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76-452: Muscle tissue varies with function and location in the body. In vertebrates , the three types are: Skeletal muscle tissue consists of elongated, multinucleate muscle cells called muscle fibers , and is responsible for movements of the body. Other tissues in skeletal muscle include tendons and perimysium . Smooth and cardiac muscle contract involuntarily, without conscious intervention. These muscle types may be activated both through

152-549: A backbone or spine, consisting of vertebrae and intervertebral discs . The vertebrae are irregular bones , and the intervertebral discs are of fibrocartilage . The vertebral column surrounds and protects the spinal cord . The other feature unique to vertebrates is the presence of a cranium , or skull. The vertebrates make up the subphylum Vertebrata with some 65,000 species in the phylum Chordata . The vertebrates include mammals , birds , amphibians , and various classes of reptiles and fish . Classes of fish include

228-427: A jaw , hyoid and/or the middle ear ossicles . An iodine-concentrating organ called the endostyle , which functions as a filter feeding organ in aquatic animals has evolved into the thyroid in most vertebrates. Vertebrates vary in body length ranging from the frog species Brachycephalus pulex , a Brazilian flea toad, with a minimum adult snout–vent length of 6.45 millimetres (0.254 in) to

304-400: A lack of oxygen reaching the body for cellular processes. In this case, an inhaler can be used to rectify the problem. The inhaler administers a bronchodilator , which serves to soothe the constricted bronchi and to re-expand the airways. This effect occurs quite quickly. Bronchial atresia is a rare congenital disorder that can have a varied appearance. A bronchial atresia is a defect in

380-407: A tracheal tube used for intubation is inserted too far, it will usually lodge in the right bronchus, allowing ventilation only of the right lung. Asthma is marked by hyperresponsiveness of the bronchi with an inflammatory component, often in response to allergens . In asthma, the constriction of the bronchi can result in difficulty in breathing giving shortness of breath ; this can lead to

456-417: A central nervous system arising from a single nerve cord dorsal to the gut tube , headed by a series of (typically paired) brain vesicles, is unique to vertebrates. This is in stark contrast to invertebrates with well-developed central nervous systems such as arthropods and cephalopods , which have an often ladder-like ventral nerve cord made of paired segmental ganglia on the opposite ( ventral ) side of

532-525: A hollow neural tube ) running along the dorsal aspect of the notochord . Of particular importance and unique to vertebrates is the presence of neural crest cells, which are progenitor cells critical to coordinating the functions of cellular components. Neural crest cells migrate through the body from the dorsal nerve cord during development, initiate the formation of neuronal ganglia and various special sense organs. The peripheral nervous system forms when neural crest cells branch out laterally from

608-589: A protein related to ubiquitin carboxyl-terminal hydrolase are exclusively shared by all vertebrates and reliably distinguish them from all other animals. A specific relationship between vertebrates and tunicates is strongly supported by two CSIs found in the proteins Rrp44 (associated with the exosome complex ) and serine palmitoyltransferase . These are exclusively shared by species from these two subphyla, but not cephalochordates . This indicates hat vertebrates are more closely related to tunicates than cephalochordates. The "Notochordata hypothesis" suggested that

684-538: A rhythmic fashion for the whole life of the organism. Hence it has special features. There are three types of muscle tissue in invertebrates that are based on their pattern of striation : transversely striated, obliquely striated, and smooth muscle. In arthropods there is no smooth muscle. The transversely striated type is the most similar to the skeletal muscle in vertebrates. Vertebrate Ossea Batsch, 1788 Vertebrates ( / ˈ v ɜːr t ə b r ɪ t s , - ˌ b r eɪ t s / ) are animals with

760-606: A series of crescentic openings from the pharynx to the outside. Each gill is supported by a cartilaginous or bony gill arch , which develop embryonically from pharyngeal arches . Bony fish have three pairs of gill arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven pairs. The ancestral vertebrates likely had more arches than seven, as some of their chordate relatives have more than 50 pairs of gill opens, although most, if not all, of these openings are actually involved in filter feeding rather than respiration . In jawed vertebrates ,

836-479: Is a passage or airway in the lower respiratory tract that conducts air into the lungs . The first or primary bronchi to branch from the trachea at the carina are the right main bronchus and the left main bronchus. These are the widest bronchi, and enter the right lung, and the left lung at each hilum . The main bronchi branch into narrower secondary bronchi or lobar bronchi, and these branch into narrower tertiary bronchi or segmental bronchi. Further divisions of

