What is the maximum volume of air that can be expelled from the lungs after maximum inspiration?

A. Calcium: Calcium is essential for bone health, neurotransmission, and muscle contraction (especially cardiac muscle), and is regulated by hormones (PTH, calcitonin, vitamin D) with renal involvement -important, but the key ion classically emphasized for fluid balance and skeletal/neuromuscular excitability in this context is potassium.
B. Chloride: Chloride is an anion that helps maintain fluid balance and acid–base status (often follows sodium) and is regulated by the kidneys, but it’s less commonly singled out as the primary regulator of nerve and muscle excitability.
C. Potassium: Potassium is crucial for maintaining intracellular fluid balance, normal nerve impulse conduction, and skeletal and cardiac muscle contraction; the kidneys are the main regulators of potassium excretion and homeostasis.
D. Phosphate: Phosphate is important for bone mineralization, energy metabolism (ATP), and acid–base buffering; the kidneys regulate phosphate, but phosphate is not the primary electrolyte described for nerve function and muscle contractions in the way potassium is.

A. Glomerulus:The glomerulus is the filtration site; ADH/aldosterone act downstream on tubular epithelial cells, not on glomerular filtration directly.
B. Loop of Henle: The loop establishes the medullary gradient; ADH/aldosterone have limited direct action here (ADH affects water permeability mainly in collecting ducts; aldosterone acts mainly on DCT/collecting duct).
C. Vasa recta:Vasa recta are blood vessels that help preserve the medullary gradient (countercurrent exchange) but are not the primary hormone-target epithelial segments for ADH/aldosterone.
D. DCT and collecting duct:Aldosterone acts on the distal convoluted tubule and cortical collecting duct to increase Na⁺ reabsorption (and K⁺ secretion); ADH acts on the late DCT and collecting duct to increase water reabsorption by inserting aquaporins -together they adjust water and sodium retention.