Tag: mechanism of hormone action

Questions Related to mechanism of hormone action

Which of the following is an example of a negative feedback?

biology chemical coordination and integration mechanism of hormone action coordination in human beings- chemical control endocrine system in humans

  1. Sucking reflex

  2. Uterine contractions during labour

  3. Secretion of CRH in response to ACTH

  4. Hair erection due to low body temperature

Show answer
Correct Option: C
Explanation:

One distinctive feature of hormones whose secretion is regulated through the hypothalamus and pituitary is that they regulate their own secretion through negative feedback inhibition. CRH (corticotropin releasing hormone) and ACTH (adrenocorticotropic hormone). Less tropic hormone secretion leads to less stimulation of cortisol secretion by cells of the zona fasciculata of the adrenal cortex. The usefulness of negative feedback inhibition is that it works to keep hormone levels within a particular appropriate physiological range.  The reduced negative feedback inhibition means that more CRH and ACTH will be secreted. More ACTH will stimulate the remaining adrenal tissue to grow and to secrete more cortisol. This will have the effect of bringing cortisol back up towards its normal daily level of secretion.

So the correct option is ' secretion of CRH in response to ACTH'

Consider the synchronization of birth and milk production. Babies can be born several months prematurely, and milk production is needed immediately after birth. How has the human body evolved to coordinate this delicate timing of events?

biology chemical coordination and integration mechanism of hormone action coordination in human beings- chemical control endocrine system in humans

  1. The ovaries signal the rest of the body tissues by varying the level of estrogen.

  2. Conscious awareness of the arrival of a baby triggers the mother's hypothalamus to secrete prolactin.

  3. The hypothalamus and pituitary that triggered the female reproductive cycle also schedule milk production on a nine-month clock basis.

  4. Oxytocin both causes the uterus to contract in labor and stimulates the release of milk from mammary glands, which is reinforced by prolactin from the pituitary.

Show answer
Correct Option: D
Explanation:

The hypothalamus and pituitary that triggered the female reproductive cycle do not schedule milk production on a nine-month clock basis. But oxytocin is released due to the stimulation by fetal ejection reflex. By this stimulation, oxytocin is released which causes contraction in uterus wall and also stimulates prolactin secretion for milk production in mammary gland. Thus, the correct answer is option D.

Which one is a positive feedback mechanism?

biology chemical coordination and integration mechanism of hormone action coordination in human beings- chemical control endocrine system in humans

  1. Sexual stimulation

  2. Allosteric inhibition

  3. Blood pressure

  4. Perspiration

Show answer
Correct Option: B
Explanation:

Allosteric inhibition is the regulation of an enzyme by an effector molecule that binds to a site other than the active site, which is called allosteric site. Since it is not blocking the active site it is called 'positive feedback' option $(B)$

Positive feedback loop between cytokines and immune cells can cause

biology chemical coordination and integration mechanism of hormone action coordination in human beings- chemical control endocrine system in humans

  1. Hypocytokinemia

  2. Hypercytokinemia

  3. Immune deficiency

  4. None of the above

Show answer
Correct Option: B

An example of negative feed back loop in humans is 

biology chemical coordination and integration mechanism of hormone action coordination in human beings- chemical control endocrine system in humans

  1. Salivation of mouth at the sight of delicious food.

  2. Constriction of skin blood vessels and contraction of skeletal muscles in cold.

  3. Secretion of tears on dust particles falling in eyes.

  4. Secretion of sweat glands and constriction of skin blood vessels when it is too hot.

Show answer
Correct Option: B
Explanation:
  • Negative feedback is a reaction that causes a decrease in function. It occurs in response to some kind of stimulus. Often it causes the output of a system to be lessened; so, the feedback tends to stabilize the system. This can be referred to as homeostasis. For example, constriction of skin blood vessels and contraction of skeletal muscles in cold.
  • So, the correct answer is 'Constriction of skin blood vessels and contraction of skeletal muscles in cold'.