Human Body_ Facts at Your Fingertips_clone

Nerves aNd NeuroNs seNses A nerve impulse (signal) takes just • Our hearing range decreases with one hundredth of a second to travel age, which is why young people hear from the spinal cord to your big toe. higher-pitched sounds than older people. The longest neurons—between • The tongue’s taste buds are replaced spinal cord and big toes—are 3¼ ft every week, but the nose’s smell (1 m) long. They are also the receptors last for a month. longest cells in the body. The shortest neurons are ⁄4 100 in • Chiles “taste” hot because they (1 mm) long. contain a substance that triggers the tongue’s pain receptors. A neuron can transmit The farthest object that we see without 1,000 nerve impulses a telescope is the • Fingers are among the every second. Andromeda galaxy, most sensitive areas of which is 2.5 million the body. Each fingertip has The widest nerve, the about 100 touch receptors. sciatic, is ¾ in (2 cm) wide. light-years away. It extends from the lower • The eyes contain back to the foot. 70 percent of the body’s sensory receptors, making A withdrawal reflex—when a nerve sight our most important sense. signal passes through the spinal cord, not the brain—can pull the hand away • Eyelids blink about 9,400 times a from a dangerously hot object in day, helping to keep our eyes clean. just 30 thousandths of a second GeNes (30 milliseconds). If the signal went via the brain it would take 800 milliseconds. • Humans have 46 gene-carrying Stretched out, the body’s nerves chromosomes inside the nucleus would extend for more than 93,000 miles of each body cell. (150,000 km)—more than the distance covered by flying between London and • Stretched out, the DNA in one human New York 25 times. cell would extend over 6½ ft (2 m). YOUR AMAZING BODY | 149

Glossar y Dendrite A short fiber Fat A group of substances that carries incoming found in food and inside Artery A thick-walled Cardiac Of or relating signals from other nerve the body. Fat stores blood vessel that carries to the heart. cells to the cell body of energy and insulates blood from the heart Cartilage A tough, a neuron. the body. to the tissues. flexible tissue that Dermis The deeper, Fertilization The Axon A long fiber helps support the body thicker layer of skin, below joining together of a that extends from and covers the ends of the epidermis. It contains male sperm and a the cell body of a bones in joints. sensory receptors and female egg to make neuron and carries Cell One of the trillions of blood vessels. a new human being. signals to other microscopic living units Digestion The process Fetus The name nerve cells. that make up the body. by which food is broken given to a developing Bacteria A group of Chromosome One of 46 down into simple nutrients baby from the ninth small, single-celled packages of DNA found in that can be absorbed into week after fertilization microorganisms, some the nucleus of each cell. the bloodstream and used until birth. of which cause disease Chyme A creamy liquid by the body. Gastric Of or relating in humans. that is produced by the Digestive enzyme A to the stomach. Bone marrow A soft part-digestion of food substance that speeds Gene One of 23,000 tissue found in the in the stomach. up the breakdown of coded instructions spaces within bones. Cilia Tiny hairlike food molecules. stored in the DNA Calcium A mineral structures found on DNA (deoxyribonucleic that makes up the used by the body to some tissue. They wave acid) A long molecule chromosomes inside build bones and teeth. to