What is another term for skin?
Common integument
What are the main functions of the skin?
- Protection
- Barrier to microbial penetration and water
- Thermoregulation
- Sensory perception
- Storage organ (adipose tissue)
- Synthesis of vitamin D
- Photoprotection
- Immunosurveillance
- Capture of prey (claws)
Name the 3 layers that make up skin and what they comprise of
- Epidermis - stratefied, keratinised, squamous epithelium that rests upon a basement membrane
- Dermis - dense irregular connective tissue
- Hypodermis - loose connective tissue consisting mainly of adipose cell. Muscle underlies it
What are the 2 types of hair follicle?
Simple and compound
What are the differences between compound and simple hair follicles?
Compound hair follicle - multiple follicles exit out of one opening (carnivores)
Simple hair follicle - one follicle exiting out of one opening (ruminants and horses)
What structures are found in the dermis?
- Sebaceous glands
- Sweat glands
- Hair follicles
What is the clinical importance of the common integument?
- Indicator of systemic conditions
- Economic significance in food producing animals
- Allergies, dermatitis and parasitic infections
- During most surgical procedures the skin is incised through
Describe the structure of the epidermis
4 layers:
- Stratum corneum - cells are dead, no nuclear material, outermost layer constantly sloughed off and replaced by underlying cells
- Stratum granulosum - cells differentiate to become spindle cells
- Stratum spinosum - contains differentiating cuboidal cells, melanocytes and Langerhans cells
- Stratum basale - basale cells
Describe the process of keratinisation
- basale cells produce keratin 5 and 14, and tonofilaments
- in the spinosum, keratin 1 and 10 are produced instead of 5 and 14. Lamellar bodies appear as cells reach the granulosum
- in the granulosum, fillagrin forms profillagrin causing keratin to aggregate. Nuclear breakdown begins and lipid forms in the lamellar bodies
- in the corneum, cornified envelope forms and lamellar bodies release lipid to form a lipid bilayer. Corneodesmosomes rivet the corneocytes (squames) together
What does dermal connective tissue comprise of?
- cells - fibroblasts, mast cells, plasma cells, macrophages, adipocytes, melanocytes, lymphocytes, neutrophils
- fibres - collagen, reticular and elastic
- ground substance - proteoglycans and glycoproteins
What are the functions of hair?
- thermoregulation
- sensory perception
- mechanical protection
How do hair follicles develop?
- localised thickening of epidermis (ectodermal bud)
- this grows down into the underlying mesenchyme
- sebaceous and sweat glands are derived from surface epidermis
- matrix cells have a close association with dermal papilla which supplies them with blood to allow them to multiply and differentiate
- matrix cells form the hair and inner root sheath
Draw the structure of a hair follicle
Explain the hair cycle
- Terminal follicle (anagen) - hair is at full length
- Regressive stage (catagen) - relationship between matrix and dermal papilla is lost
- Quiescent stage (telogen) - follicle disintegrates
- Renewed growth (endogen) - restablish relationship between dermal papilla and matrix, new hair pushes old out and replaces it
- Anagen - hair is at full length
How are signals from whiskers amplified?
Between the layers of the follicle sheath is a blood filled sinus which amplifies the signal from the whisker. Nerve at the dermal papilla transmits the signal.
What is the role of sebaceous glands?
- secrete sebum which waterproofs, increases suppleness of skin and spreads sweat
- excretory duct empties onto hair follicle
- halocrine secretion (cell explosion)
What is the role of sweat glands?
- thermoregulation, excretion, scent signalling
- secretory portion of gland is made up of simple cuboidal epithelium made up of myoepithelial cells
- apocrine and exocrine secretion
