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I heard that the human heart had a surface area of 1000 square feet, and I thought that that cannot be true. So what is the surface area of the human heart and what are the different ways it can be measured?
The number you are looking for might be quite large depending on the level of detail you demand for the measurement. There is no single number for the area of most objects in fact.
The importance of fractals is much related to the question of what is the perimeter or surface area of something. The classic example is trying to determine the length of Britain's coastline. If you took a surveyors sight and set a point every 500 ft you would get a certain number, if you paced it out in strides you would end up taking more curves and turns and you would get a longer number. If you took out a ruler and measured down to the inch you would get a still larger number. In these two wikipedia pictures you would get a perimeter of 2400 km and 3400 km for points set every 200 and 50 km respectively:
As you can see that makes a big difference. So in the same thought organs also need to be measured using fractal sorts of measurements- depending on the level of detail desired. For a heart, if you were to cover the organ with a tight stretch of Saran wrap, you'd have maybe 1-2 square feet, but if you estimate the surface area for not only the inner chambers, but the blood vessels and capillaries, it would be much larger. The latter is probably relevant if you are a physiologist and want to know how much oxygen the heart is taking in as it beats.
I can't find a reference for a human heart, but fractal calculations for the human lungs tell me that 1000 sq ft seems reasonable. If you take the oxygen accessible area of lungs, including every bronchial passage and aveoli, the answer is 50-100 m^2. This is about 538- 1,076 sq feet.
The heart does not need to have as much surface area as the lung, but the capillaries and arteries that feed the heart need to be spaced a few millimeters apart to keep the tissue oxygen saturated. 1000 sq feet seems a possible range for the heart compared to the lung's surface area, maybe on the high end…
Body surface area
In physiology and medicine, the body surface area (BSA) is the measured or calculated surface area of a human body. For many clinical purposes, BSA is a better indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass. Nevertheless, there have been several important critiques of the use of BSA in determining the dosage of medications with a narrow therapeutic index, such as chemotherapy.
Typically there is a 4–10 fold variation in drug clearance between individuals due to differing the activity of drug elimination processes related to genetic and environmental factors. This can lead to significant overdosing and underdosing (and increased risk of disease recurrence). It is also thought to be a distorting factor in Phase I and II trials that may result in potentially helpful medications being prematurely rejected.   The trend to personalized medicine is one approach to counter this weakness.
Surface area of the digestive tract much smaller than previously thought
The internal surface area of the gastro-intestinal tract has long been considered to be between 180 and 300 square meters. Scientists at the Sahlgrenska Academy have used refined microscopic techniques that indicate a much smaller area.
"Actually, the inner surface of the gastro-intestinal tract is only as large as a normal studio apartment," says scientist Lars Fändriks.
The digestive tract, which passes from the mouth through the esophagus and onwards through the intestines, has a length of about 5 meters in a normal adult, and is built up with many folds and protrusions.
Previous calculations, which are reproduced in reference works and textbooks, state that the area of the inner surface of the digestive tract is between 180 and 300 square meters -- as large as, or even larger than, a tennis court.
A new study from the Sahlgrenska Academy, published in the Scandinavian Journal of Gastroentorology, shows that these figures are wrong.
Scientists Lars Fändriks and Herbert Helander have used quantitative microscopic techniques to determine that the surface area of the gastro-intestinal tract in healthy adults is "only" between 30 and 40 square meters.
By far the greatest part of this is the small intestine. The area of the large intestine is approximately 2 square meters, while the mouth, esophagus and stomach amount to less than 1 square meter.
Half of a badminton court
Lars Fändriks finds it surprising that the area of the gastro-intestinal tract is not that of a tennis court, rather half of a badminton court.
"It may appear to be simply a curious fact, but the dimensions of the inner surface of the gastro-intestinal tract are important for the uptake of nutrients and drugs, and the new information will help us understand how the mucous membrane protects the body from harmful factors in the intestinal contents," he says.
