Normal (healthy) skin

What are the 3 layers of the skin

1. Epidermis

2. Dermis

3. Subcutis

What are the layers of the epidermis?

1. Stratum corneum

2. Stratum granulosum

3. Stratum spinosum

4. Stratum basale

What is the structure of the stratum corneum?

Contains dead keratinocytes called corneocytes. They have no nuclei and an insoluble protein shell called a cornified envelope and are linked by desmosomes which create a physical barrier.

What is the structure of the stratum granulosum?

Contains keratinocytes which have keratohyalin granules - which are aggregates of enzymes, and lamellar bodies - which contains lipids, hydrolytic enzymes and antimicrobial compounds that are released into the intracellular space to form the water barrier.

What is the structure of the stratum spinosum?

Early differentiated keratinocytes. Thickest layer.

What is the structure of the stratum basale?

Contains stem cells which differentiate into new keratinocytes and migrate upwards. They are connected to each other by desmosomes and to the basement membrane by hemidesmosomes.

What is the additional skin layer found on cat paw pads?

Stratum lucidum. Found between the stratum corneum and stratum granulosum.

What are squames?

Corneocytes which have been desquamated - released from the stratum corneum as a physical defence.

What factors control the epidermal escalator?

Transforming growth factor (TGF) and keratinocyte growth factor (KGF)

What receptors do keratinocytes express?

Toll-like receptors (TLRs) which are PRRs that recognise PAMPs and release cytokines in response.

In which layer of the skin are melanocytes found?

The stratum basale

What do melanocytes contain?

Organelles called melanosomes which contain eumelanin and pheomelanin

What causes melanogenesis (production of melanin pigments)?

Release of MSH from the pars intermedia

What are merkel discs are where are they found?

Light pressure receptors found in the stratum basale

What are Langerhans cells and where are they found?

Dendritic cells in the epidermis

What are dermal papillae?

Projections of the papillary (upper) dermis into the epidermis

What are rete ridges?

Projections of the epidermis down into the dermis which create interlocking junctions with dermal papillae.

What are the components of the skin ecosystem called?

Microbiota

How does microbiota colonisation happen in dogs?

Microbes are transferred onto the skin from the mother’s oral mucosa when she tears open the amniotic sac.

What are the 3 categories of microorganisms in the skin microbiota?

Residents - permanently present

Transient - temporarily inhabit the skin

Nomads - very briefly inhabit the skin

What is the most common skin commensal?

Staphylococcus spp.

What is the role of the skin microbiota?

To compete with pathogens to prevent colonisation and to secrete antimicrobial or anti-virulence molecules.

What is the papillary dermis?

The upper thin layer of the dermis which is composed of loose connective tissue.

What is the dermis made up of?

Collagen, elastin, water, GAGs, proteoglycans, blood supply, lymphatics, nervous innervation.

How does elastin structure vary within the dermis?

Superficially, it is perpendicular to the skin surface and deeper it is horizontal, allowing top layers to slide.

What are Meissner’s corpuscules and where are they found?

Nerve endings which detect light touch and itch, found in the papillary layer.

What are Pacinian corpuscles?

Nerve endings wrapped in layers of membranes with gel between them. they detect deep pressure and are found in the deep dermis and subcutis.

What do pilosebaceous units consist of?

An outer connective tissue sheath, and inner epithelial root sheath, and a hair bulb which contains the hair matrix.

What is the dermal papilla?

A structure which invaginates into the hair bulb, containing mesenchymal stem cells and transient amplifying cells which signal to each other to divide and produce the hair shaft and root sheath.

What are arrector pili muscles?

Smooth muscles originating in the dermal papillary layer which attach to the bottom of the hair follicle and cause piloerection.

What are the layers of the hair follicle?

1. Outer cuticle

2. Cortex (pigemented)

3. Inner medulla

What is the root of the hair?

The portion of hair below the skin

What is the shaft of the hiar?

The portion of hair above the skin

What are simple hair follicles?

One hair shaft leaves the skin via a single opening

What are compound hair follicles?

Multiple hair shafts leave the skin via a single opening

What are the stages of the hair growth cycle?

1. Anagen = growth

2. Catagen = transition

3. Telogen = resting, hair loss

What are the 3 portions of the hair follicle present in anagen?

Infundibulum - top, above where the sebaceous gland enters the follicle

Isthmus - middle, above where the arrector pili inserts on the follicle

Inferior - bottom, only present in anagen

What shape is the follicle in anagen?

Bulb shaped and attached to the dermal papilla

What shape is the follicle in catagen?

bulb shaped and detached from the dermal papilla

What shape is the follicle in telogen?

club shaped and high in the dermis

How are whiskers different to normal hairs?

Their follicles are blood-filled nerve endings.

What are sebaceous glands?

Glands attached to the hair follicles which produce sebum via holocrine secretion

What are sweat glands?

Large exocrine glands deep in the dermis?

What are atrichial (eccrine) sweat glands?

Glands which secrete fluid which is similiar to plasma directly onto the skin surface. Heavy sweating is saltier as there is less time to reabsorb NaCl.

What are epitrichial (apocrine) sweat glands?

Glands which secrete a thick fluid into the hair follicles.

What does the subcutis contain?

Adipose tissue, collagen, elastin