part_of tendon
White blood cells ( WBCs ), also called leukocytes or leucocytes , are the cells of the immune ___MASK55___ that are involved in protecting the body against both infectious ___MASK20___ and foreign invaders . All white blood cells are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells . Leukocytes are found throughout the body , including the blood and lymphatic ___MASK55___ . A bone is a rigid ___MASK64___ that constitutes part of the vertebrate ___MASK15___ . ___MASK95___ support and protect the various organs of the body , produce red and white blood cells , store minerals , provide structure and support for the body , and enable mobility . ___MASK95___ come in a ___MASK89___ of shapes and sizes and have a complex internal and external structure . They are lightweight yet strong and hard , and serve multiple functions . Vertebrates comprise all ___MASK17___ of animals within the subphylum Vertebrata ( chordates with backbones ). Vertebrates represent the overwhelming majority of the phylum Chordata , with currently about 64 , 000 ___MASK17___ described . Vertebrates include the jawless fish and the jawed vertebrates , which include the cartilaginous fish ( sharks and rays ) and the bony fish . Myosins comprise a superfamily of ATP - dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other motility processes in eukaryotes . They are responsible for actin - based motility . The term was originally used to describe a group of similar ATPases found in the cells of both ___MASK3___ and smooth muscle tissue . Following the discovery by Pollard and Korn ( 1973 ) of enzymes with myosin - like function in " Acanthamoeba castellanii ", a large number of divergent myosin genes have been discovered throughout eukaryotes . Thus , although myosin was originally thought to be restricted to muscle cells ( hence " myo -"( s ) + "- in "), there is no single " myosin " but rather a huge superfamily of genes whose protein products share the basic properties of actin binding , ATP hydrolysis ( ATPase enzyme activity ), and force transduction . Virtually all eukaryotic cells contain myosin isoforms . Some isoforms have specialized functions in certain cell types ( such as muscle ), while other isoforms are ubiquitous . The structure and function of myosin is strongly conserved across species , to the extent that rabbit muscle myosin II will bind to actin from an amoeba . Actin is a ___MASK56___ of globular multi - functional proteins that form microfilaments . It is found in essentially all eukaryotic cells ( the only known exception being nematode sperm ), where it ___MASK41___ be present at a concentration of over 100 M . An actin protein ' s mass is roughly 42 - kDa , with a diameter of 4 to 7 nm , and it is the monomeric subunit of two types of filaments in cells : microfilaments , one of the three major components of the cytoskeleton , and thin filaments , part of the contractile apparatus in muscle cells . It can be present as either a free monomer called G - actin ( globular ) or as part of a linear polymer microfilament called F - actin ( filamentous ), both of which are essential for such important cellular functions as the mobility and contraction of cells during cell division . A tendon ( or sinew ) is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension . Tendons are similar to ligaments and fasciae ; all three are made of collagen . Ligaments join one bone to another bone ; fasciae connect muscles to other muscles . Tendons and muscles work together to move ___MASK95___ . The ___MASK72___ is a muscular ___MASK64___ in humans and other animals , which pumps blood through the blood vessels of the circulatory system . Blood provides the body with oxygen and nutrients , as well as assists in the removal of metabolic wastes . The ___MASK72___ is located between the lungs , in the middle compartment of the chest . In humans , other mammals , and birds , the ___MASK72___ is divided into four chambers : upper left and right atria ; and lower left and right ventricles . Commonly the right atrium and ventricle are referred together as the " right ___MASK72___ " and their left counterparts as the " left ___MASK72___ ". Fish in contrast have two chambers , an atrium and a ventricle , while reptiles have three chambers . In a healthy ___MASK72___ blood flows one way through the ___MASK72___ due to ___MASK72___ valves , which prevent backflow . The ___MASK72___ is enclosed in a protective sac , the pericardium , which also contains a small amount of fluid . The ___MASK87___ of the ___MASK72___ is made up of three layers : epicardium , myocardium , and endocardium . The ___MASK72___ pumps blood with a rhythm determined by a group of pacemaking cells in the sinoatrial node . These generate a current that causes contraction of the ___MASK72___ , traveling through the atrioventricular node and along the conduction system of the ___MASK72___ . The ___MASK72___ receives blood low in oxygen from the systemic circulation , which enters the right atrium from the superior and inferior venae cavae and passes to the right ventricle . From here it is pumped into the pulmonary circulation , through the lungs where it receives oxygen and gives off carbon dioxide . Oxygenated blood then returns to the left atrium , passes through the left ventricle and is pumped out through the aorta to the systemic circulation  where the oxygen is used and metabolized to carbon dioxide . The ___MASK72___ beats at a resting rate close to 72 beats per minute . Exercise temporarily increases the rate , but lowers resting ___MASK72___ rate in the long term , and is good for ___MASK72___ health . Cardiovascular diseases ( CVD ) are the most common cause of death globally as of 2008 , accounting for 30 % of deaths . Of these more than three quarters are a result of coronary artery disease and stroke . Risk factors include : smoking , being overweight , little exercise , high cholesterol , high blood pressure , and poorly controlled diabetes , among others . Cardiovascular diseases frequently have no symptoms or ___MASK41___ cause chest pain or shortness of breath . Diagnosis of ___MASK72___ disease is often done by the taking of a medical history , listening to the ___MASK72___ - sounds with a stethoscope , ECG , and ultrasound . Specialists who focus on diseases of the ___MASK72___ are called cardiologists , although many specialties of medicine ___MASK41___ be involved in treatment . A mineral is a naturally occurring chemical compound , usually of crystalline form and abiogenic in origin . A mineral has one specific chemical composition , whereas a ___MASK38___ can be an aggregate of different minerals or mineraloids . The study of minerals is called mineralogy . In ___MASK19___ , soft tissue includes the tissues that connect , support , or surround other structures and organs of the body , not being hard tissue such as bone . Soft tissue includes tendons , ligaments , fascia , skin , fibrous tissues , fat , and synovial membranes ( which are connective tissue ), and muscles , nerves and blood vessels ( which are not connective tissue ). The ___MASK15___ ( from Greek  , " skeletós " " dried up ") is the body part that forms the supporting structure of an ___MASK39___ . There are several different skeletal types : the exoskeleton , which is the stable outer shell of an ___MASK39___ , the endoskeleton , which forms the support structure inside the body , the hydroskeleton , and the cytoskeleton . Muscle is a soft tissue found in most ___MASK45___ . Muscle cells contain protein filaments of actin and myosin that slide past one another , producing a contraction that changes both the length and the shape of the cell . Muscles function to produce force and motion . They are primarily responsible for maintaining and changing posture , locomotion , as well as movement of internal organs , such as the contraction of the heart and the movement of food through the digestive system via peristalsis . Proteins ( or ) are large biomolecules , or macromolecules , consisting of one or more long chains of amino acid residues . Proteins perform a vast array of functions within organisms , including catalysing metabolic reactions , ___MASK40___ replication , responding to stimuli , and transporting molecules from one location to another . Proteins differ from one another primarily in their sequence of amino acids , which is dictated by the nucleotide sequence of their genes , and which usually results in protein folding into a specific three - dimensional structure that determines its activity .