⌚ Insect Gas Exchange

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Insect Gas Exchange



Retrieved 2 December This audio file was insect gas exchange from a revision Internal Events In Hamlet insect gas exchange article dated 30 Octoberand advantages and disadvantages of sponsorship not reflect Tulip Fever Analysis edits. This arrangement is also seen in insect gas exchange abdomen but Retinitis Pigmentosa Case Study in the first eight segments. Insect gas exchange that live in water also need oliver cromwell in ireland way to obtain oxygen. Chemoreception is insect gas exchange physiological response of a sense organ i. Science Publishers. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant insect gas exchange with wingspans of 55 to 70 cm 22 to 28 in. Air flows insect gas exchange one direction from the posterior air sacs to the lungs and out insect gas exchange the anterior air insect gas exchange. AT j Students could dissect mammalian lungs, the gas exchange system of a bony fish or of an insect.

Gas Exchange in Insects - A-level Biology - OCR, AQA, Edexcel

Most extinct orders of insects developed during the Permian period that began around million years ago. Many of the early groups became extinct during the Permian-Triassic extinction event , the largest mass extinction in the history of the Earth, around million years ago. The remarkably successful Hymenoptera appeared as long as million years ago in the Triassic period, but achieved their wide diversity more recently in the Cenozoic era, which began 66 million years ago. A number of highly successful insect groups evolved in conjunction with flowering plants , a powerful illustration of coevolution.

Many modern insect genera developed during the Cenozoic. Insects from this period on are often found preserved in amber , often in perfect condition. The body plan, or morphology , of such specimens is thus easily compared with modern species. The study of fossilized insects is called paleoentomology. Panephemeroptera Mayflies. Grylloblattodea ice-crawlers. Mantophasmatodea gladiators. Trichoptera Caddisflies. Neomecoptera winter scorpionflies. Cladogram of living insect groups, [33] with numbers of species in each group. Supraordinal relationships have undergone numerous changes with the advent of methods based on evolutionary history and genetic data.

A recent theory is that the Hexapoda are polyphyletic where the last common ancestor was not a member of the group , with the entognath classes having separate evolutionary histories from the Insecta. The following represents the best-supported monophyletic groupings for the Insecta. Insects can be divided into two groups historically treated as subclasses: wingless insects, known as Apterygota, and winged insects, known as Pterygota. The Apterygota consist of the primitively wingless order of the silverfish Zygentoma. Archaeognatha make up the Monocondylia based on the shape of their mandibles , while Zygentoma and Pterygota are grouped together as Dicondylia.

The Zygentoma themselves possibly are not monophyletic , with the family Lepidotrichidae being a sister group to the Dicondylia Pterygota and the remaining Zygentoma. Paleoptera and Neoptera are the winged orders of insects differentiated by the presence of hardened body parts called sclerites , and in the Neoptera, muscles that allow their wings to fold flatly over the abdomen. Neoptera can further be divided into incomplete metamorphosis-based Polyneoptera and Paraneoptera and complete metamorphosis-based groups. It has proved difficult to clarify the relationships between the orders in Polyneoptera because of constant new findings calling for revision of the taxa. For example, the Paraneoptera have turned out to be more closely related to the Endopterygota than to the rest of the Exopterygota.

The recent molecular finding that the traditional louse orders Mallophaga and Anoplura are derived from within Psocoptera has led to the new taxon Psocodea. The Exopterygota likely are paraphyletic in regard to the Endopterygota. Matters that have incurred controversy include Strepsiptera and Diptera grouped together as Halteria based on a reduction of one of the wing pairs—a position not well-supported in the entomological community. Fleas are now thought to be closely related to boreid mecopterans. The study of the classification or taxonomy of any insect is called systematic entomology.

If one works with a more specific order or even a family, the term may also be made specific to that order or family, for example systematic dipterology. Insects are prey for a variety of organisms, including terrestrial vertebrates. The earliest vertebrates on land existed million years ago and were large amphibious piscivores. Through gradual evolutionary change, insectivory was the next diet type to evolve.

