Acetylcholine is a neurotransmitter that helps the brain retain newly learned information. It also aids in the control of the heart’s beat rate.

This called the HPA axis, which is a neuroendocrine system in the body that responds to stress and releases cortisol.

Hormones, or chemicals released by the endocrine system into the bloodstream for delivery throughout the body, have a much longer lifespan than neurotransmitters, and induce changes to body systems that last for hours, days, or which can even be permanent.

The parathyroid gland can also release large doses of parathyroid hormone into the body in response to low blood calcium, a process which may influence the development of osteoporosis.

Hyperthyroidism also causes a reduced attention span and can lead to long-term neurological problems, and is typically treated with medication and (when necessary) surgical intervention. Hyperthyrodism can often result in a loss of necessary body weight, as opposed to weight gain. Hypothyrodism can result in weight gain.

Oxytocin works on a positive feedback loop because the actions which oxytocin causes also cause more oxytocin to be produced. This can be seen, among other examples, in the contractions of labor.

Neurotransmitters and hormones are both types of chemical messages. Because hormones are transmitted through the circulatory system, they take much longer for the messages to be received compared to the nervous system, which sends signals extremely quickly. Different glands secrete hormones in the endocrine system like the pituitary gland and adrenal gland. 

Oxytocin is a hormone found in mammals that is associated with bonding, empathy, and trust. Testosterone is also a hormone, but it is associated with sexual development in males. Dopamine and endorphins are both associated with positive feelings, but they are types of neurotransmitters—a different type of chemical messengers—not hormones. 

"Eating a snack," specifically one filled with carbohydrates would introduce sugar into the body. After being absorbed into the bloodstream, the levels of glucose in the blood would rise to normal blood glucose levels. All other answer choices do not include a resolution to rectify low blood sugar levels. 

The gene for red-green color blindness is on the X chromosome, and the trait is recessive. Females carry two copies of the X chromosome, while males carry only one. The genotypes of the parents must be X^rX^r for the mother and X^RY for the father, with X^r representing the recessive color-blind allele and X^R representing the dominant healthy allele.

The possible genotypes for the children of these two individuals are: X^rX^R, X^rY, X^rX^R, X^rY. 

Any sons must receive the Y chromosome from the father and a color-blind X^r chromosome from the mother, giving them all the genotype X^rY. All of the couple's sons will be color-blind.

Any daughters must receive the dominant healthy X^R chromosome from the father and a color-blind X^r chromosome from the mother, giving the all the genotype X^rX^R. All of the couple's daughters will have normal vision.