Total amount of CO₂ / Oxygen in Bloodstream in Humans

Total amount of CO₂ / Oxygen in Bloodstream in Humans

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How much carbon dioxide and oxygen from/for respiration are in the bloodstream at any one time? (mass per litre of blood or similar)

And would there be much more aside from the blood in tissue, e.g. muscle, brain, etc.

So far the figures I have are as follows (please double check for me, I dont have a clue)

O₂ molecules per red blood cell: 1 billion. Red blood cells per micro litre of blood in males: 4.7 to 6.1 million. Molecules per mole: 6 x 10^23. Therefore moles of O2 per litre of blood: approx 0.01 (correct?) This seems quite low, since an inhalation is typically 0.5L and about a quarter of the oxygen is absorbed (oxygen by volume, 5% of the air) (1 thousandth of a mole of oxygen absorbed per inhalation?)


Your calculation for O2 is along the right direction, but missing a factor I think.

Each red blood cell holds millions of molecules of hemoglobin, each hemoglobin molecule, when saturated (at the lung), holds four O2 molecules. So this is off by a factor of millions at least. Wikipedia estimates that hemoglobin makes up about 35% of the total weight of blood. We can use this figure and an average of 4.5 l of blood for a human being ( numbers vary, but it will be within 30%).

4.5l blood * 1.060 g/ml density of blood * 1000 ml/l water * 35% = 1667 g hemoglobin

4 molecules O2/molecule hemoglobin * 1667 g hemoglobin / (64000 g/mol molecular weight of hemoglobin) = 0.104 moles O2

so I get:

0.104 moles O2 * 30 g/mol for O2 = 3.12 g O2 in the blood at a time.

In the muscle and tissues it gradually depletes so that all four molecules will usually end up somewhere in your tissue. So this is all assuming that counting all the hemoglobin bound O2 will approximate the count of O2 in the body.

We know this is a crude estimate as myoglobin in mammal muscle will store O2 for use later, and the average hemoglobin is not in the lungs and will have given up some of its O2. It also doesn't count the O2 which diffuses into the blood and is carried by the water. This is about 0.035 g / l, which is why we need hemoglobin - total blood saturation would carry about 1.15 g of O2. Hemoglobin multiplies the oxygen carrying capacity of blood by 100 fold.

CO2 is much more soluble in water (blood/tissue) than O2 is- about 1g/l. There is I think only 2 CO2 binding sites for hemoglobin, which means it carries out only half the CO2 oxygen that it carries in. Hemoglobin is is only considered to account for 10% of the total CO2 carrying capacity of humans. So calculating CO2 respiration by hemoglobin is not a good way to estimate blood CO2.

To get the answers you're looking for, you need a couple of figures to start with: (1) The amount of O2 dissolved in blood plasma: about 0.3 ml O2 per 100 ml plasma; (2) The amount of O2 bound to hemoglobin in blood: about 20 ml O2 per 100 ml blood. - Ref: (which also sources the figures used elsewhere here)

Blood makes up about 7% w/v of the human body, so a 70 Kg (154 lb) person will have about 4.9 litres of blood. 5 litres of blood would hold around 1 litre of O2 bound to the hemoglobin. However, around half of the blood will be venous, not arterial, and that only has about 75% O2 saturation, so the actual amount in arterial plus venous blood will be about 1/8 less than that calculation. Obviously, the figure will vary significantly with body weight.

At normal pressure, the arterial hemoglobin is effectively saturated with O2. However, if the ambient pressure increases, then the amount of O2 dissolved in the plasma will increase proportionately (Henry's Law). Similarly, breathing a gas with a greater O2 fraction will increase the amount of dissolved O2 in a linear fashion. Nevertheless, O2's low solubility means that the dissolved O2 is only about 1/60 of that bound to hemoglobin, so unless that is severely compromised (e.g. CO poisoning), increasing the pressure or fraction of O2 has little effect on the supply to the body.

As for the O2 stored in the body, each myoglobin molecule only binds 1 molecule of O2, compared with 4 molecules of O2 per molecule of hemoglobin, so it will contribute a much smaller amount to the total. Of course, that will vary again with body weight but also with the amount of muscle and other type of tissue making up the body.

Oxygen saturation (medicine)

Oxygen saturation is the fraction of oxygen-saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal arterial blood oxygen saturation levels in humans are 95–100 percent. If the level is below 90 percent, it is considered low and called hypoxemia. [1] Arterial blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules ( O
2 ) enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation.


