9/1/2017. BIO 1102 Lecture 4 Chapters 6-7: The Muscular System; The Blood. The Muscular System

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1 BIO 1102 Lecture 4 Chapters 6-7: The Muscular System; The Blood The Muscular System Muscles constitute about half of our body mass Allows us to move joints, maintain posture, talk, etc. Also generate body heat and help us maintain our body temperature Skeletal Muscle We have more than 600 skeletal muscles Organized into pairs or groups Controlled by nerves Muscles that work together to produce the same movement are synergistic muscles Muscles that oppose each other are called antagonistic muscles Skeletal Muscle Most attach to bones via tendons By contracting muscles, the levers of our skeletal system can be moved The origin of a skeletal muscle attaches to a bone that remains relatively stationary The other end is called the insertion; attaches to a bone at a joint When muscle contracts, the insertion is pulled toward the origin Example of Antagonistic Skeletal Muscles: Biceps and Triceps Relaxation of triceps and contraction of biceps pulls on forearm and flexes it Relaxation of biceps and contraction of triceps pulls forearm down extending it Muscle Contraction A single muscle (or whole muscle ) is composed of many muscle cells Muscle cells also called muscle fibers In cross section, whole muscles are organized into bundles called fascicles Each fascicle enclosed by layer of connective tissue called fascia Muscle cells can be very long Tubular in shape Contain multiple nuclei Muscle cells contain long, cylindrical structures called myofibrils, packed with the contractile proteins actin and myosin 1

2 Contractile proteins cause the cell to shorten Located within the myofibrils Area between 2 dark ( Z ) lines = sarcomere The contractile unit of the muscle 8 9 Muscle fibers, and myofibrils, have a banded appearance Due to arrangement of contractile proteins Bands composed of Thick filaments Composed of myosin Thin filaments Composed of actin Contraction occurs when actin filaments slide over myosin filaments heads of myosin filaments attach to actin filaments Pull the actin over the myosin, shortening the myofibril What stimulates a contraction? Nerves stimulate release of calcium from muscle cells Calcium stimulates attachment of myosin fibers to actin fibers ATP is also required for contraction Contraction occurs Skeletal muscles are controlled by motor neurons Motor neurons secrete the neurotransmitter acetylcholine, which excites the muscle cells Neuromuscular Junction Neuromuscular Junction The sarcoplasmic reticulum of the muscle cell stores calcium Similar to endoplasmic reticulum Releases calcium when stimulated by electrical impulse T-tubules transmit electrical impulse from surface of cell deep into cell Calcium triggers contraction of myofibrils Sliding filament mechanism Thick filaments of a sarcomere are made of myosin Shaped like golf clubs with heads Thin filaments of a sarcomere are made of actin Actin contains attachment sites for myosin heads These attachment sites are blocked by tropomyosin, held in place by troponin, when muscle is relaxed 2

3 Contraction occurs when heads of myosin attach to actin filaments, forming cross bridges, and actin is pulled over myosin This shortens the sarcomere Contraction only occurs when calcium is present Calcium attaches to troponin, moving the troponin-tropomyosin complex out of the way This enables myosin to attach to actin Muscle Contraction Video: Energy for Muscle Contraction Most efficient long-term source of energy = aerobic metabolism of glucose in the blood, fatty acids from fat cells, or other high-energy molecules Aerobic metabolism occurs in mitochondria Requires oxygen Respiration rate increases with exercise First minute or so of exercise, your body can rely on stored energy Stores of ATP (10 seconds worth) and creatine phosphate (30 seconds worth) Body may also use anaerobic metabolism of glycogen (first 3-5 minutes of heavy exercise) After exercising, often continue heavy respiration To reverse oxygen debt Need extra oxygen to metabolize the lactic acid that build up from anaerobic respiration and restore the muscle s stores of ATP and creatine phosphate Fast and Slow Twitch Two types of muscle fibers in human skeletal muscle Slow-twitch Fibers: Contract slowly because break down ATP slowly Store little glycogen, but store oxygen in myoglobin Have high endurance Found in greater abundance in endurance athletes (e.g. long-distance runners) Fast-twitch Fibers Contract quickly because break down ATP quickly Store much glycogen and little myoglobin Rely heavily on creatine phosphate and anaerobic metabolism for short bursts of energy Have less endurance More common in athletes who require quick bursts of activity 20 3

4 Exercise Exercising muscles increases their strength and size Due to increase in contractile protein in the muscle cells That protein is lost if the muscle is not used regularly (Half the muscle mass gained from weight training lost within two weeks if weight training stops) Exercise also reduces fat Burning of calories Muscle cells require a lot of energy, even when at rest Exercise helps your heart Muscles of heart also become stronger and larger Can beat more slowly when exercising because each beat pumps more blood Exercise also improves respiratory system Increased strength of muscles involved in breathing Further, more red blood cells are generated Delivers more oxygen to cells Allows you to exercise longer without becoming tired Bonus Activity Draw a diagram of a sarcomere illustrating the sliding filament mechanism of muscle contraction. Draw the sarcomere first in the absence of calcium (relaxed), and then in the presence of calcium (contracted). Be sure to label the following components: Actin, Myosin, Troponin, Tropomyosin, and Calcium Break Chapter 7: The Blood Functions of blood include: Transportation Oxygen, nutrients, hormones, and waste Regulation Helps regulate body temperature, water volume, and ph of body fluids Defense Contains specialized cells of the immune system, and platelets to form clots to prevent blood loss Composition of Blood Plasma comprises ~55% blood A solution composed of 90% water, plus sodium, glucose, and blood proteins Contains dissolved gases, such as oxygen and carbon dioxide Transports nutrients (macro- and micro-) and wastes Contains proteins that aid in clotting 4

