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Permineralization is a process of fossilization of bones and tissues in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue. Because of the nature of the casts, permineralization is particularly useful in studies of the internal structures of organisms, usually of ...
Tree remains that have undergone petrifaction, as seen in Petrified Forest National Park. In geology, petrifaction or petrification (from Ancient Greek πέτρα (pétra) 'rock, stone') is the process by which organic material becomes a fossil through the replacement of the original material and the filling of the original pore spaces with minerals.
The pericardium (pl.: pericardia), also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. [1] It has two layers, an outer layer made of strong inelastic connective tissue (fibrous pericardium), and an inner layer made of serous membrane (serous pericardium).
The heart derives from embryonic mesodermal germ layer cells that differentiate after gastrulation into mesothelium, endothelium, and myocardium.Heart induction occurs in the anterior mesoderm during gastrulation through interactions with adjacent endoderm (both extra-embryonic and definitive) mediated primarily by endogenous inhibitors of WNT signaling such as DKK1.
Fossils vary in size from one-micrometre (1 μm) bacteria [14] to dinosaurs and trees, many meters long and weighing many tons. A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates , or the chitinous or calcareous ...
These deposit onto the arterial walls which are already partially occluded and build upon the blockage. [36] The most common disease of the blood vessels is hypertension or high blood pressure. This is caused by an increase in the pressure of the blood flowing through the vessels. Hypertension can lead to heart failure and stroke.
Interruptions of coronary circulation quickly cause heart attacks (myocardial infarctions), in which the heart muscle is damaged by oxygen starvation. Such interruptions are usually caused by coronary ischemia linked to coronary artery disease , and sometimes to embolism from other causes like obstruction in blood flow through vessels.
Purkinje fibers take up stain differently from the surrounding muscle cells because of having relatively fewer myofibrils than other cardiac cells. The presence of glycogen around the nucleus causes Purkinje fibers to appear, on a slide, lighter and larger than their neighbors, being arranged along the longitudinal direction (parallel to the ...