Cardiovascular system

The essential components of the human cardiovascular system are the heart, blood and blood vessels. [6] It includes the pulmonary circulation, a "loop" through the lungs where blood is oxygenated and the systemic circulation, a "loop" through the rest of the body to provide oxygenated blood. The systemic circulation can also be seen to function in two parts – a macrocirculation and a microcirculation. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters) of blood, accounting for approximately 7% of their total body weight. [7] Blood consists of plasma, red blood cells, white blood cells, and platelets. Also, the digestive system works with the circulatory system to provide the nutrients the system needs to keep the heart pumping. [8]

The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of blood vessels. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enter interstitial fluid, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction. The other component of the circulatory system, the lymphatic system, is open.


Oxygenated blood enters the systemic circulation when leaving the left ventricle, through the aortic semilunar valve. The first part of the systemic circulation is the aorta, a massive and thick-walled artery. The aorta arches and gives branches supplying the upper part of the body after passing through the aortic opening of the diaphragm at the level of thoracic ten vertebra, it enters the abdomen. Later it descends down and supplies branches to abdomen, pelvis, perineum and the lower limbs. The walls of aorta are elastic. This elasticity helps to maintain the blood pressure throughout the body. When the aorta receives almost five litres of blood from the heart, it recoils and is responsible for pulsating blood pressure. Moreover, as aorta branches into smaller arteries, their elasticity goes on decreasing and their compliance goes on increasing.


Arteries branch into small passages called arterioles and then into the capillaries. [9] The capillaries merge to bring blood into the venous system. [10]


Capillaries merge into venules, which merge into veins. The venous system feeds into the two major veins: the superior vena cava – which mainly drains tissues above the heart – and the inferior vena cava – which mainly drains tissues below the heart. These two large veins empty into the right atrium of the heart.

Portal veins

The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart. Portal veins are a slight exception to this. In humans the only significant example is the hepatic portal vein which combines from capillaries around the gastrointestinal tract where the blood absorbs the various products of digestion rather than leading directly back to the heart, the hepatic portal vein branches into a second capillary system in the liver.


The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right atrium and right ventricle. The right atrium is the upper chamber of the right side of the heart. The blood that is returned to the right atrium is deoxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide. The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body.

Coronary vessels

The heart itself is supplied with oxygen and nutrients through a small "loop" of the systemic circulation and derives very little from the blood contained within the four chambers. The coronary circulation system provides a blood supply to the heart muscle itself. The coronary circulation begins near the origin of the aorta by two coronary arteries: the right coronary artery and the left coronary artery. After nourishing the heart muscle, blood returns through the coronary veins into the coronary sinus and from this one into the right atrium. Back flow of blood through its opening during atrial systole is prevented by Thebesian valve. The smallest cardiac veins drain directly into the heart chambers. [8]


The circulatory system of the lungs is the portion of the cardiovascular system in which oxygen-depleted blood is pumped away from the heart, via the pulmonary artery, to the lungs and returned, oxygenated, to the heart via the pulmonary vein.

Oxygen-deprived blood from the superior and inferior vena cava enters the right atrium of the heart and flows through the tricuspid valve (right atrioventricular valve) into the right ventricle, from which it is then pumped through the pulmonary semilunar valve into the pulmonary artery to the lungs. Gas exchange occurs in the lungs, whereby CO
2 is released from the blood, and oxygen is absorbed. The pulmonary vein returns the now oxygen-rich blood to the left atrium. [8]

A separate system known as the bronchial circulation supplies blood to the tissue of the larger airways of the lung.

Systemic circulation

Systemic circulation is the portion of the cardiovascular system which transports oxygenated blood away from the heart through the aorta from the left ventricle where the blood has been previously deposited from pulmonary circulation, to the rest of the body, and returns oxygen-depleted blood back to the heart. [8]


The brain has a dual blood supply that comes from arteries at its front and back. These are called the "anterior" and "posterior" circulation respectively. The anterior circulation arises from the internal carotid arteries and supplies the front of the brain. The posterior circulation arises from the vertebral arteries, and supplies the back of the brain and brainstem. The circulation from the front and the back join together (anastomise) at the Circle of Willis.


The renal circulation receives around 20% of the cardiac output. It branches from the abdominal aorta and returns blood to the ascending vena cava. It is the blood supply to the kidneys, and contains many specialized blood vessels.

