7B Urine Formation & Events in the Nephron

Excretion equation

Excretion = filtration + secretion - reabsorption

Where does blood flow into the nephron?

Afferent arteriole (into glomerulus)

What happens in the glomerulus?

Filtration from blood plasma into nephron

Where does filtration happen?

ONLY in the glomerulus

What is the name of fluid in the renal tubule?

filtrate

Tubular reabsorption

reabsorption from filtrate back into blood

Return to blood = ?

reabsorption

What happens to filtrate if it stays in the renal tubule?

It becomes urine

Tubular secretion

Secretion from blood into fluid (in renal tubule)

Where does secretion happen?

Everywehre except the glomerulus

Where does fluid go if it returns & stays in the blood?

The blood contains reabsorbed substances & goes to the renal vein then IVC

What is excreted?

urine

What are filtration & secretion composed of?

What you have put into the nephron/urine

What is reabsorption composed of?

What you have taken out of the nephron

What are the 4 major processes in the nephron?

1. filtration

2. reabsorption

3. secretion

4. excretion

Filtration

Movement of water & solutes from the blood plasma across the wall of the glomerular capillaries, into the glomerular capsule & into the renal tubule

Solutes

Anything that is dissolved in the solution

What 3 pressures drive filtration?

1. glomerular blood hydrostatic pressure (BGHP) = 55mmHg

2. Capsular hydrostatic pressure (CHP) = 15 mmHg

3. Blood colloid osmotic pressure (BCOP) = 30mmHg

What are the promoting pressure(s) (promotes filtration)?

Glomerular blood hydrostatic pressure (GBHP) -> wants solutes to leave the blood & enter the nephron

What are the opposing pressure(s) of filtration?

Capsular hydrostatic pressure (CHP) & Blood colloid osmotic pressure (BCOP) -> want solutes to stay in the blood

Increase in blood -> ?

Increase in GBHP pressure

Colloid

proteins

The more proteins in the blood (BCOP) -> ?

the more water they want to keep w/ them -> decrease in filtration

What leaves in the efferent arteriole?

Not filtered blood to the peritubular capillaries

Net Filtration Pressure (NFP)

GBHP - CHP - BCOP
55mmHg - 15 mmHg - 30 mmHg

= 10 mmHg -> filtration wins since it's positive (if number is - then it would be pulling filtrate into the efferent arteriole)

Glomerular filtration rate (GFR)

Volume of plasma filtrate that passes through the glomeruli every minute (rate of plasma we filter per minute)

What is the blood flow to the kidneys @ rest?

1200 - 1300mL/min (1.2-1.3L/min)

What is filtered?

Plasma

How much plasma is filtered?

720-780 ml/min (Hct = 40%)

What is the maximum filtration?

125 mL/min (17% of plasma)

Reabsorption

Return/retain

Movement of substances from the renal tubule to the blood stream (filtrate -> blood)

How much of the filtered water & solutes do cells reabsorb?

99%

Where do the water & solutes travel when reabsorbed?

Through the peritubular capillaries & vasa recta to eventually return to the IVC

Secretion

See ya!

The removal of a substance from the blood into the renal tubule (filtrate)

What is included in secretion?

What we want to get rid of: drug residuals, excess ions from blood, etc.

What happens in the proximal tubule?

Reabsorption of 99% of what was just filtered (mostly Na & glucose, also amino acids, K, Cl, bicarbonate ions) & secretion of H ions & drug residues

proximal tubule acid-base balance

Maintaining the acid-base balance

Co2 & H2O start the process by getting rid of H+ (in blood) & keeping bicarbonate (in blood) while also reabsorbing Na+ & getting rid of CO2

Why do we reabsorb HCO3- (bicarbonate)

Acts as buffers & helps get rid of H+

How much bicarbonate ions (HCO3-) are reabsorbed?

80-90% of bicarbonate ions

What happens in the descending loop of Henle?

Reabsorbs water back into blood

Secretes NaCl (salt/sodium chloride) into urine

What happens in the ascending loop of Henle?

Water impermeable (does not cross membrane/no water movement)

Reabsorbs NaCl back into blood through vasa recta

What happens if you increase osmolarity in the loop of Henle?

Increase solutes

What happens if you decrease osmolarity in the loop of Henle?

Decrease solutes & increase dilute

Where is there lower osmolarity in the loop of Henle?

At the beginning of the descending loop

where is there higher osmolarity in the loop of Henle?

At the bottom of the descending loop/beginning of the ascending loop

What happens in the distal tubule & collecting duct?

Secretion of K & H ions

Reabsorption of NaCl & water

(last chance to match solute & water to physiological needs)

What is water completely dependent on (for reabsorption in the distal tubule/collecting duct)?

On the presence of ADH & aldosterone

What is water inhibited by?

ANP (opposite of ADH & aldosterone)

Atrial natriuretic peptide (ANP)

Hormone that is release if you have high BP/BV or overhydrated that stretches the heart/atria and puts sodium into the urine (in which water will follow)

Aldosterone

Puts Na in blood (water will follow because of osmosis)

When it comes to the distal tubule/collecting duct, what determines what is reabsorbed?

If aldosterone -> Na

If ADH -> water