A&P Honors: Ch. 5.5 — Hair

What are hairs?

Flexible strands produced by hair follicles.

What do hairs consist of?

Dead, keratinixed cells.

Where is hard keratin located?

Hairs and nails.

Where is soft keratin located?

Found in typical epidermal cells.

What are the two advantages hard keratin has over soft keratin?

(1) It is tougher and more durable, (2) its individual cells do not flake off.

What are the chief regions of the hair?

The foot and the shaft.

What is the root of the hair?

The part embedded in the skin.

What is the shaft of the hair?

The part that projects above the skin’s surface.

Is the shaft is flat and ribbonlike in cross section, what is the hair?

Kinky

If the shaft is oval, what is the hair?

Silky and wavy.

If the shaft is perfectly round, what is the hair?

Straight and coarse.

What are the three concentric layers of keratinized cells in the hair?

The medulla, cortex, and cuticle.

What is the medulla?

The central core that consists of large cells and air spaces.

What 2 things are special about the medulla?

(1) Its the only part of the hair that contains soft keratin, (2) it is absent in fine hairs.

What is the cortex?

A bulky layer surrounding the medulla that consists of several layers of flattened cells.

What is the cuticle?

The outermost layer that is formed form a single layer of cells overlapping one another.

What does the cells of the cuticle being overlapping help?

Separate neighboring hairs so the hair does not mat.

What is special about the cuticle? What’s does this provide?

It is the most heavily keratinized part of the hair. This provides strength and keeps the inner layers tightly compacted.

Which concentric hair layer is subjected to the most abrasion?

The cuticle.

Since the cuticle is subjected to the most abrasion, what is the outcome of this?

The cuticle tends to wear away at the tip of the hair shaft.

What does the cuticle wearing away at the tip of the hair shaft allow?

Keratin fibrils in the cortex and medulla to frizz, creating split ends.

What is hair pigment made by?

Melanocytes at the base of the hair follicle and transferred to the cortical cells.

What is red hair colored by?

Pigment called pheomelanin.

What causes hair to turn gray or white?

Melanin production decreasing and air bubbles replacing melanin in the hair shaft.

What are hair follicles?

Tubular invaginations of the epidermis from which the hairs grow. They fold down from the epidermal surface into the dermis.

What is a hair bulb?

What forms when the deep end of the follicle, located about 4m below skin surface, expands.

What is a hair follicle receptor? What is another name for it?

A knot of sensory nerve endings. Also called root hair plexus.

What does a hair follicle receptor do?

Wraps around each hair bulb.

What stimulated the hair follicle receptor?

Bending the hair.

Consequently, what do our hairs act as?

Sensitive touch receptors.

What is a papilla of a hair follicle?

A dermal papilla that protrudes into the hair bulb.

What does the papilla of a hair follicle contain?

A knot of capillaries that supply nutrients to the growing hair and signals it to grow.

If the hair papilla is destroyed by trauma what happens?

The follicle permanently stops producing hair.

What does the wall of a hair follicle have?

A dermal and epidermal component.

What is the peripheral CT sheath? What does it form?

CT sheath derived from the dermis. Forms the external layer of the follicle wall.

Where is the glassy membrane?

At the junction of the fibrous sheath and the epithelial root sheath.

What is the glassy membrane?

The basement membrane of the follicle epithelium.

What is the epithelial root sheath?

Sheath derived from the epidermis.

What are the epithelial root sheaths two components?

The external root sheath and the internal root sheath.

What is the external root sheath?

A direct continuation of the epidermis.

What is the internal root sheath derived from?

Matrix cells.

Why does hair grow?

Because cells in the bulb of the follicle divide rapidly.

What do the dividing hair cells make up?

The hair matrix.

Where does the hair matrix lie?

Immediately adjacent to the hair papilla.

As the matrix produces new hair cells what happens to the older part?

It is pushed upward and its fused cells become increasingly keratinized and die.

What is the hair bulge?

A region closer to the skin surface where hair matrix cells migrate down to the bulb.

What is an arrector pilli muscle?

Bundle of smooth muscle cells associated with hair follicles.

How do goosebumps occur in relation to hair?

The arrector pili muscle contracts and pulls the hair follicle upright and dimples the skin surface to produce these.

What are goosebumps a stimulus in response to?

Cold temperatures or fear.

What is the more important role of the arrector pili in humans?

Its contractions force sebum out of hair follicles to the skin surface where it acts as a skin lubricant.

What can hairs be classified as?

Vellus or terminal

What are some examples of vellus hair?

The body hair of children and adult vellus hair.

Describe vellus hair.

Pale and fine.

Describe terminal hair.

Coarse and long. Also may be darker.

Where are some examples of terminal hair?

Eyebrows, eyelashes, and scalp.

At puberty, where do terminal hairs appear?

In the auxiliary and pubic regions for both sexes and on the face and chest and arms and legs of males.

What do terminal hairs grow in response to?

The stimulating effects of agrogens.

What are androgens?

Male sex hormone.

What is hirsutism?

When women develop coarse terminal hairs in a masculine distribution.

What kind of problem is hirsutism? What might it signal?

A cosmetic problem. Signals an underlying medical issue.

What happens in polycystic ovary syndrome?

The ovaries secrete larger amounts of androgens, stimulating hair growth.

How much do hairs grow per week?

An average of 2mm.

In each growth cycle of hair follicles, what phases are present?

An active growth phase followed by a resting phase.

What happens in the resting phase?

The hair matrix is inactive and the follicle shinks somewhat.

At the start of each active phase what happens?

The newly growing hair pushes out the old hair, which is shed.

In the scalp, what is the average life span of hair? What about eyebrows?

About four years for hair. Only a few months for eyebrows.

When does hair grow fastest?

From teen years to the 40s.

As humans age, what happens to terminal hairs?

They are replaces by vellus hairs and the hair becomes increasingly whispy.

What is male pattern baldness?

The most common baldness, gender-influenced condition that changes the response of the hair follicles to androgens.

How is male pattern baldness determined?

Genetically determined.

What is telogen effluvium?

When too many hair follicles enter the resting phase at the same time.

When does telogen effluvium occur? Give examples.

After a “shock to the system”. Such as surgery, car crash, hormonal changes with childbirth, crash dieting, or emotional stress.

What can hair loss or a change in texture signal?

Low thyroid levels.

What type of drugs can cause hair thinning?

Chemotherapy drugs and antidepressants.

What may result in thin, brittle hair?

Severe dietary deficiencies of protein or minerals.