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The Breathing Process - Questions and Answers
1. What is the difference between respiration meaning gas exchange and cellular respiration?
Respiration meaning gas exchange is the process in which an organism absorbs from the environment gases necessary for its cellular metabolism and expels gases that are products of this metabolism. Cellular respiration (aerobic or anaerobic) is the chemical reaction in which organic molecules are degraded to make ATP molecules, the main energy source for the metabolism.
Gas exchange is fundamental for cellular respiration since the supplying of some reagents (oxygen, in aerobic cellular respiration) and the expelling of some products (e.g., carbon dioxide) of this chemical reaction depends on gas exchange.
2. What is the chemical equation of the aerobic cellular respiration?
The chemical equation of the aerobic cellular respiration is the following:
C6H12O6 + 6 O2 + 36 ADP + 36 P --> 6 CO2 + 6 H2O + 36 ATP
3. Considering the chemical equation of the aerobic cellular respiration which molecules does the cell need and which molecules does it liberate in the process?
Considering the chemical equation of the aerobic cellular respiration it is observed that glucose and molecular oxygen are needed as reagents and carbon dioxide and water are released. The process also spends ADP and phosphate that turn into ATP.
4. What are the different types of gas exchange that occur in animals?
In beings from the kingdom Animalia the gas exchange may occur either by diffusion, tracheal respiration, cutaneous respiration, branchial respiration or pulmonary respiration.
5. Oxygen comes from the environment and carbon dioxide in the end returns to the environment. How do small animals solve the problem of taking away and bringing these molecules from/to their cells? Why isn't that solution possible for larger animals?
Small animals whose tissues make direct contact or are very close to the environment, like cnidarians and poriferans, make gas exchange by diffusion.
Larger animals with cells without direct contact with the environment or far from it need special gas transportation systems. In these animals the respiratory and the circulatory systems play this role.
Breathing Process Review - Image Diversity: respiratory system
6. Beings from four phyla of the animal kingdom “breath” (do gas exchange) by diffusion. Which are those phyla? How is this type of respiration associated to features present in those animals?
The phyla of the animal kingdom whose beings do gas exchange by diffusion are the poriferans, the cnidarians, the platyelminthes (flatworms) and the nematodes (roundworms). This type of respiration in these beings is possible because their tissues and cells are relatively close to the exterior.
7. Which animals make tracheal respiration? Is there a blood-like fluid that participates in this process?
Insects and arachnids are the arthropod animals that make tracheal respiration. In the body surface of these animals there are many orifices called spiracles that communicate with small tubules, the tracheae, through which air penetrates and carbon dioxide is expelled. The tracheae ramify into tracheoles that reach all tissues of the animal.
In the circulatory system of insects the blood only transports nutrients; gases are independently transported by the tracheal system.
8. What is the difference between respiration by diffusion and cutaneous respiration? Does blood participate in cutaneous respiration?
Cutaneous respiration is not as simple as diffusion. In diffusion the gases diffuse directly between the external environment and the cells. In cutaneous respiration molecular oxygen penetrates through the skin and it is collected by the blood circulation that then distributes the gas to the tissues. Carbon dioxide is also collected from the tissues by the blood and taken to the skin to be eliminated to the environment. So there is important participation of blood in cutaneous respiration.
Breathing Process Review - Image Diversity: cutaneous respiration
9. Which animals make cutaneous respiration?
Terrestrial annelids and adult amphibians make cutaneous respiration (in amphibians there is also pulmonary respiration).
The thin skin and the need for living in moist surrounds are typical features of these animals are.
10. What are branchiae? What are examples of animals that “breath” through branchiae?
Branchiae, also known as gills, are small portions of richly vascularized tissues internal or external to the body and in direct contact with the surrounding water. The gills are organs that make gas exchange in aquatic annelids, crustaceans, fishes and amphibian larvae (e.g., tadpoles).
Breathing Process Review - Image Diversity: gills
11. What is the difference between gills and lungs?
Gills and lungs are richly vascularized organs that serve for gas exchange between the environment and the circulatory system.
The lungs differentiate from gills in that they are saclike structures always internal to the organism and specialized in gas exchange in terrestrial environment. Branchiae, in their turn, are internal or external laminar structures in direct contact with water and specialized in gas exchange in aquatic environment.
Breathing Process Review - Image Diversity: lungs
12. Besides vertebrates two invertebrate phyla contain species that make pulmonary respiration. Which are these phyla?
Terrestrial molluscs and the arachnid arthropods are the invertebrates that present pulmonary-like respiration. Some terrestrial molluscs have a mantle cavity filled with air that makes contact with richly vascularized tissues that work as rudimentary lungs. Besides their tracheal respiration some arachnids have book lungs (thin folds resembling leaves of a book) that make gas exchange.