move things, such found inside the nucleus a cell’s nucleus. Capillary A microscopic as mucus, across of body cells. It contains Germ A common name blood vessel that links their surface. the coded instructions given to microorganisms the smallest arteries Collagen A tough needed to build and run that cause disease. to the smallest veins, protein that makes up a body. Gland A group of cells and delivers blood to the fibers that strengthen Embryo A developing that make and release tissue cells. tendons, ligaments, baby between the time specific substances Carbohydrate A and cartilage. it arrives in the uterus such as hormones group of substances CT (computed and eight weeks after and enzymes. found in food and tomography) scan fertilization. Glucose A type of sugar inside the body. It A method of producing Energy The fuel that found in the bloodstream includes sugars, 2-D and 3-D images comes from eating food. that is the main source of such as glucose— of body tissues It is essential for keeping energy for body cells. the body’s store and organs. the body’s cells working Hemoglobin A of energy. Cytoplasm The jellylike and alive. red, oxygen-carrying Carbon dioxide A fluid found between the Enzyme A protein protein found inside gas that is the waste membrane and nucleus that speeds up chemical red blood cells. product of energy of a cell. reactions inside the body. Hepatic Of or relating release inside cells. Epidermis The thin to the liver. protective layer of the skin. 150 | HUMAN BODY

Hormone A chemical Mitosis The division of Protein A group of Sweat A watery liquid messenger released by a body cell into two new, substances found in produced by glands in the endocrine glands identical offspring cells. food and inside the body. the skin. into the bloodstream. It MRI (magnetic Proteins build and run the Synapse The junction alters the activities of resonance imaging) body’s cells. between two neurons specific tissues. scan A way of using Puberty The period of that are separated by Immune system magnetism, radio rapid growth, usually in a tiny gap. A collection of cells, waves, and computers the early teens, when the Synovial joint A including macrophages to produce images of reproductive systems free-moving joint, such and lymphocytes, that body tissues and organs. start working. as the elbow or knee. protect the body from Mucus A slimy substance Pulse The rhythmic System A group of disease by destroying released by glands, throbbing of an artery linked organs that work germs such as bacteria. such as those lining as it expands when blood together, such as the Joint The place where the esophagus that is pumped through it by organs that make up two or more bones meet. leads from the throat the heart. The pulse is the the digestive system Most joints are movable. to the stomach. same as the rate the Tendon A tough cord Keratin A tough, Muscle fiber One of heart beats. that links a muscle to waterproof protein the cells that makes Reflex A rapid, a bone. found in nails, hair, up a muscle. automatic action, Tissue A group of cells and the upper layer Neuron A type of nerve such as pulling the of the same type—such of the skin’s epidermis. cell that carries signals. hand away from a hot as muscle cells—that Ligament A tough Nucleus The control object, that happens work together to perform strap that holds bones center of the cell that without our thinking a particular function. together at the joints. contains chromosomes. about it. Vein A thin-walled Lymph A liquid that is Nutrient A substance Renal Of or