lunes, 16 de febrero de 2015

Videos - Vital Functions: Nutrition.

These videos are related to Nutrition as a Vital Function of Living Beings (mainly animals).

I have divided the carpet into four parts: Nutrition, Respiration, Circulation and Excretion. The videos explain the main differences between organs and systems in different animal groups.

Level: 2nd ESO.





domingo, 15 de febrero de 2015

Breath and Hyperventilation: Functions and Risks

The Scream (Edvard Munch)
A human being can survive after more than fifteen days without eating, or more than three days without drinking. We can't, however, survive without breathing for more than a few seconds. Breathing is the process that provides oxygen to our body. Our cells need oxygen at every moment to obtain energy by respiration (into organelles called mitochondrions) and carry out their vital functions and inner or outer cellular activities.

At rest, a human being breathes about twelve times per minute, exchanging approximately six litres of air. If we are doing some physical exercise, the requirements of oxygen rise, so we will breathe with more frequency and depth. In extreme conditions we could increase the exchange to more than forty litres per minute.

We need to breathe constantly. So we can stand under water, without oxygen supply, for only little time. People who like diving must improve their capacity to hold their breath (what we call apnea). The longer you could hold your breath, the better diver you would be. Many divers use a trick called hyperventilation to increase their capacity to stand in apnea: after hyperventilation, you can really hold your breath for longer.

What is hyperventilation? Simply, hyperventilation consists of doing several very deep inhalations and exhalations. For one minute or so, we exchange as much air as possible. After that, our ability to hold our breath will be at least dobule.

How does this process work? It's important, because many people practice it when they dive, but they don't know that it could be a bit dangerous if it's done without control.

Most people think that the process works raising the amount of oxygen that we are able to take, although that is nonsense. If we measure the saturation of our arterial blood, we will find out that it must be between 99% and 100% all the time. The oxygen is transported in our blood linked to haemoglobin, into the erythrocytes (red cells of our body), and all the haemoglobin is full of oxygen for the whole time in our arteries (our veins transport deoxygenated blood from our tissues, so its saturation is quite lower).

So, if saturation is always close to 100%, it can't be higher in any way. In fact, when our cells need more oxygen, our heart pumps our blood more quickly, so more blood arrives at the lungs and the tissues, and more exchanges and respiration processes are possible.

Let's return, then, to the question, because, if hyperventilation doesn't increase our capacity to take oxygen, how does it work? The answer is not related to oxygen, but to the other gas exchanged during respiration: carbon dioxide.

Carbon dioxide is a waste product of cell metabolism. To obtain energy, cells combust glucose using oxygen and producing energy and carbon dioxide. This molecule must be eliminated, so our cells pass it to the blood. Blood carries carbon dioxide to the lungs, where it is released to the exterior.
Diving: Apnea 
Carbon dioxide is transported in our blood mainly transformed to bicarbonate. Production of bicarbonate, besides, reduce the pH of our blood, due to the acid nature of this substance. And bicarbonate and pH are the most important signals that our body detects when the amount of gases starts to be a problem.

What it means is that when we hold our breath, the supply of oxygen decreases slowly, but the amounts of bicarbonate of our blood rises quickly, and the pH decreases. Our body has many chemical receptors that alert our brain when the bicarbonate levels are high or the pH is low. In fact, these are the most important signals that make our brain urge us to breathe, because they can be detected before the levels of oxygen decrease to dramatical levels.

When we hyperventilate we don't increase the amount of oxygen of our blood, but we reduce the amount of bicarbonate and increase pH. So, after hyperventilating we will be able to hold our breath for longer, because the levels of oxygen are no higher, but the levels of carbon dioxide are much lower. And it will take long time until this level is high enough to make the receptors send the warming alert to the brain.
Diving (author: matthew lee)
Hyperventilation can be dangerous, because if it is used without control the levels of carbon dioxide could descend to extremely low levels. Sometimes, the amount of carbon dioxide is so low that the diver doesn't feel the necessity to breathe for too long, and then the levels of oxygen fall dramatically, so dramatically that it's brain lacks oxygen, but the warning signs have not been sent. And the diver, in that situation, could faint. On land that's not a problem, because when a human loses its conscientiousness starts breathing automatically. However, if this occurred under the water you would drown in few seconds.

For this reason, hyperventilation is a good way to improve our capacity to hold our breathe, but is not free from dangers, so it must be done carefully and under the control of another person.

domingo, 8 de febrero de 2015

Tipos de Metamorfismo e Intensidad.

