Physiology Dr. Thomas Exam 1 Review

A patient experiences a sudden increase in extracellular sodium concentration. Assuming the change persists long enough for water to redistribute between compartments, which intracellular change is most likely?

Decreased intracellular water

A patient loses a significant amount of blood during surgery. Which change occurs first as a direct consequence of the blood loss?

Reduced plasma volume

A patient develops generalized edema after a condition causes a major increase in capillary hydrostatic pressure. Which change in Starling forces best explains the edema?

Increased filtration from capillaries

A patient has decreased renal perfusion. Which hormonal response would help restore extracellular volume by increasing sodium retention?

Increased aldosterone secretion

A red blood cell is placed in a solution that has a lower effective osmolarity than the cell interior. What is the most likely result?

The cell gains water

A membrane becomes twice as thick while all other factors affecting oxygen diffusion remain unchanged. What would be expected?

A decrease in diffusion rate

A drug blocks a membrane protein that normally allows glucose to move down its concentration gradient without directly using ATP. Which transport process is most likely being inhibited?

Facilitated diffusion

A cell's Na⁺/K⁺ ATPase is functioning normally. Which arrangement is most consistent with the pump's activity?

Sodium moves out of the cell while potassium moves into the cell

A skeletal muscle biopsy reveals a defect specifically within the repeating contractile units containing thick and thin filaments. Which structure is affected?

Sarcomere

During skeletal muscle contraction, actin filaments move farther toward the center of the sarcomere. Which change accompanies this movement?

The I band becomes smaller

A mutation prevents voltage-gated calcium channels from opening at the motor-neuron terminal. Which event is most directly reduced?

Acetylcholine release

A patient receives a drug that blocks nicotinic acetylcholine receptors at the neuromuscular junction. Which consequence would be expected even if acetylcholine release is normal?

The muscle fiber receives less effective excitatory signaling

A skeletal muscle fiber has normal acetylcholine release and a normal muscle action potential, but calcium cannot be released from the sarcoplasmic reticulum. Which event would be impaired next?

Calcium binding to troponin C

A mutation makes troponin C unable to undergo its normal conformational change after calcium binds. Which immediate consequence would most directly reduce contraction?

Reduced exposure of myosin-binding sites on actin

A researcher increases the amount of calcium released into the cytosol during each action potential in an isolated skeletal muscle fiber. Assuming the contractile machinery is otherwise normal, what is the most likely effect?

Greater activation of the contractile apparatus

A skeletal muscle fiber is actively contracting. SERCA activity is suddenly increased while calcium release from the sarcoplasmic reticulum remains unchanged. What is the most likely effect on cytosolic calcium?

Cytosolic calcium falls more rapidly

A skeletal muscle fiber has sufficient ATP but cannot hydrolyze ATP normally at the myosin head. Which process in the cross-bridge cycle would be most directly affected?

Myosin head cycling

Which finding would most strongly distinguish smooth muscle from skeletal muscle based on the contractile regulatory mechanism?

Use of calmodulin to regulate contraction

A patient has impaired ATP production in skeletal muscle. Which combination of processes would be directly affected by the ATP deficit?

Cross-bridge cycling and calcium reuptake

A student claims that increasing the frequency of stimulation of a single skeletal muscle fiber must increase the number of motor units recruited. Which response is most accurate?

The statement is incorrect because stimulation frequency and motor-unit recruitment are distinct mechanisms.