The thorax ( pl. : thoraces or thoraxes ) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen .
67-414: In insects , crustaceans , and the extinct trilobites , the thorax is one of the three main divisions of the body, each in turn composed of multiple segments. The human thorax includes the thoracic cavity and the thoracic wall . It contains organs including the heart , lungs , and thymus gland, as well as muscles and various other internal structures. Many diseases may affect the chest, and one of
134-415: A heterogeneous mixture of smooth muscle , nerves, intimal cells, endothelial cells, immune cells, fibroblast-like cells, and a complex extracellular matrix. The vascular wall is subdivided into three layers known as the tunica externa , tunica media , and tunica intima . The aorta is covered by an extensive network of tiny blood vessels called vasa vasorum , which feed the tunica externa and tunica media,
201-563: A hundred species, are marine. Insects such as snow scorpionflies flourish in cold habitats including the Arctic and at high altitude. Insects such as desert locusts , ants, beetles, and termites are adapted to some of the hottest and driest environments on earth, such as the Sonoran Desert . Insects form a clade , a natural group with a common ancestor, among the arthropods . A phylogenetic analysis by Kjer et al. (2016) places
268-418: A more or less pigmented disc, the areola . The apex of a normal heart is in the fifth left intercostal space, three and a half inches from the mid-line. Different types of diseases or conditions that affect the chest include pleurisy , flail chest , atelectasis , and the most common condition, chest pain. These conditions can be hereditary or caused by birth defects or trauma . Any condition that lowers
335-421: A pair of antennae . Insects are the most diverse group of animals, with more than a million described species ; they represent more than half of all animal species. The insect nervous system consists of a brain and a ventral nerve cord . Most insects reproduce by laying eggs . Insects breathe air through a system of paired openings along their sides, connected to small tubes that take air directly to
402-431: A symptom of myocardial infarctions ('heart attack'). If this condition is present in the body, discomfort will be felt in the chest that is similar to a heavy weight placed on the body. Sweating, shortness of breath, lightheadedness , and irregular heartbeat may also be experienced. If a heart attack occurs, the bulk of the damage is caused during the first six hours, so getting the proper treatment as quickly as possible
469-400: Is blocked and traps air. The blockage may be caused by something inside the bronchus , such as a plug of mucus, a tumour , or an inhaled foreign object such as a coin, piece of food, or a toy. It is possible for something outside of the bronchus to cause the blockage. Pneumothorax is the condition where air or gas can build up in the pleural space. It can occur without a known cause or as
536-499: Is composed of one to several independent exoskeletal plates with membrane between them (called sclerites ), though in many cases the sclerites are fused to various degrees. Insect Insects (from Latin insectum ) are hexapod invertebrates of the class Insecta . They are the largest group within the arthropod phylum . Insects have a chitinous exoskeleton , a three-part body ( head , thorax and abdomen ), three pairs of jointed legs , compound eyes , and
603-423: Is constrained by the inelastic exoskeleton, so development involves a series of molts . The immature stages often differ from the adults in structure, habit and habitat. Groups that undergo four-stage metamorphosis often have a nearly immobile pupa . Insects that undergo three-stage metamorphosis lack a pupa, developing through a series of increasingly adult-like nymphal stages. The higher level relationship of
670-429: Is derived from mesoderm . In fact the smooth muscle within the abdominal aorta is derived from mesoderm, and the coronary arteries, which arise just above the semilunar valves , possess smooth muscle of mesodermal origin. A failure of the aorticopulmonary septum to divide the great vessels results in persistent truncus arteriosus . The aorta is an elastic artery , and as such is quite distensible. The aorta consists of
737-404: Is generally felt when deep breaths are taken or during a cough. Another non-cardiac cause of chest pain is atelectasis . It is a condition that occurs when a portion of the lung collapses from being airless. When bronchial tubes are blocked, this condition develops and causes patients to feel shortness of breath. The most common cause of atelectasis is when a bronchi that extends from the windpipe
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#1732780645443804-501: Is highest in the aorta, and the MAP decreases across the circulation from aorta to arteries to arterioles to capillaries to veins back to atrium. The difference between aortic and right atrial pressure accounts for blood flow in the circulation. When the left ventricle contracts to force blood into the aorta, the aorta expands. This stretching gives the potential energy that will help maintain blood pressure during diastole , as during this time
