Entrance Exams
Govt. Exams
pH homeostasis involves buffer systems (bicarbonate, phosphate, proteins), respiratory control of CO2, and renal regulation of H+ and HCO3- ions.
While more RBCs carry oxygen, increased blood viscosity decreases flow rate, potentially reducing net oxygen delivery. The optimal hematocrit is around 45% for maximum oxygen transport.
CFTR chloride channels regulate fluid secretion in mucus-producing tissues. Defective CFTR impairs Cl- secretion, causing secondary reduced water secretion and excessive Na+ reabsorption, producing thick, viscous mucus that obstructs respiratory airways.
The Bohr effect is multifactorial: decreased pH (lactate, CO2), increased PCO2, increased temperature, and elevated 2,3-BPG all decrease hemoglobin's O2 affinity, promoting oxygen unloading precisely where metabolic demand is highest.
Decreased GFR reduces NaCl delivery to the macula densa in the thick ascending limb. This chemoreceptor senses decreased NaCl uptake and signals JG cells to reduce renin secretion, allowing afferent arteriolar vasodilation to restore GFR.
Factor VIII is a critical cofactor in the intrinsic coagulation pathway (Factor VIII-von Willebrand complex). Its deficiency specifically impairs activation of Factor X, prolonging aPTT while PT remains normal.
Glucose is actively reabsorbed via Na-glucose cotransporter (SGLT1) at the apical membrane using Na+ gradient, then exits via facilitated diffusion (GLUT2). Water follows osmotically via aquaporins, maintaining osmotic balance.
The relative refractory period occurs during repolarization when membrane potential is more negative than resting potential (hyperpolarized). A suprathreshold stimulus can overcome this increased threshold to generate an action potential.
The ascending limb actively transports Na+/K+/Cl- without water permeability, creating osmotic gradients that concentrate urine in the collecting duct.
Nephrotic syndrome involves damage to the glomerular filtration barrier (podocytes), increasing permeability to plasma proteins like albumin.