Govt Exams
The SA node has the highest inherent rate of spontaneous depolarization (60-100 bpm), allowing it to set the rhythm for the entire heart.
Glucagon is secreted by alpha cells of pancreatic islets and increases blood glucose by promoting glycogenolysis and gluconeogenesis during fasting.
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.
S3 occurs during rapid ventricular filling phase (early diastole) when blood rapidly enters the ventricle. It's normal in young individuals but may indicate heart failure in older patients.
Lymph drains from tissue spaces into lymphatic capillaries, passes through lymph nodes for filtration and immune response, and returns to the bloodstream via the thoracic duct into the left subclavian vein.