871-526: Is important. Some people, especially those who are elderly or have diabetes, may not have typical chest pain but may have many of the other symptoms of a heart attack. It is important that these patients and their caregivers have a good understanding of heart attack symptoms. Just like with a heart attack, not all chest pain is caused by conditions involving the heart . Chest wall pain can be experienced after an increase in activity. Persons who add exercise to their daily routine generally feel this type of pain at
938-491: Is slow and smooth for gases and nutrient exchange. Central aortic blood pressure has frequently been shown to have greater prognostic value and to show a more accurate response to antihypertensive drugs than has peripheral blood pressure. All amniotes have a broadly similar arrangement to that of humans, albeit with a number of individual variations. In fish , however, there are two separate vessels referred to as aortas. The ventral aorta carries de-oxygenated blood from
1005-408: Is the main and largest artery in the human body, originating from the left ventricle of the heart , branching upwards immediately after, and extending down to the abdomen , where it splits at the aortic bifurcation into two smaller arteries (the common iliac arteries ). The aorta distributes oxygenated blood to all parts of the body through the systemic circulation . In anatomical sources,
1072-853: The Latin word insectum from in , "cut up", as insects appear to be cut into three parts. The Latin word was introduced by Pliny the Elder who calqued the Ancient Greek word ἔντομον éntomon "insect" (as in entomology ) from ἔντομος éntomos "cut in pieces"; this was Aristotle 's term for this class of life in his biology , also in reference to their notched bodies. The English word insect first appears in 1601 in Philemon Holland 's translation of Pliny. In common speech, insects and other terrestrial arthropods are often called bugs . Entomologists to some extent reserve
1139-2419: The Paraneoptera , and Kjer et al. 2016 for the Holometabola . The numbers of described extant species (boldface for groups with over 100,000 species) are from Stork 2018. Archaeognatha (hump-backed/jumping bristletails, 513 spp) [REDACTED] Zygentoma (silverfish, firebrats, fishmoths, 560 spp) [REDACTED] Odonata (dragonflies and damselflies, 5,899 spp) [REDACTED] Ephemeroptera (mayflies, 3,240 spp) [REDACTED] Zoraptera (angel insects, 37 spp) [REDACTED] Dermaptera (earwigs, 1,978 spp) [REDACTED] Plecoptera (stoneflies, 3,743 spp) [REDACTED] Orthoptera (grasshoppers, crickets, katydids, 23,855 spp) [REDACTED] Grylloblattodea (ice crawlers, 34 spp) [REDACTED] Mantophasmatodea (gladiators, 15 spp) [REDACTED] Phasmatodea (stick insects, 3,014 spp) [REDACTED] Embioptera (webspinners, 463 spp) [REDACTED] Mantodea (mantises, 2,400 spp) [REDACTED] Blattodea (cockroaches and termites, 7,314 spp) [REDACTED] Psocodea (book lice, barklice and sucking lice, 11,000 spp) [REDACTED] [REDACTED] Hemiptera (true bugs, 103,590 spp) [REDACTED] Thysanoptera (thrips, 5,864 spp) [REDACTED] Hymenoptera (sawflies, wasps, bees, ants, 116,861 spp) [REDACTED] Strepsiptera (twisted-wing flies, 609 spp) [REDACTED] Coleoptera (beetles, 386,500 spp) [REDACTED] Raphidioptera (snakeflies, 254 spp) [REDACTED] Neuroptera (lacewings, 5,868 spp) [REDACTED] Megaloptera (alderflies and dobsonflies, 354 spp) [REDACTED] Lepidoptera (butterflies and moths, 157,338 spp) [REDACTED] Trichoptera (caddisflies, 14,391 spp) [REDACTED] Diptera (true flies, 155,477 spp) [REDACTED] Mecoptera (scorpionflies, 757 spp) [REDACTED] Siphonaptera (fleas, 2,075 spp) [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Aorta Arch of aorta (supra-aortic vessels): Descending aorta, thoracic part: Descending aorta, abdominal part: Terminal branches: The aorta ( / eɪ ˈ ɔːr t ə / ay- OR -tə ; pl. : aortas or aortae )
1206-448: The esophagus , mediastinum , and pericardium . Its lowest pair of branches are the superior phrenic arteries, which supply the diaphragm, and the subcostal arteries for the twelfth rib. The abdominal aorta begins at the aortic hiatus of the diaphragm at the level of the twelfth thoracic vertebra. It gives rise to lumbar and musculophrenic arteries, renal and middle suprarenal arteries , and visceral arteries (the celiac trunk ,
1273-623: The insects is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonfly-like insects with wingspans of 55 to 70 cm (22 to 28 in). The most diverse insect groups appear to have coevolved with flowering plants . Adult insects typically move about by walking and flying; some can swim. Insects are the only invertebrates that can achieve sustained powered flight; insect flight evolved just once. Many insects are at least partly aquatic , and have larvae with gills; in some species,
1340-483: The pheromones of female moths over great distances. Other species communicate with sounds: crickets stridulate , or rub their wings together, to attract a mate and repel other males. Lampyrid beetles communicate with light. Humans regard many insects as pests , especially those that damage crops, and attempt to control them using insecticides and other techniques. Others are parasitic , and may act as vectors of diseases . Insect pollinators are essential to
