Question

Every cell in the body requires oxygen for respiration so that sufficient energy can be produced. Carbon dioxide, a waste product, is also produced and needs to be removed. Therefore, the levels of both gases must be regulated. How does this explain the changes in your pulse rate?

Answer 1

Pulse rate is the heart rate that is the number of beats per minute. Pulse rate increases during exercise and is lower when the body is at rest.

The respiratory system performs the exchange oxygen and carbon dioxide in the body. Inhaled oxygen through the lungs reaches the alveoli. Oxygen passes via the air-blood barrier into the blood in the capillaries. Oxygen binds to haemoglobin (oxyhaemoglobin) and travels from the lungs through the pulmonary veins into the left side of the heart. From here, it is pumped to the rest of the body. Tissues have less oxygen as compared to surrounding environment as they utilize oxygen. Oxygen diffuses from the blood into the tissue fluid and then into the cells. Carbon dioxide, a waste will now diffuse into the tissue fluid and then blood. It binds to deoxyHb and is transported to the heart.

Oxygen-deficient, carbon dioxide-rich blood enters the right side of the heart via the superior vena cava and the inferior vena cava veins. The blood is pumped to the lungs via pulmonary artery. Blood picks up oxygen and releases carbon dioxide. However, most of carbon dioxide is carried in plasma as bicarbonate ions.

Humans require less oxygen when sleeping as when they are awake. Similarly, oxygen requirement differs during different levels of activity. Running requires more oxygen than walking. Increased activity leads to increased buildup of carbon dioxide in the blood.

The levels of oxygen and carbon dioxide are regulated via breathing. Breathing is controlled by a reflex activity by a group of nerve cells in the brain called the respiratory centre. These cells regulate breathing automatically. However, breathing can be controlled voluntarily too. Increased breathing allows more oxygen to reach the tissues and allow removal of excess carbon dioxide that is present due to increased cellular activity.

An increased rate or depth of breathing allows extra oxygen intake into the body as required. However, this oxygen has to be transported by the body to tissues. In order to transport extra oxygen, the heart must increase the output of blood. The heart is involved in transport of oxygen and removal of carbon dioxide in blood. The built in contraction of the heart are performed by the hearts pacemaker. The pacemaker is a small clump of nervous tissue located in the wall of the right atrium, which senses the oxygen/ carbon dioxide levels in blood. Nerve impulses spread out from the pacemaker over the muscle of the atria, contracting the atria. Impulses are then passed to the ventricles causing then to contract. The pacemaker is connected to the cardiac center in the brain via nerves. The cardiac center sends messages to pacemaker to speed up or slow down the normal rhythm of the pacemaker. Thus, the rate of the heartbeat can be varied depending on the gas requirements of the cell. If there is less oxygen and more carbon dioxide, the pulse rate will increase. However, a normal oxygen and carbon dioxide levels will cause lowering of pulse rate.