The heart and blood GapFill

The heart and lungs are closely related and the lungs are well adapted for their role in  circulationtranslationphotosynthesisgas exchangetranspirationsignalling. The heart is adapted to pump blood around the body. It is a  globulartotipotentcrenelatedsmoothmuscularfibrous pump, consisting of  twoacidicthreedigestivefourvariable chambers. As blood passes through the heart twice for every heartbeat, the mammalian heart is described as being part of a  double circulatory systemduo pump systemdouble pump systemtwin circulatory systemtwin heartbeat systemtwin pump system.

Blood is pumped from the heart by the ventricles, the  leftcapillariesrightvena cavamusclesventricles to the lungs, while the  leftlungsred blood cellrightvalveatrium pumps blood to the body. Blood returns to the heart through veins - blood from the body enters the heart through the  alveolivalvesvena cavacapillariesaortaventricles, whilst blood from the lungs enters the heart through the  capillariespulmonary arteryplasmaventriclesvalvespulmonary vein.

Arteries carry blood from the heart and normally contain oxygenated blood. They deal with blood at a much higher pressure, and therefore have  muscular wallsvalvesalveolipacemakerslarge nucleicapillaries.  CapillariesAlveoliVentriclesAtriaArteriesVeins are the smallest blood vessels. They are about the width of a  mitochondrionhairred blood cellvalvehaemoglobin moleculecarbon dioxide molecule, which are adapted to carry oxygen. Blood also contains white blood cells and platelets, all suspended in a liquid called  bilecell saplymphsulfuric acidplasmastarch, which is mostly water but also contains salts, amino acids and glucose.