Bovine biology series
Part - 14 Blood (1/2)
When I was a graduate student at Wisconsin my major professor and I drove out to the Oscar Mayer plant, on the outskirts of Madison. We rode an elevator to the sixth floor, as I recall, and it was here that hundreds of cattle and hogs were killed. But one part of this visit is with me still, very plainly. Two very large tanks containing blood were situated on this floor.
We had come for fifteen gallons of the stuff. Our need was finding enough plasma from which we could isolate a very large molecule (molecular weight of 55,000), transcortin, or corticosteroid binding globulin (CBG). I remember lugging three five gallons buckets to the car, and making a mad dash to the centrifuge where upon spinning this blood volume down, two very distinct layers were found in the test tube. Now in a centrifuge, the heavier or denser stuff is shoved by the force of artificial gravity to the tube's bottom, and so this is where the red blood cells were packed so tightly. The yellow, more fluid layer was found in the top of the tube.
I have never forgotten this adventure on a fall afternoon. We froze the yellow plasma and threw the red stuff at the tube's bottom away.
By the way, that transcortin we were after serves the purpose of transporting fat-soluble molecules, like steroids and some hormones, through the blood stream in a protected manner. Kind of like wrapping them in a container until they reach their final destination, like the target organ, and then the transcortin molecule lets go, or unwraps itself from the steroid. Without the transcortin molecule, the steroid would have a most difficult journey, and would certainly meet an untimely death due to other components in blood which would catabolize, or destroy the molecular structure of the steroid, or in our case, hydrocortisone (cortisol).
With this bit of historical perspective, I introduce the substance of biological life; the water based liquid known as blood. We shall examine this substance in two parts, concluding the subject next month.
The word blood is really an Old English word, and has tracings back to the Anglo-Saxon word "blod". The Anglo-Saxon word is derived from the Old High German word "bluot".
The blood volume is largely water, 78% liquid and 22% solid. Blood can be fractionated into several major parts. Blood volumes in the adult cow are 60 ml/kg body weight, or 38 liters (almost ten gallons) for a 1400-pound cow. This is about 6% of her total weight. A 154-pound man, for instance, has a total blood volume of 1.4 gallons, which weighs 11.8 pounds; thus the blood of this man is about 7.6% of his total weight. Obese animals have a lower percentage of blood volume; stored fat contains very little vascular supply. Lean tissue, on the other hand, is like the brain, and contains a higher volume of blood per unit mass of weight.
The specific gravity of blood is slightly higher than water, at 1.05; thus a gallon of blood will weigh 8.7 pounds (slightly heavier than milk). The blood cells themselves account for this heavier than water weight.
As with the centrifuge example, blood consists of three primary parts, and on a volume basis, they are blood cells (38%), blood plasma and blood serum (62%). The blood cells consist of three types of blood cells: the red blood cells called erythrocytes, the white blood cells called leukocytes and the platelets called thrombocytes. The suffix "cyte" is derived from the Greek word "Kytos" and denotes the word "cell."
The plasma portion of blood contains all the rest of the total volume. Water, of course, makes up the biggest portion. Also in the plasma are the gases, oxygen, carbon-dioxide and nitrogen, the food metabolites, certain blood proteins, salts that comprise the electrolyte makeup of blood, and then the waste-products that are distributed back to the liver for metabolism or the kidneys for discharge as urine.
If the blood-clotting portion of blood, the fibrinogen, were removed from the plasma, the remaining watery substance would be called the blood serum. The plasma is about 90% liquid and 10% solids, the solids are described above as dissolved molecules in the plasma volume. A very large portion of these solids is comprised of the plasma proteins, albumin’s, globulin’s and fibrinogen. The mineral (electrolyte) or inorganic portion of plasma accounts for about 1% of the total volume.
As we have learned in the last several series, the blood volume is part of the respiratory-circulatory system. The heart, of course, consisting of two pumps links the lungs and the tissues together for an exchange of oxygen and carbon dioxide. All of which is facilitated by the blood. Remember that oxygen is required for the conversion of chemical energy into work energy, and that as a by-product of this energy transformation, carbon dioxide is left and must be expelled via blood through the lungs. We breathe in oxygen and breathe out carbon dioxide. Pretty simple.
But the blood serves many other purposes. One is thermoregulation. For instance when I run on a warm day and stop, my arms fall down by my side. The blood vessels, the veins that are returning blood full of muscle by-products, like carbon dioxide, are real large and easily exposed just beneath the surface of the skin. Why is this? Well, the blood vessels expand, closing the distance between the layers of skin tissue and therefore closer to the air. The blood is cooled. Likewise, an early fall morning when in the darkness of a thirty-degree day, I run the same distance but when I stop, these blood vessels are not easily found. They are withdrawn, shrunken into the warmer regions of the arm. Staying warm, they are, and thus helping to maintain a constant body temperature.
