen phase – active phase, averaging three to five years for scalp, 30-45 days for other parts of the body, hair grows about 1 cm a month. Catagen phase- intermediate period of hair growth, lasting 2-3 weeks, outer sheath shrinks to the root forming club hair, 3% of all hair at any one time Telogen phase –resting phase, 10-15% of all hair, lasts about 100 days for scalp and longer for other parts of the body, club hair fully formed.

General Function of Hair 1. Protection a. guards the scalp from injury and sunlight b. eyebrows and eyelashes protect the eye c. hair in ears and nostrils keep out foreign objects 2. Helps regulate body temperature 3. Touch receptors associated with hair follicles