Blood & Circulation

• Cardiac Action Potential Ionic Phases:
• Phase 0: Rapid depolarization due to transient $Na^+$ influx via voltage-gated Nav1.5 channels.
• Phase 1: Initial rapid partial repolarization caused by inactivation of $Na^+$ channels and transient outward $K^+$ EFFLUX ($I_{to}$), NOT $K^+$ influx [Option 2 is INCORRECT].
• Phase 2: Plateau phase maintained by inward $Ca^{2+}$ influx through L-type channels balancing outward $K^+$ efflux.
• Phase 3: Rapid repolarization mediated by delayed rectifier $K^+$ efflux.

Correct option: (2) Phase 1: K influx

• Nomenclature of Coagulation Factor XIII: Blood coagulation Factor XIII is biochemically designated Fibrin Stabilizing Factor (FSF / Laki-Lorand Factor).
• Enzymatic Function: Activated by thrombin in the presence of $Ca^{2+}$ ($Factor XIIIa$), it functions as a plasma transglutaminase that catalyzes the formation of covalent $\epsilon-(\gamma-\text{glutamyl})\text{lysine}$ isopeptide cross-links between adjacent fibrin monomers, converting a loose, soluble fibrin polymer into an insoluble, mechanically stable clot.

Correct option: (1) Fibrin stabilizing factor

• Glossopharyngeal Afferent Pathways: The peripheral arterial chemoreceptors located in the Carotid Bodies (at the bifurcation of the common carotid arteries) transmit sensory afferent impulses through the Carotid Sinus Nerve of Hering, a primary sensory branch of the Glossopharyngeal Nerve (Cranial Nerve IX).
• Contrasting Aortic Chemoreceptors: Aortic body chemoreceptors send afferents through the vagus nerve (Cranial Nerve X).

Correct option: (1) Carotid bodies