Estudiaremos ahora los tipos de metamorfismo, sus características y las zonas de la corteza en la que pueden darse.
Gneiss foliado, por Dssc49
Por un lado tenemos el metamorfismo térmico o de contacto. Es un proceso térmico. La presión juega un papel poco importante. Se desarrolla en rocas que rodean un plutón o un batolito. El magma calienta las rocas que lo rodean formando una aureola metamórfica. Las rocas afectadas dependen por lo tanto del tamaño del plutón, a mayor tamaño, mayor aureola metamórfica.

Hay una serie de minerales índice que nos indican las bandas de metamorfismos decreciente, desde lo más próximo al plutón, hasta lo más alejado. Los minerales usados para analizar esas zonas son la sillimanita en la zona que rodea el plutón, la andalucita en zonas un poco más alejaddas, la batolita más allá de la andalucita y finalmente la clorita. Esta última marca el punto final a partir del cual el plutón ya no produce metamorfismo.

A estos minerales se les denomina minerales índice y son el reflejo de unas bandas de temperatura concretas. No quiere decir que sean los únicos minerales que se forman, sino que son útiles para marcar los intervalos de temperatura concretos.

En segundo lugar tenemos el dinamometamorfismo o metamorfismo dinámico. Tiene lugar en zonas de factura donde hay movimientos o desplazamientos entre bloques de corteza. El movimiento de los bloques produce un rozamiento que, por un lado tritura la roca y por otro la calienta de tal manera que en una banda estrecha de la zona de fractura las rocas también sufren transformacones.
La roca resultante es la milonita o brecha de falla, dependiendo del grado de trituración. La milonita esá tan triturada queno se ven los granos a simple vista, mientras que la brecha de falla sí tiene granos visibles.
Dinamometamorfismo en fallas.
Estas rocas son, por lo tanto, formadas pro presiones dirigidas.

Por otro lado encontramos el metasomatismo. Va asociado al metamorfismo de contacto. Su agente principal son fluidos mineralizados. Se forma alrededor de un plutón, concretamente alrededor de una intrusión.

El metamorfismo de enterramiento lo sufren rocas a grandes produndidades y que están sometidos a presiones litostáticas muy elevadas. El agente principal es la presión litostática. El calor juega también un papel importante, aunque no es el principal. Tiene lugar en zonas profundas de la corteza, a prefundidades de alrededor de diez kilómetros, donde la presión hidrostática alcanza valores de alrededor de 10 Kbares.

El metamorfismo regional es un término que alude a la amplitud de las zonas a las implica. Es el asociado a los movimientos orogénicos, a la formación de cordilleras, es decir, zonas de convergencia entre placas. Estas áreas están sometidas a compresiones muy fuertes. Hay presiones dirigidas, puede actuar en zonas profundas, con altas presiones hidrostáticas, donde hay magmatismo y por lo tanto calor (es decir, también hay metasomatismo).
Cámaras magnéticas importantes, por USGS
Se puede hablar de muchos tipos de metamorfismo regional. Puede aparecer con altas temperaturas y presiones moderada, como por ejemplo el que encontramos un cono térmico, en los arcos de islas; y metamorfismo regional de altas presiones y bajas temperaturas, como el que se da en la zona próxima a las fosas oceánicas.

El metamorfismo regional es típico de zonas de bordes compresivos (orógenos).

Intensidad del metamorfismo.

Para medir la intensidad del metamorfismo se usaba una clasificación dividiéndose por zonas según la intensidad. En esta división hablaríamos de epizona, mesozona y catazona.

La epizona es la zona en la que las temperaturas se encuentran entre 200-450ºC. Hoy en día se habla más bien de metamorfismo de muy bajo grado y de bajo grado dentro de esta categoría.

En la mesozona las temperaturas se encuentran entre 400-650ºC. Hoy en día hablamos de metamorfismo de grado intermedio.

En la catazona las temperaturas parten de los 650ºC hasta llegar a las temperaturas de fusión. Hoy en día se habla de metamorfismo de alto grado.

viernes, 6 de febrero de 2015

Respiration: Pulmonary Ventilation and Exchange of Gases

Respiration can be divided into three different consecutive processes: ventilation, external or pulmonary respiration and internal or tissular respiration.
Respiratory System
Ventilation is the process related to the movement of the air, from the environment to the interior of our lungs and from the interior of our lungs to the environment. So, ventilation can also be split into two different processes, inhalation when the air flows into our lungs, and exhalation when the air flows from our lungs.

