Integument Flashcards
Integumentary system - functions
- Protection - external barrier protecting underlying structures from physical trauma and invading organisms
- Sensory - sensory nerve endings in the surface of the skin to monitor the external environment
- Secretion - range of glands present in skin to produce secretions onto the surface
- Production - vitamin D is synthesised in the skin
- Storage - fat is stored in the hypodermic for energy and insulation
- Thermoregulation - mechanisms present to both increase and decrease heat loss
- Communication - scents and pheromones can be produced. Visual communication
Skin
The skin is composed of layers:
- Epidermis - the superficial layer
- Dermis - the underlying layer
- Hypodermis - lies beneath the skin
The epidermis
- Stratified squamous epithelium
- These cells are continuously renewed via mitosis
- New cells are produced in the deepest layers of the epidermis and pushed to the surface
- The dead cells are shed to the surface
Cell types: - Keratinocytes = produce keratin, the tough fibrous, waterproof protein that gives skin its resiliency and strength
- Melanocytes = produce melanin pigment
- Merkel cells = close to the nerve endings that receive the sensation of touch
- Langerhans cells = found in the stratum spinosum; involved in allergic and cell-mediated immune response in the skin
Keratinocytes
- Make up 70-80% of the cells in the skin
- Structured and repackaged by 2 organelles in the cell, before it moves to the extracellular space
Epidermal layers
1) Stratum germinativum/ Basal layer
2) Stratum spinosum - Spiny layer
3) Stratum granulosum - Granular middle layer
4) Stratum lucidum - Clear layer
5) Stratum corneum - Outermost layer
Keratinisation
- Begins at granulosum
- Manufacture of skin cells starts at the base layer of the epidermis
- Keratinocytes are the primary cells that make up the epidermis
- As these cells move from deep to superficial layers they start to die (apoptosis)
- This releases both glycolipids (fat - hydrophobic) and keratin (protein)
- These form a waterproof barrier around the outside of the epidermis
Dermis
- Composed of dense irregular connective tissue
- Contains hair follicles, nerve endings, glands, smooth muscle, blood vessels and lymphatics
Also includes: - Fibroblasts, adipocytes, and macrophages also present
2 layers: - Papillary layer
- Reticular layer
Papillary layer (dermal)
- Underneath the epithelial layer of the epidermis
- Dermal papillae help cement the epidermis and the dermis together
- Blood vessels, pain, temperature, and touch receptors also present
- Blood vessels in this layer are important for thermoregulation
Dermal layers - reticular
- Consists of dense irregular connective tissue
- in areas where a great deal of bending occurs, dermal folds or flexure lines are present
Hypodermis
- Composed of areolar/adipose tissue, blood and lymphatic vessels, and nerves
- Contains special touch receptors - the Pacinian corpuscle and Meisner’s corpuscle
- Hypodermic layers permits skin to move freely over underlying bone and muscle without putting tension on the skin
Special features of integument
- Pigmentation
- Paw pads
- Planum nasale
Pigmentation
- Melanin is produced by…
- Pigmentation is the result of the presence or absence of melanin granules in the extensions of melanocytes
- The more granules present, the darker the pigmentation
- Keratocytes arrange melanin on the side of the cell with greatest amount of sun exposure
- Acts to protect keratocytes from exposure to damaging UV rays
Paw pads
- Thick layers of fat and connective tissue with exocrine sweat glands
- Outer surface is the toughest and thickest skin in the body
- Stratum corneum is thicker than all other layers combined
Planum nasale
- Top of the nose in cats, pigs, sheep and dogs
- Usually pigmented
- Mucus produced by glands within nose
- Innervated by trigeminal nerve
Chelonians
These include he species: Tortoise, terrapins and turtles
Hair
- Functions in maintaining body temperature and camouflage
- Hair shaft: visible above the skin
- Hair root: buried within the skin
- Hair follicle: anchors the hair
- Hair bulb: hair grows from here
Hair structure
- Inner medulla
- Outer cortex
- Covers with cuticle
Hair growth
- Anagen phase: cells are added at the base of the root, hair lengthens
- Catagen phase: period of transition
- Telogen phase: maximum length of hair is achieved, hair stops growing, hair follicles soften, and hair is held in a resting phase
- Shedding: new hair pushes old hair out of follicle
Types of hair
1) Primary or guard hairs - forms the outer coat
- Arrector pili muscle attached here (allows the hair to stand on end)
2) Secondary or wool-type hairs - form the undercoat
3) Tactile (or sinus) hairs -
- Contain numerous sensory endings
- Commonly known as whiskers. Also mixed intermittently throughout the hair coat
Glands of skin
- Sebaceous glands
- Sweat glands:
- Eccrine sweat glands (secretions exit onto the skin)
- Apocrine sweat glands (secretions onto the hair follicle)
- Tail glands
- Anal sacs
- Mammary glands
Exocrine cell types
Apocrine glands store their secretions and the release them in enclosed membranes
Sebaceous glands
Sebum:
- Composed primarily of glycerides and free fatty acids
- Coats the base of the hair surrounding skin
- Helps trap moisture, keep hair soft, pliant, and somewhat waterproof
- Sebum also helps reduce the skin’s risk of infection
Tail gland
- Also called preen gland
- Oval region at the dorsal base of the tails of most dogs and cats
- Contains coarse, oily hairs
- Very large apocrine and sebaceous glands present
- Thought to assist with recognition and identification of individual animals
Anal glands
- Circumanal glands
- Lined with sebaceous and apocrine glands
- Responsible for pheromone production
- Expressed naturally when dog/cat defecates
- Coats faeces
- Anal glands can become impacted and abscessed. They can require flushing, antibiotic administration, and in some cases removal
Mammary glands
- Modified skin glands
- Bitches = 5 pairs
- Queens = 4 pairs
- Glandular epithelium lined with secretory epithelium
