Urinary System Overview

Study Notes

The urinary system maintains a constant internal environment through excretion and osmoregulation.
Excretion is the removal of metabolic waste products from the body.
Osmoregulation is the maintenance of constant osmotic conditions in the body.

Nitrogenous compounds: Excreted by the kidneys and through sweat.
Carbon dioxide and water vapor: Excreted through the lungs.
Bile pigments: Derived from the breakdown of old red blood cells (RBCs). They are excreted in feces through the digestive system.

Urine is formed in the kidneys.
Urine is drained from the kidneys via ureters to the urinary bladder.
Urine is expelled from the body through the urethra via the process of urination.

Cortex: Outer region of the kidney.
Medulla: Inner region of the kidney, containing renal pyramids.
Pelvis: Funnel-shaped structure that collects urine from the pyramids.
Nephrons: Microscopic filtering units within the kidney. About one million per kidney. The basic structure and function units of the kidney.

The Renal Medulla contains fine tubules and blood vessels which together form the renal pyramids.

Glomerulus: Mass of thin-walled capillaries.
Bowman's capsule (glomerular capsule): A cup-shaped structure surrounding the glomerulus.
Renal corpuscle (malpighian corpuscle): The glomerulus + Bowman's capsule.
Proximal convoluted tubule: Reabsorbs 90% water, glucose, amino acids, and salts - by osmosis, diffusion, and active transport and returning them to the bloodstream.
Loop of Henle: Conserves water (descending limb permeable to water; ascending limb permeable to ions).
Distal convoluted tubule: Controls the precise amount of water and salts reabsorbed; and controls blood pH.
Collecting duct: Collects urine from numerous nephrons and moves it to the pelvis..

Ultrafiltration of the blood occurs in the renal corpuscle.
Inside the kidney, the renal artery branches into arterioles, then into glomerulus capillaries. This increases blood pressure.
All blood contents except larger molecules (proteins, blood cells) come out of the capillaries into Bowman’s capsule. Larger molecules remain in the capillaries.

Filtered fluid/Filtrate contains glucose, amino acids, some hormones, nitrogenous wastes (urea, uric acid), and water.

Renal tubules reabsorb useful materials needed by the body and return them to the bloodstream.

Renal corpuscle: Blood filtration.
Proximal convoluted tubule: Reabsorption of useful substances.
Loop of Henle: Water conservation.
Distal convoluted tubule: Precise control of water and salt reabsorption, and pH control.
Collecting duct: Carries the filtered fluid to the pelvis.