Skin is an accessory organ of respiration in
Frog has lungs as its main respiratory organs but during hibernation & aestivation and during its habitat in water it respires through skin
The alveolar epithelium in the lungs is
The very thin alveolar wall (about 0.0001 mm) is composed of moist, nonciliated, squamous epithelial cells.
Carbon dioxide is transported from tissues to respiratory surface by only 
CO2 from the respiratory tissues to the lungs is transported by the blood in 3 ways :
(i) In dissolved state or as a physical solution : Very small amount physically dissolved in plasma (7% i.e. @ 0.3 ml of CO2 by each 100 ml of blood)
(ii) Bicarbonate ions : @ 70% (i.e. @ 2.5 ml per 100 ml of blood) CO2 diffuses in plasma & then into RBCs where it (in the presence of carbonic anhydrase) combines with H2O to form carbonic acid which is almost spontaneously dissociated into hydrogen ion & bicarbonate ions.
(iii) Carbaminohaemoglobin : @ 23% (i.e. @ 1 ml of CO2 per 100 ml of blood) combines with haemoglobin forming an unstable compound
Oxygen dissociation curve of haemoglobin is
It is the relationship between the percentage saturation of haemoglobin (by volume) in the blood and the oxygen tension (in partial tension) PO2 of the blood.
It is usually a sigmoid plot. Haemoglobin molecules can bind up to four oxygen molecules in a reversible way. The shape of the curve results from the interaction of bound oxygen molecules with incoming molecules. The binding of the first molecule is difficult. However, this facilitates the binding of the second and third molecules, and it is only when the fourth molecule is to be bound that the difficulty increases, partly as a result of crowding of the haemoglobin molecule, partly as a natural tendency of oxygen to dissociate.
The O2-Hb dissociation curve is a sigmoidal curve that represents the relationship between O2 concentration and the percentage saturation of Hb. As the concentration increases from about 90% there is a significant plateau in the curve, which has several important biological repercussions.
Air is breathed through 
The pathway of inhaled air is - Nostrils - pharynx (common passage for food & air) - larynx (voice box) - trachea (the wind pipe) - bronchi (2 for each side lungs) - bronchioles (give arise to alveolar ducts) - alveoli (the exchange site for gases in the form of small sacs or pouches).
Although much CO2 is carried in blood, yet blood does not become acidic, because 
CO2 enters RBC and reacts with water to form carbonic acid. Carbonic acid dissociates to form bicarbonate and hydrogen ions. Some bicarbonate ions are transported in erythrocytes while some diffuse into the blood plasma. Exit of bicarbonate ions change the ionic balance between the plasma and erythrocytes. To restore this balance chloride ions diffuse from plasma into erythrocytes. Due to this the pH of blood is maintained.
The carbon dioxide is transported via blood to lungs as 
Carbon dioxide is transported via blood to lungs mostly as carbaminohaemoglobin and carbonic acid. It is released in lungs in exchange with oxygen.
People living at sea level have around 5 million RBC per cubic millimeter of their blood whereas those living at an altitude of 5400 metres have around 8 million. This is because at high altitude [1995, 2006]
At the altitude of 5400 meters the low atmospheric pressure of O2 will be too low so the solubility of oxygen in the blood will be very less hence the oxygen carried by each RBC will be too less. But to fulfill the oxygen requirement of the body blood has to carry more oxygen to the body tissue and this is done by the increased no. of RBCs.
The quantity 1500 ml in the respiratory volumes of a normal human adult refers to 
Residual air is the volume of air that remains in the lungs after the most forceful expiration. It equals to 1500 mL. Residual air mostly occurs in alveoli. Maximum air that can be breathed in and breathed out is vital capacity (3500-4500 mL) while the air that can be expired over and above the tidal air by most forceful expiration is the expiratory reserve volume (1200 mL).
In alveoli of the lungs, the air at the site of gas exchange, is separated from the blood by
Alveoli are the site of the respiratory exchange of gases. Oxygen from the alveolar air diffuses through the alveolar epithelium and the capillary endothelium into the capillary blood and carbon dioxide diffuses in the opposite direction.
The exchange of gases in the alveoli of the lungs takes place by 
Gaseous exchange between blood (dissolved phase) and alveolar air (gaseous phase) across respiratory membrane occurs by simple diffusion. Obviously, it depends upon the concentration gradient (=partial pressure) of the concerned gases in blood and alveolar air.
The process of migration of chloride ions from plasma to RBC and of carbonate ions from RBC to plasma is 
During the transport of CO2 through the blood, bicarbonate ions diffuse out of RBCs while chloride ions from plasma enter the RBCs to maintain ionic equilibrium. This is called chloride shift.
Which one of the following organs in the human body is most affected due to shortage of oxygen? 
Brain is the most vital organ. It stops functioning in the absence of O2.
