8.5: Characteristics of Blood

Blood exhibits varying shades of color, primarily contingent on its oxygenation status. When oxygenated in the lungs, blood takes on a vibrant, bright red hue. In contrast, blood that has delivered its oxygen to the body's tissues assumes a darker, more subdued red coloration. This color transformation is attributed to hemoglobin, a prominent pigment within RBCs, whose appearance shifts in response to changes in oxygen saturation.

Blood manifests a remarkable viscosity, rendering it somewhat sticky. Its viscosity surpasses that of water by a factor of approximately five. Viscosity, a property indicating a fluid's thickness and resistance to flow, owes its characteristics to the presence of plasma proteins and formed elements within the blood. The heightened viscosity significantly impacts blood pressure and circulation dynamics.

Blood temperature slightly exceeds the standard internal body temperature, measuring around 38°C (100.4°F), compared to the typical 37°C (98.6°F) body temperature. Daily temperature variations of up to 0.5°C are well within normal. As blood courses through the smooth surfaces of blood vessels, it encounters friction and resistance, particularly as vessels age and lose elasticity. This friction generates heat, contributing to the blood's slightly elevated temperature.

Blood maintains a pH level that averages around 7.4, but it can vary slightly within the healthy range of 7.35 to 7.45. On the pH scale, this makes blood slightly basic, or alkaline, compared to pure water, which has a neutral pH of 7.0. The body relies on various buffering systems to keep blood pH within this narrow range, as it is crucial for life and the proper functioning of all bodily systems. Even small shifts in blood pH can disrupt enzyme structure and activity, impairing essential metabolic processes such as energy production, digestion, and tissue repair. Additionally, pH imbalances can interfere with hemoglobin's ability to transport and release oxygen efficiently. Abnormal pH levels also disrupt the balance of key electrolytes like potassium, sodium, and calcium, which are essential for nerve signaling, muscle contraction, and maintaining a regular heart rhythm.

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