This increases the total amount of blood that is circulated in the body every minute. That increase in blood circulation is required to meet the increased demand for nitutrients and oxygen that the muscles and other tissure require during exercise or for that matter during any time that the metacbolic demand on the body is high.
The blood vessels in non essential places places in the body also constrict during exercise and this provides extra blood volume for more essential organs such as the heart lungs and the brain.
The lungs also play an important part in all of this. Their primary role is to exchange oxygen and carbon dioxide in the blood with fresh air. This increases the amount of oxygen in the blood that comes to the lungs from the body and decreases the amount of carbondioxide in the blood.
The lungs also increase their activity by increasing the number of breaths taken each minute and the amount of air taken in each breath.
Together the increase in the activity of both these organ systems increases the amount of blood and oxygen supply to the body.
The short term effects
The short-term effects of exercise usually begin before the exercise has even begun. Excitement plays an important part in preparing the body to cope with the demands of exercise. The sympathetic nervous system will be activated and parasympathetic discharge reduced or abolished, resulting in a tachycardia and vasodilation of the blood vessels supplying skeletal muscle. Blood is diverted from other organs, such as the gut, by local vasoconstriction. Myocardial contractility may increase. Venoconstriction results in an increased venous return, and splenic contraction increases the packed cell volume and oxygen carrying capacity of blood.
The long term effects
The long-term effects of exercise. Prolonged exercise training leads to eccentric hypertrophy of the LV (and presumably the RV), resulting in an increased stroke volume. The maximum heart rate appears to be similar however, trained horses appear to be able to maintain stroke volume at high heart rates better than untrained animals, resulting in an increased performance capacity. The distribution of blood flow to skeletal muscles during exercise is assisted by an increase in the ramifications of blood vessels to fibre groups. This results in an increase in the maximal aerobic oxygen capacity of exercise-trained animals. Adaptation due to selective breeding has lead to a difference in the packed cell volume and oxygen carrying capacity of the 'hot blooded' breeds. Fit animals also appear to be able to move faster at the same maximal oxygen capacity. Athletic ability may also be related to the ability to tolerate increased levels of by-products such as lactic acid, which build up in the muscles during exercise, and affect anaerobic exercise capacity.
