Histology Flashcards
Name the 3 layers of the integument.
Epidermis
Dermis
Hypodermis
What are the epidermal derivatives?
Follicular structures - hair and feather
Glandular structures - sebaceous and sweat glands
Keratinous structures - hoof, nail, beak and claw
Describe plantar skin.
- Hairless, no hair follicles
- No sebaceous or sweat glands associated with hair follicles.
- Thick layer of epidermis.
Name and describe the 4 layers that keratinocytes are arranged in.
Basal layer – stratum basale. Single layer of cells anchored by semi desmosomes and attached move towards surface from basal layer, taking about 4 weeks.
Prickle cell layer – stratum spinosum. Thickest layer. Cells that begin to start making keratin.
Granular layer – stratum granulosum. Mya be multiple layers but not as thick as prickle layer. Dead cells with nothing but keratin within them. How many layers depend on location.
Keratinised layer – stratum corneum. Flake off.
Name the 3 non-epithelial cells in the epidermis.
Melanocytes
Dendritic (Langerhans) cells
Merkel cells
Describe the structure and function of melanocytes.
- Attached to basement membrane with anchoring filaments
- Located in basal epidermis
- Smaller than keratinocytes
- Surrounded by a clear space
- Easily confused with mitotic bodies
- Melanin is synthesised from tyrosine in melanosomes
- Keratinocytes gain melanin from melanocytes
- Small round black cells with a halo around through a light microscope
Describe dendritic (Langerhans) cells.
- Dendritic, antigen-presenting cells
- Mobile and present throughout epidermis
- Dendritic processes extend between keratinocytes
- The cells are also present in the dermis, other epithelia and lymphoid organs
Describe merkel cells.
- Intra-epidermal touch receptors, occur in groups, maybe in domes
- Synapses with large myelinated afferent fibres in dermis
- Highest population density is in hairless skin (digits and lips) and in hair follicles
- Not visible in routine preparations: needs immune-histochemistry or EM
Describe the structure of the dermis.
- Superficially contains loosely arranged collagen, elastic fibres and fibroblasts
- Deeper layer may contain more densely arranged collagen and elastic fibres
- Numerous small blood vessels and nerves
- Thickness is highly variable, depending on site (thin on eyelids, thick on soles)
- Contains epidermal derivatives – hair follicles and sweat glands
What is the structure of the hypodermis?
Variable thickness and composition, predominantly composed of loose adipose tissue arranged in lobules. Lobules are separated by thin bands of fibrous tissue (interlobular septae).
What are 3 functions of subcuticular adipose tissue?
- Insulation
- Energy storage
- Shock absorption
Describe the structure of hair follicles.
- Complex epidermal invaginations
- Hair unit: follicle, arrector pili muscles, sebaceous and sweat glands
- Sinus hairs: (whiskers) specialised tactile hairs, follicles are surrounded by cavernous blood spaces
What are sebaceous glands?
- Develop as an outgrowth of the external root sheath
- Tarsal glands – enlarged sebaceous glands which open on the eyelid margin
- Holocrine glands
Describe holocrine glands.
- Secretion (sebum) formed from disintegrated cells and discharges on to hair shaft
- Sebum is oily and coats the hair and skin surface
- Lost cells are replaced by mitosis of basal cells
Describe the 3 portions of the eccrine/atrichial sweat glands.
- Secretory portion
- Ascending and initial intra-epidermal portion
- Spiral intra-epidermal portion
Describe the structure of apocrine/apitrichial sweat glands.
- Coiled tubular glands
- Secretory portion is located in the dermis and/or hypodermis
- Ductal portion is similar in appearance to an eccrine duct
- Secretion is into adjacent hair follicle
What is the function of apocrine/epitrichial sweat glands?
Lubrication and scent and us under hormonal control
Identify the histological features of a neonatal foal hoof.
- Peripole epidermis - soft horn
- Proliferation zone of periopic corium
- Dermal papilla in tubule
- Intertubular horn
- Proliferation zone of coronary corium
- Horn tubules
- Primary lamina
- Secondary lamina