1. Kidney Function Filtration, re-absorption and excretion
Filtration: dissolved fluids move inot urinary system
Re-absorption: substances move from urin into blood
secretion/excretion: substances move from blood into urine

2. Nephron
Each kidney is composed of over 1 million filters all working at the same time to filter the blood (each filter is called a nephron)
Each nephron is in both the renal cortex AND the medulla of the kidney

5. Nephron function 1: filtration
Afferent arteriole goes into bowman's capsule and becomes the glomerulus
Blood is initially filtered between the glomerulus and the bowman's capsule
Filtration occurs at 4x the pressure than in a normal capillary!

6. Dissolved substances move from areas of high pressure to low
Water, nitrogenous wastes, nutrients and ions are therefore pushed from the glomerulus into the bowman's capsule
The components of blood that do not leave the capillary are carried away through an efferent arteriole (such as blood cells and proteins, which are too big to fit through the “filter”)

7. How many evolutionists does it take to change a light bulb?
Brain break!!!!
How many evolutionists does it take to change a light bulb?

8. Only one, but it takes 8 million years!!!

9. Nephron function 2: re-absorption
The efferent arteriole then forms a true capillary network around the rest of the nephron (called peritubular capillary network)
As filtrate flows through nephron, many substances are re-absorbed both actively and passively into the peritubular capillary network

11. Proximal convoluted tubule (PCT)
Glucose, aa's and Na+ are actively reabsorbed at PCT
CL- is passively reabsorbed by following Na+ back into the blood (through Cl- channels)
Water is passively reabsorbed by diffusion
Some urea reabsorbed due to osmotic pressure

12. Loop of Henle
Water leaves the descending limb, but cannot be reabsorbed by the ascending limb because it is impermeable to water.
NaCl moves out of the thickest part of the ascending limb.
As the fluid moves up the loop, there is less NaCl available to move out, therefore the outer medulla has a lower OP than the inner medulla

13. Loop of Henle (cont'd)
Urea which leaks out of the lower part of the collecting duct, also increases the OP of the inner medulla
The establishment of this osmotic gradient ensures that water continues to move out of the entire length of both the descending loop and the collecting duct

14. Nephron function 3: Secretion/tubular excretion
Active transport of molecules from the blood to the nephron
Occurs in the distal convoluted tubule
Uric acid, ammonia and H+ (as HCO3) is secreted
Penicillin and histamine also secreted

15. Excretion cont'd...
The substances that make up urine are the substances which are filtered, secreted and not absorbed
A small amount of water
Nitrogenous wastes
Bicarbonate, sulphates and phosphates
Excess ions