NBDE -1 ques

[dr dent]

---

Members do not see this ad.

esophagus an d thoracic duct lie in what prat of mediatinum -superior or inferior ??😕

 

[PrePerio]

Are those the only 2 options? I'd say posterior mediastinum.

 

[lionelhutz]

Here is a breakdown:

Superior mediastinum:
trachea and esophagus, thymus, phrenic, aortic arch, brachiocephalic art and veins, sup. vena cava, thorocic duct, left subclavian, azygos vein, left common carotid.

The inferior mediatinum is broken down into:

Anterior mediastinum:
Sometimes the thymus gland, internal thoracic artery, and lymph nodes.

Middle mediastinum:
heart, pericardium, phrenic nerves, ascending aorta, SVC, coronary arteries and veins.

Posterior mediastinum:
descending aorta, esophagus, thoracic duct, azygos v., splanchnic nerves, and the vagus nerves.

So, to basically answer your question, the thoracic duct is in the inferior (posterior portiion) of the mediastinum and continues to the superior mediastinum to empty into the venous circulation.
And yeah, what are the options in the question?

 

[dr dent]

Thanks . it was just a ques ...🙂the options not given .i was cofused as 2 write superior or inferior mediastinum.

 

[PrePerio]

I have another question...all of these answer choices seem wrong...I wish fibrocartilage was an option:

The articulating surface of the adult mandibular condyle is covered by which of the following substances?
A. elastic tissue
B. synovial membrane
C. hyaline cartilage
D. typical perichondrium
E. collagenous connective tissue

Anyone able to explain the best option?

 

[lionelhutz]

I have another question...all of these answer choices seem wrong...I wish fibrocartilage was an option:

The articulating surface of the adult mandibular condyle is covered by which of the following substances?
A. elastic tissue
B. synovial membrane
C. hyaline cartilage
D. typical perichondrium
E. collagenous connective tissue

Anyone able to explain the best option?

We definitely know that its not hyaline tissue, elastic, or typical perichondrium. We also know that synovial membrane does not cover the articulating surfaces.

In my opinion, collagenous connective tissue is the best choice. Think about it, what is fibrous connective tissue (on the condyle)..... it is simply another form of collagenous connective tissue. So basically fibrocartilage=collagen containing tissue= answer E.

hope that helped 🙂

 

[dentheartthrob]

Hi guys, can some one be kind enough to explain this question and answer to me. Thanks in advance

For a reaction catalyzed by an enzyme with Km= 1mM, which of the following represents the effect on the velocity of is changed from 10mM to 20mM? (assuming the the enzyme obeys Michaelis-Menten kinetics.)

a. small decrease
b. small increase
c. twofold decrease
d. twofold increase
E. twentyfold increase.

The answer is B.

 

[darkshadow0574]

10 20
____=0.90 ______ =0.95
10+1 20+1

 

[darkshadow0574]

10 = 0.90
10+1

20 =0.95
20+1

s
Vo= s+km

 

[wishfulthinker]

so if your Km =1 that means that the enzyme is 50% saturated at =1. at =2, your enzyme is 100% saturated, which means it's working at full capacity.

therefore, at both concentrations of 10 and 20, your enzyme is jam packed full of substrate and is fully concentrated and is working as fast as it can chug along. so you arent goign to get a dramatic increase in the rate because the enzyme is already so full of substrate and is so immersed in substrate that it simply can't do much to change the reaction rate so its a "slight increase."

had the concentration gone from 1 to 2, then you would double the rate becuase then you are going from a = 1 so its 50% saturation of the enzyme so the rate is 50% of the Vmax. and then at =2 you are at 100% saturation so you are at 100% of Vmax. since 100/50=2, you get a twofold increase.

i dont like to think of the formulas, they are easy to forget and even easier to make a careless error on. just keep in mind that the Km signifies the concentration of the substrate at which there is 50% saturation of the enzyme and compare that to the initial and final concentrations. i hope this helps.

 

[dentheartthrob]

10 = 0.90
10+1

20 =0.95
20+1

s
Vo= s+km

thanks. if v=Vmax/Km+, shouldnt Km be half of Vmax? making the statement. 2(10)/1+10, 2(20)/1+20. 1.81, and 1.90, either way it is still increased by a little...when are you planning on taking the exam?

 

[wishfulthinker]

thanks. if v=Vmax/Km+, shouldnt Km be half of Vmax? making the statement. 2(10)/1+10, 2(20)/1+20. 1.81, and 1.90, either way it is still increased by a little...when are you planning on taking the exam?

Km is not half of Vmax. Km is a concentration value in units of M (mol/L) so its the concentration at which you are at half of Vmax in velocity. hope that clarifies

 

[dentheartthrob]

Km is not half of Vmax. Km is a concentration value in units of M (mol/L) so its the concentration at which you are at half of Vmax in velocity. hope that clarifies

well since 1 was the Km, then its assumable that Vmax is 2. since like you said Km= Vmax/2 of a substrate, simply put. 1mM=XmM/s/2, as you can see the units will cancel each other out algebraically