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

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

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!

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”)

Brain break!!!!

How many evolutionists does it take to change a light bulb?

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

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

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

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

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

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 HCO

3) is secreted

Penicillin and histamine also secreted

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