MCAT Thread: Im going to post something I learn or find interesting each day until I take my exam. Feel free to add to it!

Inhalation: external intercostal muscle and diaphragm contraction increases intrapleural volume, decreasing its pressure. In-turn it increases lung volume and creates a negative pressure allowing air to flow in.

Exhalation: the external intracostal muscles and diaphragm relax causing the intraplueral volume to decrease, increasing its pressure. This change forces the air in the lungs out. Active exhalation can also be done by internal intercostal contraction.

The three major control points of the TCA: 1. Citrate synthase in inhibited by increased levels of ATP, NADH, Succinyl-CoA, and its immediate product Citrate. Essentially, increased energy in the cell signals that the TCA does NOT need to move forward.

2. Isocitrate dehydrogenase: high energy products like ATP and NADH inhibit this step, while low energy signally by ADP and NAD+ act as activators. This makes sense in that this step is one that generates NADH which in turn generates ATP. If energy is high, TCA is not needed.

3. Alpha ketogluterate dehydrogenase: high energy products inhibit it like ATP and NADH, as well as its direct product succinyl-CoA. Low energy signals by ADP promote its activity along with increased levels calcium.