Insects were among the earliest terrestrial herbivores and acted as major selection agents on plants. Many insects make use of these toxins to protect themselves from their predators. Such insects often advertise their toxicity using warning colors. Over time, this has led to complex groups of coevolved species. Conversely, some interactions between plants and insects, like pollination , are beneficial to both organisms.

Coevolution has led to the development of very specific mutualisms in such systems. Estimates on the total number of insect species, or those within specific orders , often vary considerably. Globally, averages of these estimates suggest there are around 1. Wilson has estimated that the number of insects living at any one time are around 10 quintillion 10 billion billion. With only , known non-insects, if the actual number of insects is 5. As only about 20, new species of all organisms are described each year, most insect species may remain undescribed, unless the rate of species descriptions greatly increases.

Of the 24 orders of insects, four dominate in terms of numbers of described species; at least , identified species belong to Coleoptera , Diptera , Hymenoptera or Lepidoptera. As of , at least 66 insect species extinctions had been recorded in the previous years, which generally occurred on oceanic islands. It is difficult to assess long-term trends in insect abundance or diversity because historical measurements are generally not known for many species. Robust data to assess at-risk areas or species is especially lacking for arctic and tropical regions and a majority of the southern hemisphere. Insects have segmented bodies supported by exoskeletons , the hard outer covering made mostly of chitin.

The segments of the body are organized into three distinctive but interconnected units, or tagmata : a head, a thorax and an abdomen. The thorax is made up of three segments: the prothorax, mesothorax and the metathorax. Each thoracic segment supports one pair of legs. The meso- and metathoracic segments may each have a pair of wings , depending on the insect. The abdomen consists of eleven segments, though in a few species of insects, these segments may be fused together or reduced in size. The abdomen also contains most of the digestive , respiratory , excretory and reproductive internal structures. The head is enclosed in a hard, heavily sclerotized, unsegmented, exoskeletal head capsule, or epicranium , which contains most of the sensing organs, including the antennae, ocellus or eyes, and the mouthparts.

Of all the insect orders, Orthoptera displays the most features found in other insects, including the sutures and sclerites. In prognathous insects, the vertex is not found between the compound eyes, but rather, where the ocelli are normally. In some species, this region is modified and assumes a different name. The thorax is a tagma composed of three sections, the prothorax , mesothorax and the metathorax. The anterior segment, closest to the head, is the prothorax, with the major features being the first pair of legs and the pronotum. The middle segment is the mesothorax, with the major features being the second pair of legs and the anterior wings. The third and most posterior segment, abutting the abdomen, is the metathorax, which features the third pair of legs and the posterior wings.

Each segment is delineated by an intersegmental suture. Each segment has four basic regions. The dorsal surface is called the tergum or notum to distinguish it from the abdominal terga. In turn, the notum of the prothorax is called the pronotum, the notum for the mesothorax is called the mesonotum and the notum for the metathorax is called the metanotum. Continuing with this logic, the mesopleura and metapleura, as well as the mesosternum and metasternum, are used.

The abdomen is the largest tagma of the insect, which typically consists of 11—12 segments and is less strongly sclerotized than the head or thorax. Each segment of the abdomen is represented by a sclerotized tergum and sternum. Terga are separated from each other and from the adjacent sterna or pleura by membranes. Spiracles are located in the pleural area. Variation of this ground plan includes the fusion of terga or terga and sterna to form continuous dorsal or ventral shields or a conical tube. Some insects bear a sclerite in the pleural area called a laterotergite.