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912-519: Is about 1.06 kg/liter. This can be contrasted with the density of adipose tissue (fat), which is 0.9196 kg/liter. This makes muscle tissue approximately 15% denser than fat tissue. Skeletal muscle is a highly oxygen-consuming tissue, and oxidative DNA damage that is induced by reactive oxygen species tends to accumulate with age . The oxidative DNA damage 8-OHdG accumulates in heart and skeletal muscle of both mouse and rat with age. Also, DNA double-strand breaks accumulate with age in

988-436: Is arranged in regular, parallel bundles of myofibrils , which contain many contractile units known as sarcomeres , which give the tissue its striated (striped) appearance. Skeletal muscle is voluntary muscle, anchored by tendons or sometimes by aponeuroses to bones , and is used to effect skeletal movement such as locomotion and to maintain posture . Postural control is generally maintained as an unconscious reflex, but

1064-455: Is divided along the embryo 's length into somites , corresponding to the segmentation of the body (most obviously seen in the vertebral column . Each somite has three divisions, sclerotome (which forms vertebrae ), dermatome (which forms skin), and myotome (which forms muscle). The myotome is divided into two sections, the epimere and hypomere, which form epaxial and hypaxial muscles , respectively. The only epaxial muscles in humans are

1140-440: Is found in invertebrate chordates such as lancelets (a sister subphylum known as the cephalochordates ), though it lacks eyes and other complex special sense organs comparable to those of vertebrates. Other chordates do not show any trends towards cephalization. The rostral end of the neural tube is expanded by a thickening of the walls and expansion of the central canal of spinal cord into three primary brain vesicles :

1216-408: Is found within the walls of blood vessels (such smooth muscle specifically being termed vascular smooth muscle ) such as in the tunica media layer of the large ( aorta ) and small arteries , arterioles and veins . Smooth muscle is also found in lymphatic vessels, the urinary bladder , uterus (termed uterine smooth muscle ), male and female reproductive tracts , the gastrointestinal tract ,

1292-400: Is involuntary, striated muscle that is found in the walls and the histological foundation of the heart , specifically the myocardium. The cardiac muscle cells , (also called cardiomyocytes or myocardiocytes), predominantly contain only one nucleus, although populations with two to four nuclei do exist. The myocardium is the muscle tissue of the heart and forms a thick middle layer between

1368-407: Is no smooth muscle. The transversely striated type is the most similar to the skeletal muscle in vertebrates. Vertebrate skeletal muscle tissue is an elongated, striated muscle tissue, with the fibres ranging from 3-8 micrometers in width and from 18 to 200 micrometers in breadth. In the uterine wall, during pregnancy, they enlarge in length from 70 to 500 micrometers. Skeletal striated muscle tissue

1444-454: Is non-striated and involuntary. Smooth muscle is found within the walls of organs and structures such as the esophagus , stomach , intestines , bronchi , uterus , urethra , bladder , blood vessels , and the arrector pili in the skin that control the erection of body hair. Skeletal muscle is broadly classified into two fiber types: type I (slow-twitch) and type II (fast-twitch). The density of mammalian skeletal muscle tissue

1520-429: Is often curative. The cardiac bronchus has a prevalence of ≈0.3% and presents as an accessory bronchus arising from the bronchus intermedius between the upper lobar bronchus and the origin of the middle and lower lobar bronchi of the right main bronchus. An accessory cardiac bronchus is usually an asymptomatic condition but may be associated with persistent infection or hemoptysis . In about half of observed cases

1596-413: Is preceded by the formation of connective tissue frameworks, usually formed from the somatic lateral plate mesoderm . Myoblasts follow chemical signals to the appropriate locations, where they fuse into elongate skeletal muscle cells. The primary function of muscle tissue is contraction . The three types of muscle tissue (skeletal, cardiac and smooth) have significant differences. However, all three use

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1672-408: Is present in the bronchi, surrounding the smooth muscle layer. In the main bronchi, the cartilage forms C-shaped rings like those in the trachea, while in the smaller bronchi, hyaline cartilage is present in irregularly arranged crescent-shaped plates and islands. These plates give structural support to the bronchi and keep the airway open. The bronchial wall normally has a thickness of 10% to 20% of

