Blood has two important fractions. A cell fraction carries globules or erythrocytes, white globules or leucocytes, plackets and the so called immune cells (lymphocytes, neutrophyles). The other one contains plasma. Plasma is everything in blood which is not cellular. It has a very important liquid portion. A lot of it is water (99%) and the rest ions (potassium, calcium, and a whole lot of sodium), proteins (among them we can find hemoglobin) and loose gases (oxygen and CD).
Conceptually: level of calcium in blood will be low as compared to the rest. We will find it concentrated in the bones but in the rest of the organism is low. It has a signaling function and that is why its level has to be low. This way it remains vulnerable to any change that might carry a signal. Instead, sodium will be very high. Potassium and bi carbonate are also high. And we will find proteins, all sorts of proteins. As a concept, proteins are big, heavy, and very difficult to move. Ions instead are small, easily movable, and diffusible. Cells are also big and heavy to move. They contain mitochondria, endoplasm reticule, membrane, a whole large, complex structure. Membranes are not easy to penetrate. Water is easy moving, since it is a small molecule. And what penetrates that membrane is a gas, thus easily diffusible.
We will find gases in the plasma: Oxygen and Carbon Dioxide. Hemoglobin is a protein which will carry most of the blood’s oxygen. The process by which oxygen passes from the alveolus to the capillary is called diffusion. It is a gas passage. It slides down from a higher to a lower oxygen concentration. And CD also uses that system, from a major CD concentration in the capillary to a lower one in the alveolus. It is no doubt a passive transportation. Then, since oxygen will travel in blood, 97% will do so stuck to hemoglobin and a small percentage will be carried in the plasma. Carbon Dioxide, on the other hand, will travel the opposite way.
Hemoglobin is a molecule composed by four parts. In the center has an iron atom called tetramerous. Hemoglobin main function is carrying oxygen through the blood. People that have a low hemoglobin level will not have oxygen availability (or a low one) in their tissues. Blood can not saturate with oxygen, it is not adapted for that function, so its transportation will be low, just because those low hemoglobin levels. Hemoglobin, then, will capture oxygen through the alveolar capillary, will travel through the arterial blood to the tissues. It will liberate oxygen through the tissue capillary, also incorporate some Carbon Dioxide, but it travels without oxygen until the alveolar capillary in order to be able to charge itself again. Thus, hemoglobin mainly transports oxygen. And some oxygen can be also carried by the plasma.
In a tetra metric structure, with an iron center, anemia means to possess a low hemoglobin level. Hemoglobin’s major quantity is within the erythrocytes, in the red globules. The hg part is dissolved into plasma and part of the red globules. This means that any treatment or sickness which might provoke a red globules diminution will end up in anemia. Where is hemoglobin? It is dissolved into plasma. Where else is it? It inside the red globules which jeans that it forms part of both blood fractions: cells and plasma. Most of it we will find it inside the red globules. If red globules level diminishes, so does hemoglobin. And we will suffer from anemia as a consequence of a diminution of hemoglobin. Now, I could suffer from anemia without any diminution of red globules. That could happen if a person has any trouble when his initial composition takes place, when protein is formed. Most of the proteins are synthesized in the liver. During a hepatic sickness which might affect hemoglobin, the last will lower the hemoglobin level in erythrocytes and also in blood. We could have normal erythrocytes but with a low hemoglobin level. Hemoglobin will relate to oxygen at the iron level. So, when I mention ferropenic anemia, what am I referring to? I am referring to a low iron level. Without iron there is no hemoglobin. Iron can not be replaced. If so, other molecule would be formed. Where does iron come from? It comes from food. Once again we find the importance of alimentation.
