A&P Ch. 6

An immunosuppressed dog presents with red, hairless patches. Microscopic examination reveals a long, thin organism living its hair follicle.

Demodex mange

What type of cells does the basal layer contain?

Merkel cells, melanocytes, keratocytes

A common name for stratum granulosum is?

granular layer

A common name for stratum spinosum is?

spiny layer

What are Merkel cells?

oval-shaped mechanoreceptors essential for light touch sensation and found in the skin

What are Melanocytes?

produce melanin pigment

White fur on a cat appears yellow in discrete areas.

Salivary staining from over grooming

Epidermis on hairy skin had what kind of folds.

Scalelike

What factors stimulate contraction of the arrector pili muscle? Why is this muscle important?

The sympathetic nervous system stimulates the contraction of the arrector pili muscles when an animal is frightened or cold. This reaction is a defense mechanism designed to make the animal appear bigger and therefore less vulnerable to potential predators. In addition, hair that stands erect can better trap insulating layers of air than can nonerect hair, so animals with erect hair coats stay warmer than animals with flat coats. The arrector pili muscle also is responsible for forcing sebum from the sebaceous gland, which helps keep the integument moist and supple.

What is clear layer composed of?

a few rows of flattened dead cells

What are Keratinocytes?

produce keratin, the tough, fibrous, waterproof protein that gives skin its resiliency and strength

Hairy skin has how many layers?

3 rather than 5 layers

What are three cycles of hair growth?

1. Anagen is the time of hair growth. 2. Telogen occurs when the maximum length of hair is achieved, the hair stops growing, the hair follicle shortens, and the hair is held in a resting phase. 3. Catagen is the period of transition between the anagen and telogen phases.

Why is skin important? Can you think of six important functions of skin?

1. Skin covers and protects underlying structures. 2. By forming a critical barrier between the delicate inner workings of the body and the harsh elements of the external world, skin prevents desiccation and reduces the threat of injury. 3. Skin assists in the maintenance of normal body temperature via sweating and shivering and the presence of features such as hair and sebaceous glands. 4. Skin excretes water, salt, and organic wastes. 5. Skin is an important sensory organ that takes in information from the environment through touch and pressure and conveys this input to regions of the central nervous system. 6. Skin is engaged in the synthesis of vitamin D and the storage of nutrients

What happens in each layer?

1. The stratum germinativum, also known as the stratum basale (basal layer). For the most part, this layer consists of a single row of keratinocytes, which are firmly attached to the epithelial basement membrane and actively engaged in cell division. New daughter cells move from the stratum basale to sequentially more superficial layers as they mature. In this way, they replace epithelial cells that have exfoliated at the skin's surface. Merkel cells and melanocytes are found in this layer. 2. The stratum spinosum (the prickle-cell layer). The stratum spinosum (spiny layer) is so named because when the cells of this epidermal layer are fixed for histologic exam, they contract into speculated masses that resemble sea urchins. It contains several layers of cells that are held together by desmosomes. 3. The stratum granulosum (granular layer) is the middle layer of skin. Composed of two to four layers of flattened, diamond-shaped keratinocytes, the stratum granulosum is the highest level of the epidermis where living cells can be found. The cytoplasm of these cells begins to fill with keratohyalin and lamellated granules, which in turn leads to the dramatic degeneration of the nucleus and other organelles. Without these vital parts, the cell quickly dies. The lamellar granules contain waterproofing glycolipids and are transported to the periphery of the cell, where their contents are discharged into the extracellular space. These glycolipids play an important role in waterproofing the skin and slowing water loss across the epidermis. 4. The stratum lucidum (clear layer) is found only in very thick skin. Most skin, therefore, lacks this layer. Microscopically, the stratum lucidum appears as a translucent layer composed of a few rows of flattened dead cells. In this and the outermost epidermal layer, the sticky contents of the keratogranules combine with intracellular tonofilaments to form keratin fibrils. 5. The stratum corneum (horny layer) is the outermost layer and dominates the epidermis. It constitutes up to three quarters of the total epidermal thickness and is composed of 20 to 30 rows of keratinocytes. On sagittal section, the cells are paper thin and almost two dimensional, yet when viewed from above, they appear hexagonal. These are really only the remnants of keratinocytes, because the actual cells died in the stratum granulosum. They are sometimes called horny or cornified cells, but we commonly call them dandruff and recognize them as the flakes that occasionally drop on our shoulders.