1748-490: Is the basic anatomical unit of gas exchange in the lung. The main bronchi have relatively large lumens that are lined by respiratory epithelium . This cellular lining has cilia departing towards the mouth which removes dust and other small particles. There is a smooth muscle layer below the epithelium arranged as two ribbons of muscle that spiral in opposite directions. This smooth muscle layer contains seromucous glands , which secrete mucus , in its wall. Hyaline cartilage

1824-473: Is usually associated with smoking or long-term exposure to irritants . The left main bronchus departs from the trachea at a greater angle than that of the right main bronchus. The right bronchus is also wider than the left and these differences predispose the right lung to aspirational problems. If food, liquids, or foreign bodies are aspirated, they will tend to lodge in the right main bronchus. Bacterial pneumonia and aspiration pneumonia may result. If

1900-635: The Cephalochordata is the sister taxon to Craniata (Vertebrata). This group, called the Notochordata, was placed as sister group to the Tunicata (Urochordata). Studies since 2006 analyzing large sequencing datasets however strongly support Olfactores (tunicates + vertebrates) as a clade, and hence the placement of Cephalochordata as sister-group to Olfactores (known as the " Olfactores hypothesis "). The following cladogram summarizes

1976-559: The Chengjiang biota and lived about 518 million years ago. These include Haikouichthys , Myllokunmingia , Zhongjianichthys , and probably Haikouella . Unlike the other fauna that dominated the Cambrian, these groups had the basic vertebrate body plan: a notochord, rudimentary vertebrae, and a well-defined head and tail. All of these early vertebrates lacked jaws in the common sense and relied on filter feeding close to

2052-474: The Izu–Ogasawara Trench at a depth of 8,336 metres (27,349 feet). Many fish varieties are the main predators in most of the world's freshwater and marine water bodies . The rest of the vertebrate species are tetrapods, a single lineage that includes amphibians (with roughly 7,000 species); mammals (with approximately 5,500 species); and reptiles and birds (with about 20,000 species divided evenly between

2128-633: The Jurassic . The Cenozoic world saw great diversification of bony fishes, amphibians, reptiles, birds and mammals. Over half of all living vertebrate species (about 32,000 species) are fish (non-tetrapod craniates), a diverse set of lineages that inhabit all the world's aquatic ecosystems, from the Tibetan stone loach ( Triplophysa stolickai ) in western Tibetan hot springs near Longmu Lake at an elevation of 5,200 metres (17,100 feet) to an unknown species of snailfish (genus Pseudoliparis ) in

2204-464: The Latin vertebratus ("jointed"), from vertebra meaning "joint", in turn from Latin vertere to turn. All vertebrates are built along the basic chordate body plan of five synapomorphies . These are a rigid axial skeleton that includes a vertebral column developed around an elastic notochord . The notochord becomes the intervertebral discs , and runs dorsally to the gut tube along

2280-574: The Placodermi and the Acanthodii , both considered paraphyletic . Other ways of classifying the vertebrates have been devised, particularly with emphasis on the phylogeny of early amphibians and reptiles. An example based on Janvier (1981, 1997), Shu et al. (2003), and Benton (2004) is given here († = extinct ): While this traditional classification is orderly, most of the groups are paraphyletic , i.e. do not contain all descendants of

2356-958: The Tree of Life Web Project and Delsuc et al., and complemented (based on, and ). A dagger (†) denotes an extinct clade , whereas all other clades have living descendants . Hyperoartia ( lampreys ) [REDACTED] Myxini ( hagfish ) [REDACTED] † Euconodonta [REDACTED] † Myllokunmingiida [REDACTED]   † Pteraspidomorphi [REDACTED] † Thelodonti [REDACTED] † Anaspida [REDACTED] † Galeaspida [REDACTED] † Pituriaspida [REDACTED] † Osteostraci [REDACTED]   † Antiarchi [REDACTED] † Petalichthyida [REDACTED] † Arthrodira [REDACTED] † Ptyctodontida [REDACTED] † Entelognathus   [REDACTED]   Bronchus A bronchus ( / ˈ b r ɒ ŋ k ə s / BRONG -kəs ; pl. : bronchi , / ˈ b r ɒ ŋ k aɪ / BRONG -ky )