The Gothenburg scientists explain how the previously erroneous results were arrived at:
"The gastro-intestinal tract is a dynamic system that is difficult to access in the abdominal cavity, and this makes it difficult to measure. Since the past measurements were carried out either during post mortems or during abdominal surgery, when the tissue is relaxed, it is easy to obtain misleading measurements," says Herbert Helander.
The two scientists from Gothenburg have used data from radiological investigations, supplemented with studies of the microscopical structure of the gastro-intestinal tract, where they have used endoscopes to obtain samples of the mucous membrane of the intestines.
The scientists emphasize that the new dimensions are valid for a healthy "average" adult: the length and surface area of the digestive tract differs from person to person. In addition, the measurement for an individual is probably affected by diet and lifestyle.
"From an anatomical point of view, 30-40 square meters is more than enough for the uptake of nutrients. Furthermore, the smaller area is actually quite logical, since it means that the risk of effects from the intestinal contents is lower," says Herbert Helander.
Medical Definition of Body surface area
Body surface area: BSA. The total surface area of the human body. The body surface area is used in many measurements in medicine, including the calculation of drug dosages and the amount of fluids to be administered IV.
A number of different formulas have been developed over the years to calculate the body surface area and they give slightly different results. The most commonly used formula now is that of Mosteller, published in 1987 in The New England Journal of Medicine. According to Mosteller's "simplified calculation of body-surface area In metric terms" the body surface area = the square root of product of the weight in kg times the height in cm divided by 3600.
- Average body surface area for adult men: 1.9 m2
- Average body surface area for adult women: 1.6 m2
- Average body surface area for children (9 years): 1.07 m2
- Average body surface area for children (10 years): 1.14 m2
- Average body surface area for children (12-13 years): 1.33 m2
Body surface area is used for a determining other medical measures. As examples, renal function is measured by the glomerular filtration rate (GFR) which is calculated in regard to the body surface area. The cardiac index is a measure of cardiac output divided by the body surface area, giving a better approximation of the required cardiac output. Chemotherapy and pharmacotherapies are often dosed according to the patient's body surface area. Glucocorticoid dosing is also expressed in terms of body surface area for calculating maintenance doses or to compare high dose use with maintenance requirement.
Reference: Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987317:1098.
Adsorption: Characteristics, Principles and Importance
The process of taking up substances from so­lution on surface is called adsorption.
Characteristics of Adsorption:
1. Adsorption is a surface phenomenon.
2. The attractive forces on the surface are lim­ited to distances one molecule deep.
3. The extent to which adsorption takes place is dependent upon the nature of both adsorbing agent and the substances adsorbed.
4. The greater the surface of the adsorbing agent, the greater is the adsorption.
5. Charcoal becomes activated when it is heated at 700°-800°C in a closed container and adsorption takes place on the acti­vated charcoal due to the attraction of op­positely charged ions. Salts, acids and al­kalis restrict it.
6. It has got much importance in industry.
Principles Governing Adsorption:
1. Adsorption is a reversible process.
2. It decreases with the rise in temperature.
3. This process takes place relatively quickly. Equilibrium is reached within one hour.
4. Adsorption is proportional to the surface area and it varies with the nature of the surface of the adsorbent and of the sub­stances to be adsorbed.
5. It proceeds best from dilute solutions.
6. Narrow pores on the surface of the adsorbing agent are more effective than globular openings.
7. Heat is given off in all adsorption.
8. The molecules adsorbed on the surface are oriented and arranged in a definite man­ner.
Importance of Adsorption:
1. Many chemical reactions are speeded up by the presence of adsorptive surface. Oxygen and hydrogen are adsorbed to­gether upon platinum black and combine rapidly at ordinary temperature to form water.
2. Surface adsorption helps to combine en­zymes with substrates to give reaction products.
3. Adsorption processes taking place on the cell membranes promote many vital chemical reactions and also cause changes in surface tension and cell consistency.
4. Drugs and poisons which are adsorbed on cell surfaces exert their effects from that location. Selective adsorption may be re­lated to specific action.