The horny layer constitutes how much of the epidermal thickness?

3/4

The horny layer is composed of what?

20-30 rows of keratocyte "remnants" Sometimes called horny or cornified cells

Where are anal sacs found and what is their importance to animal?

5 and 7 o'clock positions relative to the anus. When the animal defecates or becomes frightened, some or all of the anal sac contents are expressed.

The reticular layer is _% of dermis?

80%

What does the basal layer consist of?

A single row of keratocytes attached to epithelial basement membrane

Why does hair turn gray and then white as animals age?

As animals age, melanin production decreases, and the hair begins to turn gray. White hair is formed when the cortex loses its pigment entirely and the medulla becomes completely filled with air.

A golden retriever scoots its face along the carpet and is repeatedly licks the tops of its paws

Atopy

What is the deepest layer?

Basal

A dog presents with a black pigmented excoriated, hairless area on a front limb. Owner reports the dog has been constantly scratching area for months.

Chronic Allergy

The spiny layer consists of?

Contains several layers of cells held together by desmosomes

How are paw pads and the planum nasale different from other regions of the skin?

Digital pads are formed by thick layers of fat and connective tissue that bear the weight of the animal. The pad's outer surface is the toughest and thickest skin in the body. It is often pigmented and is composed of all five epidermal layers. Of these five layers, the outermost epidermal layer, the stratum corneum, is thicker than all the others combined. This tough outer skin together with insulating fat forms a protective barrier against abrasion and thermal variances, enabling the animal to walk on rough surfaces, hot roads, and cold snow. The surface of the pad feels rough, and an uneven surface is visible to the naked eye. The pad is composed of exocrine sweat glands and lamellar corpuscles. Histologically, the ducts from these sweat glands can be seen passing through the dermis to the stratum basale of the epidermis. Their glandular excretion is then excreted onto the surface of the pad. The planum nasale is usually pigmented and appears to be a tough, thick region of integument histologically; however, the planum nasale in the dog is composed of only three epidermal layers, with the stratum lucidum and stratum granulosum absent. The outermost layer, the stratum corneum, is composed of only four to eight cell layers, surprisingly thin considering the exposed location of the nose and its heavy use, particularly in the dog. The epidermal surface of the planum nasale is divided by deep surface grooves, giving it the appearance of being composed of multiple plaques. As with other regions of the skin, the dermis and epidermis interdigitate to form an irregular line of attachment that includes dermal papillae. Although often moist from nasal secretions and licking, the planum nasale in the dog contains no glands in the epidermis or dermis. However, in the sheep, pig, and cow, tubular glands are found.

A cat presents with excessive licking, grooming, and face scratching with a hind leg.

Ectoparasite

The medial sides of the hind legs of a chow appear chewed in a corn cobbed pattern.

Ectoparasite

Epidermis cells are made up of?

Keratinocytes, Melanocytes, Merkel cells, Langerhanscells

What type of cells does the spiny layer contain?

Langerhans cells

What are skin and related structures?

Largest most extensive organ system in the body, Hair, hooves, horns, claws, skin-related glands

Where is the laminar corium located and what is the function?

Located between the hoof wall and third phalanx. Function is provides nutrients to the stratum internum.

An aged gray horse presents with nodules under the tail base and the scrotum. Nodules at first appeared small, then grew, ulcerated and spread to internal organs.

Malignant melanoma

A rabbit presents with small hairless areas on its ears and small lesions beginning on its face.

Mange (Notoedres)

A boarder collie appears with red hairless patches on its eyebrow caps and the edges of its ears. The owner reports the dog cannot sleep and is constantly scratching and appears to be miserable.

Mange (sarcoptic)

What causes pigmentation of skin?