13. What are the three types of respiration in which the circulatory system transports gases?
The circulatory system has an important role in cutaneous respiration, branchial respiration and pulmonary respiration. The respiratory function of the blood is tailored for transportation of gases for exchange between tissues and respiratory surfaces in contact with the exterior (skin, gills, lungs).
14. What are respiratory pigments? What are some respiratory pigments and in which animal groups can each of them be found?
Respiratory pigments are molecules present in the blood that bind to oxygen transporting it to the tissues.
In vertebrates the respiratory pigment is hemoglobin, reddish due to the iron of its composition. In crustacean and arachnid arthropods and in some molluscs the respiratory pigment is hemocyanin, blue due to the copper of its composition. Annelids have hemoglobin, hemerythrin and chlorocruorin as respiratory pigments.
Breathing Process Review - Image Diversity: respiratory pigments
15. What are the organs that form the human respiratory system?
The organs that are part of the human respiratory system can be divided into three groups: lungs, airway and respiratory muscles.
The lungs are the right and the left lungs made of alveoli where gas exchange (entrance of oxygen and exit of carbon dioxide) takes place; the lungs are covered by the pleura (a serous membrane). The airway comprehends the nose, the pharynx, the larynx (including the vocal cords), the trachea, the bronchi and the bronchioles. The muscles upon which the breathing process depends are mainly the diaphragm and the intercostal muscles (muscles between the ribs).
Breathing Process Review - Image Diversity: airway
16. What is the anatomical reason for the left bronchus to be more elevated than the right bronchus? Why in most cases of aspiration of foreign material by children is the object found in the right bronchus?
The left bronchus is more elevated than the right bronchus because of the position of the heart in the left side of the chest, anterior and inferior to the left bronchus.
Accidentally aspired objects are frequently found in the right bronchus because the inferior angle between the trachea and this bronchus is lower than the inferior angle between the trachea and the left bronchus since the left bronchus is more horizontalized. Therefore aspired objects tend to fall in the right side (bronchus) and not in the left.
17. How does the body defend itself from microorganisms and other harmful substances that enter the airway during the breathing process?
The epithelium of the airway is a ciliated epithelium and has mucus-secreting specialized cells. The secreted mucus covers the internal wall of the airway retaining organisms and foreign particles that then are swept by the cilia of the epithelium.
In the mucous ciliated epithelium of the airway there is also intense activity of the immune system with antibodies and leukocytes inactivating and destroying foreign agents.
Other defense mechanisms of the airway are the sneeze and the cough. They help the elimination of solid and semifluid particles like pathologic residuals (sputum) and accidentally aspired objects.
Breathing Process Review - Image Diversity: airway epithelium
18. Which are the respiratory muscles in mammals?
In mammals the muscles that participate in the breathing process are the diaphragm and the intercostal muscles. In respiratory insufficiency other muscles can help the respiration, the muscles of the shoulders, neck, thorax and abdomen.
Breathing Process Review - Image Diversity: respiratory muscles
19. How are inhalation and expiration carried out?
The diaphragm (exclusive of mammals) and the intercostal muscles can contract or relax varying the volume of the thorax (the compartment where the lungs are located). The changing of the thorax volume forces inhalation or expiration.
When the thorax volume is increased an internal pressure lower than the atmospheric pressure (external) is created and gases naturally enter the lungs. When the thorax volume is lowered the internal pressure rises above the external pressure and the air is expelled from the lungs.
20. What is the difference between arterial and venous blood?
Arterial blood is the oxygen-rich and carbon dioxide-poor blood that irrigates the tissues. Venous blood is the oxygen-poor and carbon dioxide-rich blood collected from the tissues.
21. What is hematosis? In humans where does hematosis occur?
Hematosis is the oxygenation of the blood. Venous blood (oxygen-poor) after hematosis is transformed into arterial blood (oxygen-rich).
In humans hematosis takes place in the lungs.
22. What are the blood vessels that carry venous blood to the heart? What is the blood vessel that collects arterial blood from the heart?
The blood vessels that debouch in the heart carrying venous blood are the inferior and the superior vena cava. The blood vessel that carries arterial blood from the heart is the aorta.
Breathing Process Review - Image Diversity: vena cava aorta
23. What is the gas exchange unit of the mammalian lungs?
The gas exchange units of the mammalian lungs are the alveoli.
Breathing Process Review - Image Diversity: alveoli
24. What is the physical process through which gas exchange is accomplished in the pulmonary alveoli?
The gas exchange (entry of oxygen and exit of carbon dioxide) in the pulmonary alveoli occurs by simple diffusion in favor of the partial pressure gradient.
When the oxygen partial pressure in the inhaled air is higher than the oxygen partial pressure of the capillaries of the alveoli the air diffuses to the circulatory system. If the oxygen partial pressure in the air is lower (a rare situation since the blood that reaches the alveoli is venous blood) the oxygen exits the circulatory system. The same is true for carbon dioxide.