5 Contains protein antibodies that protect against disease Plasma Proteins Albumins: carrier proteins Globulins: carrier proteins and antibodies Clotting proteins: prevent blood loss after injury Formed Elements (blood cells and platelets) comprise the remaining 45% Red Blood Cells (RBCs) = erythrocytes Most abundant type of blood cell Even more abundant in people living at higher elevations (e.g. Denver) Transport oxygen (and some carbon dioxide) Flexible disks (bend without clogging capillaries) Sickle-cell anemia: RBCs lose flexibility and become sickle-shaped Blockages form Pain Death Hematocrit = % volume of RBCs Oxygen carrying capacity of blood RBCs lack organelles (no nuclei, mitochondria, etc.) Lose organelles when cells differentiate Cannot replicate themselves Lifespan of 120 days When die, iron is recycled (but some is lost) Cellular structure: a membrane surrounding many hemoglobin molecules Hemoglobin found only in RBCs Contains Iron Binds to Oxygen Anemia: reduction in oxygen-carrying capacity of the blood Causes Excessive bleeding Tumor in red bone marrow Some diseases (e.g. malaria) Iron deficiency Symptoms Weakness Fatigue Pale skin Fainting Shortness of breath 5

6 Personal Story: My Grandma Her symptoms: Upward-curling fingernails Sores at corner of mouth Passed out Taken to hospital Hemoglobin level at 6 grams per deciliter (normal for an older woman) Cause? Diet consisting mostly of ice cream and cookies! On the other hand, too much iron can be harmful The Life of a Red Blood Cell Red blood cells (RBCs) are produced in the red bone marrow by stem cells As they differentiate to become RBCs, they lose their nuclei and organelles Hence, cannot reproduce themselves Live about 120 days Old RBCs removed by spleen and liver Much of the iron from the hemoglobin is recycled Red blood cell production controlled by negative feedback mechanism When oxygen levels drop in blood, kidneys produce a hormone called erythropoietin (EPO) (illegal performance enhancer used by some athletes blood doping ) EPO travels to red bone marrow and triggers stem cells in red bone marrow to produce more RBCs This brings up the oxygen carrying capacity of the blood White Blood Cells (WBCs) Part of the Immune System; detect chemical signs of tissue damage Only about 1% of whole blood volume WBCs also produced in bone marrow 5 Types: Neutrophils: 60% of WBCs; phagocytes (digest bacteria) Monocytes: largest WBCs; aggressive phagocytes Lymphocytes: 30% WBCs; attack foreign cells but don t engulf them; some found in blood but most in the lymphatic system»b and T Lymphocytes Eosinophils: less common; phagocytes, but can also release chemicals that can 6

7 attack parasites such as worms Basophils: rarest WBC; release histamine when detect injury, which causes blood vessels to release plasma; enhances tissue repair and causes inflammation Two types of Lymphocytes T Cells attack foreign cells directly B Cells, when activated, form plasma cells which produce antibodies Coat invading cells or foreign substances Neutralizes invaders, or marks them for destruction by phagocytic cells More on WBCs when we discuss the Immune System Leukemia When white blood cells divide uncontrollably in bone marrow Crowd out cells that produce RBCs and platelets»can cause internal bleeding (reduced clotting ability) The WBCs produced are ineffective in fighting disease Mononucleosis Caused by Epstein-Barr virus Infects lymphocytes Platelets Small fragments of cells involved in blood clotting Covered with a sticky substance Produced by megakaryocyte cells in bone marrow Lack nuclei and organelles Steps in blood clot formation: Protein fibers (fibrin) form at site of tear in blood vessel RBCs and platelets get stuck in the fibrin Flow of blood is stopped Blood Types Blood type is determined by presence of different types of antigens on surface of RBCs Antigens substances (usually proteins) that can elicit an immune response Body distinguishes its own cells from foreign cells by the antigens present on cell surface A and B represent two different types of antigen present on surface of RBCs 7

8 39 40 Why do diagrams of circulation usually show arterial blood as red and veinous blood as blue? Is it just for clarity, or do we have different colors of blood? It is just for clarity; our blood is never blue. The red color comes from the hemoglobin molecule However, blood in our arteries is a brighter shade of red Veins appear blue because the fat cells under our skin absorb red (low-energy) wavelengths of light and reflect blue (higher energy) wavelengths Fun fact There are some truly blue-blooded animals! Octopus, horseshoe crabs, lobsters Their oxygen-carrying molecule is hemocyanin, which is blue Can you have too many red blood cells? Yes If you are taking EPO or erythropoiesis-stimulating agents (ESAs) to artificially increase red blood cell counts, you could have too many This would increase risk for blood clots and consequently stroke or heart attack What are the most and least common blood types? Most Common: O+ (38% of Americans) Second Most Common: A+ (34%) Least Common: AB- (0.7%) But these frequencies vary geographically All for today 8