4.5

The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system?

After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels.

Based on the model of ferritin synthesis presented in Figure 2, which of the following describes the role of feedback on the control of intracellular iron levels?

An increase in iron levels activates synthesis of ferritin protein. Ferritin protein in turn binds iron, thereby decreasing both free iron levels and ferritin synthesis.

Based on the data, which of the following best represents how the mice with the implanted hESC-β cells use negative feedback to return blood glucose levels to normal if blood glucose levels increase?

Increased insulin secretion by hESC-β cells → increased glucose uptake by body cells → decreased insulin secretion by hESC-β cells

Which of the following observations best supports the hypothesis that CDK5 negatively regulates neurotransmitter release?

Inhibition of CDK5 activity in neurons increases the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.

Air is less dense at very high elevations, so less oxygen is available than in the denser air at sea level. Based on the model in Figure 1, if a person travels from sea level to a high elevation location, which of the following correctly predicts the response to the decreased blood oxygen level

More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes

Cyclic AMP phosphodiesterase is an enzyme that catalyzes the conversion of cyclic AMP to a different molecule. Which of the following best predicts the effect of inhibiting cyclic AMP phosphodiesterase in a muscle cell stimulated by epinephrine?

Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.

The rate of pyruvic acid formation fluctuates because

the reaction is affected by negative feedback

The model shown in the figure represents the role of two hormones, calcitonin and parathyroid hormone (PTH), in maintaining normal blood calcium levels in humans. If a dietary change results in an increase in blood calcium concentration above normal levels, which of the following is the most likely effect on calcium homeostasis?

Calcitonin levels will rise, thus promoting the deposit of calcium into bones.

The diagram above illustrates feedback control as exerted by the hormone thyroxine. Following surgical removal of the thyroid gland, the level of TSH in the blood will increase. Which of the following best explains this increase?

A decrease in thyroxine levels means a loss of inhibition to the hypothalamus and anterior pituitary, leading to increased TSH secretion.

The graph above shows changes in glucagon and insulin secretions at different concentrations of blood glucose. Which of the following feedback mechanisms is best supported by the data?

A low glucose level causes the release of glucagon, which stimulates the release of more glucose from tissues, which in turn lowers the amount of glucagon being released.

Damaged tissue releases chemicals that activate platelets and stimulate the formation of blood clots. Which of the following predictions about the activity of platelets best describes a positive feedback mechanism?

Activated platelets release chemicals that activate more platelets.

Antidiuretic hormone (ADH) is important in maintaining homeostasis in mammals. ADH is released from the hypothalamus in response to high tissue osmolarity. In response to ADH, the collecting duct and distal tubule in the kidney become more permeable to water, which increases water reabsorption into the capillaries. The amount of hormone released is controlled by a negative feedback loop. Based on the model presented, which of the following statements expresses the proper relationship between osmolarity, ADH release, and urine production?

As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine.

Thyroxin is a hormone that increases metabolic activities within various tissue targets. Low levels of circulating thyroxin trigger the secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary. TSH secretion then stimulates thyroxin production and release by the thyroid gland. The increased level of circulating thyroxin inhibits further secretion of TSH from the anterior pituitary. Based on the information provided, which of the following can most likely be concluded about the TSH-thyroxin loop?

The feedback mechanism would maintain relatively constant levels of thyroxin throughout tissue targets.