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2432-399: The blue whale , at up to 33 m (108 ft). With only one exception, the defining characteristic of all vertebrates is the vertebral column , in which the embryonic notochord found in all chordates is replaced by a segmented series of mineralized elements called vertebrae separated by fibrocartilaginous intervertebral discs , which are embryonic and evolutionary remnants of

2508-453: The erector spinae and small intervertebral muscles, and are innervated by the dorsal rami of the spinal nerves . All other muscles, including those of the limbs are hypaxial, and innervated by the ventral rami of the spinal nerves. During development, myoblasts (muscle progenitor cells) either remain in the somite to form muscles associated with the vertebral column or migrate out into the body to form all other muscles. Myoblast migration

2584-565: The genetics of organisms. Phylogenetic classification is based solely on phylogeny . Evolutionary systematics gives an overview; phylogenetic systematics gives detail. The two systems are thus complementary rather than opposed. Conventional classification has extant vertebrates grouped into seven classes based on traditional interpretations of gross anatomical and physiological traits. The commonly held classification lists three classes of fish and four of tetrapods . In addition to these, there are two classes of extinct armoured fishes,

2660-439: The neurotransmitter acetylcholine . Smooth muscle is found in almost all organ systems such as hollow organs including the stomach , and bladder ; in tubular structures such as blood and lymph vessels , and bile ducts ; in sphincters such as in the uterus, and the eye. In addition, it plays an important role in the ducts of exocrine glands. It fulfills various tasks such as sealing orifices (e.g. pylorus, uterine os) or

2736-410: The prosencephalon ( forebrain ), mesencephalon ( midbrain ) and rhombencephalon ( hindbrain ), which are further differentiated in the various vertebrate groups. Two laterally placed retinas and optical nerves form around outgrowths from the midbrain, except in hagfish which may have secondarily lost the structures. The forebrain is more well-developed in most tetrapods and subdivided into

2812-434: The respiratory tract , the arrector pili of skin , the ciliary muscle , and the iris of the eye . The structure and function is basically the same in smooth muscle cells in different organs, but the inducing stimuli differ substantially, in order to perform individual actions in the body at individual times. In addition, the glomeruli of the kidneys contain smooth muscle-like cells called mesangial cells . Cardiac muscle

2888-432: The telencephalon and diencephalon , while the midbrain dominates in fish and some salamanders . In vertebrates with paired appendages, especially tetrapods, a pair of secondary enlargements of the hindbrain become the cerebella , which modulate complex motor coordinations . The brain vesicles are usually bilaterally symmetrical , giving rise to the paired cerebral hemispheres in mammals . The resultant anatomy of

2964-405: The alveolar ducts and alveoli In 0.1 to 5% of people there is a right superior lobe bronchus arising from the main stem bronchus prior to the carina. This is known as a tracheal bronchus , and seen as an anatomical variation . It can have multiple variations and, although usually asymptomatic, it can be the root cause of pulmonary disease such as a recurrent infection. In such cases resection

3040-595: The appearance of the flexed biceps resembles the back of a mouse. The same phenomenon occurred in Greek , in which μῦς, mȳs , means both "mouse" and "muscle". There are three types of muscle tissue in vertebrates: skeletal , cardiac , and smooth . Skeletal and cardiac muscle are types of striated muscle tissue . Smooth muscle is non-striated. There are three types of muscle tissue in invertebrates that are based on their pattern of striation: transversely striated, obliquely striated, and smooth muscle. In arthropods there

3116-429: The artery, and is known as the hyparterial branch which divides into the two lobar bronchi to the middle and lower lobes. The left main bronchus is smaller in caliber but longer than the right, being 5 cm long. It enters the root of the left lung opposite the sixth thoracic vertebra. It passes beneath the aortic arch , crosses in front of the esophagus , the thoracic duct , and the descending aorta , and has

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3192-418: The axial endoskeleton (enclosed by protective skeletal extensions known as neural arches ), with a fore-end enlargement that is contained within a distinct skeletonized braincase (hence the alternative name for vertebrates, the craniates ). All vertebrate embryos develop transient pharyngeal arches , which in fish develop into the branchial arches that support the gills . Other vertebrate features are

3268-427: The brain (which itself is a fused cluster of segmental ganglia from the rostral metameres ). Molecular markers known as conserved signature indels (CSIs) in protein sequences have been identified and provide distinguishing criteria for the vertebrate subphylum. Specifically, 5 CSIs in the following proteins: protein synthesis elongation factor-2 , eukaryotic translation initiation factor 3 , adenosine kinase and

