Kidneys, nephrons and urinary tract
This track studies urinary anatomy from the kidney to urine elimination, combining gross organization, outflow pathways and basic nephron structures.
212 explained questions · practice, exam and sprint · freeThe kidneys are retroperitoneal organs near the posterior abdominal wall. The right is usually slightly lower than the left. A fibrous capsule surrounds each kidney, with cortex directly beneath it. Medullary pyramids end in papillae projecting into minor calyces. Major calyces lead to the renal pelvis and ureter. The pelvis collects urine; it is neither cortex nor the blood-filtration site.
The renal corpuscle includes the glomerulus and glomerular capsule. Filtrate enters the capsular space, then passes through proximal tubule, nephron loop and distal tubule into the collecting system. Corpuscles lie in the cortex; juxtamedullary loops extend deep into the medulla. Collecting ducts receive fluid from several nephrons and are studied with them, although some anatomical conventions exclude them from the nephron itself.
Filtration moves water and small solutes from glomerular blood into the capsular space. Reabsorption returns substances from tubular fluid to blood. Tubular secretion moves selected substances from blood into the lumen. Excretion is the final urinary output resulting from these processes. Initial filtrate differs from final urine: blood cells and most proteins normally remain in the circulation, while many filtered solutes are reclaimed.
Section references: [2]
Blood enters through the renal artery, passes through an afferent arteriole, glomerulus, efferent arteriole and downstream capillary networks before venous return. Tubular fluid follows the collecting system into calyces, pelvis, ureter, bladder and urethra. The ureter links kidney and bladder; the urethra leads outside. Kidneys also regulate water, electrolytes and acid-base balance and have endocrine roles. Urine storage belongs to the bladder, not the nephron.
| Structure or concept | Distinguishing feature |
|---|---|
| Filtration | Glomerular blood → capsular space. |
| Reabsorption | Tubular lumen → blood. |
| Tubular secretion | Blood → tubular lumen. |
| Excretion | Final elimination of substances in urine. |
Try answering before opening the explanation. Each example develops a point from the guide.
Answer: Kidney
The kidney contains nephrons where glomerular filtration initiates tubular fluid formation. Reabsorption and secretion modify it into final urine. Urine formation therefore involves more than filtration alone.
Why the other options do not fit: Bladder stores urine. Ureter and urethra convey it along different parts of the outflow route. They do not perform renal glomerular filtration.
Answer: Renal cortex
Renal cortex is the parenchymal region immediately beneath the fibrous capsule. It contains renal corpuscles and parts of the tubules. Medulla lies deeper and forms pyramids, not the stated superficial layer.
Why the other options do not fit: Renal pelvis belongs to the collecting pathway and ureter is the outlet. Medulla is deeper parenchyma. Distinguish covering, parenchyma and drainage lumen.
Answer: Ureter
The ureter continues the renal pelvis and conveys urine to the bladder through a muscular wall with peristaltic activity. The urethra is a different segment leading from bladder to exterior.
Why the other options do not fit: Renal vein carries blood, not urine. Ductus deferens belongs to the reproductive tract. Urethra does not connect the renal pelvis to the bladder.
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