Pigmentation is caused by the presence or absence of melanin granules in the armlike extensions of the melanocytes. Macroscopically, no pigmentation is apparent if the granules are concentrated around the nucleus in the cell body of the melanocyte. As the granules move into the cellular arms and into the surrounding tissue, however, pigmentation becomes apparent. The more granules that exist in the arms of the melanocyte and surrounding tissue, the darker the pigmentation. The dispersion of granules is controlled by the release of melanocyte-stimulating hormone, which, in turn, is controlled by the intermediate lobe of the hypophysis. The melanosomes are transported to the tips of the cellular projections, where they are released into the intracellular space and ultimately absorbed by keratinocytes, which arrange the melanin on the side of the cell with the greatest amount of sun exposure. In this way, pigment acts to protect cells from the damaging effects of ultraviolet rays.

What are Langerhans cells?

Projections form a weblike frame around the keratinocytes

What happens between the shoulder blades?

Shots are given here and micro chipping.

How is the skin of hairy animals different from that of human?

Skin covered with fur usually consists of three epidermal layers rather than five. These layers are the stratum basale, stratum spinosum, and stratum corneum. The stratum granulosum and stratum lucidum are generally missing. A few regions of five-layered epidermis can be found in furry mammals, but these are usually seen in places where the keratinization process has slowed and the skin is very thick. The surface of "hairy skin" is covered in scalelike folds. Hair emerges from underneath the scales and is directed away from the opening of the hair follicle. In dogs the hair is organized in clusters of three follicles per scale. Periodically throughout the surface of the epidermis a knoblike elevation can be seen. This is called a tactile elevation, or epidermal papilla. Each tactile elevation is usually associated with a tactile hair. These special hairs are called tylotrich hairs, and they are important in the perception of touch.

a white cat presents with circular ulcerated lesions on its nose tissue has been eroded by the lesion

Squamous cell carcinoma

Why is keratinization and important process?

The cells expire and in doing so form the vital protective layer that help's enables an animal's survival.

What is keratinization?

The formation of a layer of dead, protective cells filled with keratin

How does the hair form and grow?

The part of hair visible above the skin is called the shaft, and the portion buried within the skin is called the root. A web of sensory nerve endings called the root hair plexus envelops the root, making it an important touch receptor when the hair is bent. Hair is anchored by the hair follicle. The follicle is an invagination of the epidermis that extends from the skin surface to the dermis or, occasionally, the hypodermis. The deepest part of the hair follicle expands to form a hair bulb. At the base of the bulb is a mound of dermal cells called the papilla. The papilla is covered with rapidly dividing epithelial cells called the matrix. These cells are nourished by blood flow from vessels in the underlying papilla, which stimulates much cell division and growth. As cells divide, older cells are pushed upward into the follicle tunnel away from the papilla. These cells become keratinized, and as they lose contact with the nutrition provided by the papilla, they die and become part of the developing hair. In this way, hair is constructed from dead epithelial cells. The wall of a hair follicle is composed of three layers: an internal epithelial root sheath, an outer epithelial root sheath, and a dermal or connective tissue root sheath. Animals with fur often have compound follicles in which multiple hair strands emerge from a single epidermal orifice, or pore, although each strand has its own follicle and bulb. As many as 15 hairs may be associated with one pore. Usually in compound follicles a single long primary hair (also known as a guard hair or cover hair) is surrounded by shorter secondary hairs called satellite hairs. In dogs, usually three compound follicles are grouped together to emerge from the same epidermal fold. Hair is formed in three concentric layers. The innermost layer (and central core) is called the medulla. It is composed of two to three layers of loosely arranged cells that are separated by spaces filled with liquid or air. The cells themselves contain flexible, soft keratin similar to that found in the stratum corneum of the epidermis. Surrounding the medulla is the cortex. Unlike the flexible medulla, the cortex is stiff and rigid because it is composed of hard keratin and is the thickest of the three layers. A single layer of cells arising from the edge of the papilla form the hair surface, the cuticle, which is also composed of hard keratin. The cells of the cuticle are layered like shingles on a roof, which prevents the hairs from sticking together and forming mats. In some animals such as sheep, however, the edges of the cells in the cuticle are raised, enabling them to grab onto the cuticle cells from other hair strands.