So then, oxygen joins hemoglobin at iron level. We had already expressed that proteins are very complex, large, special structures. Hemoglobin possesses a system denominated cooperation system. This is because hemoglobin saturation curve is a sigmoid curve. Hemoglobin will have a great job to capture oxygen’s first molecule. It will have to alter its conformation, its spatial disposition. The second one will be an easier task. And so on. This is what we called cooperativeness. As oxygen saturation rises easier will be to catch it. The same process occurs with their liberation. Once it liberates the first, the easier it goes. It is a concept similar to inertia. Just think that oxygen it’s intimately linked to hemoglobin. Why is this useful? It is in order to comprehend the diffusion concept. In altitude, the body’s response will be hyper-ventilate. In a quasi involuntary fashion the thorax muscles will raise ventilation. Almost instinctively a body starts to hyper-ventilate be it in altitudes as in exercising. That is why oxygen availability diminishes. We had expressed that Carbon Dioxide was dissolved in blood, which allows its exit; it is available to mechanisms such as diffusion. Oxygen, however, is essentially linked to hemoglobin. And hemoglobin does not have an easy task in liberating oxygen. It will liberate what normally it is used to. But when facing an alveolar ventilation level rise (amount of gases carried from alveolus to blood per minute) oxygen will not be able to respond that easily. It will not be liberated in the same way that CD does. If I hyper-ventilate I am liberating much CD –this substance diminishes in blood-, and I am seeking for oxygen. However, the amount of oxygen that I might be able to incorporate will not be much since its transportation system is linked to hemoglobin and its amount is not as available as Carbon Dioxide is. Thus, oxygen rise in blood in not significant, and the operation will not be successful. Therefore, hyperventilation as a reflex act is not very successful. Moreover, other methods are applied and hyperventilation can even work the other way around and could provoke fainting, unbalancing. Carbon Dioxide is the main brain vessel dilatator. Vessel dilatation will help carrying blood. Thus if I diminish CD in blood I am also diminishing my brain vessel dilatation. On the contrary, there will be vessel constriction, with less oxygen available and fainting –in the best of cases is inevitable. The worst could be coma, death. Once our brain lacks any oxygen coma and death are its cruel destiny.
Conceptual Formulas
Alveolar ventilation: amount of gases which are to be exchanged between the alveolus and the capillary blood. This will be equal to current volume per respiratory frequency. Respiratory frequency is the amount of breathing per minute, and its usual amount is 12. Current volume is the amount of air exchanged through inspiration and expiration. When I perform a quiet inspiration, 500 ml of air enter the body. And the same goes on with a normal expiration. Current volume is the volume normally exchanged between inspiration and expiration.
What is dead volume? Not all the air incorporated will reach the alveolus, not all will be perform the alveolar ventilation. Therefore, out of the current volume some will be lost; it will not be used in alveolar ventilation, other part will. Then current volume equals alveolar ventilation plus dead volume. Dead volume is the air a person incorporates which will not perform the ventilation process; it will not make any gaseous exchange. This dead volume possesses two portions: an anatomic fraction given by the conduction tracts, the air that reaches the trachea or the larynges. If I have an obstruction, let us say a tumor in the trachea or in the larynges then the dead volume will increase. The second fraction of the dead volume is functional. It will be the air remaining in the apical alveolus which might be poorly per-fused. Lung has a base and a vertex or apex. In both portions we will find alveolus, and they are respectively denominated basal and apical. They are not anatomically equal nor are the pressures they deal with due to a matter of gravity.
In order to analyze the, therefore, we will introduce two concepts.
Q equals perfusion and perfusion deals with the reached blood amount.
D equals ventilation and ventilation deals with the amount of air which reaches the alveolus.
Gaseous exchange requires these two things, oxygen from the alveolus and oxygenated blood. Due to gravity the apical alveolus are larger, they are more distended. The basal alveoli are smaller. The apical will be better ventilated. They are larger then air reaches them much easier. Basal ones, instead, are worse ventilated. On the other hand, due to the heart location and the vessel distribution (lung arteries) it will be harder for blood to irrigate lung’s superior portions. And due to gravity, basal portions of the lung will be irrigated more easily. Then the basal alveolus will be better per-fused and the apical worse per-fused. Perfusion is more significant at a basal level. Blood which comes from the heart through the lung artery will reach basal alveolus rather than apical ones. If we are to make the integration with the cardiovascular: venous blood reaches the right auricle, will pass the tricuspid valve to the right ventricle, and from there to the lung artery. Lung artery branches into smaller ones. Most of them will reach the basal alveolus. A minority will reach the apical alveolus. Gaseous exchange is produced there at the lung capillary level. Carbon Dioxide is liberated and oxygen incorporated. That oxygen will travel in the lung veins to the left auricle, from there reaches the left ventricle through the mitra valve. Goes out the left ventricle in ejection phase, in the systole phase comes out in direction to the aorta. The aorta branches into other arteries. It will reach the tissue capillary where diffusion is produced. Diffusion takes place once again; oxygen and CD do it through a membrane. Oxygen is left and CD incorporated which is carried in a dissolved fashion. Oxygen, to a lesser extent, also travels dissolved. It does it together with hemoglobin and this will impede any change. It returns through the veins towards the right auricle. The Superior and Inferior Cave Veins ended in the right auricle. We see once again a sort of holistic vision of the body. Body organs do not work separately from one another. They just need to be analyzed that way.
