Veterinary Histology: Integument

Front 1

Functions of the skin

Back 1

- protective barrier from external environment
- temperature homeostasis
- sensory information
- endocrine function (vitamin D and UV light)
- excretion (sweating)
- immune function (Langerhan cells)

Front 2

Epidermis (general)

Back 2

- stratified, squamous, keratinized epithlium
- on the surface
- desquamation: continuous loss of cells due to wear and tear

Front 3

Dermis (general)

Back 3

- dense connective tissue (mostly collagen) for strength and support for epidermis
- deeper regions are called the hypodermis and have lots of fat
- muscle in skin includes panniculus sarcosus (skeletal) and arrector pili (smooth)

Front 4

Layers of the epidermis

Back 4

- starting with the deepest layer:
1. Stratum basale (stratum germinativum): mitotically active stem cells
2. Stratum spinosum: spinous connections between cells
3. Stratum granulosum: keritohyalin granules
4. Stratum lucidum: only found in thick skin
5. Stratum corneum: keratinized layer

Front 5

Dermis layers

Back 5

- superficial/papillary region: loosely organized collagen fibers with dermal papillae which correspond with similar projections of the epidermis called rete ridges (they interlock and provide more surface contact between epidermis and dermis for added support)
- deep/reticular layer
- dermis contains blood vessels, nerves and muscle that supply the epidermis

Front 6

Cell types of the epidermis

Back 6

- keratinocyte
- Melanocyte
- Langerhan cell
- Merkel Cell

Front 7

Keratinocyte

Back 7

- predominates
- stem cells make up the stratum basale and these cells differentiate into mature, keratin-producing cells as they move toward the surface

Front 8

Melanocyte

Back 8

- found in basal layer between the keratinocytes
- look like dendritic cells due to their long, cytoplasmic processes
- produce and secrete melanin which protects the epidermis from UV radiation
- can transfer melanin granules to neighboring keratinocytes (pigment donation)

Front 9

Langerhan Cell

Back 9

- dendritic
- encounters foreign antigens int he skin and present them to other cells in the immune system

Front 10

Merkel Cell

Back 10

- modified epidermal cells of the basal layer
- have sensory function
- closely associated with the terminal bulb of afferent nerve fibers

Front 11

Dermal papilla

Back 11

- highly vascular
- protrudes upward into an expanded region at the base of the hair shaft called the hair bulb

Front 12

Is hair and feather growth continuous?

Back 12

NO.

Front 13

Stages of hair growth

Back 13

- Anagen phase: active growth of hair shaft
- Catagen phase: brief period where growth ceases
- Telogen phase: long rest period in which the follicle atrophies and the shaft falls out or is pushed out by growth of a new hair follicle

Front 14

Stages of feather growth

Back 14

- similar to hair growth
- periods of feather growth (endysis) are interspersed with molting (ecdysis)
- takes about 6 weeks for a new feather to completely grow out

Front 15

Sinus or Tactile hair follicles

Back 15

- specialized hair follicles found in the head region of many species and represented by the cat whiskers
- large, single follicles
- have blood sinuses between the inner and outer layers of the dermal root sheath of the follicle

Front 16

Sebaceous glands

Back 16

- develop as outgrowth of the hair follicle
- produce sebum
- holocrine
- have well developed Golgi, ER, ribosomes, mitochondria (characteristic of a secretory cell)

Front 17

Apocrine sweat glands

Back 17

- large-lumen, coiled, tubular glands
- most common type of sweat gland in the skin of dogs and cats but not humans
- merocrine secretions...
- secrete pheromones

Front 18

Eccrine sweat glands

Back 18

- independent structures, unassociated with hair follicles
- simple, blind-ended, coiled tubular architecture with two segments
- secretory segment has secretory cells at the more terminal end of the gland
- duct segment is at the proximal portion of the gland and leads to the epidermal surface
- produce a watery secretion (sweat)
- only found in the foot pad region of dogs and cats
- has 3 cell types: clear cells, dark cells, myoepithelial cells

Front 19

Clear cells

Back 19

- produce the water component of sweat
- contain large amounts of glycogen

Front 20

Dark cells

Back 20

- large amounts of ER, secretory granules and Golgi suggest high glycoprotein secretion

Front 21

Myoepithelial cells

Back 21

- only in the basal part of the gland
- many actin filaments
- contractions of these cells results in rapid sweat expression

Front 22

Anal Sacs

Back 22

- paired cutaneous diverticula
- have ducts that lead into the anal canal
- ducts and sacs are lined by keratinized, stratified, squamous epithelium
- glands of the anal sac are modified sweat glands and their secretion is very smelly
- anal sac gland carcinoma is a common, highly malignant tumor

Front 23

Circumanal glands

Back 23

- only in dogs
- lobulated, modified sebaceous glands
- located in cutaneous region of anus
- influenced by sex hormones (increase in size during puberty and regress in older dogs)
- hepatoid gland has been used to describe them because they look like liver
- common site of neoplasia (benign)

Front 24

Mammary glands

Back 24

- modified apocrine sweat glands
- branch, tubuloacinar
- mammary gland epithelium varies a lot during lactation
- merocrine (protein) and apocrine (lipid) secretion
- estrogen and progesterone are needed for development of mammary gland tissue
- Prolactin governs milk production

Front 25

Mammary gland epithelium and lactation

Back 25

- during active lactation the basal portion of the acinar epithelial cells have a well developed endoplasmic reticulum

Front 26

Equine hoof

Back 26

- special relationships between dermis (laminar corium) and overlying epidermis
- the lamellar interaction between the epidermis and dermis that gives the hoof its strength
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Front 27

Hoof wall

Back 27

- composed of dense keratin or horn
- innermost hoof wall is epidermal lamellae which represent an exaggerated manifestation of dermal papillae and epidermal pegs called primary and secondary lamellae
- secondary lamellae are at right angles to primary lamellae and this provides a strong bond between the hoof wall and underlying laminar corium

Front 28

Laminitis

Back 28

- vascular damage to blood vessels of the laminar corium results in edema and tissue swelling
- since this region cannot adapt for such swelling there is compression which results in ischemia
- then there is necrosis of the laminar corium leading to separation of the hoof wall from teh laminar corium
- ouch.