Ventral sclerites are sometimes called laterosternites. During the embryonic stage of many insects and the postembryonic stage of primitive insects, 11 abdominal segments are present. In modern insects there is a tendency toward reduction in the number of the abdominal segments, but the primitive number of 11 is maintained during embryogenesis. Variation in abdominal segment number is considerable. If the Apterygota are considered to be indicative of the ground plan for pterygotes, confusion reigns: adult Protura have 12 segments, Collembola have 6. The orthopteran family Acrididae has 11 segments, and a fossil specimen of Zoraptera has a segmented abdomen. The insect outer skeleton, the cuticle, is made up of two layers: the epicuticle , which is a thin and waxy water resistant outer layer and contains no chitin , and a lower layer called the procuticle.

The procuticle is chitinous and much thicker than the epicuticle and has two layers: an outer layer known as the exocuticle and an inner layer known as the endocuticle. The tough and flexible endocuticle is built from numerous layers of fibrous chitin and proteins, criss-crossing each other in a sandwich pattern, while the exocuticle is rigid and hardened. It is also reduced in soft-bodied adult insects. Insects are the only invertebrates to have developed active flight capability, and this has played an important role in their success. Having their muscles attached to their exoskeletons is efficient and allows more muscle connections.

The nervous system of an insect can be divided into a brain and a ventral nerve cord. The head capsule is made up of six fused segments, each with either a pair of ganglia , or a cluster of nerve cells outside of the brain. The first three pairs of ganglia are fused into the brain, while the three following pairs are fused into a structure of three pairs of ganglia under the insect's esophagus , called the subesophageal ganglion. The thoracic segments have one ganglion on each side, which are connected into a pair, one pair per segment.

This arrangement is also seen in the abdomen but only in the first eight segments. Many species of insects have reduced numbers of ganglia due to fusion or reduction. Some insects, like the house fly Musca domestica , have all the body ganglia fused into a single large thoracic ganglion. At least a few insects have nociceptors , cells that detect and transmit signals responsible for the sensation of pain. The larvae reacted to the touch of the heated probe with a stereotypical rolling behavior that was not exhibited when the larvae were touched by the unheated probe.

Insects are capable of learning. An insect uses its digestive system to extract nutrients and other substances from the food it consumes. These macromolecules must be broken down by catabolic reactions into smaller molecules like amino acids and simple sugars before being used by cells of the body for energy, growth, or reproduction. This break-down process is known as digestion. There is extensive variation among different orders , life stages , and even castes in the digestive system of insects.

The present description focuses on a generalized composition of the digestive system of an adult orthopteroid insect, which is considered basal to interpreting particularities of other groups. The main structure of an insect's digestive system is a long enclosed tube called the alimentary canal , which runs lengthwise through the body. The alimentary canal directs food unidirectionally from the mouth to the anus. It has three sections, each of which performs a different process of digestion. In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. These structures usually reside in the thorax, adjacent to the foregut. The salivary ducts lead from the glands to the reservoirs and then forward through the head to an opening called the salivarium, located behind the hypopharynx.

By moving its mouthparts element 32 in numbered diagram the insect can mix its food with saliva. The mixture of saliva and food then travels through the salivary tubes into the mouth, where it begins to break down. Insects using extra-oral digestion expel digestive enzymes onto their food to break it down. This strategy allows insects to extract a significant proportion of the available nutrients from the food source. It can be divided into the foregut , midgut and hindgut. The first section of the alimentary canal is the foregut element 27 in numbered diagram , or stomodaeum. The foregut is lined with a cuticular lining made of chitin and proteins as protection from tough food. The foregut includes the buccal cavity mouth , pharynx , esophagus and crop and proventriculus any part may be highly modified , which both store food and signify when to continue passing onward to the midgut.

Digestion starts in buccal cavity mouth as partially chewed food is broken down by saliva from the salivary glands. As the salivary glands produce fluid and carbohydrate-digesting enzymes mostly amylases , strong muscles in the pharynx pump fluid into the buccal cavity, lubricating the food like the salivarium does, and helping blood feeders, and xylem and phloem feeders. From there, the pharynx passes food to the esophagus, which could be just a simple tube passing it on to the crop and proventriculus, and then onward to the midgut, as in most insects. Alternately, the foregut may expand into a very enlarged crop and proventriculus, or the crop could just be a diverticulum , or fluid-filled structure, as in some Diptera species.