Lymphatic system

The lymphatic system is part of the circulatory system in many complex animals such as mammals and birds. It is a network of lymphatic vessels and lymph capillaries, lymph nodes and organs, and lymphatic tissues and circulating lymph. One of its major functions is to carry the lymph, draining and returning interstitial fluid back towards the heart for return to the cardiovascular system, by emptying into the lymphatic ducts. Its other main function is in the adaptive immune system. [11]

The development of the circulatory system starts with vasculogenesis in the embryo. The human arterial and venous systems develop from different areas in the embryo. The arterial system develops mainly from the aortic arches, six pairs of arches that develop on the upper part of the embryo. The venous system arises from three bilateral veins during weeks 4 – 8 of embryogenesis. Fetal circulation begins within the 8th week of development. Fetal circulation does not include the lungs, which are bypassed via the truncus arteriosus. Before birth the fetus obtains oxygen (and nutrients) from the mother through the placenta and the umbilical cord. [12]



20 seconds of the average 60-second cycle) and shows the red blood cell deforming as it enters capillaries, as well as the bars changing color as the cell alternates in states of oxygenation along the circulatory system.

The human arterial system originates from the aortic arches and from the dorsal aortae starting from week 4 of embryonic life. The first and second aortic arches regress and form only the maxillary arteries and stapedial arteries respectively. The arterial system itself arises from aortic arches 3, 4 and 6 (aortic arch 5 completely regresses).

The dorsal aortae, present on the dorsal side of the embryo, are initially present on both sides of the embryo. They later fuse to form the basis for the aorta itself. Approximately thirty smaller arteries branch from this at the back and sides. These branches form the intercostal arteries, arteries of the arms and legs, lumbar arteries and the lateral sacral arteries. Branches to the sides of the aorta will form the definitive renal, suprarenal and gonadal arteries. Finally, branches at the front of the aorta consist of the vitelline arteries and umbilical arteries. The vitelline arteries form the celiac, superior and inferior mesenteric arteries of the gastrointestinal tract. After birth, the umbilical arteries will form the internal iliac arteries.


The human venous system develops mainly from the vitelline veins, the umbilical veins and the cardinal veins, all of which empty into the sinus venosus.

Cardiovascular system

About 98.5% of the oxygen in a sample of arterial blood in a healthy human, breathing air at sea-level pressure, is chemically combined with hemoglobin molecules. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species.

Lymphatic system

Many diseases affect the circulatory system. These include a number of cardiovascular diseases, affecting the cardiovascular system, and lymphatic diseases affecting the lymphatic system. Cardiologists are medical professionals which specialise in the heart, and cardiothoracic surgeons specialise in operating on the heart and its surrounding areas. Vascular surgeons focus on other parts of the circulatory system.

Cardiovascular disease

Diseases affecting the cardiovascular system are called cardiovascular disease.

Many of these diseases are called "lifestyle diseases" because they develop over time and are related to a person's exercise habits, diet, whether they smoke, and other lifestyle choices a person makes. Atherosclerosis is the precursor to many of these diseases. It is where small atheromatous plaques build up in the walls of medium and large arteries. This may eventually grow or rupture to occlude the arteries. It is also a risk factor for acute coronary syndromes, which are diseases that are characterised by a sudden deficit of oxygenated blood to the heart tissue. Atherosclerosis is also associated with problems such as aneurysm formation or splitting ("dissection") of arteries.

Another major cardiovascular disease involves the creation of a clot, called a "thrombus". These can originate in veins or arteries. Deep venous thrombosis, which mostly occurs in the legs, is one cause of clots in the veins of the legs, particularly when a person has been stationary for a long time. These clots may embolise, meaning travel to another location in the body. The results of this may include pulmonary embolus, transient ischaemic attacks, or stroke.

Cardiovascular diseases may also be congenital in nature, such as heart defects or persistent fetal circulation, where the circulatory changes that are supposed to happen after birth do not. Not all congenital changes to the circulatory system are associated with diseases, a large number are anatomical variations.


The function and health of the circulatory system and its parts are measured in a variety of manual and automated ways. These include simple methods such as those that are part of the cardiovascular examination, including the taking of a person's pulse as an indicator of a person's heart rate, the taking of blood pressure through a sphygmomanometer or the use of a stethoscope to listen to the heart for murmurs which may indicate problems with the heart's valves. An electrocardiogram can also be used to evaluate the way in which electricity is conducted through the heart.

Other more invasive means can also be used. A cannula or catheter inserted into an artery may be used to measure pulse pressure or pulmonary wedge pressures. Angiography, which involves injecting a dye into an artery to visualise an arterial tree, can be used in the heart (coronary angiography) or brain. At the same time as the arteries are visualised, blockages or narrowings may be fixed through the insertion of stents, and active bleeds may be managed by the insertion of coils. An MRI may be used to image arteries, called an MRI angiogram. For evaluation of the blood supply to the lungs a CT pulmonary angiogram may be used.


There are a number of surgical procedures performed on the circulatory system:

Cardiovascular procedures are more likely to be performed in an inpatient setting than in an ambulatory care setting in the United States, only 28% of cardiovascular surgeries were performed in the ambulatory care setting. [13]

In Ancient Greece, the heart was thought to be the source of innate heat for the body. The circulatory system as we know it was discovered by William Harvey.

