Gastrointestinal tract

Biological significance of elimination

Physical Health
Current Opinion in Gastroenterology. Although ulcerative colitis is often treated as though it were an autoimmune disease, there is no consensus that it actually is such. Home gardens can be raised with spare family labour and the participation of women and children. The photo to the right shows the rictal bristles of a Hooded Warbler. Good for doing salt baths, a bit of salt for livebearers, or parasite treatment. Elastic skeletons do not change shape but simply bend when a muscle contracts.

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Instead, the tongue tip is a dynamic liquid-trapping device that dynamically traps nectar by rapidly changing their shape during feeding. In addition, the tongue—fluid interactions are identical in both living and dead birds, demonstrating that this mechanism is a function of the tongue structure itself, and therefore highly efficient because no energy expenditure by the bird is required to drive the opening and closing of the trap.

These results rule out previous conclusions from capillarity-based models of nectar feeding and highlight the necessity of developing a new biophysical model for nectar intake in hummingbirds. Hummingbird tongue tips twist to trap nectar. How the hummingbird tongue really works with videos.

Close encounters with possible prey. You want to live 10—20 years. You are peering under leaves, poking into rolled ones, searching around stems, exploring bark crevices and other insect hiding places. Abruptly an eye appears, 1—5 cm from your bill. The eye or a portion of it is half seen, obstructed, shadowed, partly out of focus, more or less round, multicolored, and perhaps moving.

Now, a safe few meters away, are you going to go back to see whether that was food? Associated body patterns often suggest other head and facial features, which in turn enhance the eye-like nature of the spots. None of these patterns exactly matches the eyes or face of any particular species of predator; but, even when quickly and partially glimpsed, all give the illusion of an eye or face. These false eyes are mimicking the eyes and faces of such predators of insect-eating birds as snakes, lizards, other birds, and small mammals, as perceived at close range by the insectivorous birds in their natural world.

Note the distended throat of this American Kestrel. Pigeons generally lay two eggs one day apart, which hatch 18 days after they are laid. A similar substance is produced by flamingos and male Emperor Penguins.

The normal function of the crop is food storage. Pigeon 'milk' also contains IgA antibodies and antioxidants carotenoids.

The avian stomach is divided into 2 parts:. Photomicrograph 50X of a cross section through the proventriculus showing folds of mucous membrane P ; deep proventricular glands GP ; capsule connective tissue around the glands arrow head ; muscle layer m ; serosa connective tissue with blood vessels S , and the lumen L From: Photomicrograph X of longitudinal section of the gizzard showing folds of mucous membrane lined by simple prismatic epithelium P ; simple tubular glands Gs in the lamina propria constituted by connective tissue Lp ; secretion of glands S that are continuous with the cuticle or koilin ; C , part of muscle layer m , interpersed with bundles of connective tissue Tc From: Photomicrograph X of the koilin of an Eclectus Parrot Eclectus roratus.

Note the regular, columnated structure of the koilin layer K and its association with the glandular epithelium E of the ventriculus From: De Voe et al.

A, koilin, B, crypts, C, glands that secrete koilin, D, epithelial surface, E, desquamated epithelial cells, 2 Mucosa of the gizzard. A, koilin, B, secretion in gland lumens and crypts, and 3 Koilin layer. A, secretion column, B, koilin-layer surface, C, horizontal stripe indicating a 'pause' in secretion of the koilin, D, cellular debris. Eglitis and Knouff Vultures of the seas -- Animals are primarily limited by their capacity to acquire food, yet digestive performance also conditions energy acquisition, and ultimately fitness.

Optimal foraging theory predicts that organisms feeding on patchy resources should maximize their food loads within each patch, and should digest these loads quickly to minimize travelling costs between food patches. GPS-tracking of 40 Wandering Albatrosses from the Crozet archipelago during the incubation phase confirmed foraging movements of between — km, giving the birds access to a variety of prey, including fishery wastes.

Using miniaturized, autonomous data recorders placed in the stomach of three birds, the first-ever measurements of gastric pH and temperature in procellariformes were obtained. Such low stomach pH gives Wandering Albatrosses a strategic advantage because it allows a rapid chemical breakdown of ingested food and rapid digestion. This is useful for feeding on patchy, natural prey, but also on fishery wastes, which might be an important additional food resource for Wandering Albatrosses.

