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From Wikipedia, the free encyclopedia

Micrograph of a piece of soft tissue (tendon). H&E stain.
Micrograph of a piece of soft tissue (tendon). H&E stain.

In anatomy, soft tissue includes the tissues that connect, support, or surround other structures and organs of the body, not being hard tissue such as bone. Soft tissue includes tendons, ligaments, fascia, skin, fibrous tissues, fat, and synovial membranes (which are connective tissue), and muscles, nerves and blood vessels (which are not connective tissue).[1]

It is sometimes defined by what it is not. Soft tissue has been defined as "nonepithelial, extraskeletal mesenchyme exclusive of the reticuloendothelial system and glia".[2]

YouTube Encyclopedic

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  • Soft Tissue Found Inside a Dinosaur Bone!
  • soft tissue in dino fossils-nothing in science can allow this to be millions of years old
  • Real dinosaur still-soft biological tissue on ABC's 60 Minutes
  • DinoSummary Earth is YOUNG
  • Vascular tumors (kaposi, hemangioma, angiosarcoma) - causes & symptoms

Transcription

Stated clearly presents The scientific saga of Dr. Mary Schweitzer and her discovery of soft tissue inside a dinosaur bone! In 2003 a team of paleontologists finished excavating an incomplete, yet extremely well-preserved T. rex skeleton. During transport the animal's femur, its thigh bone, had to be broken in two. While the bone was eventually put back together, pieces that had fallen out were kept separate and then sent to Doctor Mary Schweitzer for dissection and analysis. After applying a mild acid to the fragments to remove hard minerals, a diverse collection of soft material could be seen under the microscope. It included what looked like cells and tiny blood vessels. They were very degraded but similar to those commonly found inside fresh bone. Chemical analysis further revealed what looked like animal proteins. Dr. Schweitzer was shocked. According to our understanding at the time, unless treated with chemicals, the way that leather is, for example, and then further sealed for preservation, soft tissue was predicted to completely deteriorate, even under the best of circumstances,in less than 1 million years. This t-rex leg bone, however, was thought to be millions of years old. What did this discovery of soft tissue mean? To Dr. Schweitzer, and to many other researchers, there were three main possibilities. Number 1: The fossil might be far younger than previously thought, maybe even less than 1 million years old. Number 2: The fossil could have been recently contaminated by microbes that produced the soft structures after the bone had fossilized, a substance known as biofilm. Option number 3: There might be a previously unknown natural mechanism capable of preserving soft tissue far longer than 1 million years. Having studied paleontology throughout her career, Dr. Schweitzer immediately knew that option number 1 was least likely. The fossil had been found in a set of rock layers known as the Cretaceous, ancient sediments laid down between 145 to 66 million years ago. Our understanding of the age of these rocks is founded on thousands of data points telling us how rock layers form on the careful study of the rise and fall of various ecosystems in the animal groups in the fossil record and on the clear results of hundreds of experiments on radiometric dating. Many overlapping radiometric dating methods have been used to confirm the age range of Cretaceous rocks and the results have been independently checked by laboratories around the globe. To successfully argue that her single discovery means that the fossil is actually young she would have to ignore everyone else's careful observations. Given the extreme imbalance of evidence, it seemed to her, and to other well-informed thinkers, that option number one was not plausible. Early on, her colleagues argued that option number two was most likely. As is the custom in science, papers were published critiquing Dr. Schweitzer's work. Many of them suggested that what she had found was actually biofilm. After closer examination, several years of debate and many papers published back and forth, however, the scientific community is now largely convinced: The soft tissue that Dr. Schweitzer found IS authentic. It did come from the original T. rex. This left informed thinkers to suspect that option number three was most likely, but how? What natural process or collection of natural processes could allow soft tissue to remain intact for over 66 million years? Nobody had an answer but Dr. Schweitzer was determined to figure it out. As luck would have it, when first uncovering her discovery, she randomly attended a lecture on brain disease which focused on the destructive power of free iron particles on living tissue. Iron is extremely common in our blood. Normally, however, it's trapped safely inside hemoglobin a blood protein that uses iron to capture oxygen in the lungs and deliver it throughout the body. While iron is safe and highly useful inside hemoglobin, loose iron particles can wreak havoc on our cells. In a process called cross-linking, iron can trigger a series of chemical reactions, eventually causing proteins and other cellular structures to unravel and fuse together in a tangled useless mess. In living animals, cross-linking is bad. In dead tissue, however, Dr. Schweitzer knew that cross-linking leads to preservation. Chemicals that we use to turn delicate animal skins into tough durable leather do so by cross-linking proteins. Formaldehyde, the chemical used to preserve soft tissue in museum specimens, also uses cross-linking to do its work. When Dr. Schweitzer examined the soft tissue from her dinosaur fossil she found that it was saturated in iron crystals. When the T. rex had died, blood must have begun to decompose, releasing iron from hemoglobin. As iron spread through tissue and bone it initiated cross-linking. The soft tissues most affected would have been preserved like leather for a long period of time. Tissues that were both cross-linked and sealed safely inside hard bone were double protected, allowing them to survive for millions of years until present day. Based on the evidence, her explanation seemed reasonable, but, being a trained scientist, Dr. Schweitzer was not satisfied until she found a way to test her idea. To do so, she designed an experiment. Ostriches are among the closest living relatives to dinosaurs. Their bones are rich in blood vessels, just like those found in the fossil. She obtained an ostrich femur and extracted the vessels using a series of acid and enzyme treatments. At room temperature, one group of blood vessels was placed in a watery iron-free solution. She wanted to find out how long the vessels took to decompose. A second batch was placed in a solution of iron rich hemoglobin. The vessels in normal solution turned to mush in just three days, quickly destroyed by microbes and other natural chemical reactions. After two years, vessels soaked in iron rich hemoglobin remained completely intact. No signs of degradation could be found. Now, of course, two years is a far cry from 66 million years. Further experiments may reveal that there is more to this mystery, but Mary Schweitzer's discovery has opened us up to a new understanding of how decomposition works in large animals. Furthermore, her story is a beautiful example of how good science is done. She began by making an observation; presented that observation to the scientific community, for their feedback and critique; she then came up with an explanation, or hypothesis, for the observation; and finally, using her creativity, she designed an experiment to test that hypothesis. Now that we know soft tissue can be preserved naturally, far longer than previously imagined, researchers have began looking for, and finding, soft tissue in the fossils of many different species. The study of these ancient structures is helping increase our understanding of how extinct animals once lived and evolved on our planet. I'm John Perry and that is the scientific saga of Dr. Mary Schweitzer, stated clearly. Special thanks to Dr. Mary Schweitzer. She spent a lot of time with me on the phone and back and forth in email with me as I was studying for and writing this script. Thank you Mary for all of your assistance Dr. Schweitzer's work is continuing. You can follow what she's up to at molecularpaleo.wordpress.ncsu.edu This animation was funded by viewers like you, who contribute to us on patreon.com/statedclearly. I really appreciate all the support you've given me. I really could not continue doing them without you. Last but not least, we have dinosaur t-shirts available. You can find a link to order yours down in the video description. So long for now. Stay curious.

