Filtration, Reabsorption & Secretion
If glomerular hydrostatic pressure drops significantly, what happens to GFR and why?
GFR decreases because lower hydrostatic pressure reduces net filtration pressure, limiting fluid movement into the nephron.
What is the role of the juxtaglomerular apparatus (JGA) in regulating glomerular filtration rate (GFR)?
The JGA monitors NaCl concentration in the filtrate and adjusts afferent arteriole diameter to maintain GFR.
Why does the left lung have fewer lobes than the right, and what anatomical structure causes this difference?
The left lung has two lobes because the heart occupies space in the thoracic cavity, creating the cardiac notch.
If alveolar PO₂ drops from 104 mmHg to 80 mmHg, what happens to oxygen diffusion into the blood and why?
Diffusion slows because the partial pressure gradient between alveoli and blood narrows, reducing the driving force for O₂ movement.
Why does hyperventilation before diving increase the risk of blackout rather than prevent it?
It lowers CO₂ too much, delaying the urge to breathe, but O₂ still drops to dangerous levels without warning, causing hypoxic blackout.
Why would constriction of the efferent arteriole increase GFR initially but potentially harm kidney function long-term?
Constriction raises glomerular pressure, boosting GFR short-term, but prolonged high pressure can damage filtration membranes.
how does the nephron’s structure allow for both filtration and selective reabsorption?
The renal corpuscle’s fenestrated capillaries enable filtration, while specialized tubule segments with transport proteins allow selective recovery of needed substances.
What structural feature of the proximal convoluted tubule increases its surface area for reabsorption?
The brush border of microvilli on the PCT cells increases surface area for reabsorption.
During vigorous exercise, tissue PO₂ falls and PCO₂ rises. How does this alter internal respiration and hemoglobin’s affinity for oxygen?
Oxygen unloading increases due to the Bohr effect (low pH and high CO₂ reduce hemoglobin affinity), enhancing internal respiration.
If a patient has metabolic acidosis, how will the respiratory system compensate and why?
Through increased ventilation (hyperventilation), it reduces CO₂, shifting the carbonic acid-bicarbonate buffer to lower H⁺ concentration and raise pH.
If glucose appears in urine despite normal blood glucose levels, what nephron process is likely impaired and why?
Tubular reabsorption in the PCT is impaired, possibly due to transporter dysfunction, preventing glucose recovery.
If macula densa cells detect high NaCl in filtrate, what feedback mechanism occurs and why?
They trigger afferent arteriole constriction (tubuloglomerular feedback) to reduce GFR, allowing more time for NaCl reabsorption.
Why is the respiratory membrane extremely thin, and what advantage does this provide for gas exchange?
It minimizes diffusion distance, allowing rapid exchange of O₂ and CO₂ between alveoli and capillaries.
Why does CO₂ diffuse almost as rapidly as O₂ during external respiration despite a smaller pressure gradient?
CO₂ is 20× more soluble in plasma and alveolar fluid than O₂, compensating for its smaller gradient.
If blood CO₂ levels rise, which chemoreceptors respond first and how does this affect breathing rate?
Central chemoreceptors in the medulla detect increased H⁺ in cerebrospinal fluid, stimulating the respiratory center to increase breathing rate.
How does ADH influence urine concentration during dehydration, and what would happen if ADH receptors were blocked?
ADH inserts aquaporins in collecting ducts, increasing water reabsorption and concentrating urine. Blocking receptors would cause dilute urine and worsen dehydration.
Why would chronic kidney disease lead to anemia through hormonal pathways?
Damaged kidneys produce less erythropoietin, reducing RBC production and causing anemia.
Why are juxtamedullary nephrons important for producing concentrated urine?
Their long nephron loops extend deep into the medulla, enabling the countercurrent multiplier system to create a strong osmotic gradient.
If intrapleural pressure becomes equal to atmospheric pressure, what happens to external respiration and why?
Lung collapse (atelectasis) occurs, eliminating ventilation and halting external respiration because the transpulmonary pressure is lost.
Explain why emphysema reduces oxygen diffusion even if alveolar PO₂ remains normal.
Alveolar walls are destroyed, reducing surface area for gas exchange and increasing diffusion distance, impairing O₂ transfer.
Why does the ascending limb of the nephron loop indirectly contribute to water reabsorption even though it is impermeable to water?
It actively reabsorbs NaCl, creating a medullary osmotic gradient that drives water reabsorption in the descending limb and collecting ducts.
Explain how the myogenic mechanism protects glomeruli during sudden spikes in blood pressure.
Increased pressure stretches afferent arteriole smooth muscle, causing reflex constriction to prevent excessive GFR and glomerular damage.
What is the functional significance of the pleural fluid between the visceral and parietal pleura?
It reduces friction during breathing and creates surface tension that helps keep the lungs inflated as the thoracic cavity expands.
Explain how ventilation-perfusion mismatch (e.g., blocked bronchiole) affects external respiration and blood gas levels.
Poor ventilation reduces alveolar PO₂, lowering oxygen diffusion and causing hypoxemia; CO₂ removal also decreases, leading to hypercapnia.
Why does hemoglobin release more oxygen in active tissues compared to resting tissues?
Active tissues produce more CO₂ and H⁺, lowering pH (Bohr effect), which decreases hemoglobin’s affinity for oxygen and promotes unloading.