1. Respiratory System:
The respiratory system in mammals consists of two parts: (i) air passages through which air travels to reach the blood stream and (ii) mechanism of breathing.
The first part consists of nostrils, nasal passages, larynx (voice box), trachea, bronchi, bronchial tubes and lungs while the second part includes the ribs, rib-muscles, the diaphragm and the abdominal muscles.
The lungs are a pair of conical hollow organs housed on either side of the heart and are divided into smaller tubes (bronchioles) which lead to the air sacs and alveoli.
The human lungs are made up of some 7.5 x 108 alveoli and are richly supplied by blood vessels and capillaries which provide enough surfaces to supply oxygen through the blood.
Gas Exchange in the Lungs:
The pulmonary artery brings deoxygenated blood to the lungs where moist walls of both air-sacs and capillaries allow the rapid gaseous exchange of respiratory gases, e.g., O2 passes from the air into the blood and CO2, from the blood into the air.
The pulmonary vein returns the oxygenated blood to the heart from where it is distributed to various parts of the body. The absorbed O2 is combined with the haemoglobin of R.B.C. to form temporary compound oxyhaemoglobin.
In the tissue where concentration of O2 is low, oxyhaemoglobin releases its O2 and is converted into reduced haemoglobin which is again ready to combine with thus liberated is used by the tissue cells to oxidize the digested food.
Respiratory centre which controls the respiration is located in the medulla oblongata of the brain. The maximum amount, of which the normal human blood can absorb, is 20 ml per 100 ml of blood. The total amount of CO2 in the venous blood is about 60 ml per 100 ml blood and arterial blood contains about 50 ml CO2, per 100 ml.
2. Respiratory Pigments:
The different respiratory pigments found in animals are as follows:
It is found in the plasma of molluscs, annelids and arthropods but in the R.B.C. of chordates. It is also found in muscles of birds and mammals where it is known as myoglobin. It is a red pigment formed of two components, the haem (iron component) and the hemoglobin (conjugated protein).
It is also an iron containing violet coloured pigment found commonly in polychaetes.
It is generally found in crustaceans and molluscs. It is colourless or blue and contains copper.
This is a green coloured pigment found in polychaete annelids.
When a person living on plains ascends and stays on a mountain above 8000 ft from sea level, he develops certain symptoms in 8-24 hours. These symptoms include breathlessness, headache, dizziness, irritability, nausea, vomiting, mental fatigue and a bluish tinge on the skin, nails and tips. This is known as Mountain Sickness.