BISC 101 Chapter Notes -Microorganism, Scleroprotein, Cuticle

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Published on 9 Oct 2012
School
Simon Fraser University
Department
Biological Sciences
Course
BISC 101
Professor
Week 4 Integumentary System 1
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Skin (cutaneous membrane) external surface of body; weighs about 7% of body weight
Composed of two parts:
EPIDERMIS superficial, thinner, epithelial tissue portion
DERMIS deeper, thicker, connective tissue portion
o Deep in the dermis is the SUBCUTANEOUS LAYER (aka hypodermis), but is not part of the skin.
Fibers extend from the dermis and anchor the skin to the subcutaneous layer, which connects to muscles. The
subcutaneous layer stores fat, large blood vessels that supply the skin, and nerve endings sensitive to pressure
Epidermis composed of keratinized stratified squamous epithelium; contains four cell types:
KERATINOCYTES
90% of epidermal cells and produces
o Keratin a tough fibrous protein that helps protect skin and underlying tissues
o Lamellar granules contains a waterproof sealant
MELANOCYTES
8% of epidermal cells
Produces melanin yellow-red/brown-black pigment that contributes to skin color and absorbs UV light
LANGERHANS CELLS
Helps other cells of the immune system recognize an invading microbe and destroy it
MERKEL CELLS
Least numerous of epidermal cells and located in the deepest layer of the epidermis
Helps with the sensation of touch
Thin (hairy) skin most regions of the body have an epidermis with four layers (no stratum lucidum)
Thick (hairless) skin where exposure to friction is greatest (i.e., palms and soles), five layers
STRATUM BASALE
Deepest layer of epidermis
Single row of cuboidal/columnar keratinocytes with some stem cells that continually produce new
keratinocytes
Cytoskeleton of keratinocytes contains filaments that form keratin in its more superficial epidermal layers
STRATUM SPINOSUM
Consists of numerous keratinocytes in 8-10 layers
Keratinocytes in this layer produce coarser bundles of keratin
When prepared for microscopic examination, they appear to be covered with thornlike spikes
Provides strength and flexibility
5.1 Structure of the Skin
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Week 4 Integumentary System 2
STRATUM GRANULOSUM
~middle of epidermis
3-5 layers of flattened keratinocytes that are undergoing apoptosis (programmed cell death)
Darkly stained granules of a protein called keratohyalin
Lamellar granules release a lipid-rich secretion to help propel water
STRATUM LUCIDUM
Present only in thick skin
4-6 layers of flattened, clear, dead keratinocytes
Provides additionally “toughness” for the skin
STRATUM CORNEUM
Numerous layers of flat, dead keratinocytes
Cells are continuously shed and replaced by cells from the deeper layers
The multiple layers of dead cells help protect deeper layers from injury and foreign invasion
Keratinization and Growth of the Epidermis
1. Newly formed cells in the stratum basale are slowly pushed to the surface
2. As cells move up, they accumulate more and more keratin = keratinization
3. Then they undergo apoptosis
4. The keratinized cells are eventually sloughed off and are replaced by underlying cells that go through the
same process that takes about 4-6 weeks
Dermis composed of dense irregular connective tissue containing collagen and elastic fibers
Great ability to resist pulling or stretching
Has the ability to stretch and recoil easily
Thickness varies among the body but it is always thicker than the epidermis
Cells present in the dermis are mostly fibroblasts, macrophages, and a few adipocytes near the bottom
Blood vessels, nerves, glands, and hair follicles are embedded in dermis
Divided into two regions:
1. Papillary region th of dermis
o Contains thin collagen and fine elastic fibers
o Surface area greatly increased by dermal papillae small nipple-shaped structures that project
into the undersurface of the epidermis; contains capillary loops (blood vessels)
Some contain nerve endings sensitive to touch and free nerve endings
2. Reticular region
a. Attached to subcutaneous layer
b. Consists of thick collagen fibers, scattered fibroblasts, some adipose, and other cells
c. Blood vessels, nerves, hair follicles, sebaceous (oil) glands, and sudoriferous (sweat) glands
occupy space between fibers
d. Provides dermis with strength, the ability to stretch, and the ability to return to original shape
after stretching
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Document Summary

Skin (cutaneous membrane) external surface of body; weighs about 7% of body weight. Epidermis superficial, thinner, epithelial tissue portion. Dermis deeper, thicker, connective tissue portion: deep in the dermis is the subcutaneous layer (aka hypodermis), but is not part of the skin. Fibers extend from the dermis and anchor the skin to the subcutaneous layer, which connects to muscles. The subcutaneous layer stores fat, large blood vessels that supply the skin, and nerve endings sensitive to pressure. Epidermis composed of keratinized stratified squamous epithelium; contains four cell types: 90% of epidermal cells and produces: keratin a tough fibrous protein that helps protect skin and underlying tissues. Produces melanin yellow-red/brown-black pigment that contributes to skin color and absorbs uv light. Helps other cells of the immune system recognize an invading microbe and destroy it. Least numerous of epidermal cells and located in the deepest layer of the epidermis.

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