🚽📒Renal System Anatomy

Organs of the Renal System

Two kidneys, two ureters, one bladder, and one urethra — all work together to filter and excrete urine from the body

Main Functions of the Renal System

Filters waste from blood, removes urine, and maintains water, electrolyte, and acid-base balance in the body.

Kidneys

Filter blood and remove waste and excess substances. Use nephrons to perform filtration, reabsorption, and secretion. Can lose up to 90% function due to disease.

Nephron

The kidney’s functional unit that produces urine through filtration, reabsorption, and secretion. Helps reclaim essential nutrients, water, and electrolytes

Proximal Tubule, Loop of Henle, Distal Convoluted Tubule

Regions of the nephron tubule system responsible for specific stages of filtration and reabsorption of salts, electrolytes, and water

Ureter

A tube that transports urine from each kidney to the bladder using muscular contractions (peristalsis)

Urinary Bladder

Stores 350–500 mL of urine (urge to void at ~250 mL). Releases urine via the micturition reflex when pressure builds

Micturition Reflex

Reflex that causes relaxation of sphincter muscles in response to increased bladder pressure, leading to urination

Urethra

A tube that enables excretion of urine from the body. Works with sphincter muscles to control urine release

Sphincter Muscles

Muscles that control the release of urine by tightening or relaxing around the urethra

Urine Characteristics

Color can range from clear to dark yellow depending on hydration and dietary intake

Kidney blood filtration amount per day

The kidneys filter about 180 liters of blood every 24 hours, cycling the body’s 8 liters of blood 20–25 times daily

Nephron – Glomerulus function

Acts as a sieve, filtering small molecules (like water, vitamins, minerals) from blood into the tubule

Nephron – Tubule function

Reabsorbs needed substances back into the bloodstream and secretes waste like urea into the urine

Urea

A waste product formed from the breakdown of proteins, excreted in urine by the kidneys

Urine color when dehydrated

Dark yellow, because kidneys retain water and produce more concentrated urine

Urine color when overhydrated

Pale or clear, due to excess water being filtered out and removed by the kidneys

Vitamin D (kidney function)

Kidneys activate vitamin D, which is necessary for calcium absorption and bone health

Renin

A hormone secreted by the kidneys that helps increase blood pressure by triggering vasoconstriction and fluid retention

Erythropoietin (EPO)

A hormone secreted by the kidneys that stimulates red blood cell production in the bone marrow

What would happen if kidneys stopped filtering blood?

Toxins and waste would build up in the body, leading to system failure and death. The kidneys are essential for maintaining homeostasis