Vasoconstriction and Vasodilation control. Laminar and turbulent blood flow
There are many factors and body systems that regulate normal blood flow. The blood flow is determined by the vascular tone. Vascular tone is crucial in the regulation of blood pressure as well as the distribution of blood flow between and within the body's tissues and organs. By vasoconstriction and vasodilation, this mechanism directs blood flow to areas where it is needed the most or may direct blood flow from areas where less blood is needed. We have to think about resistance, gradient, and pressure when discussing the vascular system since these factors determine normal blood flow. Resistance may inhibit blood flow down a particular gradient. The gradient is the difference in specific physical or chemical values between two areas (Charkoudian et al., 2010). The mechanism of vasoconstriction and vasodilation may overcome these barriers. Arteries and arterioles are highly innervated, and the nervous system has its impact on either dilation or constriction of these blood vessels (Marieb et al., 2018, p.713). Variations in blood pressure may be controlled by vasoconstriction or vasodilation. During an exercise, blood flow will be directed to areas needed the most. Other factors like psychological stress may increase blood pressure through neural vasocontraction. The endocrine system also has its effect on vasoconstriction or vasodilation. If, for any reason, suddenly, blood pressure drops, the endocrine system will react. Hormone aldosterone and antidiuretic hormone will be released from the adrenal gland of the kidneys and the pituitary gland, respectively. These will lead to water and sodium reabsorption. Thus, the endocrine system will increase blood pressure by increasing and retaining the fluid and the solute volume in arteries and arterioles, leading to vasoconstriction in returning blood pressure to its original set point (Marieb et al., 2018, p.720).
Laminar and turbulent blood flow
Blood flow depends on many factors such as resistance, blood viscosity, and anatomic structure of blood vessels (Marieb et al., 2018, p.712). Blood in vessels moves at a different speed due to laminar flow. Laminar flow is the concept in which blood moves one direction at different speeds through multiple layers. Red blood cells are primarily concentrated in the center of the blood vessel, and the plasma is situated near the blood vessel wall. This physiology makes blood flow easier and makes blood viscosity “neutral” or balanced. Layers prevent blood from being too thick or too thin. This determines normal blood flow. The outermost layer, closest to the blood vessel wall, is motionless. The next layer has slow velocity. The velocity increases moving towards the middle of the blood vessel where the red blood cells are, which has the greatest velocity. On the other hand, turbulent flow is the concept in which blood flow depends on its velocity and the size of the blood vessels. With the increase of velocity, blood flow turbulence will also increase. Compared to the laminar flow, layers of fluid are not moving straight forward but in a swirl fashion, like when you see an airplane in foggy weather during the take-off leaving vortices of jet streams behind. The flow is dependent on the velocity of the blood flow, the diameter of the blood vessels, density, and viscosity of the blood. The larger the blood vessels, the more turbulent the blood flow (Tabe et al., 2016, p.120). In comparison to the laminar flow, the greatest energy of the flow in the middle of the blood vessels. The heart requires more energy to produce the same amount of blood during stroke volume in the turbulent flow because of increased blood flow velocity.
Charkoudian N. (2010). Mechanisms and modifiers of reflex induced cutaneous vasodilation and vasoconstriction in humans. Journal of applied physiology (Bethesda, Md. : 1985), 109(4), 1221–1228. https://doi.org/10.1152/japplphysiol.00298.2010
Marieb, E. N. (2018). The function of blood and its constituents. In Human Anatomy and Physiology (pp. 699-730). Pearson.
Tabe, Ghalichi, F., Hossainpour, S., & Ghasemzadeh, K. (2016). Laminar-to-turbulence and relaminarization zones detection by simulation of low Reynolds number turbulent blood flow in large stenosed arteries. Bio-Medical Materials and Engineering, 27(2-3), 119–129. https://doi.org/10.3233/BME-161574