Another function of blood is the regulation of water content of the cells themselves. For instance if the body is being dehydrated, the blood volume is sacrificed in part, providing water for cellular needs. We are, as life, bathed in water. Without it we do not exist. It is the blood that transports it to our organs and tissues. This water regulatory function is helped along by electrolytes, those mixes of salts in the blood that either cling to or yield the precious water molecule. I recall one time looking in the mirror at my face after a long race on a very warm summer day. There was white residue around my mouth and eyes and even upon my neck. This is the action of the blood volume serving the dual role of thermoregulation by sweating, the movement of moisture to the surface of the skin and thus carrying muscle heat away for evaporation. The other role, of course, was the discharge of sodium chloride to the skin's surface. The blood, by hanging onto this salt, drew water from cells, especially muscle cells, and in doing so was able to transport the heat away from muscles. Truly remarkable. And extremely important in that water is our most important nutrient.
Another function is the regulation of our body’s hydrogen ion concentration. Hydrogen ions are a by-product of cellular metabolism. When they accumulate the hydrogen potential or pH is increased. This makes the blood more acidic. Blood is normally slightly alkaline with a pH of 7.4. In the normal blood volume, there are slightly more cations than ions. Remember that the cations are positively charged ions and the ions are the negative ones. Another way to explain this would be that the arterial side of the blood system is slightly more alkaline than the venous side. That is because the concentration of carbon dioxide is higher on the venous side; it is the blood carrying this slightly anionic gas to the lungs for discharge. This is important, for the carbon dioxide is a waste product in mammalian tissues and must be gotten rid of. The blood transports it to the lungs and out it goes for the plants to use.
So the blood is a buffer, and in carrying the various mixes of cations and anions around, can deal with pH changes in such a way blood pH is held within a fairly tight range (7.1 - 7.8). This only occurs if enough electrolytes are consumed by the animal.
Interestingly enough is this fact: a diet based upon high protein especially if this protein is derived from animal products tends to alter slightly the blood chemistry towards the acidic side. This is because they contain chlorides, phosphates and sulfates that are largely anions once metabolized and dumped into the blood. The urine in these animals is slightly acidic due to an increase in uric acid. Diets high in carbohydrates, especially plant-originated, are abundant in sodium and potassium, the cations that move the blood chemistry towards the alkaline side. The diets in these animals on this type of diet is alkaline.
The body performs better when the blood chemistry is favored for the alkaline side. It is simple chemistry to understand that if the blood is serving as a buffer, then when work is accomplished and the blood must absorb carbon dioxide, the metabolic by-product, a blood volume heavily concentrated with cations such as potassium and sodium, will absorb a greater volume of carbon dioxide. Another by-product of cellular metabolism is lactate, and as an acid must by absorbed into the blood for travel to the liver, where it is metabolized into glucose once more. The point is that if the blood is nearer the 7.1 pH level, then the buffering capacity of the blood is reduced. And during times of high metabolic rates, the capacity of the blood to adequately buffer cellular metabolism is impaired.
What happens? Well, if severe enough, the animal dies for the muscles simply lock up, so to speak. Runners deal with muscle cramps and for some, the tiredness feeling in the large leg muscles is the response to the muscles saying, "now wait a minute, the accumulation of lactic acid is too great. The blood has reached a point where the cationic availability to buffer acids in the blood has been reached. So no more running, fella, until you stop and get some of this lactic acid out of here." That is why runners eat lots of oranges and bananas. They increase the blood's concentration of cations, sodium and potassium, so there is plenty of room for the lactic acid to go, hence, muscles can continue to perform.
Do you remember those strips of paper ketosis test strips we would place in the urine discharge? What we were doing is detecting the presence of an acidic urine, and that is a sign of a higher than normal blood level of the intermediates of fat metabolism, most of which are acidic in nature. In the normal cow the urine is similar to the blood in pH.....slightly alkaline.
Another function of blood is concerned with nutrition. We have looked at this at length, but suffice here to write that the blood transports the end products of digestion to the cells. Not very complicated. Remember the role of the liver, for it is this organ, for a very large part, that prepares the correct molecular structures of carbohydrates, proteins and lipids that are acceptable for cellular use.
Another primary function of the blood is maintenance of fluid volume of the body. We will address this part of biology when we examine the lymphatic system. But briefly the body must maintain itself in a liquid state, for the body is at least three-quarters water. A very popular word and one that I use frequently, homeostasis, is by definition the maintenance of the body uniformity and stability. This is accomplished by a wide range of factors that are transported to the space between the cells, the extracellular space. The blood and lymph are major players in homeostasis. The study of physiology is largely concerned with the balance of the body to deal with the ebbs and flows of intakes, food, water, and air, and somehow mixes them in proper ratios so the body not only survives but grows, replaces its worn cells, deals with disease and can perform work, such as lactation or gestation.
Finally, a function of blood is that which we know as fighting disease. Those wonderful white blood cells, the leukocytes, are so necessary when invaders or foreigners breach the primary barrier, the skin, or gain entrance through a body cavity, such as bacteria entering the lung tissue (in this case, if the immune system is impaired the bacteria begin their destructive work. The infection, called pneumonia, is established in this dark, warm and moist place, and it is this infection that kills the body as the capacity for gas exchange is reduced). We know them as somatic cells too. Some of these white blood cells are formed in the bone marrow; others are formed in the lymph nodes, spleen or even the lining of capillaries of certain organs.
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