Contents

Composition

The characteristic substances inside the extracellular matrix of this kind of tissue are the collagen, elastin and ground substance. Normally the soft tissue is very hydrated because of the ground substance. The fibroblasts are the most common cell responsible for the production of soft tissues' fibers and ground substance. Variations of fibroblasts, like chondroblasts, may also produce these substances.[3]

Mechanical characteristics

At small strains, elastin confers stiffness to the tissue and stores most of the strain energy. The collagen fibers are comparatively inextensible and are usually loose (wavy, crimped). With increasing tissue deformation the collagen is gradually stretched in the direction of deformation. When taut, these fibers produce a strong growth in tissue stiffness. The composite behavior is analogous to a nylon stocking, whose rubber band does the role of elastin as the nylon does the role of collagen. In soft tissues, the collagen limits the deformation and protects the tissues from injury.

Human soft tissue is highly deformable, and its mechanical properties vary significantly from one person to another. Impact testing results showed that the stiffness and the damping resistance of a test subject’s tissue are correlated with the mass, velocity, and size of the striking object. Such properties may be useful for forensics investigation when contusions were induced.[4] When a solid object impacts a human soft tissue, the energy of the impact will be absorbed by the tissues to reduce the effect of the impact or the pain level; subjects with more soft tissue thickness tended to absorb the impacts with less aversion.[5]

Graph of lagrangian stress (T) versus stretch ratio (λ) of a preconditioned soft tissue.
Graph of lagrangian stress (T) versus stretch ratio (λ) of a preconditioned soft tissue.

