MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 3b Organ System Integration Homeostasis

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This deck focuses on 3b Organ System Integration Homeostasis, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What is the primary regulated variable in calcium homeostasis?

Answer: Ionized plasma $Ca^{2+}$ concentration. Plasma calcium levels are regulated to support nerve function, muscle contraction, and bone health through hormonal controls.

Flashcard 2: Which equation relates mean arterial pressure, cardiac output, and total peripheral resistance?

Answer: $MAP = CO \times TPR$. This relationship shows blood pressure depends on cardiac output and vascular resistance, key to homeostatic control.

Flashcard 3: Which hormone increases blood $Ca^{2+}$ and is secreted by parathyroid chief cells?

Answer: Parathyroid hormone (PTH). PTH mobilizes calcium from bone, enhances renal reabsorption, and activates vitamin D to elevate serum levels during hypocalcemia.

Flashcard 4: Which cardiac hormone promotes natriuresis in response to atrial stretch?

Answer: Atrial natriuretic peptide (ANP). ANP counters volume overload by inhibiting sodium reabsorption, promoting diuresis and natriuresis to reduce blood pressure.

Flashcard 5: What is calcitonin’s net effect on plasma $Ca^{2+}$?

Answer: Decreases plasma $Ca^{2+}$ (inhibits osteoclast activity). Calcitonin, secreted by thyroid C cells, reduces calcium by suppressing bone resorption during hypercalcemia.

Flashcard 6: What is the primary respiratory compensation for metabolic acidosis?

Answer: Hyperventilation to decrease $P_{CO_2}$. Hyperventilation expels CO2, shifting the bicarbonate equilibrium to raise pH and compensate for acid accumulation.

Flashcard 7: What is the primary renal compensation for respiratory acidosis?

Answer: Increase $H^+$ secretion and increase $HCO_3^-$ reabsorption. Kidneys enhance acid excretion and bicarbonate generation to buffer retained CO2 and restore acid-base balance.

Flashcard 8: What is the main function of the baroreceptor reflex in acute blood pressure control?

Answer: Rapidly adjusts heart rate and vascular tone to stabilize pressure. Baroreceptors detect pressure changes and trigger autonomic adjustments to maintain cardiovascular homeostasis acutely.

Flashcard 9: Identify the primary anatomical locations of arterial baroreceptors.

Answer: Carotid sinus and aortic arch. These high-pressure sites sense arterial stretch, providing rapid feedback to the brainstem for blood pressure regulation.

Flashcard 10: Which autonomic change occurs when baroreceptor firing decreases due to low blood pressure?

Answer: Increased sympathetic and decreased parasympathetic outflow. Reduced baroreceptor signaling during hypotension activates sympathetic responses to increase heart rate and vasoconstriction.

Flashcard 11: What is the primary physiological role of the renin-angiotensin-aldosterone system (RAAS)?

Answer: Increase blood pressure and extracellular fluid volume. RAAS activation conserves sodium and water, thereby expanding plasma volume and elevating blood pressure.

Flashcard 12: What is homeostasis in physiological systems?

Answer: Maintenance of a stable internal environment despite external change. Homeostasis ensures physiological variables remain constant through feedback mechanisms that counteract deviations from set points.

Flashcard 13: What is the key difference between negative and positive feedback loops?

Answer: Negative opposes change; positive amplifies change. Negative feedback restores equilibrium by reversing deviations, while positive feedback escalates them for processes like childbirth.

Flashcard 14: Identify the three core components of a homeostatic control system.

Answer: Sensor (receptor), integrator (control center), effector. These components detect changes, process information, and execute responses to maintain homeostasis in physiological systems.

Flashcard 15: What is the set point in a homeostatic feedback loop?

Answer: Target value of a regulated variable (the reference level). It represents the optimal level around which feedback mechanisms operate to minimize deviations in the variable.

Flashcard 16: What is the regulated variable in thermoregulation?

Answer: Core body temperature. Core temperature is tightly regulated via negative feedback to support enzymatic activity and metabolic processes.

Flashcard 17: Which hypothalamic region functions as the primary thermoregulatory integrator?

Answer: Hypothalamus (especially the preoptic area). This region integrates thermal sensory input and coordinates effector responses to maintain core body temperature.

Flashcard 18: What effector response increases heat loss during hyperthermia?

Answer: Cutaneous vasodilation and sweating. These mechanisms enhance evaporative and convective heat loss to counteract elevated core temperature in hot environments.

Flashcard 19: What effector response increases heat production during hypothermia?

Answer: Shivering and increased metabolic heat production. These responses generate internal heat to restore core temperature during cold exposure, preventing hypothermia.

Flashcard 20: What stimulus triggers renin release from juxtaglomerular cells?

Answer: Decreased renal perfusion pressure (low afferent arteriole stretch). Low pressure sensed by juxtaglomerular cells signals hypovolemia, prompting renin secretion to activate RAAS.

Flashcard 21: What is the direct enzymatic action of renin in the RAAS pathway?

Answer: Converts angiotensinogen to angiotensin I. Renin cleaves angiotensinogen, initiating the cascade that leads to vasoconstriction and sodium retention.

Flashcard 22: What is the main effect of angiotensin II on systemic arterioles?

Answer: Vasoconstriction, increasing total peripheral resistance. Angiotensin II constricts arterioles to elevate blood pressure, supporting perfusion during hypovolemic states.

Flashcard 23: What is aldosterone’s primary effect in the distal nephron?

Answer: Increase $Na^+$ reabsorption and $K^+$ secretion. Aldosterone promotes sodium retention and potassium excretion to increase extracellular fluid volume and maintain electrolyte balance.

Flashcard 24: What is antidiuretic hormone (ADH) effect on the collecting duct?

Answer: Increases water reabsorption by inserting aquaporin-2 channels. ADH enhances permeability of collecting ducts to water, concentrating urine and conserving body water during dehydration.

Flashcard 25: What change in plasma osmolality most strongly stimulates ADH release?

Answer: Increased plasma osmolality (hyperosmolarity). Osmoreceptors in the hypothalamus detect high osmolality, triggering ADH to restore plasma tonicity via water reabsorption.