Apical Alveolus: richly ventilated, poorly per fused
Basal Alveolus: richly per fused, poorly ventilated.
Why? It is because of gravity.Then we start to comprehend why the apical alveolus have a dead volume. They receive much air, little blood. Blood that might pass through there will oxygenate but they will receive much oxygen with little use which will form part of this dead volume, since that air will not perform any gaseous exchange.
The current volume will be equal to the useful air which will be ventilated at alveolus level and that air which will not have utility because it might remain in the conductive tracts or that might end in the apical alveolus which in turn does not receive enough blood to use it during a gaseous exchange.
Lung Volume is the amount of air that reaches the lung equal to current volume against respiratory frequency, a simple calculus. Current volume is 500 ml against 12 respiratory frequencies per minute, or 6 liters. This is the air that reaches the lung and comes out from it. However, we also do know that not every bit is useful. Only some parts receive alveolar ventilation. And current volume will include both.
Renal System: Generalities
Which is the kidney’s main function? Is it filtering? What else? What does the kidney produce? It is obviously urine. How is this produced? It starts in blood. The kidney will just make some clearing, some sort of purification. It will regulate the salt exit (this last substance entering will not be regulated; generally in water and food both entering and going out are regulated, thirst, hunger, urination, defecation)
When we analyze the renal system wee talk again about liquids, ions, we are referring once again to blood, to plasma.
The kidney will regulate the hydro saline (water and salts) equilibrium. Water in men is about 60%, and in women some 50%. Women naturally have more fat than men. Fat is a low liquid tissue. Other tissues, however, contain a lot of water, blood for example. It is a fluid tissue (99% water) but a tissue at last. This liquid is distributed in a certain way: intracellular liquid represents two thirds of the total corporal water, a 40% of the total body weight. The extra-cellular liquid represents a third of the body’s total liquids and a 20% of the body’s total weight (within the blood, for example, it represents a 5% of the total weight; within the interstice (the space between cells) we might find a 15%.
Renal Anatomy and Blood Filtration
The kidney’s function is to filter blood. Plasmatic fraction is 99% water and besides it constitutes a 5% of the body’s total weight. That water will be filtered by the kidney. At this level blood will pass through a artery-capillary-vein system. It will be filtered by one part of the kidney thus producing urine. This filtration will be produced through a membrane, very similar to membranes we have seen so far. The alveolar-capillary diffusion membrane and the diffusion membrane at a tissue level (capillary tissue) will have to be very thin in order to allow gas passage. This membrane will also be very selective, thin. It will allow the passage of water, ions, not cells, proteins. What it is filtered is water, ions, small molecules. Filtration criterion is size and weight.
Anatomic scheme of the kidney
Suprarenal glands or adrenals are nervous glands. The cellular origin of these glands is the same as in the brain. They are located over the kidney. They are made of nervous tissue. They will liberate neuronal hormones.
The kidney is formed by a fat capsule which protects them, a cortex and a medulla. Cortex and medulla will form triangular structures called Malpighi pyramids, with a medullar center, surrounded by cortex columns. These columns constitute a tubular system which contains a nefron, the functional unity of the kidney. This fraction will filter the blood until it turns it into urine.
the tissues. It will liberate oxygen through the tissue capillary, also incorporate some Carbon Dioxide, but it travels without oxygen until the alveolar capillary in order to be able to charge itself again. Thus, hemoglobin mainly transports oxygen. And some oxygen can be also carried by the plasma.
What is dead volume? Not all the air incorporated will reach the alveolus, not all will be perform the alveolar ventilation. Therefore, out of the current volume some will be lost; it will not be used in alveolar ventilation, other part will. Then current volume equals alveolar ventilation plus dead volume. Dead volume is the air a person incorporates which will not perform the ventilation process; it will not make any gaseous exchange. This dead volume possesses two portions: an anatomic fraction given by the conduction tracts, the air that reaches the trachea or the larynges. If I have an obstruction, let us say a tumor in the trachea or in the larynges then the dead volume will increase. The second fraction of the dead volume is functional. It will be the air remaining in the apical alveolus which might be poorly per-fused. Lung has a base and a vertex or apex. In both portions we will find alveolus, and they are respectively denominated basal and apical. They are not anatomically equal nor are the pressures they deal with due to a matter of gravity.