3344-420: The bronchi ( bronchitis ). Normally, the ratio of the bronchial wall thickness and the bronchial diameter is between 0.17 and 0.23. Bronchitis is defined as inflammation of the bronchi, which can either be acute or chronic . Acute bronchitis is usually caused by viral or bacterial infections . Many sufferers of chronic bronchitis also suffer from chronic obstructive pulmonary disease (COPD), and this

3420-685: The cardiac bronchus presents as a short dead-ending bronchial stump, in the remainder the bronchus may exhibit branching and associated aerated lung parenchyma . The bronchi function to carry air that is breathed in through to the functional tissues of the lungs, called alveoli. Exchange of gases between the air in the lungs and the blood in the capillaries occurs across the walls of the alveolar ducts and alveoli. The alveolar ducts and alveoli consist primarily of simple squamous epithelium , which permits rapid diffusion of oxygen and carbon dioxide . Bronchial wall thickening, as can be seen on CT scan , generally (but not always) implies inflammation of

3496-409: The class's common ancestor. For instance, descendants of the first reptiles include modern reptiles, mammals and birds; the agnathans have given rise to the jawed vertebrates ; the bony fishes have given rise to the land vertebrates ; the traditional " amphibians " have given rise to the reptiles (traditionally including the synapsids or mammal-like "reptiles"), which in turn have given rise to

3572-561: The contraction has occurred. The different muscle types vary in their response to neurotransmitters and hormones such as acetylcholine , noradrenaline , adrenaline , and nitric oxide depending on muscle type and the exact location of the muscle. Sub-categorization of muscle tissue is also possible, depending on among other things the content of myoglobin , mitochondria , and myosin ATPase etc. The word muscle comes from Latin musculus , diminutive of mus meaning mouse , because

3648-556: The demise of virtually all jawless fishes save for lampreys and hagfishes, as well as the Placodermi , a group of armoured fish that dominated the entirety of that period since the late Silurian as well as the eurypterids , dominant animals of the preceding Silurian , and the anomalocarids . By the middle of the Devonian, several droughts, anoxic events and oceanic competition led a lineage of sarcopterygii to leave water, eventually establishing themselves as terrestrial tetrapods in

3724-404: The development of the bronchi, affecting one or more bronchi – usually segmental bronchi and sometimes lobar. The defect takes the form of a blind-ended bronchus. The surrounding tissue secretes mucus normally but builds up and becomes distended. This can lead to regional emphysema . The collected mucus may form a mucoid impaction or a bronchocele , or both. A pectus excavatum may accompany

3800-408: The dorsal nerve cord and migrate together with the mesodermal somites to innervate the various different structures that develop in the body. The vertebrates are the only chordate group with neural cephalization , and their neural functions are centralized towards a series of enlarged clusters in the head , which give rise to a brain . A slight swelling of the anterior end of the nerve cord

3876-483: The first gill arch pair evolved into the jointed jaws and form an additional oral cavity ahead of the pharynx . Research also suggests that the sixth branchial arch contributed to the formation of the vertebrate shoulder, which separated the head as a distinct part of the body. In amphibians and some primitive bony fishes, the larvae bear external gills , branching off from the gill arches. These are reduced in adulthood, their respiratory function taken over by

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3952-421: The gill arches form during fetal development , and form the basis of essential structures such as jaws , the thyroid gland , the larynx , the columella (corresponding to the stapes in mammals ) and, in mammals, the malleus and incus . The central nervous system of vertebrates is based on the embryonic dorsal nerve cord (which then flattens into a neural plate before folding and fusing over into

4028-400: The gut tube, with a split brain stem circumventing the foregut around each side to form a brain on the dorsal side of the mouth . The higher functions of the vertebrate CNS are highly centralized towards the brain (particularly the forebrain), while the invertebrate CNS is significantly more decentralized with the segmental ganglia having substantial neural autonomy independent of

4104-449: The interaction of the central nervous system as well as by receiving innervation from peripheral plexus or endocrine (hormonal) activation. Striated or skeletal muscle only contracts voluntarily, upon the influence of the central nervous system. Reflexes are a form of non-conscious activation of skeletal muscles, but nonetheless arise through activation of the central nervous system, albeit not engaging cortical structures until after

