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Excretion

excretion in humans
-excretion is the last process of the role of nutrition, but just as important as everyone else. The unit responsible for carrying out the excretory, but also involved other devices diferentes.El excretory apparatus is responsible for cleaning the blood of waste products it has collected in each tissue and organ. It consists of the kidneys, ureters, bladder and urethra.

The kidneys are the organs responsible for cleansing the blood of waste, making the urine as a final product. have about 12 cm in length and are arranged in the back of abdomen.Los ureters are the tubes that start from the renal pelvis and carries urine to the bladder.

The bladder is a muscular organ, shaped like a balloon, which expands as it fills with urine and compressed in the act of urination. The bladder capacity is approximately 350 cm3. When the tension of the walls of the bladder exceeds a certain value, there is a nervous reflex, which receives Reflecting the name of urination, and urination becomes conscious.

The urethra is a tube from the bladder and the urine is expelled by urination.
The kidneys are made up of nephrons, which are responsible for producing urine. In a nephron can distinguish the following parts: glomerulus, proximal tubule, loop of Henle, distal tubule and collecting duct, which collects the urine.

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Watson and Crick article

MOLECULAR STRUCTURE OF NUCLEIC ACIDS
A Structure for Deoxyribonucleic Acid
We suggest a structure for the salt of deoxyribonucleic acid (DNA .). This structure has novel features which are of considerable biological interest.
A structure for nucleic acid has been proposed by Pauling and Corey (1). Have kindly put at our disposal the manuscript before publication. Their model consists of three intertwined chains, with phosphates near the axis of the fiber, and the bases out. In our opinion, this structure is unsatisfactory for two reasons: (1) believe that the material obtained the X-ray diagrams is the salt, not the free acid. Without the acidic hydrogen atoms is not clear what forces can hold the structure together, especially as the negatively charged phosphates near the axis will repel each other. (2) Some of the van der Waals distances appear to be too small.
Another triple chain structure has been suggested by Fraser (in press). In his model the phosphates are out and the bases inward, held together by hydrogen bonds. This structure thus described is rather ill-defined as not discussed.
We offer here a radically different structure for the salt deoxyribonucleic acid. This structure has two helical chains each lap around the same axis (see diagram). We made the usual chemical assumptions, specifically, that each chain consists of phosphate diester groups joining beta-D residues desoxirribofuranosa links-3 ', 5'. The two chains (but not their bases) are related by a dyad perpendicular to the axis of the fiber. Both chains follow right-handed helix, but due to the dyad the sequences of atoms in the two chains run in opposite directions. Each of the chains separate model resembles Furberg No. 1 (2), that is, the bases are on the inside of the loop and phosphates on the outside. The configuration of the sugar and the atoms near approaches to the "standard configuration" of Furberg, sugar is available at right angles to the base attached. There is a residue on each chain every 3.4 Å in the direction-z. We have assumed an angle of 36 degrees between adjacent residues in the same chain, so that the structure is repeated after 10 residues on each chain, ie after 34 Å. The distance of a phosphorus atom from the axis of the fiber is 10 Å. As the phosphates are on the outside, cations have easy access to them. The structure is open and the water content is rather high. For us, content low bases and the structure would approach would be more compact.
The novel aspect of the structure is the manner in which the two chains are held together by purine and pyrimidine bases. The planes of the bases are perpendicular to the axis of the fiber. They meet in pairs, a base of one of the chains connected by hydrogen bonds to a base of the other chain, and thus the two are joined side by side with identical z-coordinate One of the pair must be purine and one pyrimidine. Hydrogen bonds are as follows: purine position 1 to pyrimidine position 1; purine position 6 to pyrimidine position 6 [etc.]
This figure is purely schematic. The two ribbons symbolize the sugar-phosphate chains, and the horizontal rods the pairs of bases holding the chains together. The vertical line marks the axis of the fiber.

