Reading Essentials for Biology Glencoe (794133), страница 94
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It alsoprotects the body from invasion by bacteria. Cuts or other openings in the skin need to be repaired quickly or bacteria will enterthe body.ScabIt does not take the skin long to heal after a minor injury orwound. If the skin receives a minor scrape, cells in the deepestlayer of the epidermis divide. The cells quickly fill in the gap onthe skin. If the injury to the skin extends into theNew skin cellsdermis, bleeding usually occurs.
The skin thengoes through a series of stages to heal the damaged tissue. The body’s first reaction is to closethe break in the skin. Blood flows out onto theskin until a clot forms. A scab develops on theskin to close the wound. The scab creates a barrier that prevents bacteria on the skin fromreaching the underlying tissues. Dilated bloodvessels allow white blood cells to move to thewound site. White blood cells fight infections.New skin cells begin to form beneath the scab.These cells eventually push the scab off, and newskin can be seen. If a wound to the skin is large,dense connective tissue used to close the woundmay leave a scar.How are burns rated?5. What purpose does a scabserve?________________________________________________________________________412Chapter 34Burns result from exposure to the sun, contact with chemicals,or contact with hot objects.
Burns are rated according to howsevere they are.A first-degree burn, such as a mild sunburn, results in the deathof epidermal cells. When the skin receives a first-degree burn, theskin turns red, and you feel mild pain. A first-degree burn healsin about a week. It will not leave a scar. A second-degree burndamages the skin cells of both the epidermis and the dermis.
Asecond-degree burn can result in blisters and scars. The mostsevere burn is a third-degree burn. A third-degree burn destroysboth the epidermis and the dermis. With a third-degree burn, theskin loses its function. The cells will not be replaced by new cells.Skin grafts may be required to replace the lost skin.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Skin Injury and HealingNameDateClassSection34.1Skin: The Body’s Protection, continuedHow does skin change?As people get older, their skin changes. It becomes drier becausethe glands produce smaller amounts of skin oils.
Skin oils are amixture of fats, cholesterol, proteins, and inorganic salts. Wrinklesappear as the skin loses its elasticity. These changes happen morequickly when the skin has been repeatedly exposed to ultravioletsun rays.◗ After You ReadMini Glossarydermis: the inner, thicker portion of the skinepidermis: the outermost layer of the skinhair follicle: narrow, hollow openings in the dermis; as hair follicles develop, they are supplied with blood vessels and nerveskeratin (KER uh tun): a protein that helps protect the living cell layers in the interior layerof the epidermis from exposure to bacteria,heat, and chemicalsmelanin: a pigment that colors the skin1.
Read the terms and definitions in the Mini Glossary above. Use the space below to describethe purpose of keratin and melanin in the epidermis.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.____________________________________________________________________________________________________________________________________________________________2. Use the Venn diagram below to compare and contrast the epidermis with the dermis.DermisEpidermisBoth3. What is the purpose of hair?______________________________________________________________________________Visit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about skin, the body’s protection.READING ESSENTIALSChapter 34413NameDateClassSection34.2 Bones: The Body’s SupportSC.F.1.4.1 The student knows that the body processes involve specific biochemical reactions governed by biochemicalprinciples.◗ Before You ReadConsider how much you have grown since you were born.
As an infant, you had a completely developed skeleton. However, your bones are living tissue and they grow. Write a short paragraph on thelines below explaining how you think your bones have changed as you have grown.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnCreate a Drawing Draw apicture of a human leg, fromthe hip to the toes.
Label thedrawing to explain how thebones of the leg are joined.The adult human skeleton contains about 206 bones as shownin the illustration on page 415. The skeleton has two main parts.The axial skeleton includes the skull and the bones that supportit. These bones include the vertebral column, the ribs, and thesternum. The sternum is the breastbone. The other main partof the human skeleton is the appendicular (a pen DI kyuh lur)skeleton. It includes the bones of the arms and legs, the shoulderand hip bones, wrists, ankles, fingers, and toes.How are bones joined together?1. What are the two mainparts of the skeleton?________________________________________________414Chapter 34In vertebrates, joints are found where two or more bonesmeet. Most joints help bones move in relation to each other, andin several different directions. For example, ball-and-socket jointsallow legs to swing freely from the hip and arms to move freelyfrom the shoulders.
