Urine is formed based on three steps that will be discussed :-Filtration-Re-absorption-Secretion

- wastes are filtered from the blood by the kidneys and sent to the urinary bladder by ureters-a urinary sphincter located at the bottom of the bladder acts as a valve allowing urine to be excreted -urine is voided through the urethra-bladder can hold 200-600ml of urine

( one million tubules)-afferent arterioles supply nephrons with blood- afferent arterioles branch into a capillary bed called glomerules- efferent arterioles transfer blood out of the glomerulus- the blood from the efferent arterioles is carried to a net of capillaries called pertibular capillaries

surrounds the glomerulus-Bowmans processes fluids from the blood into urine- a thin tubule called the proximal tubule is attached to the capsule- urine travels from the loop of henle - - ->through the distal tubule - - -> into the collecting ducks

Each nephron has its own blood supply in the kidney whish allows blood to flow into the glomerulus.

Dissolved solutes are able to pass through and into bowmans capsule.

- this is due to the materials moving from high pressure to low pressure, but not all materials are able to pass through.

Transfer of glomerular filtrate back into the capillaries● Focuses on changes in concentration of fluids as they go through kidneys● About 600ml of fluid flows through kidneys every minute● About 20%(120ml) of this liquid is filtered into nephron● If liquid was not reabsorbed it would be impossible to maintain homeostasis unless 1 litre of fluid was consumed every ten minutes● because of reabsorption only 1ml of urine is formed for every 120ml of fluids that enter nephron● the rest of the 120ml of fluids and solutes is reabsorbed

Selective Reabsorption● occurs in passive and active transport

● carrier molecules move Na+ ions across cell membranes of the cells that line nephron● negative ions like Cl- and HCO3- follow positively charged Na+ ions by attraction● Mitochondria supply energy needed for transport● reabsorption occurs until the threshold level is reached● excess NaCl remains in nephron and is excreted with urine● other molecules are actively transported through the proximal tubule● Glucose and amino acids are attached to specific carrier molecules which shuttle them out of nephron and into blood stream● only so much solute can be reabsorbed

● solutes that exit nephron create an osmotic gradient that draws the water from nephron● a second osmotic force created by proteins also helps reabsorb ○ these proteins remain in the bloodstream and draw water from the interstitial fluid into the blood● as water is reabsorbed from nephron, remaining solutes become more concentrated ● Molecules such as urea and uric acid will diffuse from nephron, back into blood stream

“The movement of wastes from the blood into the nephron”

-Cells loaded with mitochondria line the distal tubule.- It is then when tubular secretion occurs in the active transport then molecules are moved from the blood into the nephrons

Complicated

Less Complicated