Name two types of sweat gland. How are they different from one another?

Two types of sweat glands are eccrine and apocrine. The excretory portion of the eccrine gland consists of a simple coiled tube located in the dermis or hypodermis and connected to the surface of the skin by a long duct. In dogs, eccrine sweat glands are found only in the deep layers of the fat and connective tissue of footpads. Like eccrine sweat glands, apocrine sweat glands have a coiled excretory portion buried in the dermis or hypodermis with a single excretory duct. However, unlike eccrine sweat glands, apocrine glands empty into hair follicles rather than onto the surface of the skin. In the dog, apocrine glands are located in the external ear canal.

How is the dermis different from the epidermis?

Unlike the epidermis, which is primarily cellular, the dermis is highly fibrous. It is composed of dense, irregular connective tissue that contains collagen, elastic, and reticular fibers. Hair follicles, nerve endings, glands, smooth muscle, blood vessels, and lymphatics are all found in the dermis as well, creating a rich and interesting tissue community. Fibroblasts, adipocytes, and macrophages also are present and represent the most commonly found cellular elements. The dermis is a tough layer that binds the superficial epidermis to the underlying tissues. It represents the "hide" of the animal and is used to make leather.

Where is the thinnest layer of skin located?

around eyes & scrotum

what are two other layers found in the Dermis?

papillary layer & reticular layer

A dog presents with a tumor that cab be palpated in its neck. The owner reports it has been present for some time without a change in size.

basal cell carcinoma

A common name for stratum basale is?

basal layer or stratum Germinativum.

Langerhans cells originate where? Where do they migrate?

bone marrow & migrates to skin

What is dermal papillae?

cement the epidermis and the dermis together

Where is the thickest layer of skin located?

center of the back, between the shoulder blades & paw pads

A common name for stratum lucidum is?

clear layer

What is in the dermis?

collagen, elastic, reticular fibers,hair follicles, nerve endings, glands, smooth muscle, blood vessels, lymphatic channels, fibroblasts, adipocytes, macrophages

What are the functions of skin?

covers and protects, prevents desiccation, reduces threat of injury, assists in maintenance of normal body temperature, excretes water, salt, organic wastes, receives and conveys sensory information, synthesizes vitamin D, stores nutrients

What does the reticular layer consists of?

dense irregular connective tissue

tactile elevations are also known as?

epidermal papillae

3 layers of the Integumentary System

epidermis, dermis = corium, hypodermis = subcutaneous layer

What are Langerhanscells?

found in stratum spinosum; may be involved in allergic and cell-mediated immune response in skin

Where is the coronary corium located and what is the function?

found in the coronary sulcus and supplies nutrients to the stratum externum and stratum medium.

greatest portion of integument is?

hide

A common name for stratum corneum is?

horny layer

Where is the clear layer found?

in thick skin (most skin lacks this layer)

Where does the papillary layer lie?

just below the epidermis

Where is the perioplic corium located and what is the function?

located between the perioplic sulcus and supplies nutrients to the overlaying periople.

The papillary layer contains?

looping blood vessels, and nerve endings

What is the papillary layer composed of?

loose connective tissue with loosely woven fibers and ground substance

A duroc-Jersey breed of pig presents with a tumor in the ocular orbit.

malignant melanoma

The papillary layer is responsible for?

pain, temperature, touch receptors

A cow presents with a circular ulcerated lesion on its eye and surrounding eyelid.

squamous cell carcinoma

List 5 layers of the epidermis.

stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum

Name the Layers of the Epidermis.

stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum basale

Where frog corium located and what is the function?

superior to the frog and provides nutrients to the frog

Where sole corium located and what is the function?

superior to the sole and provides nutrients to the sole.

parallel bundles of collagen fibers in the reticular layer

tension lines & dermal folds or flexure lines

Papillary layer

thin superficial layer of the dermis

What is the granular layer composed of?

two to four layers of flattened, diamond-shaped keratocytes that contain lamellated granules of glycolipids

tactile hairs are also known as?

tylotrich hairs

What does the granular layer do?

waterproof the skin and slowing water loss across the epidermis