1407-413: The pulmonary artery to the proximal descending aorta . The aorta supplies all of the systemic circulation, which means that the entire body, except for the respiratory zone of the lung , receives its blood from the aorta. Broadly speaking, branches from the ascending aorta supply the heart; branches from the aortic arch supply the head, neck, and arms; branches from the thoracic descending aorta supply
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#17327806454431474-403: The superior mesenteric artery and the inferior mesenteric artery ). It ends in a bifurcation into the left and right common iliac arteries . At the point of the bifurcation, there also springs a smaller branch, the median sacral artery . The ascending aorta develops from the outflow tract, which initially starts as a single tube connecting the heart with the aortic arches (which will form
1541-457: The "thoracic skeleton" is a component of the axial skeleton . It consists of the ribs and sternum . The ribs of the thorax are numbered in ascending order from 1–12. 11 and 12 are known as floating ribs because they have no anterior attachment point in particular the cartilage attached to the sternum, as 1 through 7 are, and therefore are termed "floating". Whereas ribs 8 through 10 are termed false ribs as their costal cartilage articulates with
1608-623: The Hemiptera (true bugs), Lepidoptera (butterflies and moths), Diptera (true flies), Hymenoptera (wasps, ants, and bees), and Coleoptera (beetles), each with more than 100,000 described species. Insects are distributed over every continent and almost every terrestrial habitat. There are many more species in the tropics , especially in rainforests , than in temperate zones. The world's regions have received widely differing amounts of attention from entomologists. The British Isles have been thoroughly surveyed, so that Gullan and Cranston 2014 state that
1675-833: The ability to either breathe deeply or to cough is considered a chest disease or condition. Injury to the chest (also referred to as chest trauma, thoracic injury, or thoracic trauma) results in up to 1 / 4 of all deaths due to trauma in the United States. The major pathophysiologies encountered in blunt chest trauma involve derangements in the flow of air, blood, or both in combination. Sepsis due to leakage of alimentary tract contents, as in esophageal perforations, also must be considered. Blunt trauma commonly results in chest wall injuries (e.g., rib fractures). The pain associated with these injuries can make breathing difficult, and this may compromise ventilation. Direct lung injuries, such as pulmonary contusions (see
1742-404: The adults too are aquatic. Some species, such as water striders , can walk on the surface of water. Insects are mostly solitary, but some, such as bees , ants and termites , are social and live in large, well-organized colonies . Others, such as earwigs , provide maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male moths can sense
1809-421: The aorta contracts passively. This Windkessel effect of the great elastic arteries has important biomechanical implications. The elastic recoil helps conserve the energy from the pumping heart and smooth out the pulsatile nature created by the heart. Aortic pressure is highest at the aorta and becomes less pulsatile and lower pressure as blood vessels divide into arteries, arterioles, and capillaries such that flow
1876-560: The aorta has two parallel arches. The word aorta stems from the Late Latin aorta from Classical Greek aortē ( ἀορτή ), from aeirō , "I lift, raise" ( ἀείρω ) This term was first applied by Aristotle when describing the aorta and describes accurately how it seems to be "suspended" above the heart. The function of the aorta is documented in the Talmud , where it is noted as one of three major vessels entering or leaving
1943-400: The aorta is associated with a number of diseases and pathologies, and noninvasive measures of the pulse wave velocity are an independent indicator of hypertension . Measuring the pulse wave velocity (invasively and non-invasively) is a means of determining arterial stiffness . Maximum aortic velocity may be noted as V max or less commonly as AoV max . Mean arterial pressure (MAP)
2010-435: The aorta is usually divided into sections. One way of classifying a part of the aorta is by anatomical compartment, where the thoracic aorta (or thoracic portion of the aorta) runs from the heart to the diaphragm . The aorta then continues downward as the abdominal aorta (or abdominal portion of the aorta) from the diaphragm to the aortic bifurcation . Another system divides the aorta with respect to its course and
2077-459: The aorta passes through the diaphragm , it is known as the abdominal aorta . The aorta ends by dividing into two major blood vessels, the common iliac arteries and a smaller midline vessel, the median sacral artery . The ascending aorta begins at the opening of the aortic valve in the left ventricle of the heart. It runs through a common pericardial sheath with the pulmonary trunk . These two blood vessels twist around each other, causing