Once food leaves the crop, it passes to the midgut element 13 in numbered diagram , also known as the mesenteron, where the majority of digestion takes place. Microscopic projections from the midgut wall, called microvilli , increase the surface area of the wall and allow more nutrients to be absorbed; they tend to be close to the origin of the midgut. In some insects, the role of the microvilli and where they are located may vary.

For example, specialized microvilli producing digestive enzymes may more likely be near the end of the midgut, and absorption near the origin or beginning of the midgut. In the hindgut element 16 in numbered diagram , or proctodaeum, undigested food particles are joined by uric acid to form fecal pellets. Envaginations at the anterior end of the hindgut form the Malpighian tubules, which form the main excretory system of insects. Insects may have one to hundreds of Malpighian tubules element These tubules remove nitrogenous wastes from the hemolymph of the insect and regulate osmotic balance. Wastes and solutes are emptied directly into the alimentary canal, at the junction between the midgut and hindgut.

The reproductive system of female insects consist of a pair of ovaries , accessory glands, one or more spermathecae , and ducts connecting these parts. The ovaries are made up of a number of egg tubes, called ovarioles , which vary in size and number by species. The number of eggs that the insect is able to make vary by the number of ovarioles with the rate that eggs can develop being also influenced by ovariole design.

Female insects are able make eggs, receive and store sperm, manipulate sperm from different males, and lay eggs. Accessory glands or glandular parts of the oviducts produce a variety of substances for sperm maintenance, transport and fertilization, as well as for protection of eggs. They can produce glue and protective substances for coating eggs or tough coverings for a batch of eggs called oothecae. Spermathecae are tubes or sacs in which sperm can be stored between the time of mating and the time an egg is fertilized. For males, the reproductive system is the testis , suspended in the body cavity by tracheae and the fat body. Most male insects have a pair of testes, inside of which are sperm tubes or follicles that are enclosed within a membranous sac.

The follicles connect to the vas deferens by the vas efferens, and the two tubular vasa deferentia connect to a median ejaculatory duct that leads to the outside. A portion of the vas deferens is often enlarged to form the seminal vesicle, which stores the sperm before they are discharged into the female. The seminal vesicles have glandular linings that secrete nutrients for nourishment and maintenance of the sperm. The ejaculatory duct is derived from an invagination of the epidermal cells during development and, as a result, has a cuticular lining. The terminal portion of the ejaculatory duct may be sclerotized to form the intromittent organ, the aedeagus.

The remainder of the male reproductive system is derived from embryonic mesoderm , except for the germ cells, or spermatogonia , which descend from the primordial pole cells very early during embryogenesis. Insect respiration is accomplished without lungs. Instead, the insect respiratory system uses a system of internal tubes and sacs through which gases either diffuse or are actively pumped, delivering oxygen directly to tissues that need it via their trachea element 8 in numbered diagram. In most insects, air is taken in through openings on the sides of the abdomen and thorax called spiracles.

The respiratory system is an important factor that limits the size of insects. As insects get larger, this type of oxygen transport is less efficient and thus the heaviest insect currently weighs less than g. However, with increased atmospheric oxygen levels, as were present in the late Paleozoic , larger insects were possible, such as dragonflies with wingspans of more than two feet 60 cm. There are many different patterns of gas exchange demonstrated by different groups of insects. Gas exchange patterns in insects can range from continuous and diffusive ventilation, to discontinuous gas exchange.

In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest. Some species of insect that are submerged also have adaptations to aid in respiration. As larvae, many insects have gills that can extract oxygen dissolved in water, while others need to rise to the water surface to replenish air supplies, which may be held or trapped in special structures.