4180-443: The internal gills proper in fishes and by cutaneous respiration in most amphibians. While some amphibians such as axolotl retain the external gills into adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods , who evolved lungs (which are homologous to swim bladders ) to breathe air. While the more specialized terrestrial vertebrates lack gills,

4256-407: The jawless Agnatha , and the jawed Gnathostomata . The jawed fish include both the cartilaginous fish and the bony fish . Bony fish include the lobe-finned fish , which gave rise to the tetrapods , the animals with four limbs. Vertebrates make up less than five percent of all described animal species ; the rest are all invertebrates , that lack a backbone. The word 'vertebrate' derives from

4332-581: The left lung having just two lobes, two pairs of segments fuse to give eight, four for each lobe. The tertiary bronchi divide further in another three branchings known as 4th order, 5th order and 6th order segmental bronchi which are also referred to as subsegmental bronchi . These branch into many smaller bronchioles which divide into terminal bronchioles , each of which then gives rise to several respiratory bronchioles , which go on to divide into two to eleven alveolar ducts . There are five or six alveolar sacs associated with each alveolar duct. The alveolus

4408-513: The left lung—the superior and the inferior lobe. The secondary bronchi divide further into tertiary bronchi , (also known as segmental bronchi ), each of which supplies a bronchopulmonary segment . A bronchopulmonary segment is a division of a lung separated from the rest of the lung by a septum of connective tissue . This property allows a bronchopulmonary segment to be surgically removed without affecting other segments. Initially, there are ten segments in each lung, but during development with

4484-404: The left pulmonary artery lying at first above, and then in front of it. The left bronchus has no eparterial branch , and therefore it has been supposed by some that there is no upper lobe to the left lung, but that the so-called upper lobe corresponds to the middle lobe of the right lung . The left main bronchus divides into two secondary bronchi or lobar bronchi, to deliver air to the two lobes of

4560-432: The length of an animal, hence the common name of backbone. The axial endoskeleton typically continues beyond the anus / cloaca to form an elongated tail . Some vertebrates evolved to become tailless with only a vestigial coccyx . A dorsal nerve cord , which folds and fuses into a hollow neural tube during embryonic development and eventually gives rise to the brain and spinal cord , runs more dorsally to

4636-516: The main component of mucus. Mucus plays an important role in keeping the airways clear in the mucociliary clearance process. As branching continues through the bronchial tree, the amount of hyaline cartilage in the walls decreases until it is absent in the bronchioles. As the cartilage decreases, the amount of smooth muscle increases. The mucous membrane also undergoes a transition from ciliated pseudostratified columnar epithelium, to simple ciliated cuboidal epithelium, to simple squamous epithelium in

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4712-460: The mammals and birds. Most scientists working with vertebrates use a classification based purely on phylogeny , organized by their known evolutionary history and sometimes disregarding the conventional interpretations of their anatomy and physiology. In phylogenetics , the relationships between animals are illustrated as a hierarchy known as a phylogenetic tree . The cladogram below is based on studies compiled by Philippe Janvier and others for

4788-430: The movement of actin against myosin to create contraction. In skeletal muscle, contraction is stimulated by electrical impulses transmitted by the motor nerves . Cardiac and smooth muscle contractions are stimulated by internal pacemaker cells which regularly contract, and propagate contractions to other muscle cells they are in contact with. All skeletal muscle and many smooth muscle contractions are facilitated by

4864-411: The notochord. Hagfish are the only extant vertebrate whose notochord persists and is not integrated/ replaced by the vertebral column. A few vertebrates have secondarily lost this feature and retain the notochord into adulthood, such as the sturgeon . Most vertebrates are aquatic and carry out gas exchange via gills . The gills are carried right behind the head, bordering the posterior margins of

4940-660: The outer epicardium layer and the inner endocardium layer. Coordinated contractions of cardiac muscle cells in the heart propel blood out of the atria and ventricles to the blood vessels of the left/body/systemic and right/lungs/pulmonary circulatory systems . This complex mechanism illustrates systole of the heart. Cardiac muscle cells, unlike most other tissues in the body, rely on an available blood and electrical supply to deliver oxygen and nutrients and to remove waste products such as carbon dioxide . The coronary arteries help fulfill this function. All muscles are derived from paraxial mesoderm . The paraxial mesoderm