Soft tissues have the potential to undergo large deformations and still return to the initial configuration when unloaded, i.e. they are hyperelastic materials, and their stress-strain curve is nonlinear. The soft tissues are also viscoelastic, incompressible and usually anisotropic. Some viscoelastic properties observable in soft tissues are: relaxation, creep and hysteresis.[6][7] In order to describe the mechanical response of soft tissues, several methods have been used. These methods include: hyperelastic macroscopic models based on strain energy, mathematical fits where nonlinear constitutive equations are used, and structurally based models where the response of a linear elastic material is modified by its geometric characteristics.[8]

Pseudoelasticity

Even though soft tissues have viscoelastic properties, i.e. stress as function of strain rate, it can be approximated by a hyperelastic model after precondition to a load pattern. After some cycles of loading and unloading the material, the mechanical response becomes independent of strain rate.

Despite the independence of strain rate, preconditioned soft tissues still present hysteresis, so the mechanical response can be modeled as hyperelastic with different material constants at loading and unloading. By this method the elasticity theory is used to model an inelastic material. Fung has called this model as pseudoelastic to point out that the material is not truly elastic.[7]

Residual stress

In physiological state soft tissues usually present residual stress that may be released when the tissue is excised. Physiologists and histologists must be aware of this fact to avoid mistakes when analyzing excised tissues. This retraction usually causes a visual artifact.[7]

Fung-elastic material

Fung developed a constitutive equation for preconditioned soft tissues which is

with

quadratic forms of Green-Lagrange strains and , and material constants.[7] is the strain energy function per volume unit, which is the mechanical strain energy for a given temperature.

Isotropic simplification

The Fung-model, simplified with isotropic hypothesis (same mechanical properties in all directions). This written in respect of the principal stretches ():

,

where a, b and c are constants.

Simplification for small and big stretches

For small strains, the exponential term is very small, thus negligible.

On the other hand, the linear term is negligible when the analysis rely only on big strains.

Gent-elastic material

where is the shear modulus for infinitesimal strains and is a stiffening parameter, associated with limiting chain extensibility.[9] This constitutive model cannot be stretched in uni-axial tension beyond a maximal stretch , which is the positive root of

Remodeling and growth

Soft tissues have the potential to grow and remodel reacting to chemical and mechanical long term changes. The rate the fibroblasts produce tropocollagen is proportional to these stimuli. Diseases, injuries and changes in the level of mechanical load may induce remodeling. An example of this phenomenon is the thickening of farmer's hands. The remodeling of connective tissues is well known in bones by the Wolff's law (bone remodeling). Mechanobiology is the science that study the relation between stress and growth at cellular level.[6]

Growth and remodeling have a major role in the cause of some common soft tissue diseases, like arterial stenosis and aneurisms [10][11] and any soft tissue fibrosis. Other instance of tissue remodeling is the thickening of the cardiac muscle in response to the growth of blood pressure detected by the arterial wall.

Imaging techniques

There are certain issues that have to be kept in mind when choosing an imaging technique for visualizing soft tissue ECM components. The accuracy of the image analysis relies on the properties and the quality of the raw data and, therefore, the choice of the imaging technique must be based upon issues such as:

  1. Having an optimal resolution for the components of interest;
  2. Achieving high contrast of those components;
  3. Keeping the artifact count low;
  4. Having the option of volume data acquisition;
  5. Keeping the data volume low;
  6. Establishing an easy and reproducible setup for tissue analysis.

