Which of the following describes a positive feedback loop? O When blood sugar concentration is too low, the endocrine system secretes hormones that increase blood sugar concentration to a normal level.
O When the body senses that the heart rate is very high, it secretes hormones that decrease the heart rate.
O When blood sugar concentration is too high, the endocrine system secretes hormones that decrease blood sugar concentration to a normal level.
O When someone is exercising intensely, the body secretes hormones that increase oxygen supply for cellular respiration.​

When someone is exercising intensely, the body secretes hormones that increase oxygen supply for cellular respiration.​

Explanation:

Positive feedback is defined as the reaction in nature in which the product of reaction increases. A positive feedback loop is not limited to a level but can move away from the equilibrium.

For example: During intense exercising, heart started producing more oxygen or pumps blood faster through the body.

Hence, the correct answer is "4.​"

the answer is A when blood sugar contraction is to low

Explanation:

i took the test

explanation:

the fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus eohippus.

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.