Diffen âº Science âº Biology âº Microbiology. Fraternal twins are âdizygotic,â meaning that they developed from two different eggs fertilized by two different sperm cells, while identical twins are âmonozygoticâ i.e., they developed from a single fertilized egg that split.
A T-tubule (or transverse tubule) is a deep invagination of the sarcolemma, which is the plasma membrane of skeletal muscle and cardiac muscle cells.These invaginations allow depolarization of the membrane to quickly penetrate to the interior of the cell.ransverse tubules are invaginations of the sarcolemma. Though the invaginations are normally perpendicular to the length of the fiber, many T-tubules can lie axial to the long-axis of the fiber, both wrapping around and running alongside myofilament bundles.
When thyroid function is not sufficient to meet the bodyâs needs it is called hypothyroidism, and may stem from various sourcesâ¦. â For one, the thyroid may not make enough of the T4 form of thyroid hormone due to a problem with the thyroid itself. In this case, T4 levels would be low and TSH would be high because there wouldnât be enough T4 to inhibit the pituitaryâs production of TSH in the negative feedback loop.