While humans, as well as other vertebrates, have a closed blood circulatory system (meaning that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have an open circulatory system containing a heart but limited blood vessels. The most primitive, diploblastic animal phyla lack circulatory systems.

An additional transport system, the lymphatic system, which is only found in animals with a closed blood circulation, is an open system providing an accessory route for excess interstitial fluid to be returned to the blood. [5]

The blood vascular system first appeared probably in an ancestor of the triploblasts over 600 million years ago, overcoming the time-distance constraints of diffusion, while endothelium evolved in an ancestral vertebrate some 540–510 million years ago. [14]

Open circulatory system

In arthropods, the open circulatory system is a system in which a fluid in a cavity called the hemocoel bathes the organs directly with oxygen and nutrients, with there being no distinction between blood and interstitial fluid this combined fluid is called hemolymph or haemolymph. [15] Muscular movements by the animal during locomotion can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the heart relaxes, blood is drawn back toward the heart through open-ended pores (ostia).

Hemolymph fills all of the interior hemocoel of the body and surrounds all cells. Hemolymph is composed of water, inorganic salts (mostly sodium, chloride, potassium, magnesium, and calcium), and organic compounds (mostly carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is hemocyanin.

There are free-floating cells, the hemocytes, within the hemolymph. They play a role in the arthropod immune system.

Closed circulatory system

The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squids, octopuses and relatives) always keep their circulating blood enclosed within heart chambers or blood vessels and are classified as closed, just as in humans. Still, the systems of fish, amphibians, reptiles, and birds show various stages of the evolution of the circulatory system. [16] Closed systems permit blood to be directed to the organs that require it.

In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as single cycle circulation. The heart of fish is, therefore, only a single pump (consisting of two chambers).

In amphibians and most reptiles, a double circulatory system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.

In reptiles, the ventricular septum of the heart is incomplete and the pulmonary artery is equipped with a sphincter muscle. This allows a second possible route of blood flow. Instead of blood flowing through the pulmonary artery to the lungs, the sphincter may be contracted to divert this blood flow through the incomplete ventricular septum into the left ventricle and out through the aorta. This means the blood flows from the capillaries to the heart and back to the capillaries instead of to the lungs. This process is useful to ectothermic (cold-blooded) animals in the regulation of their body temperature.

Birds, mammals, and crocodilians show complete separation of the heart into two pumps, for a total of four heart chambers it is thought that the four-chambered heart of birds and crocodilians evolved independently from that of mammals. [17] Double circulatory systems permit blood to be repressurized after returning from the lungs, speeding up delivery of oxygen to tissues.

No circulatory system

Circulatory systems are absent in some animals, including flatworms. Their body cavity has no lining or enclosed fluid. Instead, a muscular pharynx leads to an extensively branched digestive system that facilitates direct diffusion of nutrients to all cells. The flatworm's dorso-ventrally flattened body shape also restricts the distance of any cell from the digestive system or the exterior of the organism. Oxygen can diffuse from the surrounding water into the cells, and carbon dioxide can diffuse out. Consequently, every cell is able to obtain nutrients, water and oxygen without the need of a transport system.

Some animals, such as jellyfish, have more extensive branching from their gastrovascular cavity (which functions as both a place of digestion and a form of circulation), this branching allows for bodily fluids to reach the outer layers, since the digestion begins in the inner layers.

The earliest known writings on the circulatory system are found in the Ebers Papyrus (16th century BCE), an ancient Egyptian medical papyrus containing over 700 prescriptions and remedies, both physical and spiritual. In the papyrus, it acknowledges the connection of the heart to the arteries. The Egyptians thought air came in through the mouth and into the lungs and heart. From the heart, the air travelled to every member through the arteries. Although this concept of the circulatory system is only partially correct, it represents one of the earliest accounts of scientific thought.

In the 6th century BCE, the knowledge of circulation of vital fluids through the body was known to the Ayurvedic physician Sushruta in ancient India. [18] He also seems to have possessed knowledge of the arteries, described as 'channels' by Dwivedi & Dwivedi (2007). [18] The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BCE. However, their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for the transport of air.

The Greek physician, Herophilus, distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Greek anatomist Erasistratus observed that arteries that were cut during life bleed. He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood that entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood. [19]

In 2nd-century AD Rome, the Greek physician Galen knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves.

Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through 'pores' in the interventricular septum, air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created 'sooty' vapors were created and passed to the lungs also via the pulmonary artery to be exhaled.