relating blood vessel that drained from the body’s found in food that is to the kidney. returns blood to the tissues along the vessels needed by the body Saliva A liquid heart from the tissues. of the lymphatic system. to function normally. found in the mouth. Virus A disease-causing Mammal An animal, such Organ A body part, such It aids digestion by particle that invades as a rabbit or human, that as the heart or kidney, providing the lubrication the body’s cells and is warm-blooded, hairy, that is made of two or needed for chewing multiplies inside them, and feeds its young more types of tissue and and swallowing. causing infections, such with milk. has specific roles. SEM (scanning electron as colds and measles. Metabolism All the Organelle One of the tiny microscopy) A way X-ray An imaging chemical processes working structures, such of using a special technique that uses that take place inside as mitochondria, found microscope to produce radiation to reveal bones. every one of the floating in the cytoplasm magnified 3-D images of body’s cell. of cells. body tissue. Mitochondria The tiny Oxygen A gas that is used Sphincter A ring of structures inside cells by body cells to release muscle around an that release energy energy from glucose. opening that controls from glucose. the flow of materials through it. GLOSSARY | 151

Index nutrients 88, 89, 94, 96 82–3, 148, 150 two loops 53 cardiac muscle 12, 42, 43, A blood vessels 25, 34, 35, 44, 51–5, 64, 101 58, 59 abdomen muscle 41 bone-building cells 35 carotid artery 52 Achilles tendon 40 bones 19, 26–39, 147 carpals 27, 32 adipose cells 8, 9, 15 growth 128 cartilage 36, 111, 150 adolescence 143 healing fractures 34–5 cecum 98 adrenal gland 126, 127 inside 30–1 cells 6–13, 146, 150 adulthood 131, 144 joints 36–9 aging 144–5 marrow 30–31, 150 defense 69 alveoli 78, 82–3 muscles 41, 48–9 dividing 10–11, 134 anus 88, 89, 98, 99 skeletal system 26–7 energy for 87, 88 aorta 52, 53, 58 strength 28–9, 30 fibroblasts 34 appendicular skeleton 27 tissue 28–9, 30 genes and DNA 140–1 appendix 98 types 32–3 inside 6–7 arteries 20, 52–3, 54–5, 150 braille 121 stable surroundings 51 arterioles 54 brain 106–9, 148 temperature 24 atrium (atria) 58–61 muscle contraction 45 tissues, organs, and systems axial skeleton 27 nervous system 103, 104 12–13 axons 8–9, 104, 105, 150 scan 16–17 types of 8–9 senses 112–25 see also specific cells B spinal cord 110–11 cerebellum 106, 107 brain stem 81, 106 cerebral cortex 106–7, 148 babies 131, 134–9, breathing 76–85, 148 cerebrum 106, 107, 116 141, 142 lungs 82–3 cheeks 85 in and out 80–1 chest muscle 41 backbone 26, 33, 110, 111 speech 84–5 chewing 90–1 bacteria 66–7, 69, 87, 150 bronchi 78–9 childhood 142 balance 124–5 bronchioles 78–9, 82 chromosomes 10, 140, 149, 150 ball-and-socket joints 38, 39 chyme 92, 93, 150 biceps 41, 48, 49 C cilia 78, 150 bile 94, 100 circulatory system see bladder 32, 43, 67, 72, 74 calcium 26, 150 blood system blood cells 31, 62–3 calf muscle 40 clavicle 26 canals, ear 122–5 clots 64–5 see also red blood cells canine teeth 91 coccyx 110 and white blood cells capillaries 52, 54–5, 83, 147, 150 cochlea 122, 123 blood system 12, 13, 51–65, 147 carbohydrates 94 cold, feeling 25 cleaning the blood 72–73, 100 carbon dioxide 77, 80, collagen fibers 37, 41, 150 clotting 34, 62, 64–5 colon 98–9 composition of blood 62–3 communication 4, 5, 84–5, 122 exchanging gases 83 cones 112 filtering blood 72–3 cornea 112, 113 coronary arteries 59 152 | HUMAN BODY

