Urinary System and Excretion

" Healthy urine is sterile, you can drink it !! "

Excretory system - Responsible for water and salt balance in the body. Kidneys also control blood pressure, blood composition, and the pH of the blood.

Excretion - The release of metabolic waste products and excessive salts from the body.

          Nitrogenous waste - Waste products from eating protein - turn into urea in our liver.

                    Urea - The salt we turn our excess nitrogenous wastes into.

Kidney - Where the blood is filtered and urine is produced.

          Renal pelvis - A collection area in the kidney for processed urine.

Ureter - Pair of tubes leading from the kidneys.

Urinary bladder - a temporary storage site for urine. Made of smooth muscle.

Urethra - A tube connecting the bladder to the outside of the body.

Nephron - A microscopic filtering unit to filter blood and form urine.

* Pressure Filtration - Filters blood but get good and bad stuff - Nonselective

* Selective Reabsorption - Very selective - Get back good stuff leave bad stuff.

* Urine Concentration - Final water reabsorption.

Glomerulus - A knot of capillaries where pressure filtration occurs. Filters out plasma with glucose, urea, amino acids, ions, and water in it.

          Bowman's capsule - Surrounds the glomerulus and catches the filtered plasma and enters the nephron. Catches a 55 gallon drum of plasma/day.

Proximal tubule - Selective reabsorption - Dissolved nutrients (ions, amino acids, and sugars like glucose) and 75% of the water are returned to the blood stream.

Peritubular capillaries - Surround and intertwine the kidney tubules. They pick up the water and good stuff from selective reabsorption.

loop of Henle - Returns 10% of the water back to the peritubular capillaries. Involved in setting up the salt gradient that is needed for creating a concentrated urine.

Distal tubule - The last of the nephron that connects the loop of Henle to the collecting duct.

Collecting duct - Final Water Reabsorption - involved in concentrating the urine. 14% of the original water volume returns to the bloodstream.

Urine - 96% water, 2.5% nitrogenous wastes (mostly urea), 1.5% salts, and traces of other substances like bile pigments which may contribute to the characteristic color and odor.

          Diuretic - Cause us to produce and release more dilute urine. Causes us to dehydrate and lose water.



Urinary System

Kidney (through Renal Pelvis) --> Ureter --> Urinary Bladder --> Urethra


Pathway of Urine Formation

Glomerulus (Pressure Filtration) --> Bowman's Capsule --> Proximal Tubule (Selective Reabsorption) --> loop of Henle --> Distal Tubule --> Collecting Duct (Urine Concentration) --> Renal Pelvis








Return to Greg Sievert's GB 100 Syllabus
Last updated on 4 January 2018