It is likely that this physiological characteristic evolved as a response to a diet largely composed of squid, and to a patchy distribution of this food resource resulting in large, infrequent meals. The strategy of Wandering Albatrosses is to cover long distances rapidly and at low costs to increase the probability of encountering dispersed prey patches whose distribution is unpredictable. Knots with large gizzards consumed far more molluscs with shells than the birds with smaller gizzards.

Birds with smaller gizzards simply couldn't feed fast enough. By allowing them to crush more shell per gizzard-full, larger gizzards gave birds the edge.

Thus, even though it is energetically costly for the knots to maintain a larger gizzard, when the bird needs to get the most out of its crunchy diet, it's a price worth paying. So, the birds' gizzards enlarge as they fatten for migration.

Because the molluscs' shells stay the same size as the molluscs shrink, the amount of shell a bird must process to eat its fill also increases.

But with their larger gizzards, the birds can still make the most of even the crunchiest winter diet! Within 14 days, they showed a doubling of the size of their gizzards. Red Knots have strong muscular gizzards for feeding on molluscs. A shift back to a mussel diet induced about a doubling in gizzard mass in just a few days. As the knots were fed progessively smaller mussels day 22 to day 46 that are easier to crush, gizzard mass again declined.

A switch back to a soft food pellet diet caused a further decline in gizzard mass. Finally, a switch back to a mussel diet again cause a rapid increase in gizzard mass From: Piersma and Drent Ostrich Struthio camelus stomach. Note how particle size of material in the gizzard ventriculus is smaller than in the proventriculus due to the grinding action of the muscular walls plus small pebbles gastroliths.

The capacity to reduce particle size is related to the metabolic demands of a species. Therefore, particle size reduction is often considered the key digestive difference between ecto- and endotherms that allows endotherms to rely on shorter digesta retention times without losing digestive efficiency, and hence facilitate the high level of food intake necessary to meet their increased metabolic requirements.

In contrast, adaptations for chewing intrinsically increase the weight of the head. The use of the gizzard system has the potential advantages that intake rate is not limited by chewing, that no investment in dental tissue is necessary, and that dental wear is not a determinant of senescence as observed in mammals.

The absence of age-dependent tooth wear might even be a contributing factor to the slower onset of senescence in birds as compared to mammals.

On the other hand, the use of a gizzard requires the intake of suitable grit or stones—an action that represents, in the few studies where this has actually been quantified in birds, a relevant proportion of feeding time Fritz et al. Gastrointestinal tracts of a carnivorous hawk, an omnivorous chicken, and 4 herbivorous birds. Note larger size of crop in omnivore and herbivores, and particularly in hoatzin.

Ceca are small in hawks and relatively large in grouse. Although ceca are relatively small in Hoatzins , Emus, and Ostriches, an expanded foregut Hoatzins , a much longer midgut Emus , or a much longer colon Ostriches compensates for this From: Stevens and Hume Over-reliance on the passive pathway provides metabolic advantages and ecological constraints.

It does provide birds with an absorptive process that can deal with rapid and large changes in intestinal sugar concentrations. The passive pathway is also energetically inexpensive to maintain and modulate. However, passive absorption through the paracellular pathway is dependent on concentration gradients. In the absence of a transport system that selects which materials to absorb, this non-discriminatory pathway may also increase vulnerability to toxins, and thus constrain foraging behavior and limit the breadth of the dietary niche of the birds.

Another problem is that when luminal sugar concentrations are lower than those in plasma, glucose may diffuse back into the lumen. Cross-section of the intestine ileum of a Spotted Tinamou Nothura maculosa.

Villi are lined with columnar epithelium EP , including goblet cells arrows that secrete mucus. The muscle layer includes longitudinal fibers MI on the perimeter, circular fibers Mc , and additional longitudinal fibers at the base of the villi muscularis muscosae; MM From: Chikilian and de Speroni Blue-headed Parrots at clay lick. Meyer-Rochow and Gal determined that the pressures involved could be approximated if they knew the 1 distance the feces traveled, 2 density and viscosity of the material, and 3 shape, aperture, and height of the anus above ground.