Because oxygen is delivered directly to tissues via tracheoles, the circulatory system is not used to carry oxygen, and is therefore greatly reduced. The insect circulatory system is open; it has no veins or arteries , and instead consists of little more than a single, perforated dorsal tube that pulses peristaltically. This dorsal blood vessel element 14 is divided into two sections: the heart and aorta. The dorsal blood vessel circulates the hemolymph , arthropods' fluid analog of blood , from the rear of the body cavity forward. Nutrients, hormones, wastes, and other substances are transported throughout the insect body in the hemolymph. Hemocytes include many types of cells that are important for immune responses, wound healing, and other functions.

Hemolymph pressure may be increased by muscle contractions or by swallowing air into the digestive system to aid in molting. The majority of insects hatch from eggs. The fertilization and development takes place inside the egg, enclosed by a shell chorion that consists of maternal tissue. In contrast to eggs of other arthropods, most insect eggs are drought resistant. This is because inside the chorion two additional membranes develop from embryonic tissue, the amnion and the serosa. This serosa secretes a cuticle rich in chitin that protects the embryo against desiccation.

In Schizophora however the serosa does not develop, but these flies lay their eggs in damp places, such as rotting matter. The eggs of ovoviviparous animals develop entirely inside the female, and then hatch immediately upon being laid. Other developmental and reproductive variations include haplodiploidy , polymorphism , paedomorphosis or peramorphosis , sexual dimorphism , parthenogenesis and more rarely hermaphroditism. This system is typical in bees and wasps. Some insects may retain phenotypes that are normally only seen in juveniles; this is called paedomorphosis. In peramorphosis, an opposite sort of phenomenon, insects take on previously unseen traits after they have matured into adults. Many insects display sexual dimorphism, in which males and females have notably different appearances, such as the moth Orgyia recens as an exemplar of sexual dimorphism in insects.

Some insects use parthenogenesis , a process in which the female can reproduce and give birth without having the eggs fertilized by a male. Many aphids undergo a form of parthenogenesis, called cyclical parthenogenesis, in which they alternate between one or many generations of asexual and sexual reproduction. Other insects produced by parthenogenesis are bees, wasps and ants, in which they spawn males. However, overall, most individuals are female, which are produced by fertilization. The males are haploid and the females are diploid. Insect life-histories show adaptations to withstand cold and dry conditions. Some temperate region insects are capable of activity during winter, while some others migrate to a warmer climate or go into a state of torpor.

Metamorphosis in insects is the biological process of development all insects must undergo. There are two forms of metamorphosis: incomplete metamorphosis and complete metamorphosis. Hemimetabolous insects, those with incomplete metamorphosis, change gradually by undergoing a series of molts. An insect molts when it outgrows its exoskeleton, which does not stretch and would otherwise restrict the insect's growth. The molting process begins as the insect's epidermis secretes a new epicuticle inside the old one.

After this new epicuticle is secreted, the epidermis releases a mixture of enzymes that digests the endocuticle and thus detaches the old cuticle. When this stage is complete, the insect makes its body swell by taking in a large quantity of water or air, which makes the old cuticle split along predefined weaknesses where the old exocuticle was thinnest. Immature insects that go through incomplete metamorphosis are called nymphs or in the case of dragonflies and damselflies, also naiads. Nymphs are similar in form to the adult except for the presence of wings, which are not developed until adulthood. With each molt, nymphs grow larger and become more similar in appearance to adult insects.

Holometabolism , or complete metamorphosis, is where the insect changes in four stages, an egg or embryo , a larva , a pupa and the adult or imago. In these species, an egg hatches to produce a larva , which is generally worm-like in form. This worm-like form can be one of several varieties: eruciform caterpillar-like , scarabaeiform grub-like , campodeiform elongated, flattened and active , elateriform wireworm-like or vermiform maggot-like.

