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Kristina Stevens
Physiology 7-13
| Question | Answer |
|---|---|
| What is the primary function of the sodium–potassium pump, and why is it essential for maintaining resting membrane potential? | The Na⁺/K⁺ pump moves 3 sodium ions out and 2 potassium ions into the cell using ATP. This maintains the negative resting membrane potential and correct ion gradients needed for nerve and muscle excitability. |
| How does the autonomic nervous system regulate heart rate through sympathetic and parasympathetic pathways? | Sympathetic stimulation (norepinephrine) increases heart rate and contractility. Parasympathetic stimulation (vagus nerve, acetylcholine) decreases heart rate. |
| What role does aldosterone play in regulating blood volume and electrolyte balance? | Aldosterone increases sodium reabsorption and potassium excretion in the kidneys. Water follows sodium, so this increases blood volume and blood pressure. |
| Explain how the sliding filament theory describes muscle contraction at the level of actin and myosin. | Muscle contraction occurs when myosin heads bind to actin, forming cross-bridges. Myosin pulls actin filaments inward (power stroke), shortening the sarcomere. ATP is required for releasing and re-cocking myosin heads. |
| What is Starling’s Law of the Heart, and how does it affect stroke volume? | Starling’s Law: The more cardiac muscle is stretched (↑ venous return), the stronger the contraction. This increases stroke volume, allowing the heart to pump out what it receives. |
| How does antidiuretic hormone (ADH) help maintain water balance in the body? | ADH increases water reabsorption in the kidneys by adding aquaporins to the collecting duct. This decreases urine output and helps maintain blood pressure and hydration. |
| What occurs during depolarization and repolarization of a neuron, and how does this generate an action potential? | Depolarization: Na⁺ channels open → Na⁺ rushes into the neuron → inside becomes more positive. Repolarization: K⁺ channels open → K⁺ exits → membrane potential becomes more negative again. This creates an action potential that propagates along the axon. |
| How do the lungs and kidneys work together to regulate blood pH? | Lungs: remove CO₂ (acidic), adjusting pH within minutes. Kidneys: excrete H⁺ and reabsorb bicarbonate (HCO₃⁻), adjusting pH over hours–days. Together they maintain acid–base homeostasis. |
| What is the role of hemoglobin in oxygen transport, and how does pH affect its affinity for oxygen (Bohr effect)? | Hemoglobin binds oxygen in the lungs and releases it in tissues. Bohr effect: Low pH (more acidic) decreases hemoglobin’s affinity for O₂, helping oxygen unload into tissues. |
| Describe the pathway of blood flow through the heart, starting with deoxygenated blood entering from the body. | Body → Superior/Inferior vena cava → Right atrium → Right ventricle → Pulmonary artery → Lungs → Pulmonary veins → Left atrium → Left ventricle → Aorta → Body. |
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