How penguins choose the direction of defecation, and how wind direction factors into that decision, remain unknown. Avian Pancreas tissue Source: The Avian Digestive Tract. Avian geophagy and soil characteristics in southeastern Peru. Luminal morphology of the avian lower intestine: Histological aspects of the stomach proventriculus and gizzard of the Red-capped Cardinal Paroaria gularis gularis.

Comparative study of the digestive system of three species of tinamou. Crypturellus tataupa, Nothoprocta cinerascens , and Nothura maculosa Aves: Journal of Morphology Journal of Experimental Zoology Rictal bristle function in Willow Flycatcher. Dysplastic koilin causing proventricular obstruction in an Eclectus Parrot Eclectus roratus. Journal of Avian Medicine and Surgery Anatomy and physiology of the digestive system in fowl.

Pages in Proc. An histological and histochemical analysis of the inner lining and glandular epithelium of the chicken gizzard. American Journal of Anatomy An ecomorphological study of the raptorial digital tendon locking mechanism. Dietary and developmental regulation of intestinal sugar transport.

Digesta retention patterns in geese Anser anser and turkeys Meleagris gallopavo and deduced function of avian caeca. Comparative Biochemistry and Physiology A Histological and global gene expression analysis of the 'lactating' pigeon crop. Vultures of the seas: Evolution of the structure and function of the vertebrate tongue. Journal of Anatomy Light and scanning electron microscopic study of the tongue in the cormorant Phalacrocorax carbo Phalacrocoracidae, Aves.

Functional morphology of the tongue in the nutcracker Nucifraga caryocatactes. A tropical horde of counterfeit predator eyes. Instructed learning in the auditory localization pathway of the Barn Owl. The morphology of the bill apparatus in the Steller's Sea Eagle. Wild Bird Society of Japan, Tokyo. Use of dung as a tool by burrowing owls. The integration of energy and nitrogen balance in the hummingbird Sephanoides sephaniodes. Does gut function limit hummingbird food intake?

Physiological and Biochemical Zoology Pressures produced when penguins pooh—calculations on avian defaecation. Scare tactics in a neotropical warbler: Gliding flight and soaring. Theoretical Ecology Series, vol. Modelling the flying bird C. Structure, form, and function of flight in engineering and the living world.

Phenotypic flexibility and the evolution of organismal design. Trends in Ecology and Evolution The hummingbird tongue is a fluid trap, not a capillary tube. Between air and water: Use of prey hotspots by an avian predator: Structure and mechanical behavior of a toucan beak. Movement and direction of movement of a simulated prey affect the success rate in Barn Owl Tyto alba attack.

Musculoskeletal underpinnings to differences in killing behavior between North American accipiters Falconiformes: Accipitridae and falcons Falconidae. Journal of Morphology, online early. Le Bohec, and Y. Adjustments of gastric pH, motility and temperature during long-term preservation of stomach contents in free-ranging incubating King Penguins.

Journal of Experimental Biology A tough nut to crack. Adaptations to seed cracking in finches. Cost-benefit analysis of mollusc-eating in a shorebird. Optimizing gizzard size in the face of seasonal demands. How do woodpeckers extract grubs with their tongues? Why do woodpeckers resist head impact injury: Functional morphology of raptor hindlimbs: The turning- and linear-maneuvering performance of birds: Canadian Journal of Zoology Hummingbird jaw bends to aid insect capture.

A mechanical analysis of woodpecker drumming and its application to shock-absorbing systems. I - Introduction to Birds.

VII - Circulatory System. Back to Avian Biology. Drawings of the digestive tracts of A a Greylag Goose and B a Wild Turkey and retention times of a solute, 2-mm particles, and 8-mm particles in the goose and turkey digestive systems Figure from Frei et al. The closed, air-filled spaces reduce overall weight without loss of rigidity. The capillary ratchet mechanism Surface tension transport of prey by feeding shorebirds: The serrated leading-edge feather of an owl Norberg Vortex generators on an airplane wing.

