Yes blood is a liquid—well mostly. I’m sure that if you’ve ever been accidentally cut or injured, you’ve seen that blood behaves similar to any other typical liquid you encounter in your life. It flows easily due to its low viscosity and doesn’t have a defined shape, instead filling whatever container it is in. But that’s not exactly the whole story.

Due to its biological and chemical makeup, blood doesn’t always follow the rules of normal (Newtonian) fluids like water. You might not be able to see these behaviors yourself (unless you happen to have a rheometer at home), but the structure and composition of blood create some pretty interesting fluid properties that are vital to the body’s healthy operation. In fact, these non-Newtonian behaviors of fluids like blood have an entire research field (the field of rheology) dedicated to understanding where these properties originate from and how to harness them in a huge range of applications! The field of rheology even has a special subfield called hemorheology focused on understanding the properties of blood and how they impact our health! Understandably, blood has a number of dynamic properties, but here’s an overview of a few of the major ones.

Human blood is a combination of blood plasma and so-called “formed elements.” The plasma is what allows blood to flow like a liquid. It is mostly water (92%) with the remaining 8% consisting of proteins, dissolved salts, and various nutrients. The “formed elements” are the red blood cells, white blood cells, and platelets. These behave more like solid particles in the blood. When pumped around the body, these blood cells and platelets sort of just float around and flow with the plasma. Blood has quite a large amount of these formed elements in it (about 45% by volume), but the presence of the plasma keeps all the cells distanced enough that they can flow by without jamming up.

When blood is sheared (which happens when it passes through narrow veins and capillaries), fluid forces can cause the red blood cells to deform. Instead of looking like the standard biconcave disk you might see in a textbook, they can elongate or stretch. Since the interior of the blood cells is filled with fluid-like cytoplasm, the cell membrane can also undergo “tank-treading,” where the membrane moves around the cell like a conveyor belt. These changes affect the way the red blood cells pack and flow past each other in the blood, giving blood shear-thinning behavior. This means that when increasing the strain rate on blood (i.e. by increasing the flow rate), the viscosity decreases. The shear-thinning properties of blood are essential for pumping blood through all the tiny veins and capillaries throughout the human body!

As blood flows through veins, the red blood cells do not necessarily need to remain evenly distributed throughout the blood. Due to the Fåhræus-Lindqvist effect (please don’t ask me how to pronounce that), red blood cells have a tendency to clump toward the center of the veins, leaving only plasma near the vein walls. Since pure blood plasma has a lower effective viscosity than the combined plasma and blood cells, this creates a sort of lubricating layer in the veins, allowing the blood to flow more easily through them.

The red blood cells also give blood the property of viscoelasticity, meaning that it exhibits both viscous (liquid-like) and elastic (solid-like) behaviors. In a purely viscous material, energy is dissipated as heat through friction within the fluid. But in a viscoelastic fluid, energy can be stored, for instance through the stretching of the red blood cell membrane. Just like a rubber band or a spring, when the membrane is stretched, it converts kinetic energy into potential energy, which can then be released when the membrane is allowed to return to its original state. This impacts how the blood flows in the body and responds to applied stresses, such as that which occurs during the cyclic pumping of the heart.

very physical approach to this question, blood as it functions flowing around the body, delivering oxygen and other useful nutrients, is a liquid. It flows freely, it's almost incompressible, it takes the shape of whatever container it is poured into. However! Blood is a solution that, while mostly made up of water, has many other things in it that cause it to clot, congeal, and become a solid For example, when you scrape a knee falling off a bike, bright red blood will seep out from the scrapes. Your body does its best to prevent any more blood loss by blocking up the wound with cells called platelets. These platelets stick together with proteins in your blood to form what is called a fibrin clot, which acts like a barrier to stop the bleeding, finally, turning it into a solid.

Liquid blood does have an interesting property called "shear thinning". Ketchup does too, actually. Shear thinning is when a fluid viscosity decreases under shear strain. So, when you smack the bottom of a ketchup bottle, you're applying shear strain, causing the ketchup to pour out super fast. The more force applied, the faster it goes.

Blood is considered a non-Newtonian fluid, where the term fluid refers to what we broadly think of as a liquid or a gas, or basically anything for which we could specify a flow rate. The viscosity of blood is determined by the properties of its major constituents: plasma and red blood cells. We can think of the blood plasma as a liquid and the red blood cells as solid-like particles suspended in the plasma.

The volume fraction and mechanical properties of the red blood cells, which account for more than 99% of the cells present in blood, affect the overall viscosity of blood and contribute to its non-Newtonian nature. The term non-Newtonian simply refers to fluids whose viscosity changes with shear rate. For example when you exercise, your blood flows quickly in your veins, and the viscosity of the blood itself is lower because the fast flow imparts a high shear rate. Conversely when you sit still and your blood slows down, its viscosity increases relative to when you were exercising. This makes blood a shear-thinning fluid.

Other examples of shear thinning fluids are paint, ketchup, and whipped cream. Paint flows quickly while it is being spread (sheared) on a wall, but once you stop moving it, the paint does not flow down the wall because its viscosity increases. Ketchup and whipped cream flow quickly out of their containers in response to a squeeze or a spray, but once applied to food, they stop flowing because they are no longer experiencing shear.

Blood is considered a liquid. It is a non-Newtonian fluid, which means that the viscosity will change depending on how much stress is applied. An example of a non-Newtonian fluid is a concentrated suspension of starch in water, which feels very solid if we were to hammer on it! Newtonian fluids, such as water, do not have this property, so they will not feel solid even if we apply a large sudden force. As for some of the fluid properties of blood, it is thixotropic, meaning that its viscosity will decrease over time when stressed (shaken, agitated); it's also viscoelastic, meaning that it will behave as both a viscous material and an elastic material.

Viscous materials resist strain; elastic materials stretch under strain and then return to their starting state when the strain is removed.

Blood is water with stuff dissolved or suspended in it. The water is indeed a liquid, and has the same fluid dynamic properties that water would normally have with similar amounts of dissolved or suspended material. The dissolved material includes sugars, ions, hormones, etc., and the suspended material includes red and white blood cells, which have cell membranes in the liquid-crystal phase, and have other things inside of their cytoplasms.

Bood.

1. Your blood is made up of liquid and solids. The liquid part, called plasma, is made of water, salts, and protein. Over half of your blood is plasma. The solid part of your blood contains red blood cells, white blood cells, and platelets.

2. Cool - from this link. Blood is a non-Newtonian fluid or more precisely, a pseudo-plastic fluid [13]. This type of fluid is less like water and more like toothpaste or ketchup, flowing more smoothly as the velocity of flow increases. This smooth flowing phenomenon at higher velocity is related with decreased viscosity and increased shear rate of the blood. Such phenomenon is called as the shear thinning behavior of the blood as a non-Newtonian fluid (Fig. 1A of the previous link).

Blood flow is pulsatile; therefore, properties such as pressure, velocity, flow rate, and viscosity change as a function of time.

A study of the dynamic properties of the human red blood cell membrane using quasi-elastic light-scattering spectroscopy.