5. The process of adsorption is applied in the purification of enzymes.
Arrangement of Molecules at an Interface:
Solute molecules accumulated at an interface tend to arrange themselves in a definite pattern if the molecules are unsymmetrical, (i.e. if they have -COOH, -OH, and –NH2 groups), they have water attractions whereas the arrangement is symmetri­cal within the solution.
The unsymmetrical molecules align them­selves so that the polar groups are directed towards water and the non-polar groups at the other end of the molecule remain away from it (orientation). At an oil-water interface the orientation would be especially favoured since the oil would attract the non-polar groups in addition to the water at­tracting the polar groups.
In the cell (which contains both water and lipids), it is likely that some cell constituents are oriented in this way. The cell membrane absorbs oriented molecules. Orientation is an important fac­tor in adsorption and enzyme reactions. In this way, one part of a molecule can be presented to a react­ing substance.
6.1 + 6.2 IB biology study guide
h. through nerves/named example of nerve/autonomic/sympathetic/ parasympathetic nervous system ✔ In mph, only accept vagus nerve for slowing heart rate and sympathetic nerve for accelerating it.
i. one nerve increases the rate and the other decreases it ✔
j. epinephrine/adrenaline increases heart rate/force of contraction ✔
b. secreted by salivary glands/pancreas ✔
c. active/released into the mouth/small intestine ✔
d. acts on starch/polysaccharides ✔
e. breaks «glycosidic» bond by hydrolysis/adding water ✔
f. converts insoluble/large molecule to soluble/small molecules ✔
b. have specific active sites to which specific substrates bind ✔
c. enzyme catalysis involves molecular motion and the collision of substrates with the active site ✔ OWTTE
d. enzymes break macromolecules into monomers/smaller molecules indigestion ✔
e. smaller molecules/monomers more readily absorbed ✔
f. <<pancreas>> secretes enzymes into the «lumen of» small intestine ✔
g. the small intestine has an alkaline pH ✔
h. enzymes have maximum action at specific pHs
enzymes can be denatured at other pHs ✔
i. amylase breaks down starch into sugars/disaccharides ✔
j. lipase breaks lipids/triglycerides into monoglycerides/fatty acids and glycerol ✔
k. endopeptidase/protease breaks «peptide» bonds in proteins/polypeptides ✔
b. open valves allow blood to flow through
opening and closing of valves controls timing of blood flow «during cardiac cycle» ✔
c. closed «semilunar» valves allow ventricles/chambers to fill with blood
closed «semilunar» valves allow pressure in ventricles to rise «rapidly» ✔
d. valves open when pressure is higher upstream/OWTTE/converse for closed valves ✔
e. AV/bicuspid/tricuspid/mitral valves prevent backflow from ventricle to atrium
AV/bicuspid/tricuspid/mitral valves open when pressure in atrium is higher «than in the ventricle»/when atrium is pumping/contracting ✔
f. semilunar/aortic/pulmonary valves prevent backflow from artery to ventricle
semilunar/aortic/pulmonary valves open when pressure in ventricle is higher «than in the artery»/when ventricle is pumping/contracting ✔
b. example of simple diffusion, eg: fatty acids
c. facilitated diffusion of nutrients involves movement through channel proteins
d. example of nutrient for facilitated diffusion eg: fructose
e. active transport of nutrients against a concentration gradient / involving protein pumps
f. example of active transport, eg: (iron) ions/glucose/amino acids
g. endocytosis / by means of vesicles
b. nutrients move into tissues
c. gas exchange / Oxygen and carbon dioxide exchange between tissues and blood/capillaries
d. (nitrogenous) wastes/excess water move from cells/tissues into blood/capillaries
b. pressure is high in arteries/pressure is low in veins
c. arteries receive blood from ventricles/heart / carry blood away from heart
d. lumen of artery is small to keep pressure high
e. arteries have thick (muscular) walls (with elastic fibres) to withstand pressure
f. elastic fibres recoil in response to ventricle/heart contraction
g. muscle / elastic fibres help maintain pressure between heartbeats
muscle / elastic fibres help propel blood toward capillary beds
h. veins receive blood from capillaries/capillary beds / carry blood to heart
i. large lumen of veins so there is less resistance to blood flow
b. oxygen diffuses from air to blood and carbon dioxide diffuses from blood to air