When CO2 concentration in blood increases, breathing becomes 
The breathing becomes faster and deeper in order to oxygenate the blood at a fast rate. Shallow and slow breathing occurs during rest.
Blood analysis of a patient reveals an unusually high quantity of carboxyhaemoglobin content. Which of the following conclusions is most likely to be correct?The patient has been inhaling polluted air containing unusually high content of 
Carboxyhaemoglobin is the stable product formed by the association of CO and Hb in the blood. The association of carbon dioxide and haemoglobin forms carbamino haemoglobin.
Which one of the following mammalian cells is not capable of metabolising glucose to carbon-dioxide aerobically? 
Since RBCS do not have mitochondria so they can respire only anaerobically.
Intercostal muscles occur in 
Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. Theintercostal muscles are mainly involved in the mechanical aspect of breathing. These muscles help expand and shrink the size of the chest cavity to facilitate breathing.Inter-coastal muscles occur in the ribs.
What is vital capacity of our lungs?
Vital capacity of lungs is largest possible expiration after largest possible inspiration that is greatest. Volume of air can be exchanged in single respiration or amount of air breath in and out with greatest possible efforts.
VC = TRV +TV + ERV
= 3000 + 500 + 1100
= 4600 ml.
Listed below are four respiratory capacities (i–iv) and four jumbled respiratory volumes of a normal human adult: 
Which one of the following is the correct matching of two capacities and volumes?
Correct Answer :- c
Explanation : The correct matching of respiratory capacities with their respiratory volumes are : Respiratory Capacities Respiratory Volumes Residual Volume 1200mL
Vital capacity 4500mL Inspiratory reserve volume 2500mL Inspiratory volume 3500mL
Which two of the following changes (a–d) usually tend to occur in the plain dwellers when they move to high altitudes (3,500 m or more)? 
(i) Increase in red blood cell size
(ii) Increase in red blood cell production
(iii) Increased breathing rate
(iv) Increase in thrombocyte count
Changes occurring are:
At high altitude, the body undergoes numerous changes in order to increase oxygen delivery to cells and improve the efficiency of oxygen usage. The early changes include increased breathing rate and increased red blood cell production
Which one of the following is a possibility for most of us in regard to breathing, by making a conscious effort? [2011M]
During breathing, 20% oxygen is taken in and 15% oxygen is exhaled out. Movement of diaphragm is very important during breathing process. Ribs will also move in and out with the diaphragm. It is not possible to breathe by moving the diaphragm along without moving ribs. Even after forceful exhalation, lungs are never fully emptied. Residual volume, that is minimum amount of air in lungs always remain at all times. Eustachian tube connects middle ear cavity with nasopharynx and hence, one can breathe out air through it by closing both nose and mouth.
Which of the following are the correct statement for respiration in human 
Correct Answer :- c
Explanation : Cigarette smoking causes an immunogenic response. It results in increased levels of inflammatory markers. It may result in the development of irreversible narrowing of bronchial tubes due to inflammation and scarring. It causes cancer, chronic lung disease. The pneumotaxic center in the pons region of the brainstem moderate the functions of the respiratory rhythm centre. It reduces the duration of inspiration and therefore alters the respiratory rate. Workers in grinding and stone-breaking industries may suffer from lung fibrosis. Exposure to environmental pollutants like silica, metal dusts, bacteria and animal proteins can lead to lung fibrosis. Carbon dioxide is carried in blood as bicarbonate, dissolved CO2 and carbaminohemoglobin. About 29% of it is carried as carbaminohemoglobin.
The figure shows a diagrammatic view of human respiratory system with labels A, B, C and D. Select the option which gives correct identification and main function and/or characteristics. [NEET 2013]
Alveoli are very thin, irregular walled bag like structures for gaseous exchange. Tracheae bronchi and bronchioles are supported by incomplete cartilaginous rings. Double layered pleural membrane surrounds the lungs with pleural fluid between them. It reduces friction on the lung surface.
Figure shown schematic plan of blood circulation in humans with labels A to D. Identify the label and give its function’s. [NEET 2013]
A is Pulmonary vein which takes pure blood from lungs to heart. B is dorsal aorta which takes pure blood from heart to various body parts. C is Vena cava which takes impure blood from various body pars to right auricle of heart. D is pulmonary artery which takes impure blood from heart to lungs.
Which one of the following is one of the paths followed by air/O2 during respiration in an adult male Periplaneta americana as it enters the animal body? [NEET Kar. 2013]
The number of spiracles in cockroach is 10-pairs (2-pairs in thoracic and 8-pairs in abdominal region). The thoracic pairs of spiracles are present on pleuron between prothorax - mesothorax and metathorax. Each spiracle opens into a chamber called atrium. After atrium the tracheal tube ramifies into fine branches of tracheae, and then tracheoles.