Lecture 24

What does the internal epithelial root sheath do in relation to the hair follicle?

It becomes thinner and cells fuse before disintegrating, mixing with sebum.

What is the external epithelial root sheath

It is a layer of the hair follicle that extends from the epidermis with which it is continuous in the upper region of the hair follicle. Resembles cells of the stratum spinosum

What is the primary role of the dermal papilla?

It is a conical region of highly vascular connective tissue directly under the hair matrix.

What is the hair matrix

Cells that make up the hair bulb and cover the dermal papilla and coresponds to the stratum basale of epidermis. Proliferation of cells here results in hair growth

What is the dermal root sheath

Dermal connective tissue cells and fibres arranged circularly and longitudinally around the hair follicle

What is the interlocking mechanism for hair implantation

The keratinocytes in the cuticle of the hair follicle are in the opposite direction to the keratinised cells found in the internal epithelial root sheath creating a secure implantation

What cells are responsible for hair growth?

Hair matrix cells, which correspond to the stratum basale of the epidermis.

How does the arrector pili muscle contribute to hair movement?

It is anchored in the papillary dermis by elastic fibres. The muscle is under autonomic nervous control and its contraction causes elevation of hair

What distinguishes primary hair follicles from secondary hair follicles?

Primary follicles are larger, produce both primary and secondary hairs, and possess sebaceous and sweat glands; secondary follicles are smaller, may lack sweat glands, and typically produce under hairs.

What action allows for creation of air pockets in hair follicles

The contraction of the arrector pili muscle, which causes hairs to stand upright and creates spaces that trap air.

What are primary hair follicles

They are larger hair follicles that produce both primary and secondary hairs, and are associated with sebaceous and sweat glands.

What are secondary hair follicles

Smaller hair follicles with that may have a sebaceous gland but lack sweat gland and arrector pili muscle. They produce secondary hairs which lack a medulla

What is a guard hair

A primary hair that is the stiff, straight fibres that are regularly arranged in broad tracts creating the smooth appearing topcoat of animals. Contains all three regions in a hair shaft

What is a fine hair

The fine wavy hair fibres that comprise the undercoat. These fibres often lack a medulla such as wool

What is a tactile hair

A large (primary) hair in the head region which is highly adapted for tactile sensitivity and perception of touch and space. These arise from large simple follicles that have a blood-filled sinus between the two layers of dermal root sheaths and have many nerve endings

What are the three types of wool hair fibres

Kemp, true wool and heterotype

Describe the three phases of hair growth.

1. Anagen - growing phase with cell proliferation; 2. Catagen - regressive phase where mitosis ceases; 3. Telogen - resting phase where hair is anchored but not growing.

What external factors can control hair growth?

Photoperiod, ambient temperature, nutrition, and hormones (e.g., estrogen, testosterone).

What are anal sacs and their function?

Invaginations of skin associated with modified sweat glands that can become impacted or infected.

What type of epithelium is seen in anal sacs

The inside of the sac is heavily keratinised epithelium

What are circumanal glands

Modified sebaceous glands found in the anal region, groin and prepuce

What is the veterinary significance of anal sacs

The duct that connects the sac to the epidermis of the anus is narrow and can be obstructed easily → results in anal sac impaction, infection and/or abscessation

What is the veterinary significance of circumanal glands

They can be sites of tumours in dogs

What is the significance of the tarsal or Meibomian glands?

These are multilobular sebaceous glands in the eyelids that can get blocked, causing cystic swelling.

How do wool fibers differ from true wool fibers?

Wool is the textile fiber produced from sheep, while true wool lacks a medulla and is fine and elastic.

What are the two main types of horn produced by the epidermis?

Tubular horn, produced by epithelium over dermal papillae, and intertubular horn, produced between the papillae.

What tissue makes up the pinna and ear canal

The pinna consists of two layers of skin with an elastic cartilage in between them. The skin here is haired and has both sebaceous and sweat glands and has blood vessels.

The skin covering the external ear canal is haired and contains sebaceous glands as well as modified sweat glands known as ceruminous glands

What is cerumen

Also known as ear wax, a mixture of glandular secretions and desquamated keratinocytes

What is unique about avian integument compared to mammalian skin?

It is keratinized stratified squamous epithelium, thinner than mammals, and completely aglandular except for the uropygial gland.

What tissue makes up foot pads

The thick epidermis has a stratum lucidum and the digital cushion is a mix of fat and connective tissue. The dermis has merocrine sweat glands

What role do chestnuts and ergots play in horses?

They are thick patches of epidermis composed of tubular and intertubular horn, found medially and on the palmar/plantar sides

What can cause moulting in animals?

Moulting is influenced by photoperiod and temperature changes and is mainly seen in spring and autumn

What is the composition of claw structure in animals?

Claws consist of a claw plate (dorsal ridge, walls) and sole, formed from keratinized epithelium supported by a thick dermis.