循环系统的生理学

Blood pressure is the lateral pressure produced by blood upon vessel walls. Measuring blood pressure helps detect hypertension, a condition affecting one in three American adults and a leading cause of cardiovascular disease. Blood pressure readings consist of systolic pressure during heart contractions and diastolic pressure during relaxation, recorded as systolic over diastolic in millimeters of mercury.

A sphygmomanometer consists of an inflatable cuff, rubber bulb with adjustable valve, tubing, and manometer. The examiner wraps the cuff around the brachial artery and inflates it above expected systolic pressure. As the cuff deflates, Korotkoff sounds indicate systolic pressure at first sound and diastolic pressure at the last sound heard through a stethoscope.

Endotherms, like humans, maintain a relatively constant internal body temperature independent of environmental conditions, keeping metabolic and respiration rates stable. Ectotherms, such as fish, have internal body temperatures matching their environment. Since ectotherms don't actively maintain constant temperature, their metabolic and respiration rates change to compensate for environmental temperature variations.

Fish respiration rate is measured by counting gill beats per minute. Temperature affects fish respiration in two ways: it directly influences metabolic rate, and it determines dissolved oxygen availability in water. Dissolved oxygen decreases with increased water temperature, reducing available oxygen for fish and affecting their respiration rate accordingly.

Homeostasis is the balanced state in which organisms maintain a relatively constant internal environment despite external changes. Organisms must regulate temperature, pH, and other factors to survive. Specialized physiological processes in distinct cells and organ systems work together to keep internal conditions optimal, allowing organisms to function properly.

The circulatory system transports blood, nutrients, oxygen, and hormones throughout the body. In humans, the closed circulatory system confines blood within vessels that branch extensively into tissues. The four-chambered heart pumps oxygen-depleted blood to the lungs for gas exchange, then distributes oxygen-rich blood to the rest of the body, enabling rapid and efficient material transport.

Korotkoff sounds are audible noises produced by blood being forcibly pushed through partially squeezed arteries during blood pressure measurement. The first Korotkoff sound heard during cuff deflation indicates systolic pressure, while the last sound heard indicates diastolic pressure. These sounds result from turbulent blood flow and are essential for accurate indirect blood pressure measurement.