cranial nerves 104 esophagus 85, 88, 90, 91, 92 gluteus maximus 40, 147 CT (computed tomography) exercise 81 Golgi complex 6 expressions, facial 49 gray matter 110–11 scans 15, 150 eyelashes 146 great saphenous vein 53 cytoplasm 6, 10 eyes 46–7, 112–15, 141, 149 grip 21, 22 growth 10–11, 126, 127, 131, D F 142–5 dendrite 9, 105 facial muscles 48–9, 147 dentine 91 fallopian tubes 133, 134–5 H dermis 20–1, 120, 145, 146, 150 fat 9, 21, 26, 94, 100, 150 descending aorta 52 feces 89, 98–9 hair 20–3, 25, 146 diabetes 129 female reproductive system hands 5, 128, 147 diaphragm 79, 80–1 healing 10, 11, 62, 64–5 digestive system 42, 86–101, 133 hearing 19, 106–7, 122–3, 149 femoral artery 53 heart 12–13, 51–61, 147 148, 150 femoral vein 53 chewing and swallowing 90–1 femur 27, 32, 147 beating 43, 51, 60–1, 151 feeding the body 88–9 fertilization 133, 134–5, 150 inside 58–9 intestines 94–9 fetus 15, 136–9, 150 listening to 61 liver 100–1 fibrin threads 64–5 heart strings 58 stomach 92–3 fibroblasts 34 heartbeat 43, 51, 60–1 digestive tract 88–9, 90 fibula 27 heat 24–5, 51, 62 digital artery 53 filaments 44, 45, 47 losing 24–5 disease, fighting 66–7 fingerprints 21 hemoglobin 62, 150 dislocations 37 fingers 5, 49, 121, 149 hepatic portal vein 100, 101 dizziness 125 fixed joints 38 hinge joints 39 DNA 131, 140–1, 149, 150 flat bones 33 hormones 11, 126–9, 143, 151 duodenum 92, 93, 94 fluid 51, 70–5 hot, feeling 25 food humerus 26 E hypothalmus 127 blood 51, 52, 59, 62 ear 19, 122–3, 124–5 digestion 87–93 IJK eardrum 123 taste 116–17 eggs 131–4, 141, 146 fractures 34–5 ileum 94 ellipsoidal joints 38 imaging techniques 14–15 embryo 136, 150 G immune system 66–9 enamel 91, 148 incisors 91 endocrine system 126–9 gall bladder 89, 94, 100 infancy 142 endoplasmic reticulum 7 gastric glands 93 infection 64, 66–7 endoscopy 15 gastric juice 66, 92, 148 inferior vena cava 52, 58 enzymes 66, 92, 94 genes 132–4, 140–1, 149, 150 inner ear 122, 123 epidermis 20–1, 120, 146 germs 62, 64, 66–7, 69, 70, 150 insulin 129 epiglottis 85, 90, 91 glands 20,93,126–9 intelligence 4 epithelial cells 8 glucose 101, 129, 150 intercostal muscles 80–1 INDEX | 153

intestines 87, 88, 89, 94–9 colon 99 oxygen 51–7, 59, 77–83, 151 iris 113, 114–15 joints 36–9 blood 51, 52, 53, 59, 62, 67 irregular bones 33 muscles 40–1, 42, 48–9 breathing 77, 78, 80–3, 148 jaw muscle 41 reflexes 111 jejunum 94 MRI (magnetic resonance P joints 27, 36–9, 151 imaging) scans 14, 16–17, 151 keratin 21, 22, 151 mucus 66, 78, 79, 148, 151 pain 111 kidneys 72–3, 74, 126, 147 muscle cells 9, 12, 40 pancreas 94 muscles 19, 26, 40–9 papillae 116 L contraction 42, 45, 48–9 patella 27, 33 fibers 42, 43, 44, 46–7, 151 pelvic girdle 26, 33, 38 language 5, 85, 106, 107 movement 40–1 penis 132 large intestine 66, 70, 88, structure 44–5 peristalsis 95, 99 tissues 12–13 personality 106 89, 98–9 types of 42–3 pharynx 85 larynx 84 working of 48–9 photoreceptor cells 9 laughter 68 see also specific muscles pituitary gland 126, 127, 128 lens 112, 113 pivot joints 39 ligaments 36, 37, 151 NO placenta 136 lips 85 plane joints 39 liver 89, 100–1, 146 nails 22–3, 146 plasma 62–3 lobules 101 nasal cavity 78, 118 plaster casts 35 long bones 32 neck muscle 41 platelets 62–4 lungs 53, 76–83 nephrons 73 plugs 64 nerve cells 8, 9, 103, 105 pregnancy 136–7 inside 82–3 nervous system 20, 102–29, premolar teeth 91 lymph 70, 71 prostate gland 132 lymphatic system 51, 70–1 148–9 protein 44, 45, 92, 94, 151 lyosomes 6 brain 106–7 puberty 143, 151 senses 112–25 pulmonary artery 52, 53, 59 M spinal cord 110–11 pulmonary vein 59 neurons 8, 9, 104–11, 148–9, 151 pulse 