Question

1. Which of the following statements about the adrenergic receptors is TRUE? Select one:

a. Alpha 1, alpha 2, and beta 1 receptors have greater affinity (or sensitivity) to norepinephrine than epinephrine.

b. Beta 2 receptor has an equal affinity for norepinephrine and epinephrine while beta 3 receptor has a greater affinity for epinephrine than norepinephrine.

c. Beta 1, beta 2, and beta 3 receptors increase cAMP but only beta 1 receptor causes an excitatory response in the heart muscle.

d. Alpha 1receptor activates cAMP and causes an excitatory response to most of the sympathetic target tissues.

e. Alpha 2 activates cAMP and causes an inhibitory response in the gastrointestinal tract.

2. Which line of defense mechanisms against acid-base disturbances will be the quickest to maintain blood pH?

a. Buffered by bicarbonate in the blood

b. Respiratory compensation by expiration of carbon dioxide

c. Renal compensation by tubular reabsorption of bicarbonate and tubular secretion of H⁺

3. Which of the following is TRUE about the signal transduction for cyclic AMP (cAMP)?

a. Beta 1, Beta 2, and Beta 3 increases cAMP while Alpha 2 deactivates cAMP.   

b. Epinephrine and norepinephrine are first messengers that bind equally to Beta 1 receptors to activate adenylyl cyclase in the heart muscle or kidney.

c. Adenylyl cyclase, an amplifier enzyme, converts an intracellular ATP into cAMP, a second messenger.

d. Cyclic AMP (cAMP) activates protein kinase A. Protein kinase A phosphorylates other proteins that will lead into a cellular response.

e. All of the above

f. None of the above

Answer 1

1.

A	Wrong	All the alpha receptors have equal affinity for both norepinephrine and epinephrine.
B	wrong	beta2 receptors have more affinity for epinephrine than norepinephrine while beta 3 receptors have more affinity for norepinephrine than Epinephrine.
C	right	beta receptors increase cAMP as they function by Gs subunit of G protein coupled receptors. But only beta 1 receptors have excitatory function like increase in heart rate and other beta receptors have inhibitory function like relaxation of bronchial smooth muscles.
D	wrong	Alpha 1 receptor function by Gq subunit of G protein coupled receptors which activates the phospholipase C.
E	wrong	alpha 2 receptors function primarily by Gi subunit of G protein coupled receptors which inhibit the enzyme adenylyl cyclase leading to decrease in cAMP .

2. Three main defence mechanism to who regulate the blood pH are buffer systems, respiratory system and kidneys. Out of these, buffer systems (bicarbonate) are the quickest, respiratory system has intermediate speed and kidneys are the slowest. Although the buffers are quickest, the do not maintain the blood pH for long time. Maintenance is the function of kidneys. Answer is buffer by bicarbonate in blood.

3.

A	right	it is true that beta receptor increases cAMP by functioning by Gs subunit of G protein coupled receptors and alpha 2 receptors decreases cAMP by functioning by Gi subunit of G protein coupled receptors.
B	right	beta 1 receptors have equal affinity for norepinephrine as well as epinephrine in the heart or kidney.
C	right	Adenylyl cyclase converts Intracellular ATP into cAMP which acts as a second messenger.
D	right	cAMP acts as a second messenger and activates a protein called protein kinase A. This protein kinase A phosphorylates the other proteins that lead to cellular response.
E	right	All of the above are right. (Answer)