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2144-449: The aorta to start out posterior to the pulmonary trunk, but end by twisting to its right and anterior side. The transition from ascending aorta to aortic arch is at the pericardial reflection on the aorta. At the root of the ascending aorta, the lumen has small pockets between the cusps of the aortic valve and the wall of the aorta, which are called the aortic sinuses or the sinuses of Valsalva. The left aortic sinus contains
2211-415: The aortic arch, gives off a major branch, the recurrent laryngeal nerve , which loops under the aortic arch just lateral to the ligamentum arteriosum. It then runs back to the neck. The aortic arch has three major branches: from proximal to distal , they are the brachiocephalic trunk , the left common carotid artery , and the left subclavian artery . The brachiocephalic trunk supplies the right side of
2278-418: The base and middle part of the right subclavian artery and the left 4th being the central part of the aortic arch . The smooth muscle of the great arteries and the population of cells that form the aorticopulmonary septum that separates the aorta and pulmonary artery is derived from cardiac neural crest . This contribution of the neural crest to the great artery smooth muscle is unusual as most smooth muscle
2345-428: The beginning. It is important to monitor the pain to ensure that it is not a sign of something more serious. Pain can also be experienced in persons who have an upper respiratory infection . This virus is also accompanied by a fever and cough. Shingles is another viral infection that can give symptoms of chest or rib pain before a rash develops. Injuries to the rib cage or sternum is also a common cause of chest pain. It
2412-417: The biomechanical properties of the aorta. The smooth muscle component, while contractile, does not substantially alter the diameter of the aorta, but rather serves to increase the stiffness and viscoelasticity of the aortic wall when activated. Variations may occur in the location of the aorta, and the way in which arteries branch off the aorta. The aorta, normally on the left side of the body, may be found on
2479-420: The cause of the pain. While cardiac issues cause feelings of sudden pressure in the chest or a crushing pain in the back, neck, and arms, pain that is felt due to noncardiac issues gives a burning feeling along the digestive tract or pain when deep breaths are attempted. Different people feel pains differently for the same condition. Only a patient truly knows if the symptoms are mild or serious. Chest pain may be
2546-504: The chest (excluding the heart and the respiratory zone of the lung); and branches from the abdominal aorta supply the abdomen . The pelvis and legs get their blood from the common iliac arteries. The contraction of the heart during systole is responsible for ejection and creates a (pulse) wave that is propagated down the aorta, into the arterial tree . The wave is reflected at sites of impedance mismatching, such as bifurcations , where reflected waves rebound to return to semilunar valves and
2613-418: The chest does not correspond to that part of the thoracic skeleton that encloses the heart and lungs . All the breadth of the shoulders is due to the shoulder girdle, and contains the axillae and the heads of the humeri . In the middle line the suprasternal notch is seen above, while about three fingers' breadth below it a transverse ridge can be felt, which is known as the sternal angle and this marks
2680-418: The costal cartilage of the rib above. The thorax bones also have the main function of protecting the heart, lungs, and major blood vessels in the thorax area, such as the aorta . The anatomy of the chest can also be described through the use of anatomical landmarks . The nipple in the male is situated in front of the fourth rib or a little below; vertically it lies a little external to a line drawn down from
2747-418: The direction of blood flow. In this system, the aorta starts as the ascending aorta , travels superiorly from the heart, and then makes a hairpin turn known as the aortic arch . Following the aortic arch, the aorta then travels inferiorly as the descending aorta . The descending aorta has two parts. The aorta begins to descend in the thoracic cavity and is consequently known as the thoracic aorta . After
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2814-414: The extinct trilobites , the thorax is one of the three main divisions of the creature's body, each of which is in turn composed of multiple segments. It is the area where the wings and legs attach in insects, or an area of multiple articulating plates in trilobites. In most insects, the thorax itself is composed of three segments; the prothorax , the mesothorax , and the metathorax . In extant insects,
2881-434: The functional thorax is composed of four segments, and is therefore typically called the mesosoma to distinguish it from the "thorax" of other insects. Each thoracic segment in an insect is further subdivided into various parts, the most significant of which are the dorsal portion (the notum ), the lateral portion (the pleuron ; one on each side), and the ventral portion (the sternum ). In some insects, each of these parts