151 macrophages 67, 68–9 nose 78, 81, 118–19 pupil 113–15, 129 male reproductive system 132 nucleus 6, 10, 133, 134, 151 pyloric sphincter 92, 93 melanin 146 nutrients 87, 88–9, 94, membranes, cell 6–7 97, 100, 151 R metabolism 75, 151 old age 131, 144–5 middle ear 122, 123 optic nerve 112, 113 radius 26 mitochondria 7, 151 organelles 6, 151 receptor cells 117, 118, 119, 124 mitosis 10, 151 organs 12, 13, 151 rectum 89, 98, 99 molar teeth 91 ossicles 19, 122, 123 red blood cells 8, 62–7, 83, 146 mouth 81, 85, 90–1 osteons 30, 31 reflexes 111, 149, 151 movable joints 38–9 outer ear 122 renal artery 73 movement 4, 40–1, 147 ovaries 133, 134 brain 106–7 154 | HUMAN BODY

renal vein 73 sounds 84–5, 122 trachea 66, 78–9, 84 repairs 10, 11, 64–5 speech 5, 84–5, 106, 122 triceps 48, 49 reproduction 126, 130–41, sperm 132, 133, 134 twins 141 sphincters 74, 92, 93, 99, 151 143 spinal cord 33, 104, UV respiration see breathing retina 112 106, 149 ulna 26 ribs 26, 33, 80 spinal nerves 104, 110 ultrasound 15, 138–9 rods 112 spine 26, 33, 110 umbilical cord 136 spleen 70 upright stance 4, 124 S spongy bone 30 urea 75 sternum 26, 33 ureter 72, 73 saddle joints 38 stethoscopes 61 urethra 72, 74, 132 saliva 66, 88, 90, 116, 148, 151 stomach 66, 88, 89, 92–3 urinary system 51, 67, scabs 65 superior vena cava 58 scapula 26, 33 swallowing 85, 90–1 72–5, 147 sciatic nerve 105 sweat 20, 25, 146, 151 filtering blood 72–3 seeing 9, 107, 112–13, 149 synapses 105 waste disposal 74–5 SEM (scanning electron synovial joints 36–7, 38, 151 urine 42, 51, 72, 74–5 systems 12, 13, 151 uterus 133, 134–9 microscopy) 15, 46–7, 65, 151 vagina 133 semimovable joints 38 T valves 55, 58, 60–1 senses 112–23, 149 veins 52–5, 100–1, 151 sensors 103, 118, 120, 123–5 taste buds 116, 149 ventricles 58–61 sesamoid bones 33 tasting 116–17 vertebrae 33, 38, 110, sex cells 132 tears 66 111 shape 18–49, 142–3 teeth 88, 90, 91, 148 villi 95–7 short bones 32 temperature, body 24–5 viruses 66, 151 skeletal muscles 40, 42, 44–9 tendons 40, 41, 49, 151 visual cortex 107, 113 skeletal system 19, 26–7, 147 testes 132 vocal cords 84–5 skin 19, 20–1, 146 thalamus 113 thinking 106 WX aging 145 throat 88, 90–1 as barrier 66–7 thumbs 5 warm, keeping 4, 5, 24–5 hair and nails 22–3 thyroid gland 126 waste 51, 67, 74–5, 77, 82–3, healing 11, 64–5 tibia 27 keeping warm 24–5 tissues 8, 12–13, 151 89, 98–9 sensations 107 water 72, 73, 75 touch 120–1 drainage 51, 70–1 white blood cells 62–4, 67 skin cells 21 repairs 11 white matter 110–11 skin flakes 21, 146 tongue 85, 88, 90, 91, windpipe see trachea skull 26, 33, 38 116–18, 149 withdrawal reflex 111, 149 small intestine 66, 70, 88, 89, tonsils 70 words 85, 107 92, 94–7, 100, 146 touch 103, 107, wounds 11, 62, 64–5 smelling 117, 118–19 120–1, 149 X-rays 14, 35, 37, 151 smooth muscles 42, 43 INDEX | 155

Acknowledgments Dorling Kindersley would like to thank: Corbis: Ralph Hutchings / Visuals Getty Images: UIG (tl). 123 Corbis: Lorrie Mack for proofreading; Helen Unlimited (cb). 35 Corbis: MedicalRF.com (tc). 124–125 Getty Peters for indexing; Joe Fullman ERproductions Ltd. / Blend Images (tl). Images: Sajjad Hussain / AFP (c). and Catherine Saunders for editorial Dreamstime.com: Fotokon (tr). 37 125 Corbis: RelaXimages (br). 128 assistance; and Vikas Chauhan Corbis: Kallista Images / Visuals Corbis: Yoav Levy / MedNet (bl); for design assistance. Unlimited (l). 42 Corbis: Mediscan Visuals Unlimited (bc). 128–129 Getty (clb). 43 Corbis: Carolina Biological / Images: Oliver Furrer. 