Circulation and Gas Exchange

Which statement correctly describes every artery in a vertebrate?

Cells growing on the bottom of a culture dish get their O₂ by diffusion down through the liquid medium above them. A technician lowers the depth of the medium from 6 mm to 2 mm. Roughly how long does it now take O₂ to diffuse down to the cells, compared with before?

Researchers inject a harmless dye into the heart of a newly described marine invertebrate. Within seconds the dye appears in open spaces around the gut and reproductive organs, and fluid sampled from between the organs has the same makeup as fluid taken from the heart. Which conclusion is best supported?

Two invertebrate species of similar body size were compared (invented data). Species X: highest fluid pressure 4 mm Hg; fluid between cells matches the circulating fluid; O₂ use at rest 0.05 mL per gram per hour. Species Y: highest fluid pressure 35 mm Hg; fluid between cells differs from the circulating fluid; O₂ use at rest 0.30 mL per gram per hour. Which statement is best supported?

A cyclist's resting heart rate is 58 beats per minute with a stroke volume of 90 mL. Near the end of a race, her heart rate is 172 beats per minute and her stroke volume is 125 mL. By about what factor has her cardiac output increased?

A blood clot forms in a deep vein of a patient's calf, then breaks loose and travels with the blood. Where is it most likely to get stuck first?

In a patient, the AV valve between the left atrium and left ventricle doesn't close completely. What most likely happens when the left ventricle contracts?

A drug lengthens the time between the electrical signal that spreads across the atria and the signal that spreads across the ventricles, but it doesn't change how often the atrial signals begin. Which part of the heart is the drug most likely acting on?

A researcher uses a simplified model of the circulation in which 90 cm³ of blood flows through each level of vessels every second (invented values). Total cross-sectional area at each level: aorta, 4.5 cm²; all arteries together, 20 cm²; all arterioles, 400 cm²; all capillaries, 4,500 cm²; all veins, 18 cm². What is the average speed of blood in the capillaries?

A person with severe liver disease makes too little albumin, the most common protein in blood plasma. Their legs and abdomen gradually swell with fluid. Which explanation best fits?

Endothelin binds receptors on the smooth muscle of small arteries and triggers a pathway that makes the muscle contract. Doctors treat some patients with high blood pressure in the lungs using a drug that blocks endothelin receptors. What is the most likely effect of the drug on those vessels?

After surgery, patients lying in bed often wear inflatable leg sleeves that squeeze the calves every few seconds. Which normal body mechanism do these sleeves imitate?

In a test tube of plasma, adding a tiny amount of thrombin starts clotting slowly at first, then faster and faster until the sample has turned solid. Thrombin is known to activate factors that produce more thrombin. Which statement best describes this process?

A healthy adult donates about half a liter of blood. Over the next several weeks, the kidneys release more erythropoietin (EPO), the bone marrow makes red blood cells faster, and then EPO falls back to its usual level once the red cell count recovers. Which statement best describes this response?

Mature mammalian red blood cells have no mitochondria. A poison completely blocks the electron transport chain throughout the body. How is ATP production in mature red blood cells most likely affected?

In sickle-cell disease, a single base change in the hemoglobin gene swaps a charged amino acid on the protein's surface for a nonpolar one. Which explanation best links this change to the blocked blood vessels seen in the disease?

A mountain town has an air pressure of 470 mm Hg. Air there is still about 21% O₂, just as at sea level. What is the partial pressure of O₂ in the town's air?

Suppose researchers could make water flow across a fish's gill lamellae in the same direction as the blood inside them, instead of the opposite direction. What would most likely happen?

In a lung disease called pulmonary fibrosis, scar tissue builds up and thickens the walls between the alveoli and the capillaries around them. Why does this make it harder for O₂ to reach the blood?

On a hot, still summer afternoon, fish in a shallow pond swim at the surface gulping, though they behave normally on cool mornings. Which explanation best accounts for this?

Which sequence correctly describes how a mammal breathes in?

At rest, a student breathes 14 times per minute with a tidal volume of 450 mL. During a hard run, she breathes 32 times per minute with a tidal volume of 1,800 mL. How much air does she move per minute during the run?

Volunteers at rest breathed different gas mixtures for 10 minutes while researchers measured air moved per minute (invented data, change from breathing normal air). 15% O₂, no CO₂: +5%. 10% O₂, no CO₂: +60%. 21% O₂ with 3% CO₂: +100%. 21% O₂ with 5% CO₂: +250%. Which conclusion is best supported?

At the same high altitude, the air spaces where gas exchange happens in a bird's lungs hold air with more O₂ than the alveoli of a mammal. Which feature of bird breathing best explains this?

O₂ saturation of hemoglobin at two pH values (invented data). At PO₂ 20 mm Hg: 35% at pH 7.4, 25% at pH 7.25. At PO₂ 40: 75% and 62%. At PO₂ 60: 89% and 82%. At PO₂ 100: 97% and 95%. Blood leaves the lungs (PO₂ 100, pH 7.4) and reaches hard-working muscle where the PO₂ is 20 and the pH is 7.25. How many more percentage points of saturation does hemoglobin give up there than it would if the muscle's pH were 7.4?

Hemoglobin's O₂ dissociation curve is S-shaped, but the curve for myoglobin, a muscle protein made of a single polypeptide chain with one heme group, is a smooth curve that rises steeply right from the start. Which explanation best accounts for the difference?

A drug blocks carbonic anhydrase inside red blood cells. Which effect is most likely in blood passing through a working muscle?

Carbon monoxide (CO) binds the iron in hemoglobin more than 200 times more tightly than O₂ does. A person with CO poisoning has a normal amount of O₂ dissolved in their arterial plasma, yet their tissues are short of O₂. Which explanation is best supported?