Fish-eating species like cormorants below - typically have small, undifferentiated tongue because fish are often swallowed whole.

Representative caterpillar false eyes and faces. In some, like woodpeckers, the 'sticky' saliva aids in capturing prey. In others, like swifts, saliva is used in nest building see photo below. The muscular walls of the esophagus produce wave-like contractions peristalsis that help propel food from the oral cavity to the stomach. Anhinga swallowing a large fish. HCL and pepsinogen are secreted by the deep glands see photomicrograph below.

Pepsinogen is converted into pepsin a proteolytic, or protein-digesting, enzyme by the HCl. The cuticle is secreted by simple tubular glands see photomicrograph below. Grinding action may, particularly in seed-eating birds, be assisted by grit and stones deliberately ingested.

The avian gastrointestinal tract, unlike that of mammals, executes distinct reverse peristaltic movements that are critical to optimal digestive function Duke The gastric reflux allows material in the gizzard to reenter the proventriculus for additional treatment with acid and pepsin.

Villi are projections from the intestinal wall that increase the amount of surface area available for absorption. Further increasing the surface area are the numerous microvilli of the cells lining the surface of the villi. Inside each villus are blood vessels that absorb nutrients for transport throughout the body. Caeca are histologically similar to the small and large intestines and found in a wide variety of birds.

In these large ceca, food particles are acted upon by cecal secretions, bacteria, and fungi and nutrients can be absorbed. Lymphoid ceca are not important in digestion but contain lymphocytes white blood cells that produce antibodies Clench At various times and under various conditions, ceca are the site for 1 fermentation and further digestion of food especially for the breakdown of cellulose and absorption of nutrients, 2 production of antibodies, and 3 the use and absorption of water and nitrogenous components Clench The bursa is most prominent in young birds and serves as the area where B-lymphocytes the white blood cells that produce antibodies are generated T-lymphocytes are generated in the Thymus.

Bile emulsifies fats or, in other words, breaks fats down into tiny particles. Emulsification is important because it physically breaks down fats into particles than can then be more easily digested by enzymes lipase produced by intestinal cells and the pancreas.

This 'juice' contains a bicarbonate solution that helps neutralize the acids coming into the intestine from the stomach plus a variety of digestive enzymes. The enzymes help break down fats, proteins, and carbohydrates.

The pancreas also produces the hormones insulin and glucagon which regulate blood sugar levels cells that produce these two hormones make up the 'islets of Langerhans', one of which is represented by the light-colored, circular structure in the photomicrograph below. Hit 'Reload' or 'Refresh' to View Again!

Particle retention time hr. Flamingos use a series of projections, or lamellae, to filter tiny food items from debris in the water.

Wrens use their thin, probing bill to capture small insects. Curlews use their long bill to probe mudflats for small invertebrates. Finches do not simply bite the seeds; instead; the lower mandible is moved toward the tip of the bill in a slicing motion. When most of the coat has been cracked or removed, the lower mandible is moved from side to side to remove the rest of the shell, thus releasing the kernel.

Some large finches also have raised hard surfaces in the upper palate that function as anvils so large seeds can be held firmly while the lower mandible slices and cracks the sides of the seed.

As tricky as nutcracking sounds, most birds accomplish it rapidly, shelling small seeds in a few seconds and large finches can crack open and devour a large seed or nut in less than twenty seconds.

Big mouths get hummingbirds an in-flight meal - Hummingbirds have bendy lower beaks to help them catch insects Yanega and Rubega The flexibility allows long-beaked birds to open their mouths wide enough to hunt on the wing.

Hummingbirds use their long, narrow beaks to probe flowers for nectar, but they also need insects for essential nutrients. It wasn't clear how they could catch them; birds that hunt flying insects usually have short beaks to help them open their mouths wide.

Pilcher, Nature Science Update. The force produced by talons may be related to time of activity. Owls hunt when light levels are low so if an attacking owl misses its prey, relocating it may be difficult. Hawks are diurnal hunters and can use visual cues during and after an attack.

If unable to subdue prey initially, they can relocate prey visually and catch it. Given the morphological differences and hunting behaviors of these raptors, how well do those characteristics relate to prey-size selection?

