Khankeldiev Sh. Kh. Regional features of the physical status of youth students fergana 2022 Reviewer

1.5. THE ACTIVITY OF THE PHYSIOLOGICAL SYSTEMS OF THE BODY DURING PHYSICAL ACTIVITY IN CONDITIONS OF HIGH EXTERNAL TEMPERATURE
1.5.1. THE CARDIOVASCULAR SYSTEM
Since all types of heat transfer occur only from the surface of the body, with an increase in the internal temperature of the body, the body is able to transfer excess heat to the skin. Some of this may be due to the direct transfer of heat, but the main mechanism in this case is the transfer of heat with the blood. This mechanism is sometimes referred to as "circulatory heat convection".
The magnitude of the severity of cardiovascular reactions to an increase in the temperature of the external environment depends on the intensity and duration of physical activity. In a person at rest who performs only light physical work, subcutaneous blood flow can reach 9-10 l / min. With short, intense exercises, the amount of subcutaneous blood flow changes to a relatively small extent. With longer training loads, there is a kind of competition for the supply of blood between working muscles and skin. On the one hand, increased muscle activity requires an adequate supply of arterial blood to the working muscles. On the other hand, the need to return to the external environment causes the need to increase skin blood flow.
Some authors see this as the main mechanism (or at least one of the main mechanisms) that prevent the performance of significant physical work in conditions of high ambient temperature.
The increase in skin blood flow is determined by the combined action of 4 main physiological mechanisms.
1. A decrease in the tone of vasoconstrictors in the sympathetically innervated vessels of the hands and arms.
2. Active vasodilation of the subcutaneous vessels of the trunk and proximal segments of the extremities.
3. By the direct action of bradykinin, which is released by the sweat glands when the temperature rises.
4. Localized temperature effects, including cooling due to sweat evaporation.
The nervous components of the regulation of subcutaneous blood flow are under the control of the hypothalamus. Usually, an increase in the core temperature of the body leads to the opening of arterial-venous anastomoses, in particular, in the vascular bed of the extremities. This provides a much greater circulation of blood than occurs under normal conditions. When performing physical exercises in conditions of high ambient temperature, a decrease in systolic discharge may occur.
As a result of this, and also due to increased blood flow through the skin, a decrease in blood plasma volume and an increase in core body temperature during exercise in hot conditions, tachycardia is usually observed. It has been noted that when the temperature rises by one degree (with a constant oxygen consumption of 22 ml / kg of body weight per minute), the heart rate increases by 17-18 beats per minute. The foregoing explains the well-known fact of a decrease in endurance indicators when performing physical exercises in conditions of high external temperatures. The main reason for this is the need for additional body heat transfer and competition between muscle and subcutaneous blood flow. The body is not able to supply enough blood to both working muscles and superficial skin formations.