In which of the following structures does fertilization of an ovum by a spermatozoa occur?

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.

a: Electrolytes - Electrolytes are ions such as sodium, potassium, and chloride that play essential roles in various physiological processes but are not directly involved in protecting the body from pathogens.

b. Leukocytes: Leukocytes, also known as white blood cells, are involved in the immune response and protect the body from pathogens such as bacteria, viruses, and fungi.

c: Thrombocytes - Thrombocytes, or platelets, are involved in blood clotting but not in protecting the body from pathogens.

d: Erythrocytes - Erythrocytes, or red blood cells, are primarily involved in transporting oxygen and carbon dioxide and do not play a direct role in immune defense.