2948-415: The great arteries) in early development but is then separated into the aorta and the pulmonary trunk. The aortic arches start as five pairs of symmetrical arteries connecting the heart with the dorsal aorta , and then undergo a significant remodelling to form the final asymmetrical structure of the great arteries , with the 3rd pair of arteries contributing to the common carotids , the right 4th forming
3015-455: The head and neck as well as the right arm and chest wall , while the latter two together supply the left side of the same regions. The aortic arch ends, and the descending aorta begins at the level of the intervertebral disc between the fourth and fifth thoracic vertebrae . The thoracic aorta gives rise to the intercostal and subcostal arteries, as well as to the superior and inferior left bronchial arteries and variable branches to
3082-433: The heart to the gills ; part of this vessel forms the ascending aorta in tetrapods (the remainder forms the pulmonary artery ). A second, dorsal aorta carries oxygenated blood from the gills to the rest of the body and is homologous with the descending aorta of tetrapods. The two aortas are connected by a number of vessels, one passing through each of the gills. Amphibians also retain the fifth connecting vessel, so that
3149-445: The image below), are frequently associated with major chest trauma and may impair ventilation by a similar mechanism. Chest pain can be the result of multiple issues, including respiratory problems, digestive issues, and musculoskeletal complications. The pain can trigger cardiac issues as well. Not all pain that is felt is associated with the heart, but it should not be taken lightly either. Symptoms can be different depending on
3216-608: The insects among the Hexapoda , six-legged animals with segmented bodies; their closest relatives are the Diplura (bristletails). Collembola (springtails) [REDACTED] Protura (coneheads) [REDACTED] Diplura (two-pronged bristletails) [REDACTED] Insecta (=Ectognatha) [REDACTED] The internal phylogeny is based on the works of Wipfler et al. 2019 for the Polyneoptera , Johnson et al. 2018 for
3283-402: The junction between the manubrium and body of the sternum . Level with this line the second ribs join the sternum, and when these are found the lower ribs can often be counted. At the lower part of the sternum, where the seventh or last true ribs join it, the ensiform cartilage begins, and above this there is often a depression known as the pit of the stomach . The bones of the thorax, called
3350-482: The left pulmonary artery and the bifurcation of the pulmonary trunk , to which it remains connected by the ligamentum arteriosum , a remnant of the fetal circulation that is obliterated a few days after birth. In addition to these blood vessels, the aortic arch crosses the left main bronchus . Between the aortic arch and the pulmonary trunk is a network of autonomic nerve fibers, the cardiac plexus or aortic plexus . The left vagus nerve , which passes anterior to
3417-514: The lung or as a shortness of breath. In mammals , the thorax is the region of the body formed by the sternum , the thoracic vertebrae , and the ribs . It extends from the neck to the diaphragm , and does not include the upper limbs . The heart and the lungs reside in the thoracic cavity , as well as many blood vessels . The inner organs are protected by the rib cage and the sternum. Thoracic vertebrae are also distinguished in birds , but not in reptiles . In insects , crustaceans , and
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#17327806454433484-406: The middle of the clavicle ; in the female it is not so constant. A little below it the lower limit of the great pectoral muscle is seen running upward and outward to the axilla; in the female this is obscured by the breast , which extends from the second to the sixth rib vertically and from the edge of the sternum to the mid-axillary line laterally. The female nipple is surrounded for half an inch by
3551-485: The most common symptoms is chest pain . The word thorax comes from the Greek θώραξ thṓrax " breastplate , cuirass , corslet " via Latin : thorax . In humans and other hominids , the thorax is the chest region of the body between the neck and the abdomen , along with its internal organs and other contents. It is mostly protected and supported by the rib cage , spine , and shoulder girdle . The contents of
3618-402: The name "bugs" for a narrow category of " true bugs ", insects of the order Hemiptera , such as cicadas and shield bugs . Other terrestrial arthropods, such as centipedes , millipedes , woodlice , spiders , mites and scorpions , are sometimes confused with insects, since they have a jointed exoskeleton. Adult insects are the only arthropods that ever have wings, with up to two pairs on
3685-402: The origin of the left coronary artery and the right aortic sinus likewise gives rise to the right coronary artery . Together, these two arteries supply the heart. The posterior aortic sinus does not give rise to a coronary artery. For this reason the left, right and posterior aortic sinuses are also called left-coronary, right-coronary and non-coronary sinuses. The aortic arch loops over
3752-408: The origin of the aorta. These return waves create the dicrotic notch displayed in the aortic pressure curve during the cardiac cycle as these reflected waves push on the aortic semilunar valve . With age, the aorta stiffens such that the pulse wave is propagated faster and reflected waves return to the heart faster before the semilunar valve closes, which raises the blood pressure. The stiffness of
