Flashcards in Test yourself ?s Chpt 5 The Integument Deck (12)
Why is skin important? Can you think of five important functions of skin?
It's composed of all four tissue types and covers and protects the underlying structures.
Reduces threat of injury
Assists in maintaining normal body temperature
Excretes water, salt and organic waste
Important sensory organ
Synthesizes Vitamin D
What is keratinization and why is it an important process?
Everything visible, from hair to skin, is composed of dead cells.
Cells gave up their vital organelles and nuclei to make room for the tough, protective substance called keratin, which helps protect and waterproof.
Millions of dead cells rub off or exfoliate daily to reveal a new epidermis (in humans every 7 to 8 weeks).
Can you list all five layers of the epidermis? What is happening in each layer?
1. Stratum basale (or stratum germinativum): consists mostly of a single layer of keratinocytes, actively engaged in cell division. You can also find Merkel cells and melanocytes in this layer.
2. Stratum spinosum (or spiny layer): contains several layers of cells held together by desmosomes. Langerhans cells are found here, forming a weblike frame around the keratinocytes.
3. Stratum granulosum (or granual layer): the middle layer of skin. Composed of two to four layers of flattened, diamond-shaped keratinocytes. This is where the cells die filling with keratohyaline and lamellated granules, containing waterproofing glycolipids.
4. Stratum lucidum (or clear layer): only found in very thick skin, so most skin lacks this layer. Has a translucent layer composed of a few rows of flattened, dead cells.
Kertogranules with intracellular tonofilaments form keratin fibrils in this layer.
5. Stratum corneum (or horny layer): outermost layer, dominates the epidermis. 20-30 rows of keratinocytes (only remnants of keratinocytes, the actual cell died in the stratum granulosum). These remnants are called horny or cornified cells, better known as dandruff.
How is the skin of hairy animals different from that of humans?
It usually consists of three epidermal layers, rather than five in humans.
These layers are the stratum basale, stratum spinosum and stratum corneum.
The surface is covered in scalelike folds with hair emerging from beneath the scales, directed away from opening. There are tactile elevations or epidermal papillae, each associated with usually one tactile hair. They are also called tylotrich hairs, important in perception of touch.
How is the dermis different from the epidermis?
The epidermis is primarily cellular while the dermis is highly fibrous.
It's composed of dense irregular connective tissue containing collagen, elastic, and reticular fibers.
What causes pigmentation of skin?
It's caused by the presence or absence of melanin granules in the armlike extensions of the melanocytes.
How are paw pads and the planum nasale different from other regions of skin?
The outer layer of skin of a paw pad is the thickest and is composed of thousands of conical papillae.
The planum nasale is composed of polygonal plaques separated by epidermal grooves. It's pretty thin and only contains three layers rather than five.
How does hair form and grow?
What are the three cycles of hair growth?
The growth cycle has three phases:
In the ANAGEN phase the follicle is longest.
The CATAGEN phase occurs with the appearance of a thick, glassy membrane and a shortening of the hair follicle. Thickening of basement membrane in the matrix separates epidermal cells from the dermal papilla.
In the TELOGEN phase the hair follicle is very short, and the dermal papilla is separated from the bulb. The hair strand is rounded and resembles a club and is therefore called a club hair.
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.
What factors stimulate contraction of the arrector pili muscle? Why is this muscle important?
When frightened or cold, animals can make their hair stand up beyond the normal implantation angle.
The arrector pili muscle is attached to the hair follicle and is innervated by the sympathetic nervous system. When the muscle contracts, it pulls the hair to an erect position. this may happen when an animal is frightened or cold, as hair that stands erect can better trap insulating layers of air. The arrector pili muscle is also responsible for forcing sebum from the sebaceous gland, which helps keep the integument moist and supple.
Name two types of sweat glands. How are they different from one another?
ECCRINE SWEAT GLANDS: excretory portion of this gland consists of a simple, coiled tube located in the dermis or hypodermis. It is connected to the surface of the skin by a long duct.
APOCRINE SWEAT GLANDS: they look pretty similar to eccrine glands, but empty into hair follicles, instead of onto the surface of the skin. Dogs have these in their external ear canal.