Eastern Screech-Owls prey on insects, small birds, and small mammals. Red-tailed Hawks subsist primarily on rodents and larger mammals such as skunks and rabbits. Red-shouldered Hawks , like Barred Owls, subsist mainly on medium-sized mammals such as squirrels and chipmunks, but also prey on frogs and salamanders.

American Kestrels , like Eastern Screech-Owls, eat mostly insects and small mammals. Bristles occur most prominently around the eyes "eyelashes" , the lores, the nostrils, and around the rictus corners of the mouth. Not all birds have bristles. Rictal bristles are prominent in many insectivorous birds, particularly aerial insectivores like nightjars Order Caprimulgiformes and flycatchers Family Tyrannidae , and may be used as sensory organs to help locate and capture prey, much like mammals use whiskers.

In addition, bristles around the mouth may help protect the eyes from food items a bird is trying to capture Conover and Miller The photo to the right shows the rictal bristles of a Hooded Warbler.

Goose tongue -- The dorsal surface of the tongue of Middendorff's Bean Goose Anser fabalis middendorffii has an anterior region that extends for five-sixths of its length plus a posterior region. Large conical papillae indicated by arrowhead to the right are located in a row between the anterior and posterior regions. The plant kingdom is divided into algae, ferns, mosses, and seed plants.

Angiosperms are divided into two groups: There are two main groups in the animal kingdom: The invertebrates consist of Nematodes , Annelids , Molluscs and Arthropods. Yes No Yes Movement Use chaetae bristles to move from place to place Wriggles but lives in one place Creeps on foot from place to place Feeding method Herbivore Mainly parasites Mainly herbivores, some carnivores.

Fish , Amphibians , Reptiles , Birds , and Mammals. Some can camouflage e. Non-living structure which is made of cellulose. It supports the plant from pressure and gives it a regular shape. A fluid made of cell sap. It contains some useful materials and waste products Chloroplast: Large bodies containing chlorophyll where photosynthesis takes place Mitochondria: It consists of a double membrane and is the site of aerobic respiration. Plant Animal Root hair cell: Tissues, organs and systems.

The greater the difference, the higher the rate of diffusion. The rate of diffusion depends on: A hypertonic solution has higher concentration of salt; a hypotonic solution has a higher concentration of water and an isotonic solution as an equal concentration of water and salt. No No Yes Partially permeable membrane required? General characteristics of enzymes: Enzymes are sensitive to a certain temperature and pH.

Each enzyme has different optimum temperature and pH. If the pH is too high or too low the enzyme will be denatured and would not work anymore. Enzymes are also used in washing powders as they can remove stains such as blood and milk. Add drops of water to the clear solution Milky emulsion or turbid solution is formed The solution remains clear.

Vitamins are organic substances and are only needed in small amounts in the body to perform specific functions. The alimentary canal is lined with epithelial, goblet, and muscle cells Ingestion: Getting rid of undigested materials.

The mouth Food is ingested and chewed. The teeth help to tear and grind the food into small pieces. This increases the surface area for the action of enzymes. The food is mixed with saliva which has two functions. The saliva contains mucus which is a slimy substance which helps the food to be swallowed.

It contains the enzyme amylase which begins the digestion of starch into the sugar maltose. As food does not remain in the mouth for very long, only a small amount of starch is digested here. The food is then turned to a bolus shape by the action of the mouth and then swallowed. Oesophagus This tube pushes the food to the stomach by way of rhythmic contractions. There are two sets of muscles in the oesophagus.

Circular muscles - these make the oesophagus narrower. Longitudinal muscles - these make the oesophagus wider. Gastric juice contains two substances.

Pepsin - an enzyme which breaks proteins down into shorter chains called polypeptides. Hydrochloric acid - needed to help pepsin work and also helps to kill any ingested bacteria. The stomach has two rings of muscles at the top and bottom, called sphincter muscles which prevent food from leaving the stomach while it is being churned around. After a few hours, the food is now a mushy liquid called chyme. It is then allowed to continue on its journey a bit at a time. Duodenum, Liver, Gall Bladder and Pancreas When food enters the duodenum the first 30cm of the small intestine a number of secretions are added to it.