In 1025, The Canon of Medicine by the Persian physician, Avicenna, "erroneously accepted the Greek notion regarding the existence of a hole in the ventricular septum by which the blood traveled between the ventricles." Despite this, Avicenna "correctly wrote on the cardiac cycles and valvular function", and "had a vision of blood circulation" in his Treatise on Pulse. [20] [ verification needed ] While also refining Galen's erroneous theory of the pulse, Avicenna provided the first correct explanation of pulsation: "Every beat of the pulse comprises two movements and two pauses. Thus, expansion : pause : contraction : pause. [. ] The pulse is a movement in the heart and arteries . which takes the form of alternate expansion and contraction." [21]

In 1242, the Arabian physician, Ibn al-Nafis, became the first person to accurately describe the process of pulmonary circulation, for which he is sometimes considered the father of circulatory physiology. [22] [ failed verification ] Ibn al-Nafis stated in his Commentary on Anatomy in Avicenna's Canon:

". the blood from the right chamber of the heart must arrive at the left chamber but there is no direct pathway between them. The thick septum of the heart is not perforated and does not have visible pores as some people thought or invisible pores as Galen thought. The blood from the right chamber must flow through the vena arteriosa (pulmonary artery) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa (pulmonary vein) to reach the left chamber of the heart and there form the vital spirit. "

In addition, Ibn al-Nafis had an insight into what would become a larger theory of the capillary circulation. He stated that "there must be small communications or pores (manafidh in Arabic) between the pulmonary artery and vein," a prediction that preceded the discovery of the capillary system by more than 400 years. [23] Ibn al-Nafis' theory, however, was confined to blood transit in the lungs and did not extend to the entire body.

Michael Servetus was the first European to describe the function of pulmonary circulation, although his achievement was not widely recognized at the time, for a few reasons. He firstly described it in the "Manuscript of Paris" [24] [25] (near 1546), but this work was never published. And later he published this description, but in a theological treatise, Christianismi Restitutio, not in a book on medicine. Only three copies of the book survived but these remained hidden for decades, the rest were burned shortly after its publication in 1553 because of persecution of Servetus by religious authorities.

Better known discovery of pulmonary circulation was by Vesalius's successor at Padua, Realdo Colombo, in 1559.

Finally, the English physician William Harvey, a pupil of Hieronymus Fabricius (who had earlier described the valves of the veins without recognizing their function), performed a sequence of experiments and published his Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus in 1628, which "demonstrated that there had to be a direct connection between the venous and arterial systems throughout the body, and not just the lungs. Most importantly, he argued that the beat of the heart produced a continuous circulation of blood through minute connections at the extremities of the body. This is a conceptual leap that was quite different from Ibn al-Nafis' refinement of the anatomy and bloodflow in the heart and lungs." [26] This work, with its essentially correct exposition, slowly convinced the medical world. However, Harvey was not able to identify the capillary system connecting arteries and veins these were later discovered by Marcello Malpighi in 1661.

In 1956, André Frédéric Cournand, Werner Forssmann and Dickinson W. Richards were awarded the Nobel Prize in Medicine "for their discoveries concerning heart catheterization and pathological changes in the circulatory system." [27] In his Nobel lecture, Forssmann credits Harvey as birthing cardiology with the publication of his book in 1628. [28]

In the 1970s, Diana McSherry developed computer-based systems to create images of the circulatory system and heart without the need for surgery. [29]

Total amount of CO₂ / Oxygen in Bloodstream in Humans - Biology

Oxygen's influence and its role in Human Body

In the human body, the oxygen is absorbed by the blood stream in the lungs, being then transported to the cells where an elaborated change process takes place.

Oxygen plays a vital role in the breathing processes and in the metabolism of the living organisms.

Probably, the only living cells that do not need oxygen are some anaerobic bacteria that obtain energy from other metabolic processes.

The nutrient compounds, inside of the cell, are oxidized through complex enzymatic processes.

This oxidation is the source of energy of most of the animals, mainly of mammals.

The products are carbon dioxide and water (exhaled air has a relative humidity of 100%), which are eliminated by the human body through the lungs.

Click the link below to read more about:

Appropriate levels of oxygen are vital to support cell respiration. Oxygen plays an important role in the energy metabolism of living organisms.

The living cell is the site of tremendous biochemical activity called metabolism.

This is the process of chemical and physical change which goes on continually in the human body: build-up of new tissue, replacement of old tissue, conversion of food to energy, disposal of waste materials, reproduction - all the activities that we characterize as "life."

Research shows that cells have only a "limited number" of cell divisions possible in a human lifetime.

Studies show that by the time you're 20 most of the cells that make up your body have used up half of the divisions available in their cell lifespan.