The larva grows and eventually becomes a pupa , a stage marked by reduced movement and often sealed within a cocoon. There are three types of pupae: obtect, exarate or coarctate. Obtect pupae are compact, with the legs and other appendages enclosed. Exarate pupae have their legs and other appendages free and extended. Coarctate pupae develop inside the larval skin. Butterflies are a well-known example of insects that undergo complete metamorphosis, although most insects use this life cycle. Some insects have evolved this system to hypermetamorphosis. Complete metamorphosis is a trait of the most diverse insect group, the Endopterygota.

This form of development is exclusive to insects and not seen in any other arthropods. Many insects possess very sensitive and specialized organs of perception. Some insects such as bees can perceive ultraviolet wavelengths, or detect polarized light , while the antennae of male moths can detect the pheromones of female moths over distances of many kilometers. These wagging movements can signal the arrival of new material into the nest and aggression between workers can be used to stimulate others to increase foraging expeditions.

There are a variety of different mechanisms by which insects perceive sound; while the patterns are not universal, insects can generally hear sound if they can produce it. Different insect species can have varying hearing , though most insects can hear only a narrow range of frequencies related to the frequency of the sounds they can produce. Mosquitoes have been found to hear up to 2 kHz, and some grasshoppers can hear up to 50 kHz. For instance, some nocturnal moths can perceive the ultrasonic emissions of bats , which helps them avoid predation. Some insects display a rudimentary sense of numbers , [91] such as the solitary wasps that prey upon a single species.

The mother wasp lays her eggs in individual cells and provides each egg with a number of live caterpillars on which the young feed when hatched. Some species of wasp always provide five, others twelve, and others as high as twenty-four caterpillars per cell. The number of caterpillars is different among species, but always the same for each sex of larva. The male solitary wasp in the genus Eumenes is smaller than the female, so the mother of one species supplies him with only five caterpillars; the larger female receives ten caterpillars in her cell.

A few insects, such as members of the families Poduridae and Onychiuridae Collembola , Mycetophilidae Diptera and the beetle families Lampyridae , Phengodidae , Elateridae and Staphylinidae are bioluminescent. The most familiar group are the fireflies , beetles of the family Lampyridae. Some species are able to control this light generation to produce flashes. The function varies with some species using them to attract mates, while others use them to lure prey. Cave dwelling larvae of Arachnocampa Mycetophilidae, fungus gnats glow to lure small flying insects into sticky strands of silk.

Most insects, except some species of cave crickets , are able to perceive light and dark. Many species have acute vision capable of detecting minute movements. The eyes may include simple eyes or ocelli as well as compound eyes of varying sizes. Many species are able to detect light in the infrared, ultraviolet and the visible light wavelengths. Color vision has been demonstrated in many species and phylogenetic analysis suggests that UV-green-blue trichromacy existed from at least the Devonian period between and million years ago. Insects were the earliest organisms to produce and sense sounds. Insects make sounds mostly by mechanical action of appendages. In grasshoppers and crickets, this is achieved by stridulation. Cicadas make the loudest sounds among the insects by producing and amplifying sounds with special modifications to their body to form tymbals and associated musculature.

The African cicada Brevisana brevis has been measured at The ultrasonic clicks were subsequently found to be produced mostly by unpalatable moths to warn bats, just as warning colorations are used against predators that hunt by sight. Ultrasonic recording and high-speed infrared videography of bat-moth interactions suggest the palatable tiger moth really does defend against attacking big brown bats using ultrasonic clicks that jam bat sonar. Very low sounds are also produced in various species of Coleoptera , Hymenoptera , Lepidoptera , Mantodea and Neuroptera.

These low sounds are simply the sounds made by the insect's movement. Through microscopic stridulatory structures located on the insect's muscles and joints, the normal sounds of the insect moving are amplified and can be used to warn or communicate with other insects. Most sound-making insects also have tympanal organs that can perceive airborne sounds. Some species in Hemiptera , such as the corixids water boatmen , are known to communicate via underwater sounds. Communication using surface-borne vibrational signals is more widespread among insects because of size constraints in producing air-borne sounds.

