High School Biology : Understanding Negative Feedback Loops
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Example Question #1 : Understanding Negative Feedback Loops
Which of the following hormones will be elevated in the body when blood sugar levels are high?
Insulin
Parathyroid hormone
Glucagon
Thyroxine (T4)
Insulin
Hormones will be elevated in response to the conditions of the body. In other words, the body's hormones will be elevated in order to provide a negative feedback response. When blood glucose is high, insulin is released to lower these levels to the normal range. In contrast, when blood glucose is low, glucagon is released to raise these levels back to normal.
Thyroxine (T4) is released by the thyroid in order to increase the basal metabolic activity of the body, causing it to produce more ATP energy. Parathyroid hormone is released to stimulate osteoclast activity and raise blood calcium levels when they are too low.
Example Question #2 : Understanding Negative Feedback Loops
In primary hypothyroidism, patients are frequently diagnosed with a low free T4 (low thyroid hormone), but a high TSH (thyroid stimulating hormone). Which answer best explains the association, if there is any?
A decrease in thyroid hormone causes an increase in TSH to stimulate the secretion of more thyroid hormone.
An increase in serum TSH causes the inhibition of thyroid hormone secretion by negative feedback.
There is no association between the levels of TSH and thyroid hormone, it's a mere coincident that these findings are observed in the patient.
There is a tumor of the hypothalamus that is secreting a lot of TRH that is causing increased TSH.
There is a tumor in the thyroid that is secreting a lot of TSH that overtakes the remaining functions of the thyroid.
A decrease in thyroid hormone causes an increase in TSH to stimulate the secretion of more thyroid hormone.
TSH is secreted by the anterior pituitary in response to TRH (thyrotropin-releasing hormone), which is secreted by the hypothalamus. TSH then acts on the thyroid to stimulate the release of thyroid hormone into the blood. Adequate levels of thyroid hormone then cause negative feedback on the hypothalamus and pituitary to decrease the release of TRH and TSH.
In primary hypothyroidism, the problem lies in the thyroid-- the thyroid is not releasing enough thyroid hormone and it can be due to a variety of causes. What's important here is that there is no negative feedback on the pituitary to decrease its synthesis of TSH and therefore, the TSH levels are higher. It's just not able to function to increase the level of thyroid hormone and bring it to normal.
Example Question #2 : Understanding Negative Feedback Loops
Increase in thyrotropin-releasing hormone and thyroid-stimulating hormone can lead to increase activity of the heart, brain maturation, bone maturation and increased in metabolic rate. Increased in thyrotropin-releasing hormone also leads to an increase in what hormone being produced by the pituitary?
Antidiuretic hormone
Prolactin
Growth hormone
Somatostatin
Prolactin
Thyrotropin-releasing hormone leads to the stimulation of prolactin at the same time as thyroid-stimulating hormone. Oxytocin and antidiuretic hormone are produced by the hypothalamus and stored and secreted by the posterior pituitary. Somatostatin and growth hormone are not influenced by thyrotropin-releasing hormone.
Example Question #3 : Understanding Negative Feedback Loops
Which of the following is not released by the anterior pituitary?
Follicle-stimulating hormone
Adrenocorticotropic hormone
Growth hormone
Oxytocin
Oxytocin
Oxytocin and antidiuretic hormone are released from the posterior pituitary. All other choices are released from the anterior pituitary.
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