urine formation

urine is formed in the _ of kidneys

nephrons

what are the 3 steps of urine formation

1. glomerular filtration

2. tubular reabsorption

3. tubular secretion

the first step in urine formation is glomerular filtration which involves material leaking form the blood and running through the

glomerulus

the material that leaves the glomerulus is called

filtrate

what does filtrate contain (combination of good stuff and bad stuff)

• water

• cellular wastes

• electrolytes

_ mL of filtrate is produced each minute

120 mL

_% of filtrate is reabsorbed into the blood

99%

amount of filtrate being produced in a given period of time

• result of filtration pressure

filtration rate

the blood pressure inside the glomerulus

• need to use pressure (filtration) because diffusion alone would be too slow

filtration pressure

in order to change the filtration rate, we must first change the

filtration pressure

how do you change filtration pressure

changing the diameter of the efferent arteriole

• (thumb on garden hose)

if the efferent arteriole contracts, blood pressure back in the glomerulus _

increase (because arteriole constricts)

if the efferent arteriole relaxes, blood pressure back in the glomerulus _

decreases (because arteriole dilates)

this is a hormone produced by the juxtaglomerular cells that causes contraction of the efferent arteriole

• helps to control filtration rate

renin

this step of urine formation involves moving portions of filtrate within the renal tubule back into the blood in the peritubular capillaries

• selective process (only want to reabsorb desirable materials)

• taking desirable material back in

tubular reabsorption

most reabsorption occurs in the

• glucose, Na, and water are reabsorbed here (the good stuff)

proximal convoluted tubule

_ L of water is filtered from the blood everyday

180 liters

why is ADH important in urine formation

because ADH makes the renal tubule more permeable to water (makes reabsorption possible)

active transport is used to reabsorb (4)

• burn ATP to transport these things

1. glucose

2. amino acids

3. vitamins

4. Na

passive transport is used to reabsorb (3)

1. water

2. urea

3. electrolytes (Cl, Mg, K, Ca)

reabsorption of water and electrolytes takes place in the

nephron loop

• some reabsorption also takes place in the distal convoluted tubule

reabsorption of any product takes place until the _ is reached

renal plasma threshold

cellular waste produces ed fromt eh metabolism of proteins

urea

cellular waste produced from the metabolism of nucleic acids

uric acid

urea and uric acid are toxic if too much accumulate in the blood because

they are considered nitrogenous waste (contain nitrogen)

why is it good to reabsorb small amounts of urea and uric acid

because they play a role in maintaining water balance in the blood

this is the level that dictates the amount of material that is reabsorbed

renal plasma threshold

this step of urine formation involves secreting substances from the blood (in the peritubular capillaries) out into the filtrate within the PCT and collecting ducts

tubular secretion

• opposite of tubular reabsorption

in tubular reabsorption, _ transport is used to move urea, hydrogen ions, drug excess, and excess potassium

active

hydrogen is secreted to control blood

pH

material is considered filtrate until it goes through the _ step

tubular secretion

• (after tubular secretion, it is considered urine)