Oxytocin is a hormone that intensifies the contractions that take place during childbirth. The stretching of the uterus triggers the secretion of oxytocin, which stimulates uterine contractions. These contractions further stretch the uterus, which cause the secretion of more oxytocin and speeds up labor. Is this a example of positive or negative feedback

Im not sure

Explanation:

for the points

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

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