c. oxygen binds to hemoglobin in red blood cells
d. pressure inside/volume of alveoli increases/decreases / air enters/exits alveoli during inspiration/expiration/ventilation
e. blood flow through capillaries / concentration gradients of gases/oxygen/CO2 maintained
f. type II pneumocytes secrete fluid/surfactant / secretion of surfactant to prevent sides of alveolus adhering
b. heart is a double pump / heart has separate pumps for lungs and other systems / left and right sides of heart are separate / no hole in heart (after birth)
c. deoxygenated blood pumped to the lungs and oxygenated to other organs/tissues/whole body (apart from lungs)
d. each side of the heart has an atrium and a ventricle
e. left ventricle/side pumps blood to the systems/tissues and right ventricle/side pumps blood to the lungs
f. left atrium receives blood from the lungs and right atrium receives blood from systems/tissues
g. left ventricle pumps blood via the aorta and right ventricle pumps blood via the pulmonary artery
h. left atrium receives blood via the pulmonary vein and right atrium receives blood via the vena cava
i. lungs require lower pressure blood / high pressure blood would damage lungs
j. high pressure required to pump blood to all systems/tissues apart from lungs
k. pressure of blood returning from lungs not high enough to continue to tissues / blood has to be pumped again after returning from lungs
l. oxygenated blood and deoxygenated blood kept separate / all tissues receive blood with high oxygen content/saturation
What is Body Surface Area (BSA) and Why is it Important?
You’ve probably heard of BMI (Body Mass Index) in reference to overall health, weight loss or exercise, but what about BSA (Body Surface Area)? How is this different from BMI and how is it calculated? Moreover, why should you care?
While Body Mass Index (BMI) is a measure of a person’s body fat mass, Body Surface Area measures the total surface area of a person’s body and is frequently used in order to calculate drug dosage and the amount of fluids to be administered by IV.
Various formulas have been used over the last century to calculate BSA. They all give slightly different results, which has created issues of standardization. For the sake of example, the Mosteller formula is commonly referred to and often used in clinical trials. It calculates BSA by taking the square root of height (cm) multiplied by weight (kg) divided by 3600.
Many online calculators offer the conversion from centimeters to inches and from kilograms to pounds, which makes calculating one’s own BSA fairly easy. Take, for instance, a woman who is five feet, 5 inches tall (65 inches) and who weighs 150 pounds. This calculator allows you to select inches and pounds and the type of formula you want to use. You’ll see that the woman in this example has a BSA of 1.75 m 2 (meters squared) using the DuBoise formula.
Body surface area measurement, in medical terms, has many significant implications. For example, it is used during the clinical assessment and diagnosis of Vitiligo, a chronic disorder that causes patches of skin to lose pigment. According to the journal Pediatrics , topical therapies for Vitiligo can be used solely in limited surface involvement (<20% of body surface area) or in combination with other treatments, mainly phototherapy, in wider involvement (>20% of body surface area).
It is also routinely calculated in the cardiovascular field, and research has shown that body surface area is a strong predictor of mortality in chronic heart failure patients.
Also, BSA calculation is used in chemotherapy dosing, with the idea that each patient receives an individualized dose of chemo specific to their height and weight.
While no means a full list of the many applications of body surface area measurement, the conditions described illustrate the vital importance of this metric in health and wellness assessments.
This blog is intended to be informational in nature. The information and other content provided in this blog, or in any linked materials, are not intended and should not be construed as medical advice, nor is the information a substitute for professional medical expertise or treatment.
If you have any questions or concerns, please talk to your doctor. Never disregard professional medical advice or delay in seeking it because of something you have read on this blog or in any linked materials. If you think you may have a medical emergency, call your doctor or emergency services immediately.
