Tag: transport of respiratory gases

Every living cell requires oxygen for performing cellular respiration. In unicellular organisms (e.g amoeba), the single cell is in direct contact with environment. Oxygen passes into it through diffusion. In simple multicellular organisms (e.g, hydra), every cell may take also oxygen through diffusion from environment. This is not possible in multicellular organisms like humans. The body is covered by dead cells. The living cells are not in contact with the external environment. Air containing intercellular spaces are absent. Therefore, quick diffusion cannot occur. Cell to cell diffusion is a very slow process. Passage of oxygen from lungs to toes through cell to cell diffusion will take about three years. Therefore, diffusion cannot meet the oxygen requirements of multicellular organisms like humans.

Asphyxia is a condition of severely deficient supply of oxygen to the body that arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can induce asphyxia, all of which are characterized by an inability of an individual to acquire sufficient oxygen through breathing for an extended period of time.

Multicellular organisms need oxygen to live. The multiple layer of cells in multicellular organism means that the surface area to volume ratio is low; so, diffusion happens slowly. If only diffusion would have been the source then only the outer layer of the body would get oxygen and the inner layers would be oxygen deprived.  So, the organism will die.

Deep breathing rises the $O _2$ level of the blood. By excess formation of oxyhaemoglobin the acidity of blood increases. To control it, more of free $CO _2$ changes into bicarbonates and the free $CO _2$ level in the blood decreases. So due to lack of stimulant for inspiratory centre cessation of breathing takes place, after some time $O _2$ is consumed by the tissues and rise in $CO _2$ stimulates breathing again. So, the correct answer is 'Both too much O$ _2$ and very little CO$ _2$ in the blood'.

When the concentration of carbon dioxide increases in blood that results in decreasing the affinity of hemoglobin towards oxygen or amount of oxygen is less in blood. To compensate the oxygen amount breathing goes faster and deeper and is known as hyperventilation which is controlled by the medullary respiratory center.

• Regulation of Respiration is done by the nervous mechanism.
  
• A specialised centre present in the medulla region of the brain called the respiratory rhythm centre is primarily responsible for this regulation.
  
• Another centre is present in the Pons region in the brain called pneumotaxis centre can moderate the function of Respiratory Rhythm Centre.
  

• The respiratory center is located in the medulla oblongata and pons, in the brainstem.
• The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. It is responsible for generating and maintaining the rhythm of respiration.
• Hence Respiratory rhythm center is present Medulla and pons.
• So, the correct answer is 'Medulla and Pons.