Hinge joints allow back-and-forth movementfrom knees, elbows, and fingers. The joints in the skull, however,are fixed. The bones of the skull do not move. Skull joints areheld together by bone that has grown together, or by fibrouscartilage. Recall that cartilage is not bone.
It is a tough, flexiblematerial that makes up portions of the skeletons of bony animals.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Skeletal System StructureNameDateClassSection34.2Bones: The Body’s Support, continuedJoints are often held together by ligaments. A ligament is atough band of connective tissue that attaches one bone to another.Joints with large ranges of motion, such as the knee, usually havemore ligaments surrounding them. In movable joints, the endsof the bones are covered in cartilage.
This layer of cartilageallows for smooth movement between the bones. In some joints,Skeletal 206system bonesAxial80skeletonAppendicularskeleton126Skull (22)Skull andassociatedbones29CraniumFace814Clavicle2Associatedbones (7)Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.EarbonesHyoidThoraciccageScapula2Humerus261Sternum1Ribs2425Radius2Ulna2CarpalbonesVertebrae 2426SacrumCoccyx114Upperlimbs60Pelvicgirdle2Lowerlimbs6016Metacarpal10bonesPhalangesVertebralcolumnPectoralgirdlesHip bone(coxa)2Femur2Patella2Tibia2Fibula228Tarsal bones 14Metatarsal10bonesPhalangesREADING ESSENTIALS28Chapter 34415NameDateClassSectionBones: The Body’s Support, continued2.
Compare/Contrast Whatis the difference betweena ligament and a tendon?________________________________________________________________________Cartilageincluding the shoulder and the knee, there are fluid-filled sacslocated on the outside of joints. These sacs are called bursae.The bursae decrease friction and keep bones and tendons fromrubbing against each other. Tendons are thick bands of connective tissue that attach muscles to bones.When a joint is twisted with force, an injury called a sprain canresult.
Sprains usually occur in joints that have a wide range ofmotion, such as the wrist, ankle, and knee.Diseases also can harm joints. One common joint disease isarthritis. Arthritis is an inflammation, or serious irritation, of thejoint that causes swelling or deformity. One kind of arthritiscauses bony growths inside the joints. These growths, or bonespurs, make it painful to move because bone is rubbing on bone.CapillaryOsteonsystemsSpongyboneWhat are the two typesof bone tissue?Notice that bones are madeof two different types of bone tissue: compact bone and spongySpongybone. Every bone is covered inbonea layer of hard bone called compact bone. Tubular structuresMarrow cavityknown as osteon or HaversianArteryCompact bone(ha VER zhen) systems run downVeinthe entire length of compact bone.MembraneBloodOsteocytes (AHS tee oh sitz) arevesselliving bone cells that receive oxygen and other nutrients fromsmall blood vessels running withinOsteocytethe osteon systems.
Nerves in thecanals of the osteon system conduct impulses to and from eachbone cell.Compact bone surrounds spongy bone. Spongy bone getsits name from its appearance. Like a sponge, it has many holes3. What are the two typesand spaces.of bone tissue, and howdo they differ?________________________________________________________________________Formation of BoneThe skeleton of a vertebrate embryo is made of cartilage. Inthe human embryo, bone begins to replace cartilage by the ninthweek of development.
Blood vessels penetrate the membrane covering the embryo’s cartilage. The blood vessels stimulate the________________________416Chapter 34READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.34.2NameDateClassSection34.2Bones: The Body’s Support, continuedembryo’s cartilage cells to become potential bone cells. Thesepotential bone cells are called osteoblasts (AHS tee oh blastz).Osteoblasts secrete a protein called collagen.
Minerals from thebloodstream begin to deposit themselves in the collagen. Calciumsalts and other ions harden the newly formed bone cells. Thesenew living bone cells are osteocytes.The skeleton of an adult human is almost all bone. Cartilage isfound only where flexibility is needed. Regions with cartilageinclude the nose tip, the external ears, discs between individualvertebrae, and movable joint linings.4. What are osteoblasts?________________________________________________________________________How do bones grow?Bones grow in both length and in diameter.
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