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Guyton's Textbook of Medical Physiology states that "the total amount of water in a man of average weight (70 kilograms) is approximately 40 liters, averaging 57 percent of his total body weight. In a newborn infant, this may be as high as 75 percent of the body weight, but it progressively decreases from birth to old age, most of the decrease occurring during the first 10 years of life. Also, obesity decreases the percentage of water in the body, sometimes to as low as 45 percent". These figures are statistical averages, so are illustrative, and like all biostatistics, will vary with things like type of population, age and number of people sampled, and methodology. So there is not, and cannot be, a figure that is exactly the same for all people, for this or any other physiological measure. For example, Jackson's (1985) Anatomy & Physiology for Nurses gives a figure of 60% for the proportion of body-weight attributable to water, which approximates Guyton's 57%.
Skin also contains much water. The human body is about 60% water in adult males and 55% in adult females.
In diseased states where body water is affected, the compartment or compartments that have changed can give clues to the nature of the problem. Body water is regulated by hormones, including anti-diuretic hormone (ADH), aldosterone and atrial natriuretic peptide.
There are many methods to determine body water. One way to get a simple estimate is by calculation.
Per Netter's Atlas of Human Physiology, body water is broken down into the following compartments:
- Intracellular fluid (2/3 of body water). Per Guyton, in a body containing 40 liters of fluid, about 25 liters is intracellular, which amounts to 62.5% (5/8), close enough to the 2/3 rule of thumb. Jackson's texts states 70% of body fluid is intracellular.
- Extracellular fluid (1/3 of body water). Per Guyton's illustration, for a 40 litre body, about 15 litres is extracellular, which amounts to 37.5% Again, this is close to the 1/3 rule of thumb cited here.
- Plasma (1/5 of extracellular fluid). Per Guyton's illustration, of the 15 litres of extracellular fluid, plasma volume averages 3 litres. This amounts to 20%, the same as per Netter's Atlas.
- Interstitial fluid (4/5 of extracellular fluid)
- Transcellular fluid (a.k.a. "third space," normally ignored in calculations)
Measurement of body water
Dilution and equilibration
Total body water can be determined using Flowing afterglow mass spectrometry [http://www.fa-ms.com FA-MS] measurement of deuterium abundance in breath samples from individuals. A known dose of deuterated water (Heavy water, D2O) is ingested and allowed to equilibrate within the body water. The FA-MS instrument then measures the deuterium-to-hydrogen (D:H) ratio in the exhaled breath water vapour. The total body water is then accurately measured from the increase in breath deuterium content in relation to the volume of D2O ingested.
Different substances can be used to measure different fluid compartments:
- total body water: tritiated water or heavy water.
- extracellular fluid: inulin
- blood plasma: Evans blue
Intracellular fluid may then be estimated by subtracting extracellular fluid from total body water.
Bioelectrical impedance analysis
Another method of determining total body water percentage (TBW%) is via Bioelectrical Impedance Analysis (BIA). In the traditional BIA method, a person lies on a cot and spot electrodes are placed on the hands and bare feet. Electrolyte gel is applied first, and then a current of 50 kHz is introduced. BIA has emerged as a promising technique because of its simplicity, low cost, high reproducibility and noninvasiveness. BIA prediction equations can be either generalized or population-specific, allowing this method to be potentially very accurate. Selecting the appropriate equation is important to determining the quality of the results.
For clinical purposes, scientists are developing a multi-frequency BIA method that may further improve the method's ability to predict a person's hydration level. New segmental BIA equipment that uses more electrodes may lead to more precise measurements of specific parts of the body.
Na+ loss approximately correlates with fluid loss from extracellular fluid (ECF), since Na+ has a much higher concentration in ECF than intracellular fluid (ICF). In contrast, K+ has a much higher concentration in ICF than ECF, and therefore its loss rather correlates with fluid loss from ICF, since K+ loss from ECF causes the K+ in ICF to diffuse out of the cells, dragging water with it by osmosis.
The human heart is a muscular organ that provides a continuous bloodcirculation through the cardiac cycle and is one of the most vital organs in the human body. The heart is an organ but made up of a collection of different tissues. It is divided into four main chambers: the two upper chambers are called the left and right atria and two lower chambers are called the right and left ventricles.There is a thick wall of muscle separating the right side and the left side of the heart called the septum. Normally with each beat the right ventricle pumps the same amount of blood into the lungs that the left ventricle pumps out into the body. Physicians commonly refer to the right atrium and right ventricle together as the right heart and to the left atrium and ventricle as the left heart.
