Reading Essentials for Biology Glencoe (794133), страница 96
Текст из файла (страница 96)
When adequate oxygen is delivered to muscle cells, theaerobic respiration process dominates. This occurs when a muscleis resting or during moderate activity.During vigorous activity, your muscles may not be able to getoxygen fast enough to sustain aerobic respiration and produceadequate ATP. The amount of available ATP becomes limited.For your muscle cells to get the energy they need, they must relyon lactic fermentation, an anaerobic process.Lactic acid can build up in muscle cells as you exercise. As theexcess lactic acid goes into the bloodstream, the blood becomesmore acidic, rapid breathing begins, and cramping may occur. Asyou catch your breath after vigorous activity or exercise, adequateamounts of oxygen are supplied to your muscles and the lacticacid is broken down.◗ After You ReadMini Glossaryactin: the protein that makes up the thin filaments of myofibrilsskeletal muscle: attached to and moves bones;contracts under conscious controlcardiac muscle: heart muscle; cardiac muscle isan involuntary musclesliding filament theory: theory that statesthat when actin filaments receive a signal,the actin filaments in each sarcomereslide toward each other, shortening thesarcomeres in a fiber and causing the muscleto contractinvoluntary muscle: contracts by itself, not byconscious controlmyofibril (mi oh FI brul): small units of musclefiber; myofibrils are made up of smallprotein filaments that can be either thickor thinmyosin: the protein that makes up the thick filaments of myofibrilssarcomere (SAR kuh meer): the functional unitof muscle; myofibrils can be divided intosections, called sarcomeres422Chapter 34smooth muscle: made of sheets of cells that lineorgans; the most common job of smoothmuscle is to squeezevoluntary muscle: a muscle that contracts underconscious controlREADING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.34.3NameDateClassSection34.3Muscles for Locomotion, continued1.
Read the terms and their definitions in the Mini Glossary on page 422. Use the space belowto describe the purpose and relationship of myofibrils, myosin, actin, and sarcomeres.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2.
Use the cause and effect diagram to show what happens when you exercise moderately andwhen you exercise vigorously.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.ModerateExerciseVigorousExercise1. Leads to2. WhichLeads to3. WhichLeads to4. WhichLeads to1. Leads to2. WhichLeads to3. WhichLeads to4. WhichLeads toVisit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about muscles for locomotion.READING ESSENTIALSChapter 34423NameDateClassSection35.1 Following Digestion of a MealSC.F.1.4.1 The student knows that the body processes involve specific biochemical reactions governed by biochemicalprinciples.◗ Before You ReadYour stomach growls, indicating hunger.
You eat your lunch, and the process of digestion begins.Digestion is complex. What roles do you think the mouth and the stomach play in digestion?Write your thoughts on the lines below. After you have read this section, add any new informationyou learned.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnIdentify KeyParts The digestive system ismade up of nine main parts.As you read, highlight eachpart in the diagram.SalivaryglandsTeethMouthTongueThe main function of the digestive system is to change the foodyou eat into molecules that your body can use for energy.
Thereare a number of steps in the digestive process. Digestion beginswhen you put food into your mouth. This is called ingestion. Thesystem takes the ingested food and begins moving it through thedigestive tract. As food is digested, the complex food molecules arebroken down both mechanically and chemically. The digestive system absorbs the digested food and sends it to your cells.Finally, the materials that cannot be digested are eliminated from your body.
The digestive system includesseveral organs.PharynxThe MouthThe first step in the digestive process begins in yourmouth. You bite food, and you chew it.EsophagusDiaphragmWhat happens as you chew?LiverStomachGallbladderPancreasLargeintestineSmallintestineAppendixRectumAs you chew food, your tongue moves the food aroundin your mouth. Your tongue helps move the food betweenyour teeth. Chewing is a form of mechanical digestion.It is the physical process of breaking food down intosmaller pieces.
Mechanical digestion prepares the foodparticles for chemical digestion. Chemical digestion is theprocess of changing food on a molecular level. Thischange occurs because of the actions of enzymes in yourdigestive system.Anus424Chapter 35READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Functions of the Digestive SystemNameDateClassSection35.1Following Digestion of a Meal, continuedWhere does chemical digestion begin?Chemical digestion begins in the mouth. Salivary glands inyour mouth secrete saliva.
Saliva contains a digestive enzymecalled amylase. Amylase breaks down the starches in food intosmaller molecules. Many of the nutrients in the food you eat contain starches, large molecules known as polysaccharides. Thepolysaccharides are broken down into di- or monosaccharides. Inthe stomach, which is a muscular, pouchlike enlargement in thedigestive tract, amylase digests the swallowed starches for about30 minutes.1. Compare/Contrast Whatis the difference betweenmechanical digestion andchemical digestion?________________________________________________________________________Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What happens after you have swallowed your food?Once food is chewed, the tongue shapes it into a ball.
Thetongue moves this ball of chewed food into the back of themouth. The food is swallowed. Swallowing food forces it fromthe mouth into the throat. Food then movesfrom the mouth into the esophagus. Theesophagus is a muscular tube that connectsthe mouth to the stomach. Food moves downthe esophagus by peristalsis.
Peristalsis(per uh STAHL sus) is a series of involuntary,smooth muscle contractions along the walls ofthe digestive tract. The contractions occur inwaves called peristaltic waves. First, circularmuscles relax and longitudinal muscles contract. Then, circular muscles contract andlongitudinal muscles relax. Since smoothmuscles are involuntary, you do not consciously control these contractions.When you swallow, food enters the esophTongueagus.
Usually, a flap of cartilage called theepiglottis (ep uh GLAH tus) closes over theopening to the respiratory tract as you swallow. This prevents food from entering therespiratory tract. If you talk while swallowing,the epiglottis may open, and food can enterthe respiratory tract. The body responds bychoking and coughing, forcing the food outof the respiratory tube and back intothe throat.TeethOpening of salivary gland ductREADING ESSENTIALSChapter 35425NameDateClassSection35.1Following Digestion of a Meal, continuedThe Stomach2. What types of digestiontake place in the stomach?________________________When chewed food reaches the end of the esophagus, it entersthe stomach. The stomach is a muscular, pouchlike enlargement ofthe digestive tract.
Both mechanical and chemical digestion takeplace in the stomach.________________________________________________How do muscles in the stomach break down food?The stomach contains three layers of involuntary muscles.They lie across each other, and they are located within the stomach’s walls. When these muscles contract, they physically breakdown swallowed food into smaller pieces. As the muscles continueto work on the pieces of food, the pieces are mixed with digestivejuices produced by the stomach.EsophagusStomachSmall intestine3.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