Local Control in the Capillary Beds
- Nitric oxide (NO) is a potent dilator of arteries and arterioles.
- When the endothelial cells that line these vessels are stimulated, they synthesize nitric oxide. It quickly diffuses into the muscular walls of the vessels causing them to relax.
- In addition, as the hemoglobin in red blood cells releases its O2 in actively-respiring tissues, the lowered pH [Link] causes it to also release NO which helps dilate the vessels to meet the increased need of the tissue.
Nitroglycerine, which is often prescribed to reduce the pain of angina, does so by generating nitric oxide, which relaxes the walls of the arteries and arterioles. The prescription drug sildenafil citrate ("Viagra") does the same for vessels supplying blood to the penis. The effects of these two drugs are additive and using them together could precipitate a dangerous drop in blood pressure.
What is the surface area of the human heart? - Biology
4. Make your own x-y graph with Create-A-Graph or Excel where x is surface area and y is volume, and plug in a range of values. What is happening to the surface area to volume ratio as cell size increases? (If the surface area and volume were increasing at the same rate, the line would be diagonal with a slope of 1.) What is actually happening at small sizes? At intermediate sizes? At large sizes? Download the Excel spreadsheet where I did my calculations and created these graphs: surface_area_volume_graph.xlsx.
Fig. 1: Cell surface area (SA) plotted against cell volume (V). As cell size increases, V increases faster than SA. The red dashed line represents a 1:1 ratio.
Fig. 2: Cell side length plotted against the surface area to volume ratio. As cell size decreases towards zero, the SA:V ratio approaches infinity.
5. Since transport of materials in and out of the cell can only happen at the cell's surface, what happens as cells get larger? How does this impose a limit on cell size?
6. It's not just cells that scale up in this way. Whole animals do too. The study of body size as it relates to anatomy, physiology, and behavior is called allometry. For homeotherms (animals that try to maintain a constant body temperature), it is necessary to make heat as it is lost to the environment in order to maintain equilibrium. If heat loss occurs only at the exposed surfaces, what would you predict about the metabolic rate per unit of body tissue of a large animal compared to a small one?
7. Take what you know about surface area to volume ratio and try to explain the following graph, which is known as the "mouse-to-elephant curve." Assume that metabolic rate relates to heat production and that all of these animals are trying to keep their bodies warm under the same environmental conditions. Note for example that an elephant has a mass (and volume) of more than 1000 times that of a mouse while its metabolic rate (and heat production) is only about 100 times that of a mouse. In other words, "Why can an elephant heat itself more efficiently (per unit of mass) than a mouse?"
Brody's (1945) Mouse-to-Elephant Curve
8. "Allen's Rule" predicts that endothermic animals (ones that regulate their body temperature internally) with the same body volume should have different surface areas designed to either aid or impede their heat dissipation, depending on the temperature of their surroundings. Explain with reference to surface area and volume. (Think about the need for heat retention in cold climates or heat shedding in hot climates and make a prediction about body types.)
9. "Bergman's Rule" says that among species of animals which have a global distribution, adult body size tends to be largest in the polar regions, medium in temperate climates and smallest in tropical ones. Although there are exceptions, this is generally true. Why should it be so?
10. Challenge Question: In one of my favorite old monster movies, Them , giant ants attack the city. Unfortunately, it could never happen. The incredible strength of the ant is dependent upon its small size. Scale him up to even human size and he'd collapse under his own weight on those skinny little legs. Volume (and therefore weight) scales to the power of 3 while surface area (and size) scale to the power of 2. Create a graph that shows why the giant ant can't destroy the city, but instead would collapse under its own weight.
11. Challenge Question: As shown empirically in Brody's graph, power is proportional to mass to the power of 0.734, roughly 3/4, yet surface area to volume ratio predicts a value of only 2/3 or 0.67. Animals in the real world do better than expected, but animals in the real world don't rely entirely on surface area for heating, cooling, gas exchange, etc. Is is possible that the circulatory system allows larger organisms to improve upon the surface area to volume problem? Explain.
