Q:Information: - Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. - Oxygen is a chemical element with symbolO and atomic number8. It is a member of the chalcogen group on the periodic table and is a highly reactive nonmetal and oxidizing agent that readily forms oxides with most elements as well as other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula . This is an important part of the atmosphere and diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. Additionally, as oxides the element makes up almost half of the Earth's crust. - Body fluid, bodily fluids or biofluids are liquids originating from inside the bodies of living people. They include fluids that are excreted or secreted from the body, and body water that normally is not. - The lungs are the primary organs of respiration in humans and many other animals including a few fish and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the atmosphere and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. Respiration is driven by different muscular systems in different species. Mammals, reptiles and birds use their musculoskeletal systems to support and foster breathing. In early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, a mechanism still seen in amphibians. In humans, the primary muscle that drives breathing is the diaphragm. The lungs also provide airflow that makes vocal sounds including human speech possible. - The liver is a vital organ of vertebrates and some other animals. In the human, it is located in the upper right quadrant of the abdomen, below the diaphragm. The liver has a wide range of functions, including detoxification of various metabolites, protein synthesis, and the production of biochemicals necessary for digestion. - The heart is a muscular organ 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 heart is located between the lungs, in the middle compartment of the chest. In humans, other mammals, and birds, the heart 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 heart" and their left counterparts as the "left heart". Fish in contrast have two chambers, an atrium and a ventricle, while reptiles have three chambers. In a healthy heart blood flows one way through the heart due to heart valves, which prevent backflow. The heart is enclosed in a protective sac, the pericardium, which also contains a small amount of fluid. The wall of the heart is made up of three layers: epicardium, myocardium, and endocardium. The heart 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 heart, traveling through the atrioventricular node and along the conduction system of the heart. The heart 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 circulationwhere the oxygen is used and metabolized to carbon dioxide. The heart beats at a resting rate close to 72 beats per minute. Exercise temporarily increases the rate, but lowers resting heart rate in the long term, and is good for heart health. Cardiovascular diseases (CVD) are the most common cause of death globally as of 2008, accounting for 30%... - A nutrient is a component in foods that an organism uses to survive and grow. Macronutrients provide the bulk energy an organism's metabolic system needs to function while micronutrients provide the necessary cofactors for metabolism to be carried out. Both types of nutrients can be acquired from the environment. Micronutrients are used to build and repair tissues and to regulate body processes while macronutrients are converted to, and used for, energy. Methods of nutrient intake are different for plants and animals. Plants take in nutrients directly from the soil through their roots and from the atmosphere through their leaves. Animals and protists have specialized digestive systems that work to break down macronutrients for energy and utilize micronutrients for both metabolism and anabolism (constructive synthesis) in the body. - Metabolic wastes or excretes are substances left over from metabolic processes (such as cellular respiration), which cannot be used by the organism (they are surplus or toxic), and must therefore be excreted. This includes nitrogen compounds, water, CO, phosphates, sulfates, etc. Animals treat these compounds as excretes. Plants have chemical "machinery" which transforms some of them (primarily the nitrogen compounds) into useful substances, and it has been shown by Brian J. Ford that abscissa leaves also carry wastes away from the parent plant. In this way, Ford argues that the shed leaf acts as an "excretory" (an organ carrying away excretory products). - Pulmonary circulation is the portion of the cardiovascular system which carries deoxygenated blood away from the heart , to the lungs , and returns oxygenated ( oxygen - rich ) blood back to the heart . The term pulmonary circulation is readily paired and contrasted with the systemic circulation . A separate system known as the bronchial circulation supplies blood to the tissue of the larger airways of the lung . After reading the paragraphs above, we are interested in knowing the entity with which 'pulmonary circulation' exhibits the relationship of 'subclass of'. Find the answer from the choices below. Choices: - atmosphere - body fluid - cellular respiration - chemical element - circulatory system - energy - formula - function - human - mass - member - nitrogen - nonmetal - number - nutrient - organ - oxygen - parent - people - plant - production - protein - range - soil - symbol - system - third - water - work
A:
circulatory system