Integument System 2

What are the 3 main layers of the skin?

Epidermis, dermis, hypodermis

What are the epidermal layers bottom to top?

Stratum germinativum/basale, Stratum spinosum, Stratum granulosum, Stratum lucidum, Stratum corenum.

what cells can you find in the skin?

Keratinocytes, Melanocytes/Melanin, Langerhans cells, and Merkel Cells/Disks

Define Keratinocyte(s).

A cell that lives in the basement membrane that produces keratin, a tough waterproof substance. Grow and divide, pushing old cells superficially.

Define keratinization. 

The process that keratinocyte cells go through as they are pushed superficially; as they are pushed, they fill with keratohyline granules, losing organelles, dying, and becoming keratin sheets. 

Length of time for a whole new epidermis to form?

7-8wks in humans.

Define melanocyte.

A cell that produces melanin, the pigment that causes darkness. In deepest epidermal layer. Armlike projections reach out to keratinocytes of the basal layer. 

Define Langerhans Cell.

A specific type of macrophage (WBC) that is endemic ONLY to the epidermis. They phagocytize invaders. 

Define Merkel Cell.

A cell that aids in touch perception. At the epidermis and dermis junction. Contains Merkel disks, which are the components of the Merkel cell and complementary nerve endings.

Describe the Straum basale/germinativum.

Bottom-most layer of epidermis. Single layer of keratinocytes. Merkel cells, keratinocytes, and melanocytes live here. Actively divides and makes daughter cells.

Describe the Stratum Spinosum.

AKA spiny layer. 2nd bottom-most epidermal layer. Look like sea urchins on a fixed histological slide but are smooth inside body. Infrequent dividers. Langerhans found here in great numbers, making weblike frame around keratinocytes. 

Describe the stratum granulosum.

AKA the granular layer. Middle layer. 2-4 layers of flat keratinocytes. Cells’ cytoplasm fills with keratinohyline and lamellated granules, causing degeneration of organelles and cell dies.

Define lamellated granules.

Granules that are waterproofing glycolipids; moved to cell periphery and discharged into extracellular space.

Describe stratum lucidum.

AKA clear layer. Only found in VERY thick skin, such as the pawpads. Most skin lacks this layer; composed of rows of flat dead cells.

Describe the stratum corenum.

AKA horny later. Outermost epidermal layer. Makes ¾ total thickness of epidermis; 20-30 keratinocyte layers; keratinized stratified squamous cells.

How many layers does haired skin have? What are they? Characteristics?

3; germinativum/basale, spinosum, corenum. Hair emerges from below scale like folds. Knob-like elevations on surface called epidermal papillae, containing tylotrich hairs (tactile hairs for touch perception, ex: whiskers).

How many layers is the dermis made of? What are they?

2; papillary layer and reticular layer.

Describe the dermal papillary layer.

Just below the epidermis, made of loose ct woven fibers and ground substance. Has nipple like projections that shoot up into epidermis, helping cement them together (called dermal papillae). ONLY layer w blood vessels; provides nutrients to basale cells and removes wastes.

What corpuscle does the papillary dermal layer contain? What is its function?

Meissener’s corpuscle. LIGHT touch receptors. Sensitive to changes in temp.

Describe the dermal reticular layer.

Made of dense irregular CT; makes up 80% of dermis.

Describe the dermis layer of the skin.

Largest portion of the integument, providing strength. Contains DICT (collagen, elastic, reticular fibers), hair follicles, nerve endings, glands, smooth muscle, and blood and lymphatic vessels. Dense fibro-elastic CT.

Describe the hypodermic layer of the skin.

One layer thick, below the dermis. Made of loose areolar tissue. Rich in adipose, blood/lymphatic vessels, and nerve endings. Permits skin to move freely over bone and muscle without tearing. Thermoinsulator.

What corpuscle is found in the hypodermis layer of the skin? Function?

Pacinian Corpuscle; DEEP pain/touch receptors.

What are the 5 special features of the skin?

Pigmentation, paw pads, plenum nasale/nasoblale, ergots/chestnuts, and cutaneous pouches (sheep).

Describe the pigmentation feature of the skin.

Presence or absence of melanin granules in the extensions of melanocyte cells. Dispersion controlled by melanocyte stimulating hormone (MSH). Released into intracellular space, absorbed by keratinocytes, and arranged in most sun exposed side to protect from UV rays.

Describe paw pads.

Thick layers of adipose and CT. outer surface is toughest and thickest skin. Contains all 5 epidermis layers. Covered with conical papillae. Carpal, metacarpal/metacarsal, and digital pads. Has exocrine sweat glands and lamellar corpuscles.

Describe the planum nasale/nasobiale

Polygonal packed plates, 3 epiderm layers; cornenum =4-8 layers. Nasale: dog, cat, pig, sheep. Nasobiale: horses, cows.

Describe ergots and chestnuts.

Ergot: dark brown projection at the medial aspect of the carpus/tarsus (knee/hock). Chestnuts: dark brown projection buried in the long hairs of the caudal fetlock.

Describe the cutaneous pouches of sheep.

Skin infoldings, 3 locations: infraorbital (front of eyes), interdigital (btwn toes), and inguinal (groin). Contain fine hairs and sebaceous oil glands that secret a fatty yellow substance called lanolin.