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Cell theory, developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, and that all cells come from pre-existing cells.
The typical normal human fetal cell will divide between 50 and 70 times before experiencing senescence. As the cell divides, the telomeres on the ends of chromosomes shorten. The Hayflick limit is the limit on cell replication imposed by the shortening of telomeres with each division. This end stage is known as cellular senescence.
The generally accepted parts of modern cell theory include: All known living things are made up of one or more cells [13] All living cells arise from pre-existing cells by division. The cell is the fundamental unit of structure and function in all living organisms. [14] The activity of an organism depends on the total activity of independent ...
Light micrograph of a moss's leaf cells at 400X magnification. The following outline is provided as an overview of and topical guide to cell biology: . Cell biology – A branch of biology that includes study of cells regarding their physiological properties, structure, and function; the organelles they contain; interactions with their environment; and their life cycle, division, and death.
Photograph of an adult female human, with an adult male for comparison. (Both models have partially shaved body hair to show anatomy, i.e., clean-shaven pubic regions.) A distinguishing characteristic of the class Mammalia is the presence of mammary glands. Mammary glands are modified sweat glands that produce milk, which is used to feed the ...
Gross anatomy has become a key part of visual arts. Basic concepts of how muscles and bones function and deform with movement is key to drawing, painting or animating a human figure. Many books such as "Human Anatomy for Artists: The Elements of Form", are written as a guide to drawing the human body anatomically correctly. [4]
Human biology tries to understand and promotes research on humans as living beings as a scientific discipline. It makes use of various scientific methods, such as experiments and observations, to detail the biochemical and biophysical foundations of human life describe and formulate the underlying processes using models. As a basic science, it ...
Cellular atrophy is a decrease in cell size. If enough cells in an organ undergo atrophy the entire organ will decrease in size. Thymus atrophy during early human development (childhood) is an example of physiologic atrophy. Skeletal muscle atrophy is a common pathologic adaptation to skeletal muscle disuse (commonly called "disuse atrophy").