5016-609: The relationships between the Olfactores (vertebrates and tunicates) and the Cephalochordata.   Amphioxiformes (lancelets)  [REDACTED]   Tunicata /Urochordata ( sea squirts , salps , larvaceans )  [REDACTED]   Vertebrata   [REDACTED] Vertebrates originated during the Cambrian explosion , which saw a rise in organism diversity. The earliest known vertebrates belongs to

5092-639: The responsible muscles can also react to conscious control. The body mass of an average adult man is made up of 42% of skeletal muscle, and an average adult woman is made up of 36%. Cardiac muscle tissue is found only in the walls of the heart as myocardium , and it is an involuntary muscle controlled by the autonomic nervous system . Cardiac muscle tissue is striated like skeletal muscle, containing sarcomeres in highly regular arrangements of bundles. While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angles known as intercalated discs . Smooth muscle tissue

5168-661: The seabed. A vertebrate group of uncertain phylogeny, small eel-like conodonts , are known from microfossils of their paired tooth segments from the late Cambrian to the end of the Triassic. The first jawed vertebrates may have appeared in the late Ordovician (~445 mya) and became common in the Devonian period , often known as the "Age of Fishes". The two groups of bony fishes , the Actinopterygii and Sarcopterygii , evolved and became common. The Devonian also saw

5244-412: The segmental bronchi are known as 4th order, 5th order, and 6th order segmental bronchi, or grouped together as subsegmental bronchi. The bronchi, when too narrow to be supported by cartilage, are known as bronchioles . No gas exchange takes place in the bronchi. The trachea (windpipe) divides at the carina into two main or primary bronchi , the left bronchus and the right bronchus. The carina of

5320-523: The skeletal muscle of mice. Smooth muscle is involuntary and non-striated. It is divided into two subgroups: the single-unit (unitary) and multiunit smooth muscle . Within single-unit cells, the whole bundle or sheet contracts as a syncytium (i.e. a multinucleate mass of cytoplasm that is not separated into cells). Multiunit smooth muscle tissues innervate individual cells; as such, they allow for fine control and gradual responses, much like motor unit recruitment in skeletal muscle. Smooth muscle

5396-650: The succeeding Carboniferous . Amniotes branched from amphibious tetrapods early in the Carboniferous period. The synapsid amniotes were dominant during the late Paleozoic, the Permian , while diapsid amniotes became dominant during the Mesozoic . In the sea, the teleosts and sharks became dominant. Mesothermic synapsids called cynodonts gave rise to endothermic mammals and diapsids called dinosaurs eventually gave rise to endothermic birds , both in

5472-454: The three lobes of the right lung—the superior, middle and inferior lobe. The azygos vein arches over it from behind; and the right pulmonary artery lies at first below and then in front of it. About 2 cm from its commencement it gives off a branch to the superior lobe of the right lung, which is also called the eparterial bronchus . Eparterial refers to its position above the right pulmonary artery . The right bronchus now passes below

5548-415: The total bronchial diameter. The cartilage and mucous membrane of the main bronchus (primary bronchi) are similar to those in the trachea. They are lined with respiratory epithelium , which is classified as ciliated pseudostratified columnar epithelium . The epithelium in the main bronchi contains goblet cells , which are glandular , modified simple columnar epithelial cells that produce mucins ,

5624-440: The trachea is located at the level of the sternal angle and the fifth thoracic vertebra (at rest). The right main bronchus is wider, shorter, and more vertical than the left main bronchus, its mean length is 1.09 cm. It enters the root of the right lung at approximately the fifth thoracic vertebra. The right main bronchus subdivides into three secondary bronchi (also known as lobar bronchi ), which deliver oxygen to

5700-426: The transport of the chyme through wavelike contractions of the intestinal tube. Smooth muscle cells contract more slowly than skeletal muscle cells, but they are stronger, more sustained and require less energy. Smooth muscle is also involuntary, unlike skeletal muscle, which requires a stimulus. Cardiac muscle is the muscle of the heart. It is self-contracting, autonomically regulated and must continue to contract in

5776-402: The two classes). Tetrapods comprise the dominant megafauna of most terrestrial environments and also include many partially or fully aquatic groups (e.g., sea snakes , penguins , cetaceans). There are several ways of classifying animals. Evolutionary systematics relies on anatomy , physiology and evolutionary history, which is determined through similarities in anatomy and, if possible,

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