The collagen fibers are approximately 1-2 μm thick. Thus, the resolution of the imaging technique needs to be approximately 0.5 μm. Some techniques allow the direct acquisition of volume data while other need the slicing of the specimen. In both cases, the volume that is extracted must be able to follow the fiber bundles across the volume. High contrast makes segmentation easier, especially when color information is available. In addition, the need for fixation must also be addressed. It has been shown that soft tissue fixation in formalin causes shrinkage, altering the structure of the original tissue. Some typical values of contraction for different fixation are: formalin (5% - 10%), alcohol (10%), bouin (<5%).[12]

Imaging methods used in ECM visualization and their properties.[12][13]

Transmission Light

Confocal

Multi-Photon Excitation Fluorescence

Second Harmonic Generation

Optical Coherence Tomography

Resolution

0.25 μm

Axial: 0.25-0.5 μm

Lateral: 1 μm

Axial: 0.5 μm

Lateral: 1 μm

Axial: 0.5 μm

Lateral: 1 μm

Axial: 3-15 μm

Lateral: 1-15 μm

Contrast

Very High

Low

High

High

Moderate

Penetration

N/A

10 μm-300 μm

100-1000 μm

100-1000 μm

Up to 2–3 mm

Image stack cost

High

Low

Low

Low

Low

Fixation

Required

Required

Not required

Not required

Not required

Embedding

Required

Required

Not required

Not required

Not required

Staining

Required

Not required

Not required

Not required

Not required

Cost

Low

Moderate to high

High

High

Moderate

See also

References

  1. ^ Definition at National Cancer Institute
  2. ^ Skinner, Harry B. (2006). Current diagnosis & treatment in orthopedics. Stamford, Conn: Lange Medical Books/McGraw Hill. p. 346. ISBN 0-07-143833-5.
  3. ^ Junqueira, L.C.U.; Carneiro, J.; Gratzl, M. (2005). Histologie. Heidelberg: Springer Medizin Verlag. p. 479. ISBN 3-540-21965-X.
  4. ^ Amar, M., Alkhaledi, K., and Cochran, D., (2014). Estimation of mechanical properties of soft tissue subjected to dynamic impact. Journal of Eng. Research Vol. 2 (4), pp. 87-101
  5. ^ Alkhaledi, K., Cochran, D., Riley, M., Bashford, G., and Meyer, G. (2011). The psychophysical effects of physical impact to human soft tissue. ECCE '11 Proceedings of the 29th Annual European Conference on Cognitive Ergonomics Pages 269-270
  6. ^ a b Humphrey, Jay D. (2003). The Royal Society, ed. "Continuum biomechanics of soft biological tissues" (PDF). Proceedings of the Royal Society of London A. 459 (2029): 3–46. Bibcode:2003RSPSA.459....3H. doi:10.1098/rspa.2002.1060.
  7. ^ a b c d Fung, Y.-C. (1993). Biomechanics: Mechanical Properties of Living Tissues. New York: Springer-Verlag. p. 568. ISBN 0-387-97947-6.
  8. ^ Sherman, Vincent R. (2015). "The materials science of collagen". Journal of the Mechanical Behavior of Biomedical Materials. 52: 22–50. doi:10.1016/j.jmbbm.2015.05.023. PMID 26144973.
  9. ^ Gent, A. N. (1996). "A new constitutive relation for rubber". Rub. Chem. Tech. 69: 59–61. doi:10.5254/1.3538357.
  10. ^ Humphrey, Jay D. (2008). Springer-Verlag, ed. "Vascular adaptation and mechanical homeostasis at tissue, cellular, and sub-cellular levels". Cell Biochemistry and Biophysics. 50 (2): 53–78. doi:10.1007/s12013-007-9002-3. PMID 18209957.
  11. ^ Holzapfel, G.A.; Ogden, R.W. (2010). The Royal Society, ed. "Constitutive modelling of arteries". Proceedings of the Royal Society of London A. 466 (2118): 1551–1597. Bibcode:2010RSPSA.466.1551H. doi:10.1098/rspa.2010.0058.
  12. ^ a b Elbischger, P. J; Bischof, H; Holzapfel, G. A; Regitnig, P (2005). "Computer vision analysis of collagen fiber bundles in the adventitia of human blood vessels". Studies in Health Technology and Informatics. 113: 97–129. PMID 15923739.
  13. ^ Georgakoudi, I; Rice, W. L; Hronik-Tupaj, M; Kaplan, D. L (2008). "Optical Spectroscopy and Imaging for the Noninvasive Evaluation of Engineered Tissues". Tissue Engineering Part B: Reviews. 14 (4): 321–340. doi:10.1089/ten.teb.2008.0248. PMC 2817652. PMID 18844604.
This page was last edited on 22 August 2018, at 20:53
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