A researcher is conducting an experiment to determine factors affecting vascular resistance. Experiment animals are anesthetized, intubated, and attached to a controlled ventilation system. A catheter is placed into a small artery in various organs in each animal. The catheter is connected to a manometer for recording pressure and to an oximeter for continuous recording of oxygen saturation. The fraction of inspired oxygen is gradually changed, and arteriolar resistance is calculated from the manometer readings at regular intervals. The results shown below were most likely obtained from which of the following organs?

Question

A researcher is conducting an experiment to determine factors affecting vascular resistance.  Experiment animals are anesthetized, intubated, and attached to a controlled ventilation system.  A catheter is placed into a small artery in various organs in each animal.  The catheter is connected to a manometer for recording pressure and to an oximeter for continuous recording of oxygen saturation.  The fraction of inspired oxygen is gradually changed, and arteriolar resistance is calculated from the manometer readings at regular intervals.  The results shown below were most likely obtained from which of the following organs?

Quizplus · Accepted Answer

11ec160b_3cd0_54df_9249_e3b54555fba8_MD0001_00 This graph depicts a vascular bed in which arterial/arteriolar resistance increases as the tissue O₂ content decreases. This response is unique to the pulmonary vasculature, in which hypoxic vasoconstriction occurs to divert blood flow away from underventilated lung regions and toward well-ventilated lung areas. This phenomenon improves ventilation-perfusion mismatch by decreasing physiologic shunting in poorly ventilated alveoli, leading to overall more efficient gas exchange. The relationship between hypoxia and vascular resistance is reversed throughout the rest of the body, ensuring that hypoxic organs and tissues receive increased blood flow. (Choice A) Although the cerebral circulation is more sensitive to blood CO₂ levels (small degrees of hypercapnia lead to vasodilation), hypoxia causes significant arteriolar dilation when the partial pressure of oxygen (PO₂) falls below 50 mm Hg. (Choice B) In the coronary vasculature, subendocardial blood flow is mediated by the local tissue PO₂, adenosine, prostacyclin, and nitric oxide. Decreased tissue PO₂ promotes vasodilation of arterioles in the myocardium. (Choice C) A large increase in sympathetic tone may cause vasoconstriction of the renal vasculature, but hypoxia does not have this effect. (Choice E) Parasympathetic-induced intestinal vasodilation occurs in response to digestive chyme passing over intestinal mucosa. Sympathetic tone (not hypoxia) plays a large role in the splanchnic vasoconstriction that occurs with exercise or significant hypovolemia. Educational objective: The pulmonary vascular bed is unique in that tissue hypoxia results in a vasoconstrictive response. Such hypoxic vasoconstriction occurs in the small muscular pulmonary arteries to divert blood flow away from underventilated lung regions and toward well-ventilated lung areas to minimize ventilation-perfusion mismatch, leading to more efficient overall gas exchange. __________ References: Hypoxic pulmonary vasoconstriction in humans. (http://www.ncbi.nlm.nih.gov/pubmed/24024204) Hypoxic pulmonary vasoconstriction. (http://www.ncbi.nlm.nih.gov/pubmed/22298659)

A Researcher Is Conducting an Experiment to Determine Factors Affecting