Excretory System: Kidney Structure and Urine Formation

Kidney (Excretory Functions)

An organ responsible for removing metabolic waste (urea, creatinine), regulating water content and blood volume, maintaining pH of body fluids, and controlling ion composition via selective reabsorption and secretion.

Retroperitoneal Placement (Kidneys)

The anatomical location of the two bean-shaped kidneys situated along the vertebral column, where the left kidney sits slightly higher.

Renal Artery and Renal Vein

The blood vessels through which each kidney receives blood (renal artery) and returns cleansed blood to the circulation (renal vein).

Urinary Drainage Pathway

The route by which formed urine drains into the renal pelvis, passes down a ureter into the bladder, and is ultimately expelled via the urethra.

Fibrous Capsule

The tough external covering that encases each kidney.

Renal Cortex

The outer region of the kidney transverse section that contains the glomeruli.

Renal Medulla

The inner region of the kidney subdivided into pyramids, with the apex (papilla) projecting into the renal pelvis.

Nephron (Tubular Statistics)

The functional unit of the kidney, with approximately $1\text{ million}$ nephrons per kidney and a total tubular length of approximately $120\text{ km}$.

Glomerular Filtration Rate (GFR)

The volume of plasma filtered per minute, which is approximately $125\text{ cm}^3\text{/min}$; approximately $99\text{\%}$ is reabsorbed, resulting in about $1\text{ cm}^3\text{/min}$ of urine produced.

Renal Corpuscle

The initial blood-filtering component of the nephron, consisting of Bowman's capsule and the glomerulus.

Proximal Convoluted Tubule (PCT)

The segment of the nephron tubule leading immediately out from the renal corpuscle.

Loop of Henle

The hairpin-shaped section of the nephron tubule consisting of a descending limb and an ascending limb.

Distal Convoluted Tubule (DCT)

The coiled section of the