If only cells were cubes
I have deliberately not used actual units in this section.
For a cube of size 1:
The surface area is 6 (6 sides, each 1x1).
The volume is 1 (1x1x1).
So the surface area:volume ratio is 6
For a cube of size 2:
The surface area is 24 (6 sides, each 2x2).
The volume is 8 (2x2x2).
So the surface area:volume ratio is 3
For a cube of size 3:
The surface area is 54 (6 sides, each 3x3).
The volume is 27 (3x3x3).
So the surface area:volume ratio is 2.
What about a cube of size 4?
The surface area is > 96 (6 sides, each 4x4).
The volume is > 64 (4x4x4).
So the surface area:volume ratio is > 1.5.
How does this relate to cubes of size 2? > Half and 1? > quarter
A value for surface area:volume ratio is not a simple number because area and volume have different numbers of dimensions, the ratio has units, which are the reciprocal of the distance L used in these measurements. If different units are used, this will result in a different surface area:volume ratio.
So, measuring in millimetres will give a SA:vol value 1000 times larger than measurements in µmetres
Sometimes instead of the surface area:volume ratio, the surface area of an organism is expressed in relation to body mass (perhaps as mm 2 mg -1 ). For example in comparisons between different stages in the life cycle of an organism, its volume may not be directly proportional to its mass over the entire range, because the amounts of various tissues may change.
Spherical objects, real units
Surface area of a sphere A=4 &pi r 2
Volume of a sphere V=4/3 &pi r 3
&pi = 3.14
The human egg cell is in fact the largest cell in the human body.
Organism + cell Cell diameter /mm radius /mm Surface area /mm 2 Volume /mm 3 SA:Vol ratio /mm -1 Zebrafish egg
0.70 0.35 1.538 0.1795 > 8.55 Human ovum
1.00 0.50 3.14 0.52 6.00 Frog's egg
(Southern leopard frog)
1.76 0.88 9.73 2.853 > 3.41
You can work out the missing SA:Vol ratios, then mouseover to check your figures.
What trend does this show?
> As size increases, surface area:volume ratio decreases
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Allometry, also called biological scaling, in biology, the change in organisms in relation to proportional changes in body size. An example of allometry can be seen in mammals. Ranging from the mouse to the elephant, as the body gets larger, in general hearts beat more slowly, brains get bigger, bones get proportionally shorter and thinner, and life spans lengthen. Even ecologically flexible characteristics, such as population density and the size of home ranges, scale in a predictive way with body size. The study of allometry stems from work in the late 19th century by the Scottish zoologist D’arcy Thompson and in the early 20th century by the English biologist Julian Huxley, the latter of whom coined the term for this field of study.
Scaling is often considered to be one of the few laws in biology. Allometric equations take the general form Y = aM b , where Y is some biological variable, M is a measure of body size, and b is some scaling exponent. In allometry, equations are often presented in logarithmic form so that a diverse range of body sizes can be plotted on a single graph.
The most common example of allometry is geometric scaling, in which surface area is a function of body mass. In general, for organisms that preserve their basic shape as they vary in size, the organism’s linear dimensions vary as the 1 /3 and their surface area as the 2 /3 powers of their body mass. The relationship of energy consumption (or metabolic rate) and body mass in mammals is another well-known example of scaling ( Kleiber’s law): metabolic rate scales as the 3 /4 power of body mass.
Biologists have studied scaling within individual organisms, among different individual organisms, and across groups of many individuals or species. Studies of allometry take two basic forms. One approach emphasizes determination of the exponents, or invariant properties across organisms, as in Kleiber’s law. The other approach concerns how and why organisms change relative to size—for example, why deer that have large antlers for their size tend to use them more for fighting and aggressive behaviour.
One mechanism proposed to account for scaling states that biological organisms are limited by the rates at which energy and materials can be distributed between surfaces where they are physiologically exchanged and the tissues are used. Thus, allometric relations may be ultimately related to anatomical and physiological features of energy usage.
Watch the video: The Human Heart (January 2023).