By the time you're 40, there are maybe only 30% of your possible cell divisions left. When the cells use up their natural allotted cell divisions, the end is death!

Molecular oxygen, O 2 , is essential for cellular respiration in all aerobic organisms. Oxygen is used as an electron acceptor in mitochondria to generate chemical energy.

Take a look inside the cell to see these "powerhouses" of the cell,

In the human body, oxygen uptake is carried out by the following processes:

Oxygen diffuses through membranes and into red blood cells after inhalation into the lungs. The heme group (that consists of an iron) of hemoglobin binds oxygen when it is present, changing haemoglobin’s color from bluish red to bright red.

A liter of blood can dissolve 200 cc of oxygen gas, which is much more than water can dissolve.

After being carried in blood to a body tissue in need of oxygen, O2 is handed-off to an enzyme (monooxygenase) that also has an active site with an atom of iron.

The enzyme uses oxygen to catalyze many oxidation reactions in the body (metabolism). Carbon dioxide, a waste product, is released from the cell and into the blood, where it combines with bicarbonate and hemoglobin for transport to the lungs. Blood circulates back to the lungs and the process repeats.

A small part of the waste that comes from our body cells is watery, or easily dissolved in water Furthermore, this is transported in the blood to a specific set of filter organs—the liver and the kidneys—and poured out of the body as the urine.

Another part of waste is passed off through the skin in the form of watery vapor as perspiration, or sweat. But part of the waste can be gotten rid of only by burning, and what we call burning is another name for combining with oxygen, or to use one word—oxidation

Moreover, this is precisely the purpose of the carrying of oxygen by the little red blood cells from the lungs to the deeper parts of the body—to burn up, or oxidize, these waste materials which would otherwise poison our cells. When they are burnt, or oxidized, they become almost harmless.

While oxygen supports our life, and "oxidizes" or "burns" food to create energy and heat for our bodies, certain types of altered oxygen molecules called "Free Radicals" which are ever-present in our bodies, will damage our own cells and even our DNA, causing degeneration and diseases such as cancer.

A "radical" is an atom with an unbalanced electrical charge, and it will seek to steal electrons from other atoms - such as the atoms of our body cells!

As Dr. Tai likes to say, the oxidation of cells by free radicals makes the human body "rust" like oxidation of metal makes it rust - and you know what rust does to the strength and natural beauty of the metal.

Our bodies need the help of "antioxidants" to neutralize the oxidation properties of those invading free radicals.

There are thousands of research papers that point to the production of free radicals as the primary cause of aging.

Free radicals are unstable molecules in the body created as part of the waste products or normal cellular metabolic activities. YOU ARE ONLY AS OLD AS YOUR CELLS! Recent research has given new hope to the task of rejuvenating and extending the lifespan of cells.

This cellular rejuvenation, life extension, and improved vitality has been achieved using special antioxidants that can actually keep cells looking and acting younger - and may even reverse the aging process !

The human body represents one of the most perfectly designed and coordinated structures. However, all these structures are held in position by a dense network of systems which constantly work together to keep us going.

The brain represents only 2% of the human body weight it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization.

The energy consumption for the brain to simply survive is 0.1 calories per minute, while this value can be as high as 1.5 calories per minute during crossword puzzle-solving.

When neurons in a particular region of the brain are highly active, they consume a great deal of oxygen, which results in recruitment of extra blood flow to that region.

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, motor neurone disease, and Huntington's disease are caused by the gradual death of individual neurons, leading to decrements in movement control, memory, and cognition.

Mental performance in the human body can be improved by "feeding" the brain with extra oxygen or glucose, according to research published today that could have implications for the treatment of dementia.

It's well known that after about nine minutes of no oxygen, from drowning or whatever, you can kiss your brain good-bye. Brain cells are extremely sensitive to oxygen deprivation and can begin to die within five minutes after oxygen supply has been cut off.

Decrease of oxygen supply to the brain even though there is adequate blood flow caused by carbon monoxide poisoning, pollution in our cities, choking or suffocation can create conditions like tiredness, depression, irritability, poor judgment and health problems.

Increasing the oxygen supply to the brain and nervous system will reverse these conditions.

The oxygen regimen improves alertness, reflexes, memory and apparently intelligence, and may offer the elderly a new weapon against senility and related disorders. Alzheimer's and Parkinson's are reported to be responding to it. Alcoholics who start taking oxygen supplement soon loose interest in alcohol.

Chemical composition of the human body

The size of the human body is firstly determined by diet and secondly by genes. Body type (slim, fat, tall, petite, wide-shouldered, etc) and body composition (percentages of fat, bone and muscle) are influenced by postnatal factors such as diet and exercise.