Digestive enzymes from the wall of the duodenum and from the pancreas are added. There are a number of enzymes here which will complete the digestive process. Another substance is added from the gall bladder: Bile , made in the liver and stored in the gall bladder, contains no digestive enzymes but it contains bile salts which play a vital role in fat digestion.

Fats and oils do not mix with water, but the enzyme lipase which digests them needs water in order to work. Bile salts break down the large fat drops into tiny droplets which can mix better with water to create an emulsion.

This makes it easier for lipase digest the chemicals as it increases the surface area of the fat. Enzymes of the small intestine work best in a slightly alkaline environment Digestive enzymes in the small intestine.

Green plants make their own food from sunlight, using the following process: The leaf has a waxy cuticle to prevent it from losing water and drying out. The epidermis is a protective layer of cells and contains no chloroplasts. The palisade layer contains the most chloroplasts as it is near the top of the leaf.

It is here that photosynthesis takes place. The palisade cells are arranged upright to increases the chance of photosynthesis. The spongy layer contains fewer chloroplasts, but enough to catch what the palisade layer cannot absorb. The spongy layer has air spaces to make it easier for gases to circulate in the leaf. The vascular bundle provides the leaf with water via the xylem vessels.

Food, such as sugar, made in the leaf is transported in the phloem vessels to the rest of the leaf. The stomata stoma - singular are tiny pores that allow carbon dioxide to enter the leaf while oxygen leaves the leaf. Guard cells can open or close the stomata pores to regulate how much gas can enter or leave the leaf. At night the pores close, opening in the daytime. Temperature When the temperature rises the rate of photosynthesis rises also.

This is because the particles in the reaction move faster and collide more. At optimum temperature, the rate of photosynthesis progresses as fast as it can, limited only by the other factors. Beyond this temperature the enzymes controlling the reaction become denatured and the reaction quickly comes to a halt.

Light intensity The plant can photosynthesize faster as a result of a higher light intensity. As the light intensity decreases the rate of photosynthesis decreases.

Light is a limiting factor at low light intensities. There will come a point where any extra light energy will not increase the rate of the reaction. T his is because the enzymes controlling the reaction are working at maximum rate. At this point light is no longer a limiting factor.

This is because the plant has to spend a certain amount of time doing nothing, waiting for more carbon dioxide to arrive. Increasing the concentration of carbon dioxide increases the rate of photosynthesis.

Plants need a number of minerals to be healthy. These mineral ions are needed to make certain chemicals or to make certain reactions work properly. Plant absorbs these minerals from the soil when water is absorbed.

Transport in plants Transport is the movement or flow of different substances within a living organism. The transport system in plants is the vascular bundles xylem and phloem. Cambium tissue contains cells which divide by mitosis to produce more phloem and xylem. Xylem Phloem Description Consists of non-living woody lignified cells elements joined together to form continuous tubes vessels Consists of living cells sieve elements Substances carried Sap: Transpiration Water enters the plant via the roots by osmosis.

They are then carried up the xylem vessels and lost through transpiration which is when water is lost through the stomata. When water is lost through the stomata it forces the water to be sucked upwards. Factors affecting rate of transpiration Temperature: The higher the humidity the lower the uptake Air current: Plants with a thick waxy layer will reduce water loss through the leaves.

Plants can have needle-like leaves. Hair-like fibre on the leaf traps air close to the leaf. It creates a microclimate around the leaf. As water is lost from the leaf the microclimate becomes very humid. The hairs prevent this humid air from being blown away. Leaves can be folded. The leaf blade is curled in on itself so that the stomata are on the inside. This creates a humid micro-climate which slows down water loss. Transport in humans Transportation in humans is done by the circulatory system which involves blood being pumped around the body by the heart.

Humans have a double circulatory system which means that the blood is pumped twice around the body - once to the heart and another to the rest of the body. Blood transports O 2 , CO 2 , nutrients, hormones and waste products so the movement must be fast. The heart is really two pumps stuck together. There are two chambers to each side of the heart. The first chamber is called the atrium and is the smaller of the two chambers. The larger one is called the ventricle.