25. What is the structure of the central nervous system that regulates pulmonary respiration?
The pulmonary respiration is controlled by the neural respiratory center located within the medulla (the lower part of the brain continuous to the spinal cord).
Breathing Process Review - Image Diversity: medulla respiratory center
26. What is the chemical equation of the formation of bicarbonate from carbon dioxide and water? What is the enzyme that catalyzes this reaction?
The chemical equation of the chemical equilibrium of the formation of bicarbonate having as reagents carbon dioxide and water is as follows:
CO2 + H20 --> H2CO3 --> H+ + HCO3-
The reaction is catalyzed by the enzyme carbonic anhydrase present in red blood cells.
27. What are the consequences of shifting the chemical equilibrium of the formation of bicarbonate from carbon dioxide and water towards the increase of product (bicarbonate) formation?
The increase in product formation in the chemical equilibrium of the formation of bicarbonate from carbon dioxide and water heightens the concentration of hydrogen ions and thus lowers the pH of the solution.
28. What are the consequences of shifting the chemical equilibrium of the formation of bicarbonate from carbon dioxide and water towards the consumption of products of the reverse reaction?
The shifting of the chemical equilibrium of the formation of bicarbonate from carbon dioxide and water into the reverse reaction (production of water and carbon dioxide) means spending of hydrogen ions and thus it increases the solution pH.
29. How does the pulmonary ventilation affect the carbon dioxide concentration in blood? What happens to the carbon dioxide concentration and to the blood pH when the respiratory frequency is either lowered or increased?
The pulmonary ventilation frequency (number of inhalations per time unit) rises or lowers the carbon dioxide concentration in blood. If it is intense the gas is more eliminated to the exterior and if it is reduced the gas is retained inside the organism.
Applying the principles of chemical equilibriums to the formation of bicarbonate from carbon dioxide and water one gets the following: if the carbon dioxide concentration is increased the equilibrium shifts towards the formation of bicarbonate and liberation of hydrogen ions and the pH of the solution is lowered; if the carbon dioxide concentration is lowered the equilibrium shifts reversely towards the formation of water and carbon dioxide and also of more hydrogen ions spending and the pH of the solution is raised.
30. What are acidosis and alkalosis?
Acidosis is the condition in which the blood pH is abnormally low. Alkalosis is the condition in which the blood pH is abnormally high. Normal pH levels for the human blood are between 7.35 and 7.45 - slightly alkaline.
31. How does the breathing process correct acidosis?
If the body experiences acidosis the respiratory center located in the medulla gets the information and induces the increase of the respiratory frequency. The increment of the respiratory frequency makes the body eliminate more carbon dioxide and to shift the equilibrium of the formation of bicarbonate towards the spending of more hydrogen ions and thus the blood pH raises.
32. How does the breathing process correct alkalosis?
If the body undergoes alkalosis the respiratory center located in the medulla gets the information and induces the lowering of the respiratory frequency. The reduction of the respiratory frequency makes the body retain more carbon dioxide and to shift the equilibrium of the formation of bicarbonate towards the production of more hydrogen ions and thus the blood pH lowers.
33. What is the difference between respiratory acidosis and metabolic acidosis and what is the difference between respiratory alkalosis and metabolic alkalosis?
Respiratory acidosis is that in which the blood pH is low due to increased retention of carbon dioxide caused by the lowering of the respiratory frequency or by pulmonary diseases that impair the gas exchange. So the cause of the respiratory acidosis is the pulmonary respiration. Metabolic acidosis is that in which the blood pH is low not due to the pulmonary retention of carbon dioxide but due to metabolic disturbances. Some metabolic disturbances result in liberation in the blood of nonvolatile acids that release hydrogen ions lowering the blood pH (e.g., diabetic ketoacidosis).
Respiratory alkalosis is that in which the pH is high due to increased expelling of carbon dioxide caused by elevated respiratory frequency. Metabolic alkalosis is the alkalosis caused by metabolic disturbances that increase the concentration of bases (alkalis) in the blood.
34. Where are the chemoreceptors that detect the acidity of the blood and trigger the respiratory compensation located?
The chemoreceptors that participate in the ventilation control are structures that collect information about the acidity and alkalinity of the blood. The information is then transmitted by nervous fibers to the respiratory center located within the medulla. The center then commands the respiratory muscles to compensate the abnormal pH.
There are central and peripheral chemoreceptors. Peripheral chemoreceptors of pH, carbon dioxide partial pressure and oxygen partial pressure are located in the walls of the aorta and of the carotid arteries. Central chemoreceptors that get pH information are located within the medulla in the respiratory center. (The pulmonary ventilation is also controlled by receptors that receive pH information from the cerebrospinal fluid.)
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