Q: About a patient with a glucagonoma.


 

Mouse Islet of Langerhans immunostained for Glucagon

 

Assume that you find a patient with a glucagon-secreting pancreatic tumor (glucagonoma). Which one of the following is most likely to result from hyperglucagonemia?

 

a)     Decreased lipolysis

 

b)     Hyperglycemia

 

c)      Increased muscle protein synthesis.

 

d)     Increased liver glycolytic rate

 

e)     Increased glycogenesis

Biochemistry Question CM-21


 

A 13 year-old patient with Type I diabetes mellitus, home alone,  takes an insulin injection before lunch but then he gets concentrated in a videogame he is playing and does not eat. Approximately 3 hours later, he becomes sweat, shaky and confused. These symptoms have appeared as a consequence of:

 

a) increased glucagon release from the pancreas

 

b) decreased glucagon release from the pancreas

 

c) increased insulin  release from the pancreas

 

d) decreased insulin release from the pancreas

 

e) high sugar levels in blood

 

f) low sugar levels in blood

 

 

Q: About the Postprandial state (I-13)


 

Which of the following responses of glucagon and/or insulin is most likely to occur in a normal individual after ingesting a high-carbohydrate meal?

 

a)     insulin levels decreases

 

b)     insulin levels increases

 

c)      glucagon levels increases

 

d)     insulin and glucagon levels decreases

 

e)     insulin and glucagon levels increases

 

Dont forget the dessert!

Don't forget the dessert!

 

 

 

 

 

 

Q: About Congenital Adrenal Hyperplasia


Question about Hormones (H-07)

 

Congenital Adrenal Hyperplasia (CAH) occurs as a consequence of genetic deficit of enzymes that participate in the conversion of cholesterol to cortisol. Failure in producing cortisol results in an increase of ACTH secretion and consequently an increased production of androgens and aldosterone disbalance, (most of the cases also show an unability to synthesize aldosterone).  As a result, clinical consequences can be detected in the newborn, from ambiguous genitalia up to salt-losing crisis that threatens the life of the newborn. That is why newborn screening for this disease exists in almost all states. The enzyme deficiency that is most common in CAH is:

 

a)     11 hydroxylase

 

b)     17 hydroxylase

 

c)      21 hydroxylase

 

d)     Desmolase

 

e)     HMGCoA reductase

 

f)       HMGCoA synthase

 

g)     HMGCoA Lyase

 

h)    Sterol cyclase

 

 

Q: About Epinephrine action


 

 

(CM-06) In recent years, Oral Glucose Tolerance Tests have lost support as a diagnostic tool for Diabetes Mellitus. It overdiagnoses diabetes, because a variety of stresses can produce an abnormal response as a consequence of an epinephrine discharge. Even anxiety over venipunctures may generate sufficient epinephrine to produce an abnormal test. Epinephrine induce an elevation in glycemia because this hormone:

 

a)     inhibits gluconeogenesis and  glycogenesis

 

b)     inhibits gluconeogenesis and glycogenolysis

 

c)      inhibits glycogenolysis and glycolysis.

 

d)     stimulates glycogenolysis and inhibits glycogenesis

 

e)     stimulates glycogenesis and gluconeogenesis

 

   

G Protein-Phospholipase C Signal System


Answer to Question about Hormones H-05:

 

(g) Ca++, Diacylglycerol and Inositol 1,4,5 triphosphate

 

 

As was discussed in the answer to H-04, some hormones that can not penetrate the plasma membrane, interact with receptors in membrane that are linked to a G-protein. As a result of the interaction hormone-receptor, the a subunit of the G-protein binds to GTP and separates from the bg subunit. The a subunit-GTP complex activates an specific effector protein, depending on the kind of a subunit. In case the a subunit is Gas,  it activates Adenylate Cyclase, increasing the production of cAMP.

 

If the Hormone-receptor complex interacts with a Gaq/11 kind of G protein, then the activated enzyme is Phospholipase C.

 

Hormones that bind to receptors related to this Protein Gaq/11-Phospholipase C system include:

 

-Angiotensine II

 

-Catecholamines (alpha-receptors)

 

-Godatrophin Releasing Hormone GnRH)

 

-Growth Hormone Relaeasing Hormone

 

-Oxytocin

 

-Thyroid-releasing Hormone

 

-Vasopresin

 

Phospholipase C catalyze the hydrolysis of Phosphatidyl inositol 4,5 biphosphate that is forming part of the plasma membrane.

 

 

 

                                  

   

The action of the enzyme on this substrate produces IP3 (Inositol triphosphate) and diacylglycerol.

 

IP3 difuses into the cytosol and binds to its receptor in the sarcoplasmic reticulum and opens a Calcium channel

 

Diacylglycerol remains close to the membrane and, with the participation of Ca++ released by IP3, activates Protein Kinase C, that phosphorylates other proteins, modifying its function (for the general action of Kinases, see related post)

 

 

 

       

 

Ca++ binds to Calmodulin, Troponin C and other Ca++ binding proteins provoking activation of some enzymes, actin myosine interaction, promotes exocytosis, synthesis of NO, and other effects.

 

Recommended sites:

 

http://www3.us.elsevierhealth.com/promo/Guyton/ch74.pdf),

 

http://mcb.berkeley.edu/courses/mcb136/topic/Endocrine_Autonomic/SlideSet1/endo1.pdf

 

An excellent animation here!