By the time the human reaches adult-hood, the body consists of close to 100 trillion cells. Each is part of an organ system designed to perform essential life functions.

By mass, human cells consist of 65-90% water (H2O), and a significant portion is composed of carbon-containing organic molecules. Oxygen therefore contributes a majority of a human body's mass, followed by carbon.

99% of the mass of the human body is made up of the six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.

In order to understand the relation of food to the sustenance and repairing of the body, it will be necessary to learn, first, of what the human body is composed, and the corresponding elements contained in the food required to build and keep the body in a healthy condition.

The following table gives the approximate analysis of a man weighing 148 pounds:


The microcirculation deserves special attention since it is across the walls of these vessels that the exchange of oxygen, among other substances, takes place [82]. Furthermore, the arterioles, also known as the “resistance” vessels, are the primary site for control of blood flow. Thus, the blood vessels of the microcirculation play important roles in both the convective (arterioles) and diffusive (capillaries) transport of oxygen. These blood vessels are classified as arterioles, capillaries and venules and vary in diameter from about 100� μm for the largest arterioles and venules down to about 5 μm for capillaries. In terms of their structure, all these vessels possess an inner layer of endothelial cells. In addition, the arterioles have a circumferential layer of vascular smooth muscle with which they can control blood flow and its distribution within organs. Venules typically have thinner layers of smooth muscle.

The primary function of the circulatory system is to exchange substances between blood and tissue, and these exchange processes take place in the microcirculation. The classes of vessels playing a role there are the arterioles (resistance vessels which regulate flow), capillaries (the primary exchange vessels) and venules (exchange and collecting vessels). The amount of flow through the capillaries appears to be regulated to maintain adequate tissue oxygenation. The regulation of blood flow appears to be accomplished by the coordination of several different mechanisms which affect the flow of blood through precapillary vessels.

For small multicellular organisms, diffusion across the outer membrane is sufficient to meet their oxygen needs. Gas exchange by direct diffusion across surface membranes is efficient for organisms less than 1 mm in diameter. In simple organisms, such as cnidarians and flatworms, every cell in the body is close to the external environment. Their cells are kept moist and gases diffuse quickly via direct diffusion. Flatworms are small, literally flat worms, which “breathe” through diffusion across the outer membrane. The flat shape of these organisms increases the surface area for diffusion, ensuring that each cell within the body is close to the outer membrane surface and has access to oxygen. If the flatworm had a cylindrical body, then the cells in the center would not be able to get oxygen.

This flatworm’s process of respiration works by diffusion across the outer membrane. (credit: Stephen Childs)

The Oxygen Cycle

Photosynthesis is the driver of the oxygen cycle. In this process, plants transform CO2 and water into sugars to use in their metabolism, help them to grow and to provide food for other organisms. The atmosphere, the total content of biological matter on the planet and the Earth’s crust are the three main reservoirs of oxygen. About 20% of the Earth’s atmosphere is composed of molecular oxygen. Some atmospheric oxygen is in the form of ozone (CO3) which makes up the ozone layer and absorbs much of the sun’s ultraviolet radiation, protecting the planet surface. Scientists think that early in the Earth’s history, oxygen was first released into the atmosphere by the action of ultraviolet light on water vapor.

Breathing & Respiratory System

When we breathe in and out we suck air into them then expel it again.

Oxygen is absorbed from the lungs into the blood, and carbon dioxide is removed from the blood and breathed out from the lungs. This exchange is vital.

This video explains more about out lungs and how they work

Respiratory System

Respiration is the release of energy from glucose or other organic substances. Energy is required for growth, repair, movement and other metabolic activities. There are two main types of respiration, aerobic and anaerobic.

This video explains respiration

Alveoli are the final branchings of the respiratory tree and act as the primary gas exchange units of the lung

Used for exchanging gases: Deoxygenated enters lungs from body, oxygenated enters capillaries from lungs

Advantages of alveoli

Aerobic Respiration

Aerobic respiration takes place in the presence of oxygen. Aerobic respiration = glucose reacts with oxygen to release energy. Carbon dioxide and water are released as waste products.

Glucose molecules react with oxygen molecules to form carbon dioxide and water molecules, with energy being released by the breaking of bonds in the glucose molecules. Our bodies require energy for the seven life processes This energy is obtained from respiration.

glucose + oxygen > water + carbon dioxide + energy .

We use the energy released from respiration for many processes. Respiration also gives off heat, which is used to maintain our high body temperature. Our rate of respiration can be estimated by measuring how much oxygen we use. During exercise, the body needs more energy and so the rate of respiration increases - The breathing rate increases to obtain extra oxygen and remove carbon dioxide from the body. The heart beats faster so that the blood can transport the oxygen and carbon dioxide faster. This is why our pulse rate increases. It is actually the build up of carbon dioxide that makes us breathe faster.

