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Home , Glomerulus (kidney), Urine

Ò Formation in the Urine Formation: the Essential Processes

1. Glomerular : movement of fluid from the to the Bowman’s Capsule. 2. Tubular : the transfer of filtrate back into the . 3. Tubular secretion: transport of materials from the blood into the distal tubule ( and some drugs). 4. reabsorption: returns the much needed amount of water back to the blood to be reused by the body Glomerulas and Bowman’s Capsule

Ò This filtration forces water and dissolved substances in the from the to the Bowman’s capsule

Ò Remember this is happening in MILLIONS of at one time

Ò The capillaries must be able to allow water and MOST dissolves substances OUT to the Bowman’s capsule and the pores MUST be small enough to to prevent and blood cells IN!

Ò is also an issue. In the glomerulus it is up to FOUR times as much as in the capillaries in the rest of the body Blood through the Kidneys

Ò Upwards to 2000L of blood goes though your kidneys daily.

Ò They produce approximately 180 L of glomerular filtrate each day. This filtrate is very similar to blood proteins

CHEMICALS BLOOD PLASMA (g/L) GLOMERULAR FILTRATE (g/L) 44.4 0.0 sodium 3.0 3.0 chloride 3.5 3.5 glucose 1.0 1.0 0.3 0.3 The

Ò Almost 65% of the filtrate is reabsorbed into the body Ò Uses both active and passive transport Ò The tube is full of mitrochondria with uses ATP to drive the transport of the sodium ions, glucose and other solutes in the blood. Ò Ions that are negatively charged tag along on the transported ions Ò Water follows the ions by osmosis and is reabsorbed by the capillaries

Ò Its job is to reabsorb the water and other ions from the filtrate

Ò As it manouvers itself into the medulla of the , it because an enviroment that is quite salty

Ò The decending loops is permeable to water by osmosis and only slight to other ions

Ò As the water leaves the filtrate, the sodium ions inside the tubule increases and reaches its maximum at the bottom of the loop!

Ò As the filtrate comes around to the ascending loop the permiability changes

Ò Here the water is impermiable and the sodium ion diffuse across the concentration gradient and move to the blood vessels Ò The thicker portion of the ascending loop allows the sodium ions to move by active transport.

Ò By moving out it: Ò Replaces the salty environment of the medulla Ò Decreases the concentration of the filtrate in the tissues and the blood into the cortex tissues

Ò By now the more than 2/3 of the sodium has been reabsorbed by the body! Tubular Reabsorption

Ò The absorption into the capillaries will be decided dependent on what the need of the body is Ò Passive reabsorption of negatively charged ions decrease the concentration more of the filtrate – hence more water is absorbed by osmosis! Ò is secreted into the distal tube from the capillaries Ò To balance the pH, hydrogen ions will be secreted as well! The Collecting Duct

Ò As the filtrate moves here it still has a large amount of water in it

Ò As this duct runs itself into the medulla of the kidney, the concentation along its lengths increases

Ò Passive reabsorption of the water occurs from the filtrate in the collecting duct by way of osmosis.

Ò If a person is dehydrated, the permiability of water in the distal tube and collecting duct increases as well as the capilliaries in order to help maintain the homeostasis in the body. The END results:

Ò The filtrate is now up to FOUR times as concentrated now from when it started

Ò This form is now called urine

Ò It descends to the and is transported to the where it is stored until it is to be released from the body

Ò It will exit the body via the of the body 200mL: stretches slightly and signals to the brain. 400mL: almost full and stretch receptors send a more urgent message. 600mL: voluntary control is lost. The Review:

Ò What does each part of the nephron do?

Ò What is absorbed during each part of the process?

Ò What are the methods of transport?

Ò Review the functions of the parts of the nephron

Ò Animation –Nephron

Ò Animation Nephron 2