Exercise and the cardiovascular system
During exercise there is an increased demand for oxygen. This can increase by a factor of 10 to 15. The job of the cardiovascular system and the pulmonary system is to supply blood back to these muscles and remove waste substances from body tissues. The respiratory system and the circulatory system also have important roles during exercise. The circulatory system is involved in temperature regulation and is also involved in transporting nutrients and oxygenated blood to body tissues and transporting carbon dioxide from the tissues. The circulatory system and the respiratory system work together as functional units. They are involved in homeostatic role in controlling blood content of carbon dioxide and oxygen. The respiratory system fuels the blood with oxygen.
Erythrocytes
Erythrocytes are known as red blood cells. They are involved in transport of oxygen and carbon dioxide. They contain roughly 200 to 300 million molecules of haemoglobin. Red blood cells have biconcave shape which allows for oxygen to bind to them easily. In areas where the partial pressure of oxygen is high the blood will readily attach to the haemoglobin molecule. Each haemoglobin molecule can carry 4 oxygen molecules to make oxyhaemoglobin. When there is low oxygen partial pressure they will readily dissociate the oxygen molecules and pick up carbon dioxide molecules.
Myoglobin
Myoglobin has a similar structure to haemoglobin. It is found in the sarcoplasm of muscle fibres (usually slow twitch type 1 muscle fibres). it is made up of 4 polypeptide chains surrounded by haem groups and each haemoglobin molecule can attach oxygen molecules to itself. These have a higher affinity for oxygen and can release oxygen more readily when needed by the muscle.
To meet the demand of oxygen the body carries out 2 main functions. To help supply oxygen to where it is needed.
- Increase cardiac output
- Redistribution of blood: The blood is redistributed from body parts where it is not needed to body parts where it is needed for example the muscles.
Certain organs cannot have blood redirected for example the brain as this is vital for normal bodily function and thus blood flow to the brain is maintained.
The cardiac system and exercise
Cardiac output is the amount of blood pumped out of each ventricle in 1 minute
The cardiac output can be defined as:
Cardiac Output (CO) = SV × HR
In this equation SV represents the stroke volume. The stroke volume is the amount of blood each ventricle can pump out each time it contracts.
As the stroke volume increases so does the cardiac output and vice versa.
- Venous return during exercise
During exercise blood is continuously pumped out of the heart. The heart can only pump out blood it receives and if it is empty blood cannot be pumped out so during exercise and equal amount of blood needs to be pumped back to the heart matching the volume leaving the heart. This is assisted through three main systems.
- Muscle pump
The muscles that contract are the striated muscles. When they contract the veins decrease in diameter and when they relax they open up allowing more blood to flow in. There are semi lunar valves present in the veins and these are designed to prevent backflow in the veins and make sure the blood flows in one direction.
- Respiratory pump
The respiratory pump occurs during ventilation movements. When the pressure in the thorax decreases blood tends to flow towards the place of low pressure, which is near the heart and vice versa. The is enhanced during exercise because the amount for blood is greater due larger ventilation movements.
- Venoconstriction
During venoconstriction the veins constrict this causes the diameter of the vein to decrease allowing more blood to flow back to the heart because it is under increased pressure This occurs by a reflex action controlled by the sympathetic nervous system. The muscle pump occurs when muscles contract.
Exercise and the pulmonary system
The whole purpose of the pulmonary system is to provide a system for gas exchange between the internal environment and the external environment. Exchange of oxygen and carbon dioxide occurs by diffusion and ventilation. The process of ventilation occurs through changes in the volume of the lungs causing air to be rushed in or out. This occurs by the contraction of the intercostal muscles and the diaphragm. When you inhale the external intercostal muscles contract and the diaphragm contracts and flattens causing the pressure to increase in the lungs and an increase in intra pulmonary pressure is witnessed leading to air rushing into the lungs. During exhalation all muscles relax and air rushes out because there is a decrease in pressure. The respiratory substrates used by the muscles in the intercostal and diaphragm are oxygen and glucose. Breathing out is a passive process and breathing in is an active process.
During exercise this process increases the amount of air rushing into the lungs by causing larger contractions in muscle. This provides more oxygen for the blood to feed muscles.
Conclusion
Training has the affect of increasing the tidal volume and also increasing the strength of the muscles and increasing the size of the lungs. In addition exercise can also greatly improve the efficiency of the cardiovascular system and how well it works.
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