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regulates the flow of contents from the stomach to the duodenum.

A. Organogenesis: This is the process during which the three germ layers (ectoderm, mesoderm, endoderm) give rise to organs and organ systems.
B. Embryogenesis: Broad term that includes all development from fertilization to the fetal stage.
C. Gastrulation: Earlier stage in which the three germ layers form from the epiblast.
D. Cleavage: Series of mitotic divisions that create the blastocyst; occurs before germ layer formation.

E. Neurulation: This is a fundamental process in the early development of vertebrate embryos that establishes the central nervous system. It's the intricate series of events where a flat sheet of cells, the neural plate, folds and transforms into a hollow structure called the neural tube.

A. Decrease in aldosterone production: Aldosterone regulates sodium and potassium levels, not calcium homeostasis.
B. Secretion of parathyroid hormone: PTH is released in response to low calcium levels. It increases calcium reabsorption from bone, the kidneys, and enhances activation of vitamin D to increase calcium absorption in the intestines.
C. Secretion of renin: Renin responds to decreased renal perfusion pressure or sodium levels, not calcium levels.
D. An increase in blood urea nitrogen: This may indicate renal dysfunction or dehydration, but it's not directly related to calcium levels.
E. Vasoconstriction of the afferent arterioles: Occurs in response to sympathetic stimulation or reduced perfusion, not hypocalcemia.