This chamber is the more powerful of the two as it has to force blood out of the heart. The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs. The left side of the body receives oxygenated blood and pumps it around the body so its force must be stronger. In the heart both sides pump together at the same time.

The blood must flow through the heart in one direction. Blood enters the atria from the veins and is then forced into the ventricles. The ventricles force the blood into the arteries. There are a number of sphincter muscles and valves that prevent blood flowing in the wrong direction.

The valves are a little like parachutes. When blood flows the wrong way the valves bulge out, blocking the path. Heartbeat Involves three distinct stages: The atria and the ventricles relax. The semi-lunar valves close, preventing back flow into the ventricles. The elastic walls of the aorta and pulmonary artery contract, forcing blood towards the body and the lungs.

Blood from the veins flows into the atria, which begin to fill. Deoxygenated blood enters the right atrium, and oxygenated blood flows into the left atrium. The atria contract, forcing blood into the ventricles, which then fill up. Sphincter ring muscles close off the venae cavae and the pulmonary veins prevents backflow of blood from the atria into the main veins.

The ventricles contract, forcing blood into the aorta and pulmonary artery. This happens because the pressure of blood in the ventricles is higher than the pressure in the atria. The valve cord prevents the valve from being pushed back too far. The walls of the aorta and pulmonary artery expand. The heart rate can be measured by the heart pace. There are muscles in the wall of the heart that receive hormones from the brain telling it to speed up or slow down e. The vessel supplying the heart with blood is called the coronary artery.

This is one of the most important arteries in the body because it supplies the heart with all the nutrients it needs. If this artery is blocked the heart will slow down or stop causing a heart attack. This is how coronary heart diseases CHD happen - by the build up of fats inside the vessel. The more the amount of fats build up, the slower the heart pumps and the more easily the heart gets tired.

There are different types of blood vessels. Arteries carry blood away from the heart. These vessels split up into smaller ones called arterioles. Arterioles split up into tiny blood vessels called capillaries. It is from these vessels that movement of particles to and from the blood takes place.

Capillaries join together to form larger vessels called venules which join together to form veins. White blood cells and immunity. Respiration is the chemical breakdown of food molecules to release energy. Breathing is the mechanical movement to ventilate the respiratory surface. It includes inhaling and exhaling. Gaseous exchange is the diffusion of O 2 on a moist surface into an organism and the diffusion of CO 2 out of the organism.

Aerobic respiration Anaerobic respiration. In this process glucose is completely oxidized into carbon dioxide and water. This process is slow and is controlled by many enzymes and the energy produced is not used immediately but stored as ATP. The energy released from ATP can be used in many activities such as: In this process the energy produced is relatively small and the product is variable. Alcohol can be produced when anaerobic respiration happens during fermentation in yeast.

In the human body, lactic acid is a product of anaerobic respiration during heavy exercise. The lactic acid produced needs to be broken down further by oxygen.

That is why we continue to breathe heavily after exercising. The oxygen required for the subsequent breakdown of lactic acid is called oxygen debt. The lungs are located in the chest inside a lubricated membrane called the pleural membrane. This allows the lungs to move freely inside the pleural cavity. The lungs are connected to the outside via the trachea windpipe.

The trachea is a tube kept in a rigid shape due to rings of cartilage. The larynx or voice box is located at the top of the trachea while at the bottom end it branches into two bronchi. These lead into the lungs. The bronchi in turn branch off into smaller and smaller bronchioles. These end in tiny air sacs called alveoli. It is here that gaseous exchange takes place. The surface area of all these alveoli is very large so as to be able to absorb oxygen very quickly.

The lungs are very delicate and can easily be damaged. The cells lining the airways have very tiny hair like structures called cilia on them. These cilia are coated with sticky mucus. The beating cilia force the mucus and any particles of dirt up out of the lungs. These together increase the volume of the chest. Air is drawn into the lungs because the the pressure inside them is lowered as the chest volume is increased.

When we breathe out the diaphragm relaxes as does the intercostal muscles. This decreases the volume of the chest, increasing the pressure. This forces air out of the lungs.

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