Assuming that the bases only occur within the structure in the most plausible tautomeric forms (that is, setting the keto rather than enol) are the specific pairs of bases can join. These pairs are: adenine (purine) with thymine (pyrimidine) and guanine (purine) with cytosine (pyrimidine).
In other words, if an adenine is a member of a couple, on a string, then the other member must be thymine; something similar happens for the guanine and cytosine. The sequence of bases on a single chain does not appear to be restricted in any way. However, if they can only form specific base pairs, it follows that knowing the sequence of bases on one strand, then the sequence on the other chain is automatically determined.
has been found experimentally (3.4) that the ratio of adenine to thymine, and the ratio of guanine to cytosine, are always very close to unity for deoxyribonucleic acid. It is probably impossible to build this structure with a ribose sugar instead of deoxyribose, the extra oxygen atom would make too closed and form a van der Waals bond.
The X-ray data previously published (5.6) on deoxyribonucleic acid are insufficient for a rigorous test of our structure. So far we can say is roughly compatible with the experimental data, but should be seen as unproven until you have verified with more accurate results. Some of these will be submitted on the following communications. We were not aware of the details of the results presented when we devised our structure, which rests mainly but not entirely on published and experimental data and stereochemical arguments.
not escaped our communication pairing específico que hemos postulado sugiere inmediatamente un mecanismo copiador para el material genético .
Todos los detalles de la estructura, incluyendo las condiciones presumidas para su construcción, junto con un conjunto de coordenadas para los átomos, se publicarán con posterioridad.
Estamos en deuda con el Dr. Jerry Donohue por las constantes críticas y consejos, especialmente sobre distancias interatómicas. También hemos sido estimulados por el conocimiento general de la naturaleza y los resultados experimentales inéditos así como ideas del Dr. M.H.F. Wilkins , la Dra. R.E. Franklin y sus colaboradores del King's College , en Londres. Uno Whom (JDW) has been funded by a grant from the National Foundation for infantile paralysis.
JD Watson FHC Crick

Medical Research Council Unit for the Study of the Structure Molecular Biological Systems
Cavendish Laboratory, Cambridge


April 2 (1) Pauling, L. and Corey, RB, Nature, 171, 346 (1953); Proc.USNat.Sci., 39, 84 (1953).
(2) Furberg, S. Minutes Chem.Scand., 6, 634 (1952).
(3) Chargaff, e. For reference see Zamenhof, S, Brawerman, G. and Chargaff, E., Biochem. et. Biophys. Ata, 9, 402 (1952).
(4) Wyatt, GR, J. Gen.Physiol., 36, 201 (1952).
(5) Astbury, WT, Symp.Soc.Exp.Biol. 1, Nucleic Acid, 66 (Cambridge University Press, 1947).
(6) Wilkins, MHF and Randall, JT, Biochim. et Biophys. Acta, 10, 192 (1953).

Article published in the journal Nature , April 25, 1953, p. 737.

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The heart is a hollow organ that is located roughly in the middle of the chest. Is just above the diaphragm muscle, in front of the spine, behind the sternum and between the two lungs.

heart shape resembles a triangle with the base toward the apex up and down and left. In the adult weighs between 250 and 300 gr. and is about the size of a fist. Inside

differ

4 chambers: two upper atria and two lower chambers called ventricles. A vertical wall (called the atrio-ventricular septum) divides the heart into 2 halves: right and left. The atrium and ventricle on one side, are in communication with each other by the atrio-ventricular orifice.

These holes are provided with a triangular sheet called valves, whose mission is to control the flow of blood that circulates inside the heart by opening or closing. The valve on the right side is called the tricuspid because it consists of three layers. The left valve is called mitral valve and consists of two sheets.

contractility and elasticity of the heart walls allow it to contract and dilate in a rhythm in what is known as heart rate, functioning as a pump and driving the blood, causing it to circulate continuously around the body. heartbeats occur 75 times per minute, varying according to age, sex, exercise and health status of the individual.

Inside the body, blood is constantly moving through the activity of the heart, which through its contraction forces her to move continuously in the same direction.

However, this blood, no massive floods and uncontrolled organs and body structures but their displacement occurs along the inside of a blood vessel called channels, which allow you from the heart to each and every body parts.

elements known as the blood vessels are arteries the veins and capillaries.

Arteries are vessels that starting from the ventricles carry blood to different organs.

Veins are blood vessels coming from the various organs of the body carrying blood to the heart, reaching their atria.

Capillaries are small-bore tubes that are in communication by a party with the ramifications of the arteries and the other with smaller veins, acting therefore as a bridge between both systems.

The heart and blood vessels are the transportation system, and thanks to him, it's possible contribution oxygen and nutrients to all parts of the body and the collection and carbon dioxide and waste products that occur therein.

blood (venous blood-CO2-) after returning from the body enters the right atrium, passes into the right ventricle is pumped from there to the "artery" lung, which is divided into two branches of which will the right lung and one to the left lung.

in the lungs is exchanged for O2 and CO2-rich blood with sufficient oxygen (arterial blood), returns for the "veins" lung to the left atrium, thus passes into the left ventricle to the aorta exit throughout the body where new tissues made in exchange oxygen for carbon dioxide.

The movement of blood in the transport system can be divided into two cycles: the greater circulation or general circulation and the pulmonary circulation, pulmonary circulation also called .

The pulmonary circulation was discovered in 1553 by English Miguel Servet and is known as pulmonary circulation because it corresponds to the stretch run in which the blood passes through the lungs.

largest circulation was discovered by the English physiologist William Harvey in 1628 for the passage of blood through the body.