BIOL 1051H Chapter Notes - Chapter 18: Osmotic Concentration, Blood Vessel, Capillary
Blood
The circulatory system is that system responsible for circulating blood and lymph
throughout the body. Blood serves as a transport for many essential things including: oxygen
and carbon dioxide, nutrients including water, and wastes, hormones and other chemicals, heat,
and immune system cells. Although we normally think of the circulatory system as the system
that moves blood, it is important to realize that the circulatory system includes the lymphatic
system as well. The blood portion of the circulatory system is a closed system in that blood as a
whole does not leave the confines of the vasculature and heart. However, some fluid is always
lost in the capillary bed. This fluid would remain in the tissues as edema (fluid filled swelling) if
the lymphatic vessels did not pick up the fluid and return it to the blood stream. We will look at
the lymphatic portion of the circulatory system later in the module
Blood is a connective tissue that is comprised of formed elements (cells and cell
fragments) in fluid called plasma. If you collect blood from a person and put it in a tube
containing anticoagulant it will separate into three layers. This separation will happen on its own
if the blood tube is allowed to stand but will happen faster if spun in a centrifuge. The top layer
of the tube contains the plasma. This liquid portion is mostly water, but it also contains
electrolytes, nutrients, and many types of plasma proteins. The plasma proteins make up about
7 – 9% of the plasma volume. The most abundant protein is albumin. Albumin is very important
for maintaining the osmotic pressure of the blood. Because albumin is made by the liver and is
so abundant in the blood it is often used as an indicator of liver function. If albumin is low it
suggests serious liver disease. If the albumin is very low a person may not be able to keep fluid
in the blood vessels and will experience edema.
There are two very important properties of blood—viscosity and osmolarity—that you will
need to understand to understand how and why fluids such as blood and urine move the way
that they do. Viscosity and osmolarity arise from the formed elements and plasma composition.
Viscosity is the resistance of a fluid to flow, which in general terms means the thickness or
stickiness of a fluid. A RBC or protein deficiency reduces the viscosity of blood and causes it to
flow too easily, whereas an excess causes blood to flow too sluggishly.
The osmolarity of blood is the total molarity of dissolved particles that cannot pass
through the blood vessel wall. This is another important factor in cardiovascular function
because substances and fluid must pass between the blood and tissue fluids in order to nourish
them and remove wastes. This is in part dependent on the osmolarity of the blood in relation to
that of the surrounding tissue. If the osmolarity of the blood is too high, water will move into the
blood and raise blood pressure. On the other hand, if the osmolarity of the blood is too low too
much water remains in the tissues and they can become swollen (edema). Blood pressure may
also drop to low levels because of the water lost from the bloodstream.
Document Summary
The circulatory system is that system responsible for circulating blood and lymph throughout the body. Blood serves as a transport for many essential things including: oxygen and carbon dioxide, nutrients including water, and wastes, hormones and other chemicals, heat, and immune system cells. Although we normally think of the circulatory system as the system that moves blood, it is important to realize that the circulatory system includes the lymphatic system as well. The blood portion of the circulatory system is a closed system in that blood as a whole does not leave the confines of the vasculature and heart. However, some fluid is always lost in the capillary bed. This fluid would remain in the tissues as edema (fluid filled swelling) if the lymphatic vessels did not pick up the fluid and return it to the blood stream. We will look at the lymphatic portion of the circulatory system later in the module.
