The Integument 2 (Hair, glands, hoofs, claws, feathers and scales)

What are the important functions of hair?

• Mechanical protection

• Thermoregulation

• Sensory perception - specialized tactile hair

What two types of hair follicles are there?

simple and compound

What structures compose a simple hair?

cuticle, cortex, medulla

What portion of the hair projects above the surface of the skin epidermis?

the shaft

What part of the skin is hair embedded?

dermis and hypodermis

What does the root of the hair consist of?

• Consist of hair and surrounding root sheaths

  • Internal root sheath and external root sheath, all surrounded by a connective tissue sheath

What does the bulb of the hair follicle consist of?

dermal papilla and hair matrix cells (stem cells)

Where do cells in the hair follicle become keratinized?

• keratogenous zone

Describe how cells in the hair follicle become keratinized, what cells are responsible for this process?

• Matrix cells are mitotically active, their activity is dependent on the dermal papilla

• Migrating matrix cells pass through the keratogenous zone producing the hard form of keratin and differentiate to form hair and root sheath

What cells associated with the hair bulb provide pigmentation?

melanocytes (Associated with matrix cells)

Keratinization is ___ in hair follicles.

cyclic

Summarize the hair growth cycle. (4 main steps)

1. Anagen - normal process of division

2. Catagen - transient phase, hair bulb begins to cease action and slows down, hair is still in follicle but begins to move towards the surface

3. Telogen - cells are quiesent, hair is moving towards surface where it will eventually fall, dermal papilla has almost no association or connection with matrix cells

4. Early Anagen - before hair following, early anagen begins below, forming new hair follicle

How does the embryological development of a simple hair follicle and associated skin gland begin?

Begins with a localised thickening of epidermis (ectodermal bud) which grows down into underlying mesenchyme

Describe how the development of compound hair follicles in carnivores occurs and their subsequent terminology by stage.

• Compound hair follicles contain a primary, long hair with a deep root called a guard hair and several more shallowly rooted and short hairs known as the undercoat

At birth, there are only guard hairs

• In about 6 months there are development of secondary follicles giving rise to the undercoat, to allow for compound hair follicles as adults

What are some features of sinus or tactile hairs (vibrissae)?

• Limited facial distribution

• Extremely large

• Specialised for tactile sense - blood filled sinus, innervated, which is sensitive to movement and external stimuli, is vibrated and amplified by the sinus which is sensed by nerve endings

What is sweat composed of?

ultra-filtrate of blood plasma

What are the functions of sweat glands?

• Thermoregulation (some species)

• Excretion

• Scent signalling (some species)

Histology

What cells makeup the secretory portion of sweat glands and aid secretion?

What cells makeup the excretory portion / duct of sweat glands?

Secretory

• Simple cuboidal epithelium

• Myoepithelial or 'basket' cells surround aid secretion

Excretory

• 2 layers cuboidal epithelium

• Exit = Hair follicle or sweat pore

What are the differences between apocrine sweat glands and eccrine sweat glands?

• Apocrine sweat glands- hair follicle

• Eccrine sweat glands - empty directly onto skin surtace via sweat pore

REMINDER: mammary glands are modified _____ glands!

sweat

What is the secretory product of sebaceous glands?

sebum

What is the function of sebaceous glands?

waterproofing, suppleness, spread sweat via sebum

Describe the cells and features of the secretory portion and excretory duct of sebaceous glands.

Secretory Portion

• Pale staining, flask shaped, holocrine secretion

Excretory Duct

• Empties into hair follicle

What are specialized skin glands and name an example.

• Localized accumulations of sweat or sebaceous glands in some domestic animals such as:

  • Supra caudal or tail gland in the dog (Concentration of sebaceous glands on dorsum of tail)

Do claws, hoofs and horns contain all layers of the normal integument?

Yes, retain structural organisation of epidermal, dermal and subcutis equivalent layers albeit in modified form

What are the functions of claws, hoofs and horns?

protection of underlying tissues but also scratching, digging and as weapons

What muscle is responsible for erecting the hair in animal which is cold or alert?

Arrector pili muscle, by raising the hair, air can be trapped which cain raise body temperature

What is different about the keratin in hair compared to the keratin found in the skin epidermis?

“hard keratin” has a lower lipid content, and higher sulfur content

How do sweat glands eject their contents to the surface of the skin?

Myoepithelial cells act a bit like smooth muscle to propel substance to the surface, much like mammary glands