Our lungs have no inner muscles, the movement of the air depends on the muscular movements that involve the rib cage and the diaphragm. The lungs are surrounded by two thin tissular layers called pleurae. The outer one, called parietal pleura, covers the inner surface of the rig cage. The inner one, called visceral pleura, covers the surface of the lungs. Between these two pleura we can find a fluid called pleural liquid. Pleural liquid maintains both pleurae bounded.

When the rib cage moves, the parietal pleura moves too, and it leaves to the movement of visceral pleura, that is firmly stuck due to the pleural liquid. Visceral pleura moves lungs.
Respiratory System, by LadyofHats
How does inhalation take place? It is quite simple. External intercostal muscles contract, and this movement makes the rib cage ascend. This makes the rib cage increase its volume. At the same time, the diaphragm contracts. Both muscular contractions cause the lungs to increase their volume, because they are bound to the rib cage and the diaphragm. So the pressure inside the lungs falls, and becomes lower than air pressure. Gases flow from places with high pressure to places with low pressure, so the air enters the lungs.

Exhalation is a passive process. Lung are made up of many contractile fibers, they are very elastic structures. So, when rib external intercostal muscles and diaphragm relax, the elastic properties of lungs make them return to their original size. Lungs decrease in size, so air pressure inside them rises and becomes higher than air pressure. And the air exits the lungs, because fluids flow from high pressure places to low pressure places.

Sometimes we need to increase the speed of inhalation and exhalation. when this happens the elastic properties of the lung are not sufficient to maintain the ventilatory rate. We must expel air more quickly. This process is called forced exhalation, and is carried out by internal intercostal muscles and abdominal muscles. When these muscles contract, the rib cage returns to its original position very quickly, making the lungs shrink in few seconds.

This happens, for instance, when we are doing physical exercise and we need to breathe quickly to provide oxygen to our muscles, or when we want to shout, or whistle or even sing.
Inhalation and exhalation
When we talk about external respiration we refer to the process of gases exchange between lungs and blood. It takes place in pulmonar alveoli, tiny spherical structures of our lungs, covered by a very thin epithelial layer and surrounded by capilar vessels.

The air from our environment enters into the alveoli (thanks to inhalation). This air is rich in oxygen, but has a low quantity of carbon dioxide. The blood that has reached the capilar vessels of the alveoli comes from the body, and has a low quantity of oxygen, and a high quantity of carbon dioxide.

Chemical substances tend to move from high concentration places to low concentration places (this is called osmosis), so oxygen moves from the air to the blood, whereas carbon dioxide moves from the blood to the air. This process is called pulmonary or external respiration.

Due to this, when the blood exits the lungs it has a high concentration of oxygen and a low concentration of carbon dioxide.

To improve the transport, oxygen travels in the blood linked to a protein called hemoglobin. This protein can be found inside the red cells (erythrocytes). This is the reason why erythrocytes are very important to our body: they are the cells that transport oxygen from the lungs to the tissues.
Hemoglobin and hero group by Openstax College
Carbon dioxide travels in our blood transformed in carbonic acid. This is why when we consume a big amount of oxygen, because we are doing hard physical exercise, for instance, the pH of our blood decreases: the accumulation of carbon dioxide increase the amount of carbonic acid in the blood and acids tend to reduce the pH of solutions.
Respiratory System and Exchange of Gases, by NLHBI
When the blood arrives at the tissues the situation is just the opposite as in the lungs: the erythrocytes are charged with oxygen, however the cells of the tissues have consumed the oxygen to obtain energy (during the cell respiration), so there are a low quantity of oxygen in there. On the other hand, cell respiration has produce a high amounts of carbon dioxide, so the tissues have a high quantity of this product.

This is the reason why oxygen moves from the blood (that comes from the lungs with high amounts of oxygen) to the tissues, and at the same time carbon dioxide moves from the tissues to the blood. This exchange is called tissular or internal respiration.

Deoxygenated blood, full of carbon dioxide, must return to the lungs to exchange gases again, and the cycle has been completed.

domingo, 1 de febrero de 2015

Youtube Videos: Minerals and Rocks.

Two new videos added to my youtube channel.

The first one is related to the minerals and their main properties.
Level: 1st ESO.

The second one is related to rocks and their main properties. It finish with the rock cycle.
Level: 1st ESO.