Blood usually does not flow continuously through the capillaries. Instead, it flows intermittently, turning on and off every few seconds or minutes. The cause of this intermittency is the phenomenon called vasomotion, which means intermittent contraction of the metarterioles and precapillary sphincters (and sometimes even the very small arterioles).

Regulation of Vasomotion. The most important factor affecting the degree of opening and closing of the metarterioles and precapillary sphincters that has been found thus far is the concentration of oxygen in the tissues. When the rate of oxygen usage by the tissue is great so that tissue oxygen concentration decreases below normal, the intermittent periods of capillary blood f low occur more often, and the duration of each period of flow lasts longer, thereby allowing the capillary blood to carry increased quantities of oxygen (as well as other nutrients) to the tissues. This effect, along with multiple other factors that control local tissue blood flow.

Average Function of the Capillary System. Despite the fact that blood flow through each capillary is intermit tent, so many capillaries are present in the tissues that their overall function becomes averaged. That is, there is an average rate of blood flow through each tissue capillary bed, an average capillary pressure within the capillaries, and an average rate of transfer of substances between the blood of the capillaries and the surrounding interstitial fluid. In the remainder of this chapter, we are concerned with these averages, although one should remember that the average functions are, in reality, the functions of literally billions of individual capillaries, each operating intermittently in response to local conditions in the tissues.

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المزيد

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دراسة تدفعك لشراء ساعة ذكية "فورا".. هذا ما تقوله عن قلبك

علماء حاصلون على "نوبل": الذكاء الاصطناعي لن يستبدل الإنسان

وانغ هو: القمة العالمية للعلماء تجسد تقدير الإمارات للعلم

رئيس رابطة كبار العلماء يعلن تأسيس مقر في الإمارات

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مواضيع ذات صلة

Role of the Nervous System in Rapid Control of Arterial Pressure

Special Features of Nervous Control of Arterial Pressure

The Lymphatic System Plays A Key Role in Controlling Interstitial Fluid Protein Concentration, Volume, and Pressure

Formation of Lymph

Rate of Lymph Flow

Exchange of Water, Nutrients, and Other Substances Between the Blood and Interstitial Fluid

Structure of the Microcirculation and Capillary System

Basic Principles of Circulatory Function

Physical Characteristics of the Circulation

Abnormal Rhythms That Result From Block of Heart Signals Within the Intracardiac Conduction Pathways Sinoatrial Block

Abnormal Sinus Rhythms Tachycardia

Flow of Current Around the Heart During the Cardiac Cycle