Qs....................:) - medicus

[ArchivalUser]

thank you psychmledr!

[ArchivalUser]

Thanks psychmledr Nice explanation.
This is the explanation what they gave for Q 1, a little confusing for me,

1.correct answer: C
There is a one-one relation between the motor neuron and muscle cells (ie one motor neuron for each muscle cell). There is only one active end-plate from each motor neuron per muscle cell; therefore, option D is incorrect.

In addition, the action potential in the neuron will be transferred to create a distinct action potential in each muscle innervated by the neuron. The action potential is constant in its duration and in its amplitude; therefore options A and B are incorrect because these parameters cannot be changed.

Although the rate of synthesis of acetylcholine would increase the amount released by the axon terminal, the normal amount of acetylcholine released into the neuromuscular junction is enough to excite the muscle cell beyond the action threshold potential. Therefore, increasing the rate of synthesis (option E) would not effect the force of contraction.

Increasing the frequency of firing of individual motorneurons (option C) will increase the force of contraction because with each action potential firing in the muscle cell, more calcium enters the cell. Calcium drives the force of contraction and therefore with more calcium in the cell, the stronger the force of contraction will be.

[ArchivalUser]

2. correct answer: B

An increase in sodium intake will cause an increase in plasma osmolality, triggering the release of antidiuretic hormone (ADH), a.k.a. vasopressin. The immediate effect of ADH is movement of aquaporin channels to the apical surface of collecting duct cells (ChoiceB).

Increase in aquaporin gene expression by collecting duct cells (Choice A) is incorrect. Although this action is the long-term effect of ADH, an upregulation of gene expression occurs over a scale of days, not minutes.
Receptor binding of atrial natriuretic peptide (ANP) in distal tubule cells (Choice C) is incorrect.

ANP is released by the atria of the heart in response to an increase in blood volume, and acts on the collecting duct cells to decrease NaCl and water reabsorption. This would not decrease plasma osmolality.
Receptor binding of spironolactone in distal tubule cells (Choice D) is incorrect. Spironolactone is an exogenous medication that effects a diuresis by antagonizing the aldosterone receptor in cortical collecting tubules. This would not decrease plasma osmolality.

Release of urodilatin by collecting duct cells (Choice E) is incorrect. Urodilatin is a peptide produced by the distal tubule collecting duct in response to an increase in blood pressure/volume. It causes local inhibition of NaCl and water reabsorption; this would not decrease plasma osmolality.

[ArchivalUser]

3.correct answer: C
Prior to week 7 of gestation, the left and right sides of the primitive ventricle communicate through the interventricular foramen.

During week 7, the right and left bulbar ridges and endocardial cushions fuse to form the membranous portion of the interventricular septum.

Failure of the interventricular foramen to close at this time results in a ventricular septal defect (VSD), the most common congenital heart disorder.

A small VSD is typically asymptomatic and can be heard as a high-pitched, holosystolic murmur. Larger VSDs can cause left-to-right shunting, increased pulmonary blood flow, and pulmonary hypertension. They can present during the newborn period with failure to thrive.

During the third week of gestation (Choice A), the paired endothelial heart tubes formed by the angioblastic cords fuse in the ventral midline to form a single endocardial tube that begins to function as a primitive heart.

During the fourth week of gestation (Choice B), the septa primum and secundum divide the primordial atrium into the left and right atrium.

During the twenty-fourth week of gestation (Choice D), the primitive alveoli are formed and begin to produce surfactant.

During the twenty-eight week of gestation (Choice E), fetal hematopoiesis begins to occur in the bone marrow.

[ArchivalUser]

Good!! fr1234.
Didnt see your post.

[ArchivalUser]

Thanks, Medicus.

[ArchivalUser]

You are welcome

[ArchivalUser]

Thanks >>

[ArchivalUser]

Thank you medicus!!!