Some species use vibrations for communicating within members of the same species, such as to attract mates as in the songs of the shield bug Nezara viridula. Chemical communications in animals rely on a variety of aspects including taste and smell. Chemoreception is the physiological response of a sense organ i. A semiochemical is a message-carrying chemical that is meant to attract, repel, and convey information. Types of semiochemicals include pheromones and kairomones.

One example is the butterfly Phengaris arion which uses chemical signals as a form of mimicry to aid in predation. In addition to the use of sound for communication, a wide range of insects have evolved chemical means for communication. These chemicals, termed semiochemicals , are often derived from plant metabolites including those meant to attract, repel and provide other kinds of information. Pheromones , a type of semiochemical, are used for attracting mates of the opposite sex, for aggregating conspecific individuals of both sexes, for deterring other individuals from approaching, to mark a trail, and to trigger aggression in nearby individuals.

Allomones benefit their producer by the effect they have upon the receiver. Kairomones benefit their receiver instead of their producer. Synomones benefit the producer and the receiver. While some chemicals are targeted at individuals of the same species, others are used for communication across species. The use of scents is especially well known to have developed in social insects. These tracheae are highly '''branched''' helping to increase the '''Surface area : volume ratio''' available for gas exchange. Respiratory gasses '''can dissolve''' into this fluid and '''easily diffuse''' into surrounding tissues because the tracheoles have such '''thin''' walls.

The fluid lining the tracheoles normally fills the ends of these small tubes. This further increases the '''surface area'''available for gas exchange. The small size of insects mean that they are often lower in the food chain. Flight is often an essential mechanism to escape predation, however, it demands considerable amounts of energy. The increased surface area helps the insect meet the respiratory demands associated with an increased rate of cellular respiration.

This acts like a reinforcing wire that '''keeps the airways open''' during body movements, while allowing some flexibility. This ensures that the gas exchange surface is ventilated - that a concentration gradient is maintained. Air flows into the atrium of the alveolar sac, then circulates into alveoli where gas exchange occurs with the capillaries. Mucous glands secrete mucous into the airways, keeping them moist and flexible.

Birds face a unique challenge with respect to breathing: They fly. Flying consumes a great amount of energy; therefore, birds require a lot of oxygen to aid their metabolic processes. Birds have evolved a respiratory system that supplies them with the oxygen needed to enable flying. Similar to mammals, birds have lungs, which are organs specialized for gas exchange. Oxygenated air, taken in during inhalation, diffuses across the surface of the lungs into the bloodstream, and carbon dioxide diffuses from the blood into the lungs and expelled during exhalation. The details of breathing between birds and mammals differ substantially. In addition to lungs, birds have air sacs inside their body. Air flows in one direction from the posterior air sacs to the lungs and out of the anterior air sacs.

The flow of air is in the opposite direction from blood flow, and gas exchange takes place much more efficiently. This type of breathing enables birds to obtain the requisite oxygen, even at higher altitudes where the oxygen concentration is low. This directionality of airflow requires two cycles of air intake and exhalation to completely get the air out of the lungs. Decades of research by paleontologists have shown that birds evolved from therapods, meat-eating dinosaurs. In fact, fossil evidence shows that meat-eating dinosaurs that lived more than million years ago had a similar flow-through respiratory system with lungs and air sacs.

Archaeopteryx and Xiaotingia , for example, were flying dinosaurs and are believed to be early precursors of birds. The air sacs connect to openings in hollow bones. Most of us consider that dinosaurs are extinct. However, modern birds are descendants of avian dinosaurs. The respiratory system of modern birds has been evolving for hundreds of millions of years.

The video below provides an overview of the human respiratory system:. Once the oxygen diffuses across the alveoli, it enters the bloodstream and is transported to the tissues where it is unloaded, and carbon dioxide diffuses out of the blood and into the alveoli to be expelled from the body. Although gas exchange is a continuous process, the oxygen and carbon dioxide are transported by different mechanisms.