129 Getty The publisher would like to Visuals Unlimited (tr); Steve Images: Science Photo Library (br). thank the following for their kind Gschmeissner / Science Photo Library 130 Getty Images: SCIEPRO / permission to reproduce their (br). 46–47 Corbis: Dennis Kunkel Science Photo Library. 131 Fotolia: photographs: Microscopy, Inc. / Visuals Unlimited. adimas (bc). 137 Science Photo 50 Fotolia: michelangelus. 56–57 Library: Jellyfish Pictures (b). 138–139 (Key: a-above; b-below/bottom; Corbis: Science Picture Co / Science Science Photo Library: GE Medical c-center; f-far; l-left; r-right; t-top) Faction. 58 Science Photo Library: Systems. 141 Dreamstime.com: Bill Susumu Nishinaga (bc). 59 Corbis: Warchol (br). Fotolia: IKO (cra). 1 Science Photo Library: Howard Sochurek (r). 61 Dreamstime. 142 Dreamstime.com: Val Thoermer Gustoimages. 2–3 Corbis: Dennis com: Citalliance (tr). 65 Corbis: (tl). (r). 143 Corbis: David Katzenstein / Kunkel Microscopy, Inc. / Visuals 68–69 Corbis: Dr. David Phillips / Citizen Stock (br). 144 Corbis: Richard Unlimited. 4 Corbis: Isaac Lane Koval Visuals Unlimited. 76 Corbis: Science Lewisohn / Image Source (r). (cl). 4–5 Corbis: Michael Keller. 5 Picture Co / Science Faction (l). 77 Dreamstime.com: Tom Wang (l). Corbis: Ton Koene / Visuals Unlimited Alamy Images: Enigma (cb). 78 145 Fotolia: keki (br); Rohit Seth (l). (br). Dreamstime.com: Jacek Corbis: Veronika Burmeister / Visuals Chabraszewski (tr). 6 Alamy Images: Unlimited (ca). 79 Science Photo Jacket images: Front: Science Photo Phototake Inc. (bc). 7 Corbis: Dennis Library: CNRI (tc). 85 Dreamstime. Library: Pasieka c; Spine: Science Kunkel Microscopy, Inc. / Visuals com: Gemenacom (r). 86 Photo Library: Pasieka t. Unlimited (cr); Visuals Unlimited (tr). Dreamstime.com: Sebastian 8–9 Fotolia: martanfoto. 11 Getty Kaulitzki. 87 Corbis: Mediscan (cb). All other images © Dorling Kindersley Images: Image Source (tr); Michel 92 Science Photo Library: Dr. K. F. R. Tcherevkoff / Stone (l). 13 Getty Schiller (bl). 93 Corbis: Micro For further information see: Images: Zephyr / Science Photo Discovery (bl). 96–97 Science Photo www.dkimages.com Library (ca). 14 Corbis: Dan McCoy— Library: Eye of Science. 100 Science Rainbow / Science Faction (br). Photo Library: David Mccarthy (cl). Dreamstime.com: Peterfactors (cl). 102 Getty Images: Jan Scherders / 15 Corbis: Photo Quest Ltd. / Science Blend Images. 103 Dreamstime.com: Photo Library (br); Zephyr / Science Venki3503 (cb). 105 Getty Images: Photo Library (tl). Getty Images: UHB Visuals Unlimited, Inc. / Carol & Mike Trust / Stone (cra); BSIP / Universal Werner (cb). 108–109 Corbis: Dennis Images Group (bl). 16–17 Corbis: Kunkel Microscopy, Inc. / Visuals Image Source. 22–23 Science Photo Unlimited. 112 Getty Images: Steve Library: Steve Gschmeissner. 23 Gschmeissner / Science Photo Library Fotolia: Aaron Amat (tr). 24 Corbis: (ca). 113 Science Photo Library: Scientifica / Visuals Unlimited. 25 BSIP, Chassenet (ca, tr). 114-115 Getty Images: Sam Jordash / Digital Corbis: Jens Nieth. 116 Dreamstime. Vision (tl); Michael Krasowitz / Taxi (br). com: Kamil Macniak (bl). 117 Corbis: 28–29 Corbis: Photo Quest Ltd. / Fabrice Lerouge / Onoky (tc). 119 Science Photo Library. 30 Corbis: Fotolia: dragon_fang (br). 120 Corbis: Steve Gschmeissner / Science Photo Ondrea Barbe (bc). Dreamstime.com: Library (bc). 31 Corbis: Dennis Kunkel Zigf (br). 121 Corbis: Claire Artman Microscopy, Inc. / Visuals Unlimited (br); Tom Grill (cr); Chris Whitehead / (bc); Lester V. Bergman (cr). 33 cultura (bc). Fotolia: April Cat (bl). 156 | HUMAN BODY