Evolution of the Human Heart into Four Chambers

Evolution of the Human Heart into Four Chambers The human heart does not look much like those Valentines Day candies or the pictures we drew on our love notes when we were in elementary school. The current human heart is a large muscular organ with four chambers, a septum, several valves, and other various parts necessary for pumping blood all around the human body. However, this amazing organ is a product of evolution and has spent millions of years perfecting itself in order to keep humans alive. Invertebrate Hearts Invertebrate animals have very simple circulatory systems. Many do not have a heart or blood because they are not complex enough to need a way to get nutrients to their body cells. Their cells are able to just absorb nutrients through their skin or from other cells. As the invertebrates become a little more complex, they use an open circulatory system. This type of circulatory system does not have any blood vessels or has very few. The blood is pumped throughout the tissues and filters back to the pumping mechanism. Like in earthworms, this type of circulatory system does not use an actual heart. It has one or more small muscular areas capable of contracting and pushing the blood and then reabsorbing it as it filters back. However, these muscular regions were the precursors to our complex human heart. Fish Hearts Of the vertebrates, fish have the simplest type of heart. While it is a closed circulatory system, it has only two chambers. The top is called the atrium and the bottom chamber is called the ventricle. It has only one large vessel that feeds the blood into the gills to get oxygen and then transports it around the fishs body. Frog Hearts It is thought that while fish only lived in the oceans, amphibians like the frog were the link between water-dwelling animals and the newer land animals that evolved. Logically, it follows that frogs would, therefore, have a more complex heart than fish since they are higher on the evolutionary chain. In fact, frogs have a three-chambered heart. Frogs evolved to have two atria instead of one, but still only have one ventricle. The separation of the atria allows frogs to keep the oxygenated and deoxygenated blood separate as they come into the heart. The single ventricle is very large and very muscular so it can pump the oxygenated blood throughout the various blood vessels in the body. Turtle Hearts The next step up on the evolutionary ladder is the reptiles. It was recently discovered that some reptiles, like turtles, actually have a heart that has a sort of a three and a half chambered heart. There is a small septum that goes about halfway down the ventricle. The blood is still able to mix in the ventricle, but the timing of the pumping of the ventricle minimizes that mixing of the blood. Human Hearts The human heart, along with the rest of the mammals, is the most complex having four chambers. The human heart has a fully formed septum that separates both the atria and the ventricles. The atria sit on top of the ventricles. The right atrium receives deoxygenated blood coming back from various parts of the body. That blood is then let into the right ventricle which pumps the blood to the lungs through the pulmonary artery. The blood gets oxygenated and then returns to the left atrium through the pulmonary veins. The oxygenated blood then goes into the left ventricle and is pumped out to the body through the largest artery in the body, the aorta. This complex, but efficient, way of getting oxygen and nutrients to body tissues took billions of years to evolve and perfect.

Two-Letter Words in Spanish

Two-Letter Words in Spanish If youve played Scrabble or similar games, you know how handy two-letter words can be. Thats true in Spanish versions of Scrabble as well as online games such as Apalabrados (Angry Words) and Wordfeud too. Following is a list of the two-letter words of Spanish that are listed in the Spanish Royal Academys dictionary, along with definitions and links to relevant articles and lessons. The list may not coincide with words that are legal to use in a specific game. Not all possible definitions are given. Words containing the combinations of ch and ll are also included here, as they used to be recognized as separate letters of the Spanish alphabet and are still treated as such in some games. ad - Word used in Latin phrases such as ad hoc ah - Interjection used to express sympathy and other emotions, sometimes similarly to ah aj - ailment (seldom used, and then usually in the plural) al - contraction of a el ar - interjection used in the military to order the immediate execution of a movement as - ace ax - ouch (antiquated) ay - ouch, oh be - the letter b bu - boo ca - a synonym for porque (antiquated) ce - the letter c cu - the letter q da - a conjugated form of dar de - of, from di - a conjugated form of dar do - do (first note of the musical scale) ea - interjection of encouragement or resolution eh - interjection used to get attention el - the masculine singular definite article en - in, on es - conjugated form of ser et - and (antiquated) ex - former fa - fa fe - faith fo - exclamation indicating displeasure or disgust fu - snort ge - the letter g ha - conjugated form of haber he - conjugated form of haber hi - shortened form of hijo (son) used in some expressions (antiquated) id - conjugated form of ir in - Word used in Latin phrases such as in promptu ir - to go ja - ha je - ha ji - ha; 22nd letter of the Greek alphabet ju - ha la - the feminine singular definite article le - a third-person object pronoun lo - a word of various uses as a pronoun or neuter definite article lle - variation of le (antiquated) me - me mi - my mu - moo na - contraction for en la (antiquated) ne - synonym for ni (antiquated) ni - nor no - no, not à ±a - shortened form of seà ±ora (antiquated) à ±o - shortened form of seà ±or (antiquated) à ±u - gnu oa - a Honduran childrens game oc - Occitan (a language related to Catalan) oh - oh os - the plural familiar second-person pronoun ox - interjection used to frighten birds and other animals pe - the letter p pi - pi pu - variation of puf (interjection used as a reaction to a bad smell) re - re (second note of the musical scale) ro - interjection, usually repeated, used in calming children se - the third-person reflexive pronoun so - under (rarely used); variation of su (antiquated); whoa su - his, her, your ta - interjection imitating a knock on a door te - you (as the second-person singular object pronoun) to - interjection used for calling dogs; whoa tu - second-person familiar singular possessive adjective (the pronoun form is tà º, although most games dont distinguish between accented and unaccented vowels) uf - whew, yuck uh - interjection of hesitation or disdain un - a, an, one va - conjugated form of ir ve - conjugated form of ver vi - conjugated form of ver xi - 14th letter of the Greek alphabet ya - adverb of vague meaning often used to add emphasis ye - the letter y yo - I (first-person singular subject pronoun)