The electric energy that stimulates the heart occurs in the sinoatrial node, which produces a definite potential and then discharges, sending an impulse across the atria. In the atria the electrical signal move from cell to cell while in the ventricles the signal is carried by specialized tissue called the Purkinje fibers which then transmit the electric charge to the myocardium
The human heart has a mass of between 250 and 350 grams and is about the size of a fist.
It is enclosed in a double-walled protective sac called the pericardium. The superficial part of this sac is called the fibrous pericardium. This sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood.
The outer wall of the human heart is composed of three layers. The outer layer is called the epicardium, or visceral pericardium since it is also the inner wall of the pericardium. The middle layer is called the myocardium and is composed of muscle which contracts. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. Also, it merges with the inner lining (endothelium) of blood vessels and covers heart valves.
The human heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers.
The pathways of blood through the human heart are part of the pulmonary and systemic circuits. These pathways include the tricuspid valve, the mitral valve, the aortic valve, and the pulmonary valve. The mitral and tricuspid valves are classified as the atrioventricular (AV) valves. This is because they are found between the atria and ventricles. The aortic and pulmonary semi-lunar valves separate the left and right ventricle from the pulmonary artery and the aorta respectively. These valves are attached to the chordae tendinae (literally the heartstrings), which anchors the valves to the papilla muscles of the heart.
The interatrioventricular septum separates the left atrium and ventricle from the right atrium and ventricle, dividing the heart into two functionally separate and anatomically distinct units.
Blood flows through the heart in one direction, from the atria to the ventricles, and out of the great arteries, or the aorta for example. Blood is prevented from flowing backwards by the tricuspid,bicuspid, aortic, and pulmonary valve.
The heart acts as a double pump. The function of the right side of the heart (see right heart) is to collect de-oxygenated blood, in the right atrium, from the body (via superior and inferior vena cavae) and pump it, via the right ventricle, into the lungs (pulmonary circulation) so that carbon dioxide can be dropped off and oxygen picked up (gas exchange). This happens through the passive process of diffusion.
The left side (see left heart) collects oxygenated blood from the lungs into the left atrium. From the left atrium the blood moves to the left ventricle which pumps it out to the body (via the aorta).
On both sides, the lower ventricles are thicker and stronger than the upper atria. The muscle wall surrounding the left ventricle is thicker than the wall surrounding the right ventricle due to the higher force needed to pump the blood through the systemic circulation.
Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. Here, it is pumped out of the pulmonary semilunar valve and travels through the pulmonary artery to the lungs. From there, blood flows back through the pulmonary vein to the left atrium. It then travels through the mitral valve to the left ventricle, from where it is pumped through the aortic semilunar valve to the aorta and to the rest of the body. The (relatively) deoxygenated blood finally returns to the heart through the inferior vena cava and From Yahoo Answers
Answers:Think of diffusion as a process that tries to fill an "empty void" in a system. In the lungs, the pressure of oxygen is much higher compared to the pressure of oxygen in the blood. This is because of two reasons: 1. We just breathed oxygen into our lungs, so it is high there. 2. The blood coming back to the lungs has had the oxygen taken from it by the cells of our body, so it is low there. Because the pressure of oxygen is low in the blood and high in the lungs, the laws of physics/equilibrium want everything to be equal. How can this occur? By letting the large amount of oxygen in the lungs flow into the blood, which has low oxygen. The same goes for other processes, like a normal cell in a salty solution. Salt cannot cross the membrane of the cell, so water must cross the membrane in order to restore equilibrium. How can water do this? It can try to dilute the salty solution that is outside the cell. Therefore, you will see water diffuse out of the cell and the cell "shrivel up" when placed in a salty solution. The water diffused out of the cell in order to try and dilute the salt outside the cell. It was an attempt to restore equilibrium between the cell and its environment. Try to think of diffusion as a process of equalizing.
Answers:the thing is....that in the time it took you to typle this you could have searched it on the web...
Answers:OK Diffusion is the process by which two liquids naturally mix together for example if you pour squash into water they will eventually mix completely together even without stirring. Osmosis is essentially the same thing but it must be 'the diffusion of water across a partially permeable membrane'. A partially permeable membrane is essentially like a sieve but much finer it can seperate water from things its dissolved in. Active transport takes place when a substance is absorbed across the concentration gradient, this doesn't happen much in the body, one example is the re-absorption of glucose in the kidneys. These things all help to maintain homeostasis by keeping conditions and concentrations of liquids in cells the same at all times. Hope this helped but i guess you might have wanted a simpler answer sorry this is all i know.