Hormones and Blood Calcium Levels - Essay Example

When calcium levels fall below 9mg/100 ml of blood, the parathyroid gland is stimulated to release the parathyroid hormone or PTH. This hormone stimulates the activity of osteoclasts to break bone and bone matrix down so as to release more calcium into the blood. It acts on PTH 1 receptor in the kidney and bone, as well as PTH 2 receptor on the testis, pancreas and nervous system to increase calcium levels. Parathyroid hormone has a half-life of four hours after which it decreases its own production through a negative feedback mechanism when calcium levels stabilize (Bronner, 2012: p45).

Oxytocin acts on various body organs, including the uterus and breasts, especially as a mediator of human behaviour, lactation and, in this case, labour and childbirth. It is controlled via a positive feedback mechanism, in which the hormone’s release leads to an action that stimulates the additional release of oxytocin. When uterine contractions begin, for instance, oxytocin release is mediated through positive feedback, in which release of oxytocin leads to more release of the same (Poulain et al, 2012: p55). This mechanism allows for the uterine contractions during labour and childbirth to increase in frequency and intensity, which stops at childbirth.

A rat’s testicles, in comparison to human testicles, are much larger, which is because they have patterns of mating that involve multiple males breeding with females as they come into heat. In addition, they produce more sperm to increase the odds that they will be successful. Another difference between testes in humans and rats is that the testes form part of a urogenital aperture in rats, which is not the case for humans (Söder, 2013: p66). Finally, the testes of rats can retract back to the abdominal cavity when they are not breeding, which is not the case for humans.