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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.
Levels of body fat are epidemiologically dependent on gender and age. Different authorities have developed different recommendations for ideal body fat...
Human body shape is a complex phenomenon with sophisticated detail and function. The general shape or figure of a person is defined mainly by skeletal structure, muscles and fat. Skeletal structure grows and changes only up to the point at which a human reaches adulthood and remains essentially the same for rest of his or her life.
During puberty, differentiation of the male and female body occurs for the purposes of reproduction. In adult humans, muscle mass may change due to exercise, and fat distribution may change due to hormone fluctuations. Inherited genes play a large part in the development of body shape.
Body shape has effects on body posture and gait, and has a major role in physical attraction. This is because a body's shape implies an individual's hormone levels during puberty, which implies fertility, and it also indicates current levels of sex hormones. A pleasing shape also implies good health and fitness of the body. The art of figure drawing defines body proportions that are considered ideal.
Skeletal structure frames the overall shape of the body and does not alter much over a lifetime. Males are generally taller, but body shape may be analyzed after normalizing with respect to height.
- Broad shoulders and expanded chest (in males):
- Widening of the shoulders occurs as part of the male pubertal process. Expansion of the ribcage is caused by the effects of testosterone during puberty. Hence males generally have broad shoulders and expanded chests, allowing them to inhale more air to supply their muscles with oxygen.
- Wide hips (in females):
- Widening of the hip bones occurs as part of the female pubertal process, and estrogen (the predominant sex hormone in females) causes a widening of the pelvis as a part of sexual differentiation. Hence females generally have wider hips, permitting childbirth. Because the female pelvis is flatter, more rounded and proportionally larger, the head of the fetus may pass during childbirth. The sacrum in females is shorter and wider, and also directed more toward the rear (see image). This affects their walking style, resulting in hip sway; also, females generally stand with hips relaxed to one side.
After puberty, female hips are generally wider than female shoulders; males exhibit the opposite configuration. But not everyone follows this stereotypical pattern of secondary sex characteristics. Both male and female hormones are present in the human body, and though only one of them is predominant in an adult, the other hormone has effects on body's shape to some extent.
Due to the action of testosterone, males develop these facial-bone features during puberty:
Because females have around 20 times less testosterone, these features do not develop to the same extent. Hence female faces are generally more similar to those of pre-pubertal children.
Fat distribution, muscles and tissues
Body shape is affected by body fat distribution, which is correlated to current levels of sex hormones. Muscles and fat distribution may change from time to time, unlike bone structure, depending on food habits, exercises and hormone levels.
Estrogen causes fat to be stored in the buttocks, thighs, and hips in women. When women reach menopause and the oestrogen produced by ovaries declines, fat migrates from their buttocks, hips and thighs to their waists; later fat is stored in the belly. Thus females generally have relatively narrow waists and large buttocks, and this along with wide hips make for a wider hip section and a lower waist-hip ratio compared to men.
Estrogen increases fat storage in the body, which results in more fat stored in the female body. Body fat percentage recommendations are higher for females, as this may serve as an energy reserve for pregnancy. Males have less subcutaneous fat in their faces due to the effects of testosterone; testosterone also reduces fat by aiding fat metabolism. Males generally deposit fat around waists and From Yahoo Answers
Answers:If you are a female with 10 percent body fat then I would say you re a hard core athlete or just really skinny. Men can have 10 percent no problem but women . I am athletic and I weight 155 and about 5 10 with 16 percent body fat which is considered excellent 19 percent body fat is considered athletic or lean for women.
Answers:It is probably not very accurate in absolute terms but it will tell you if you are gaining or losing fat.
Answers:BMI (body mass index) . People with a normal range would have a BMI of 20/30% of body fat. Water weight should be about 60% of your total body weight. We are between 60-70% water!
Answers:It's actually closer to 70% than 55%.