|
Here's a table listing all the components and their function. Only the lipids of the blood require a bit more explanation
than a table can provide, so they are explained at the bottom of the page.
Category
|
Specific Items
|
Function
|
| Water |
water |
Water dissolves all the other plasma materials and provides a liquid
medium in which blood cells can travel |
| Proteins |
albumins |
These are small proteins, but are the most abundant in the plasma (60% of
all plasma proteins by weight). Their role is to maintain osmotic
balance. |
| globulins |
These large proteins tend to act as carriers for
other molecules through the blood, especially important for transporting hydrophobic
(lipid) materials. They are also the proteins that are antibodies.
(36% of all plasma proteins by weight) |
| fibrinogen |
This very large protein is not abundant in the blood (constitues 4% of all
plasma proteins by weight), but it is important in blood clotting. |
| Gases |
oxygen |
Oxygen is not present in high quantities in the plasma... instead, it gets
grabbed up pretty quickly by hemoglobin. Only 2% of all the blood oxygen is in the
plasma. |
| carbon dioxide |
Only about 7% of all blood carbon dioxide exists as the free gas dissolved
in the plasma. A much more commonly used way for CO2 to travel in blood
plasma is by undergoing a chemical change into bicarbonate ions. This is how it regulates
blood pH. (CO2 can also travel attached to hemoglobin, but
that's not plasma CO2) |
| other gases |
Whatever gases are in our air can enter our blood plasma, and the most
prevalent gas is nitrogen gas (which makes up more than 70% of our air!). These
gases typically have no function, for example-- nitrogen gas does nothing
in our bodies. |
| Nutrients |
Small dissolved organic molecules |
Monomers of proteins, carbohydrates, and nucleic acids travel through the
blood. These are used for producing energy and for building new
macromolecules. |
| vitamins |
These have individual functions that go beyond the scope of our needs
right now. |
| lipids |
Lipids (mainly taken in through the diet) do not travel through the
hydrophilic plasma unaccompanied... instead, they travel in association with proteins in
special complexes called lipoproteins. These are discussed more at
the bottom of this page. One of their major functions is to be used for
producing energy. |
| Hormones |
many varieties |
These were overlooked in Figure 14.16 in your book. Some of these
are proteins, others are small dissolved organic molecules (like amines and peptides), and
some are steroids... so they fit into many other categories in this table as well.
I'm just separating them out to maintain the layout your book uses, and because their
functions are so varied that they took up an entire week! |
| Wastes |
Nitrogenous wastes |
Our cells produce many nitrogenous wastes, as a result of gluconeogenesis,
or from the break down of other nitrogen-containing molecules, like creatine. They
are removed from the blood with the efficient work of the kidneys in the urinary system.
The plasma simply carries these wastes from wherever they were generated in the
body to the kidneys for removal from the body. |
| Electrolytes |
many different ions |
Electrolytes are simply ions, like Na+, K+, Cl-,
etc., that are found in the plasma (or any liquid in the body, like extracellular spaces).
These are important for regulating osmotic balance and maintaining pH. |
Lipoproteins in plasma
When lipids are in the plasma, they cannot handle facing the
water... so they associate with proteins. The proteins surround the lipid, running
interference between the hydrophobic lipid and the water. There can be a lot of
lipid in the center of the protein sheath around it, or there can be just a little.
There are also different types of lipids, each having different functions and different
characteristics in plasma.
Of course lipids have to be in blood. They are nutrients we
take in with our food, and they are essential for our bodies. Of course, too much of
them is also not good, especially too much of the "bad" lipids. All of
that is described below. Just step through it.
Think about how lipid behaves in water. If you pour oil into
water, the oil not only separates out, but it goes to the top. That indicates that
oil is less dense than water. If a lipoprotein complex (the lipid with the sheath of
protein) has a lot of lipid in it, then, it should also be very light, or be less dense
than water. A way to describe this is to say that such a large pile of lipid would
have a low-density. Meanwhile, if a lipoprotein has very little
lipid, but is mostly protein, it would have a very high-density, since
protein is more like water in its density than it is like lipid.
When you remove the lipoproteins from the blood and look to see what
they are like, you find some are low density and others are high density. Here are
the four major categories in which they are described:
 | chylomicrons |
| VLDL (very low-density
lipoproteins) |
| LDL (low density
lipoproteins) |
| HDL (high-density
lipoproteins) |
I have drawn out these four lipoproteins here, attempting to draw them to scale in
size, as well as to indicate how much & what types of lipids they contain.
The chylomicrons are mainly made up of triglycerides, with only 5%
of its composition due to protein. The HDLs are the smallest lipoproteins, made up
equally of protein and lipid, and its lipid does not include triglycerides (only
cholesterol and phospholipids). You should be able to use the figure to understand
the intermediate VLDLs and LDLs.
Chylomicrons and VLDLs are both nutrient sources for our bodies.
Our bodies make chylomicrons from dietary fats. Our livers make VLDLs from
excess dietary carbohydrates.
| When you eat fats, you make chylomicrons. As the fats are used
up from the chylomicrons, you are left with HDLs. These are easily removed from the
blood by the liver. |
| When you eat too many carbohydrates, you make VLDLs (you make these
because your body is storing the extra carbohydrates as fats). As the fats are used
up from the VLDLs, you are left with LDLs. These can get removed from the blood by
the liver or by other cells. |
Meanwhile, you have probably heard of good and bad fats. LDLs
are typically called the bad lipoproteins, because they are the ones that tend to get
stuck and build up into arterial plaques.
Finally, how is it possible for cells (of the liver and others) to
recognize the lipoproteins like LDLs and HDLs to remove them from the blood? These
lipoproteins contain special recognition proteins within their protein coats. These
recognition proteins are called apoproteins. The liver cells only
have to bind to these apoproteins to be able to grab the lipoproteins up! It's just
another case of receptors (on liver cells) and ligands (the apoproteins on the
lipoprotein). "Apo-" simply means from, indicating that the proteins that
offer recognition are simply from the protein coating of the lipoprotein.
|
