The Kidney in Detail SBI4U

The Kidneys Kidneys play a key role in removing waste, balancing blood pH and maintaining water balance.

The Kidneys… Each kidney has a mass of 150 g and are the size of your fist. They hold 25% of the body’s blood. They filter 200 L of fluid each day!

The Urinary System Wastes filtered by the kidneys travel along the ureters to the urinary bladder. A urinary sphincter is found at the base of the bladder. –Upon relaxation, urine enters the urethra and it is voided.

Bladder Capacity 200 ml: stretch receptors send impulses to the brain; urge to urinate. 400 ml: more receptors activated & higher frequency of impulses; feeling of urination more urgent. 600 ml: voluntary control is lost; micturition reflex occurs.

Excretion by the Kidney Urea -nitrogenous waste -made by liver -excess amino acids in blood -toxic Why must nitrogenous waste be excreted?

Metabolic Wastes WasteOrigin of WasteOrgan of Excretion AmmoniaDeamination of a.a. by liver kidneys UreaTwo ammonia combine with CO 2 Uric AcidByproduct of nucleic acid breakdown (e.g., DNA)

The 3 Regions of the Kidney Renal Cortex Renal Medulla Renal Pelvis

Nephrons Over 1 million per kidney. The smallest functional units of the kidneys.

Nephrons Afferent arterioles from the renal artery branch into a capillary bed (glomerulus). –Supplies the nephrons with blood. Blood leaves via efferent arterioles that form the peritubular capillaries that wrap around the nephron.

1 – Filtration by the Kidney Renal artery Ureter Renal vein Supplied with blood from renal artery Inside it splits into many fine capillaries Each capillary supplies blood to hundreds of thousands of tiny filtration units called nephrons Lets have a look at a nephron!!!

Nephrons Bowman’s capsule surrounds the glomerulus. Water and other solutes filter into the Bowman’s capsule.

Nephrons The capsule tapers off into the proximal tubule. Carries the filtrate to the loop of Henle. Filtrate passes through the distal tubule and then the collecting ducts. The collecting ducts collect urine from many nephrons, which merge in the renal pelvis.

1.Glomerulus brings a large surface area of blood capillaries in close contact with Bowman’s capsule 2.Liquid filtered from blood under pressure (filtration) 3.Glomerular filtrate produced containing: -water -glucose -salts -urea (Protein molecules and red blood cells do not pass into tubule as they are TOO BIG!!!!) Blood from renal artery enters wide capillary Blood travels through narrow capillary towards renal vein Glomerular filtrate Filtration

Key Words!! Nephron:structure in the kidney that acts as a microscopic filtration unit Glomerulus:dense mass of very fine blood capillaries at the nephron that act as a filter Bowman’s capusle:cup-shaped part of the nephron that holds a glomerulus and collects the products of filtration from it Glomerular filtrate:liquid removed from the blood by filtration in the kidney

2 – Reabsorption by the Kidney Once the main components of glomerulur filtrate enter the bloodstream -they are no longer in bloodstream If nothing more happened in the nephron then all the useful stuff would be lost in the urine! Therefore, glucose, water and some salts need to be reabsorbed!

Glucose reabsorbed Variable amounts of water and salts reabsorbed and filtrate gradually turning into urine More water reabsorbed Final urine containing: -excess water -unneeded salts -waste urea