Although oxygen dissolves in blood, only a small amount of oxygen is transported this way. Only 1. Most oxygen, about Hemoglobin , or Hb, is a protein molecule found in red blood cells erythrocytes made of four subunits: two alpha subunits and two beta subunits. Each subunit surrounds a central heme group that contains iron and binds one oxygen molecule, allowing each hemoglobin molecule to bind four oxygen molecules. Molecules with more oxygen bound to the heme groups are brighter red.

As a result, oxygenated arterial blood where the Hb is carrying four oxygen molecules is bright red, while venous blood that is deoxygenated is darker red. The protein inside a red blood cells that carries oxygen to cells and carbon dioxide to the lungs is b hemoglobin. Hemoglobin is made up of four symmetrical subunits and four heme groups. Iron associated with the heme binds oxygen. It is the iron in hemoglobin that gives blood its red color. It is easier to bind a second and third oxygen molecule to Hb than the first molecule. This is because the hemoglobin molecule changes its shape, or conformation, as oxygen binds. The binding of oxygen to hemoglobin can be plotted as a function of the partial pressure of oxygen in the blood x-axis versus the relative Hb-oxygen saturation y-axis.

The resulting graph, an oxygen dissociation curve, is sigmoidal, or S-shaped. As the partial pressure of oxygen increases, the hemoglobin becomes increasingly saturated with oxygen. The oxygen dissociation curve demonstrates that, as the partial pressure of oxygen increases, more oxygen binds hemoglobin. However, the affinity of hemoglobin for oxygen may shift to the left or the right depending on environmental conditions. If the kidneys fail, what would happen to blood pH and to hemoglobin affinity for oxygen?

The oxygen-carrying capacity of hemoglobin determines how much oxygen is carried in the blood. In addition to P O 2 , other environmental factors and diseases can affect oxygen carrying capacity and delivery. Carbon dioxide levels, blood pH, and body temperature affect oxygen-carrying capacity. When carbon dioxide is in the blood, it reacts with water to form bicarbonate HCO This increase in carbon dioxide and subsequent decrease in pH reduce the affinity of hemoglobin for oxygen. The oxygen dissociates from the Hb molecule, shifting the oxygen dissociation curve to the right. Therefore, more oxygen is needed to reach the same hemoglobin saturation level as when the pH was higher. A similar shift in the curve also results from an increase in body temperature.

Increased temperature, such as from increased activity of skeletal muscle, causes the affinity of hemoglobin for oxygen to be reduced. Carbon dioxide molecules are transported in the blood from body tissues to the lungs by one of three methods: dissolution directly into the blood, binding to hemoglobin, or carried as a bicarbonate ion. Several properties of carbon dioxide in the blood affect its transport. First, carbon dioxide is more soluble in blood than oxygen. About 5 to 7 percent of all carbon dioxide is dissolved in the plasma.

Second, carbon dioxide can bind to plasma proteins or can enter red blood cells and bind to hemoglobin. This form transports about 10 percent of the carbon dioxide. When carbon dioxide binds to hemoglobin, a molecule called carbaminohemoglobin is formed. Binding of carbon dioxide to hemoglobin is reversible. Therefore, when it reaches the lungs, the carbon dioxide can freely dissociate from the hemoglobin and be expelled from the body.

Third, the majority of carbon dioxide molecules 85 percent are carried as part of the bicarbonate buffer system. In this system, carbon dioxide diffuses into the red blood cells. Carbonic anhydrase CA within the red blood cells quickly converts the carbon dioxide into carbonic acid H 2 CO 3. Since carbon dioxide is quickly converted into bicarbonate ions, this reaction allows for the continued uptake of carbon dioxide into the blood down its concentration gradient. When the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for the chloride ion. This produces the carbonic acid intermediate, which is converted back into carbon dioxide through the enzymatic action of CA.

The carbon dioxide produced is expelled through the lungs during exhalation.

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