Glucose comes from our food, oxygen and from breathing

Water and carbon dioxide are exhaled

This video looks at Aerobic Respiration

Anaerobic respiration

Anaerobic respiration occurs when oxygen is not available. When not enough oxygen is available, glucose can be broken down by anaerobic respiration. This may happen during hard exercise.

Glucose is only partially broken down, and lactic acid is produced - together with a much smaller amount of energy.

Energy can still be produced without oxygen

Only a little bit of energy is obtained from respiration

glucose > lactic acid + energy

Anaerobic respiration occurs in humans when oxygen is not obtained quick enough (e.g. running fast)

Only 1/20th energy amount is produced compared to aerobic respiration

Lactic acid builds up, which causes muscle fatigue due to oxygen debt . This is overcome by deep breathing to oxidise the acid. After the exercise is finished, extra oxygen is needed by the liver to remove the lactic acid.

  • Anaerobic respiration releases less than half the energy of that released by aerobic respiration.
  • Anaerobic respiration produces lactic acid. Lactic acid causes muscle fatigue and pain.

This video explains Human Respiration covering Aerobic and Anaerobic respiration.

Don’t forget to breathe

There are many everyday situations in which holding your breath is very detrimental to your health and well being. Apnea is the medical term for the temporary cessation of breath, and sleep apnea is a major cause of high blood pressure and other heart ailments, as well as diabetes and depression.

More directly relevant to our working lives is what writer Linda Stone calls email apnea, “a temporary absence or suspension of breathing, or shallow breathing, while doing email.” Both Stone and Nestor consulted with Dr. Margaret Chesney of UCSF, who’s been researching stress for forty years. Chesney demonstrated in a paper from 2002 the connection between perceived stress and diminished resting breathing rate, resulting from breath holding, and showed the effect is stronger in women than in men.

Stone related this interruption of breathing to a phenomenon that digitally-mediated work has made familiar to many of us, what she calls continuous partial attention. Simple multitasking involves sharing our attention between an undemanding background task and a more demanding foreground task, like eating lunch at your desk while replying to email. With continuous partial attention we’re constantly switching between many cognitively demanding activities: The now daily experience of being on a Zoom call while simultaneously monitoring a Slack channel and our email inboxes.

“A large percentage of the population now, they’re half awake when they're trying to sleep and they’re half asleep when they’re trying to be awake and work.” —James Nestor

“A large percentage of the population now, they’re half awake when they're trying to sleep and they’re half asleep when they’re trying to be awake and work,” says Nestor. “We’ve gotten so accustomed to this constant low-grade stress.”

Reduced heart rate variability may be one of the underlying causes of sustained distractibility at work and may explain the connection between fitness and focus. A 2019 meta-analysis of relevant research concluded that “slow breathing techniques enhance autonomic, cerebral and psychological flexibility,” including increased heart rate variability. A 2016 University of Wisconsin-Madison study showed that short term awareness of breath reduced “the negative attentional effects associated with heavy media multitasking.” As is often the case, we can enlist one technology to help us manage another.


Hemoglobin is a protein found in red blood cells that is comprised of two alpha and two beta subunits that surround an iron-containing heme group. Oxygen readily binds this heme group. The ability of oxygen to bind increases as more oxygen molecules are bound to heme. Disease states and altered conditions in the body can affect the binding ability of oxygen, and increase or decrease its ability to dissociate from hemoglobin.

Carbon dioxide can be transported through the blood via three methods. It is dissolved directly in the blood, bound to plasma proteins or hemoglobin, or converted into bicarbonate. The majority of carbon dioxide is transported as part of the bicarbonate system. Carbon dioxide diffuses into red blood cells. Inside, carbonic anhydrase converts carbon dioxide into carbonic acid (H2CO3), which is subsequently hydrolyzed into bicarbonate (HCO − 3) and H + . The H + ion binds to hemoglobin in red blood cells, and bicarbonate is transported out of the red blood cells in exchange for a chloride ion. This is called the chloride shift. Bicarbonate leaves the red blood cells and enters the blood plasma. In the lungs, bicarbonate is transported back into the red blood cells in exchange for chloride. The H + dissociates from hemoglobin and combines with bicarbonate to form carbonic acid with the help of carbonic anhydrase, which further catalyzes the reaction to convert carbonic acid back into carbon dioxide and water. The carbon dioxide is then expelled from the lungs.

Watch the video: Μικρή και μεγάλη κυκλοφορία του αίματος 2 (December 2022).