Physiology Flashcards

In skeletal muscle, calcium released from the sarcoplasmic reticulum binds to which protein to initiate contraction?

Answer: Troponin C

Ca²⁺ binds troponin C, causing a conformational change that moves tropomyosin away from actin's myosin-binding sites, allowing cross-bridge cycling.

Which hormone acts on bone to INCREASE osteoclast activity and raise serum calcium?

Answer: Parathyroid hormone (PTH)

PTH stimulates osteoclast-mediated bone resorption (via RANKL on osteoblasts), releasing calcium and phosphate into the blood to correct hypocalcemia.

The cerebellum contributes to motor coordination primarily by:

Answer: Comparing intended movement to actual movement and correcting errors

The cerebellum receives efference copies of motor commands and proprioceptive feedback, computing error signals to fine-tune movement smoothness and timing.

In the proximal convoluted tubule, approximately what percentage of filtered sodium is reabsorbed?

Answer: 67%

About two-thirds (67%) of filtered Na⁺ is reabsorbed in the PCT via Na⁺/H⁺ exchange and cotransport, making it the major site of bulk tubular reabsorption.

Which change would increase airway resistance the MOST according to Poiseuille's law?

Answer: Halving airway radius

Resistance is inversely proportional to radius to the fourth power (R ∝ 1/r⁴), so halving the radius increases resistance 16-fold—far more than other changes.

The sympathetic nervous system's effect on the pupil is:

Answer: Mydriasis via stimulation of the dilator pupillae

Sympathetic α₁ adrenergic stimulation contracts the radial dilator pupillae muscle, widening the pupil (mydriasis) to maximize light entry under threat.

Chronic hyperventilation leads to which acid-base disturbance?

Answer: Respiratory alkalosis due to excess CO₂ elimination

Excess CO₂ washout from hyperventilation reduces PCO₂, shifting the carbonic acid equilibrium and raising pH—producing primary respiratory alkalosis.