Q.Describe, with reference to their structure and function, the gross anatomy of the human excretory system, including the kidneys (external and internal features), the ureters, the urinary bladder and the urethra.

[!TLDR]

The excretory system = paired kidneys (cortex/medulla/pyramids/calyces/pelvis) + two ureters + urinary bladder + urethra, carrying urine from formation to expulsion.

[!ANSWER]

Kidneys (bean-shaped, retroperitoneal, cortex+medulla+pyramids+calyces+pelvis, hilum for vessels/ureter) -> ureters (peristaltic transport to bladder) -> urinary bladder (muscular storage sac) -> urethra (expulsion, controlled by internal+external sphincters).

The human excretory system consists of a pair of kidneys together with the ureters, urinary bladder and urethra that carry urine onward to the exterior. Each kidney is a reddish-brown, bean-shaped organ roughly 10-12 cm long, lying against the posterior abdominal wall on either side of the vertebral column, behind the peritoneum (retroperitoneal), with the right kidney positioned slightly lower than the left due to the liver above it. Its concave inner border bears a notch, the hilum, through which the renal artery enters and the renal vein and ureter leave. Internally, the kidney shows an outer, granular cortex packed with the coiled portions of nephrons, and an inner medulla organised into 8-12 cone-shaped renal pyramids whose apices (papillae) point inward; urine draining from each papilla is collected by a minor calyx, several of which unite into a major calyx, and the major calyces open into the funnel-shaped renal pelvis, which narrows to become the ureter.

Each ureter is a narrow, muscular tube, roughly 25-30 cm long, running from the renal pelvis down the posterior abdominal wall to the urinary bladder; its smooth muscle contracts in rhythmic peristaltic waves that actively propel urine downward rather than relying on gravity alone. The urinary bladder is a hollow, distensible, muscular sac in the pelvic cavity that temporarily stores urine, its wall (the detrusor muscle) able to stretch considerably before the urge to void becomes strong and then contracting to expel urine during urination. Finally, the urethra is the single tube carrying urine from the bladder to the exterior; its opening is normally kept closed by an internal urethral sphincter (involuntary smooth muscle) and an external urethral sphincter (voluntary skeletal muscle), whose coordinated relaxation permits controlled, voluntary release of urine. Together, this connected sequence of organs -- kidney, ureter, bladder, urethra -- carries urine from the point it is formed to the point it finally leaves the body.

[!ANSWER]

Kidneys (bean-shaped, retroperitoneal, cortex+medulla+pyramids+calyces+pelvis, hilum for vessels/ureter) -> ureters (peristaltic transport to bladder) -> urinary bladder (muscular storage sac) -> urethra (expulsion, controlled by internal+external sphincters).

Work through the system in the order urine actually travels: kidney (external position + internal cortex/medulla/pyramid/calyx/pelvis structure) -> ureter (peristaltic transport) -> bladder (storage) -> urethra (controlled expulsion via two sphincters).

Omitting the internal structure of the kidney (cortex, medulla, pyramids, calyces, pelvis) and describing only its external bean shape and position -- a full description needs both the gross external anatomy and the internal drainage structures.