Respiratory system in the context of "Terrestrial animal"

Exhalation (or expiration) is the flow of the breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing.This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume. As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air. During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles generate abdominal and thoracic pressure, which forces air out of the lungs.

Exhaled air is 4% carbon dioxide, a waste product of cellular respiration during the production of energy, which is stored as ATP. Exhalation has a complementary relationship to inhalation which together make up the respiratory cycle of a breath.

An aquatic animal is any animal, whether vertebrate or invertebrate, that lives in a body of water for all or most of its lifetime. Aquatic animals generally conduct aquatic respiration by extracting dissolved oxygen in water via specialised respiratory organs called gills, through the skin or across enteral mucosae, although some are secondarily aquatic animals (e.g. marine reptiles and marine mammals) evolved from terrestrial ancestors that re-adapted to aquatic environments, in which case they actually use lungs to breathe air and are essentially holding their breath when living in water. Some species of gastropod mollusc, such as the eastern emerald sea slug, are even capable of kleptoplastic photosynthesis via endosymbiosis with ingested yellow-green algae.

Almost all aquatic animals reproduce in water, either oviparously or viviparously, and many species routinely migrate between different water bodies during their life cycle. Some animals have fully aquatic life stages (typically as eggs and larvae), while as adults they become terrestrial or semi-aquatic after undergoing metamorphosis. Such examples include amphibians such as frogs, many flying insects such as mosquitoes, mayflies, dragonflies, damselflies and caddisflies, as well as some species of cephalopod molluscs such as the algae octopus (whose larvae are completely planktonic, but adults are highly terrestrial).

The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.

The brainstem is very small, making up around only 2.6 percent of the brain's total weight. It has the critical roles of regulating heart and respiratory function, helping to control heart rate and breathing rate. It also provides the main motor and sensory nerve supply to the face and neck via the cranial nerves. Ten pairs of cranial nerves come from the brainstem. Other roles include the regulation of the central nervous system and the body's sleep cycle. It is also of prime importance in the conveyance of motor and sensory pathways from the rest of the brain to the body, and from the body back to the brain. These pathways include the corticospinal tract (motor function), the dorsal column-medial lemniscus pathway (fine touch, vibration sensation, and proprioception), and the spinothalamic tract (pain, temperature, itch, and crude touch).

The lungs are the primary organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, 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 vocalisation including speech possible.

Humans have two lungs, a right lung and a left lung. They are situated within the thoracic cavity of the chest. The right lung is bigger than the left, and the left lung shares space in the chest with the heart. The lungs together weigh approximately 1.3 kilograms (2.9 lb), and the right is heavier. The lungs are part of the lower respiratory tract that begins at the trachea and branches into the bronchi and bronchioles, which receive air breathed in via the conducting zone. These divide until air reaches microscopic alveoli, where gas exchange takes place. Together, the lungs contain approximately 2,400 kilometers (1,500 mi) of airways and 300 to 500 million alveoli. Each lung is enclosed within a pleural sac of two pleurae which allows the inner and outer walls to slide over each other whilst breathing takes place, without much friction. The inner visceral pleura divides each lung as fissures into sections called lobes. The right lung has three lobes and the left has two. The lobes are further divided into bronchopulmonary segments and lobules. The lungs have a unique blood supply, receiving deoxygenated blood sent from the heart to receive oxygen (the pulmonary circulation) and a separate supply of oxygenated blood (the bronchial circulation).

A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are determined based different structures depending on what the system is. Examples of biological systems at the macro scale are populations of organisms. On the organ and tissue scale in mammals and other animals, examples include the circulatory system, the respiratory system, and the nervous system. On the micro to the nanoscopic scale, examples of biological systems are cells, organelles, macromolecular complexes and regulatory pathways. A biological system is not to be confused with a living system, such as a living organism.

The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.

Air is breathed in through the nose to the nasal cavity, where a layer of nasal mucosa acts as a filter and traps pollutants and other harmful substances found in the air. The turbinates increase the nasal cavity, helping it warm, humidify, and filter the incoming air (Sobiesk & Munakomi, 2023). Next, air moves into the pharynx, a passage that contains the intersection between the esophagus and the larynx. The opening of the larynx has a special flap of cartilage, the epiglottis, that opens to allow air to pass through but closes to prevent food from moving into the airway.

Soil gases (soil atmosphere) are the gases found in the air space between soil components. The spaces between the solid soil particles, if they do not contain water, are filled with air. The primary soil gases are nitrogen, carbon dioxide and oxygen. Oxygen is critical because it allows for respiration of both plant roots and soil organisms. Other natural soil gases include nitric oxide, nitrous oxide, methane, and ammonia. Some environmental contaminants below ground produce gas which diffuses through the soil such as from landfill wastes, mining activities, and contamination by petroleum hydrocarbons which produce volatile organic compounds. The soil atmosphere is also made of a variety of volatile compounds emitted by soil organisms, as respiratory metabolites, allelopathic compounds or semiochemical signals used in within-species and between-species communication. Soil is a net emitter of greenhouse gases, in particular when and where permafrost is thawing and degassing under the influence of climate warming.

Gases fill soil pores in the soil structure as water drains or is removed from a soil pore by evaporation or root absorption. The network of pores within the soil aerates, or ventilates, the soil. This aeration network becomes blocked when water enters soil pores. Not only are both soil air and soil water very dynamic parts of soil, but both are often inversely related.