3819-432: The outer layers of the aorta. The aortic arch contains baroreceptors and chemoreceptors that relay information concerning blood pressure and blood pH and carbon dioxide levels to the medulla oblongata of the brain. This information along with information from baroreceptors and chemoreceptors located elsewhere is processed by the brain and the autonomic nervous system mediates appropriate homeostatic responses. Within
3886-417: The prothorax never has wings, though legs are always present in adults; wings (when present) are restricted to at least the mesothorax, and typically also the metathorax, though the wings may be reduced or modified on either or both segments. In the apocritan Hymenoptera , the first abdominal segment is fused to the metathorax, where it forms a structure known as the propodeum . Accordingly, in these insects,
3953-535: The reproduction of many flowering plants and so to their ecosystems. Many insects are ecologically beneficial as predators of pest insects, while a few provide direct economic benefit. Two species in particular are economically important and were domesticated many centuries ago: silkworms for silk and honey bees for honey . Insects are consumed as food in 80% of the world's nations, by people in roughly 3000 ethnic groups. Human activities are having serious effects on insect biodiversity . The word insect comes from
4020-412: The result of a lung disease or acute lung injury. The size of the pneumothorax changes as air or gas builds up, so a medical procedure can release the pressure with a needle. If it is untreated, blood flow can be interrupted and cause a drop in blood pressure known as tension pneumothorax. It is possible for smaller cases to clear up on their own. Symptoms of this condition are often felt only on one side of
4087-461: The right in dextrocardia , in which the heart is found on the right, or situs inversus , in which the location of all organs are flipped. Variations in the branching of individual arteries may also occur. For example, the left vertebral artery may arise from the aorta, instead of the left common carotid artery . In patent ductus arteriosus , a congenital disorder, the fetal ductus arteriosus fails to close, leaving an open vessel connecting
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#17327806454434154-453: The thorax include the heart and lungs (and the thymus gland); the major and minor pectoral muscles, trapezius muscles , and neck muscle; and internal structures such as the diaphragm , the esophagus , the trachea , and a part of the sternum known as the xiphoid process . Arteries and veins are also contained – ( aorta , superior vena cava , inferior vena cava and the pulmonary artery ); bones (the shoulder socket containing
4221-527: The thorax. Whether winged or not, adult insects can be distinguished by their three-part body plan, with head, thorax, and abdomen; they have three pairs of legs on the thorax. Estimates of the total number of insect species vary considerably, suggesting that there are perhaps some 5.5 million insect species in existence, of which about one million have been described and named. These constitute around half of all eukaryote species, including animals , plants , and fungi . The most diverse insect orders are
4288-466: The tissues. The blood therefore does not carry oxygen; it is only partly contained in vessels, and some circulates in an open hemocoel . Insect vision is mainly through their compound eyes , with additional small ocelli . Many insects can hear, using tympanal organs , which may be on the legs or other parts of the body. Their sense of smell is via receptors, usually on the antennae and the mouthparts. Nearly all insects hatch from eggs . Insect growth
4355-525: The total of around 22,500 species is probably within 5% of the actual number there; they comment that Canada's list of 30,000 described species is surely over half of the actual total. They add that the 3000 species of the American Arctic must be broadly accurate. In contrast, a large majority of the insect species of the tropics and the southern hemisphere are probably undescribed. Some 30–40,000 species inhabit freshwater ; very few insects, perhaps
4422-475: The tunica media, smooth muscle and the extracellular matrix are quantitatively the largest components, these are arranged concentrically as musculoelastic layers (the elastic lamella) in mammals. The elastic lamella, which comprise smooth muscle and elastic matrix, can be considered as the fundamental structural unit of the aorta and consist of elastic fibers , collagens (predominately type III), proteoglycans , and glycoaminoglycans . The elastic matrix dominates
4489-414: The upper part of the humerus , the scapula , sternum , thoracic portion of the spine , collarbone , and the rib cage and floating ribs ). External structures are the skin and nipples . In the human body , the region of the thorax between the neck and diaphragm in the front of the body is called the chest. The corresponding area in an animal can also be referred to as the chest. The shape of
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