Which of the following structures controls the release of chyme into the duodenum?

a. Insulin and glucagon: These hormones have opposite effects on blood glucose levels; insulin decreases blood glucose by facilitating cellular uptake, while glucagon increases blood glucose by stimulating glycogen breakdown and gluconeogenesis.

b. Ghrelin and gastrin: Ghrelin stimulates appetite, and gastrin stimulates gastric acid secretion, but they do not directly oppose each other.

c. Calcitonin and melatonin: Calcitonin lowers blood calcium levels, while melatonin regulates sleep-wake cycles; they do not act as antagonists.

d. Androsterone and estradiol: These are sex hormones with different roles but are not direct antagonists; they do not have opposing effects in the body.

a. The outer tissue layer consisting of renal corpuscles and convoluted tubules: This describes the renal cortex, not the renal pelvis.

b. The inner tissue layer consisting of the loop of Henle and collecting tubules: This describes the renal medulla, not the renal pelvis.

c. The expanded area of a renal tubule that encloses the glomerulus: This describes Bowman's capsule, not the renal pelvis.

d. The cavity where urine flows from the calyces to enter the ureters: Correct. The renal pelvis is the funnel-shaped cavity that collects urine from the calyces and channels it into the ureter.