Homework Quiz Question 1

Homework Quiz Question 2You are sick and take an antibiotic. Describe the pathway of the drug through the urinary

system, starting from the aorta to the toilet!

Passive transport. Substances move spontaneously down their concentration gradients, crossing a membrane with no expenditure of energy by the cell. The rate of diffusion can be greatly increased by transport proteins in the membrane.

Active transport. Some transport proteins act as pumps, moving substances across a membrane against their concentration gradients. Energy for this work is usually supplied by ATP.

Diffusion. Hydrophobicmolecules and (at a slow rate) very small uncharged polar molecules can diffuse through thelipid bilayer.

Facilitated diffusion. Many hydrophilic substances diffuse through membranes with the assistance of transport proteins,either channel or carrier proteins.

ATP

Three Functions of Urine Formation1. Filtration – movement of

fluids from the blood in the glomerulus to the Bowman’s capsule

2. Reabsorption – transfer of fluids from nephron into peritubular capillaries

3. Secretion – transfer of fluids from peritubular capillaries into nephron

Filtration.

Reabsorption.

Secretion.

Excretion.

Capillary

Excretorytubule

Filtrate

Urine

1

2

3

4

interstitial fluid

FiltrationWater and solutes flow from the

glomerulus into Bowman’s capsule due to high blood pressure flow65 mmHg vs. normall ~ 25 mmHg

Semi-permeable membraneRed blood cells, platelettes and

some blood proteins are too large to fit through the filtration slits and pores.

Filtration.

Reabsorption.

Secretion.

Excretion.

Capillary

Excretorytubule

Filtrate

Urine

1

2

3

4

Nutrient FlowSolute Glomerulus Bowman’s

Capsule?

water yes

NaCl yes

H+ ions yes

amino acids yes

glucose yes

plasma proteins no

red blood cells (erythrocytes)

no

platelets no

Reabsorption reclaims valuable substances from the filtrate and returns them to the body fluids.Water, salt and nutrientssaves us from having to

continuously replenish our body with fluid.

Filtration.

Reabsorption.

Secretion.

Excretion.

Capillary

Excretorytubule

Filtrate

Urine

1

2

3

4

Reabsorption

20% of fluid flowing into kidney is filtered into nephrons; however less than 1% of the fluid in the nephron is used to make urine.

A LOT OF REABSORPTION!

SecretionOther substances are

extracted from body fluids and added to the contents of the nephron toxins and excess ions

Filtration.

Reabsorption.

Secretion.

Excretion.

Capillary

Excretorytubule

Filtrate

Urine

1

2

3

4

Reabsorption

Secretion

protein transporters move nutrients into interstitial fluid and blood

kidney tissue will only reabsorb a certain level of nutrients – threshold level

Filtration.

Reabsorption.

Secretion.

Excretion.

Capillary

Excretorytubule

Filtrate

Urine

1

2

3

4

Diffusion. Hydrophobicmolecules and (at a slow rate) very small uncharged polar molecules can diffuse through thelipid bilayer.

Facilitated diffusion. Many hydrophilic substances diffuse through membranes with the assistance of transport proteins,either channel or carrier proteins.

ATP

protein transporters move wastes from blood to interstitial fluid to nephron

The Details…

1. Bowman’s CapsuleHigh pressure filterwater and dissolved solutes leave

glomerulus; enter Bowman’s capsule water

Na+

H+

Cl-

glucoseamino acidsvitaminsmineralsureauric acid

2. Proximal Tubule

Selective reabsorption of nutrients (need transporters)

Secretion of H+ and ammonia

pH determined by HCO3-

reabsorption and H+ secretion

H+

NH3

HCO3-, K+

Na+, Cl-

H2Oamino acidsglucosevitamins

3. Loop of Henle – Descending Limb

Nephron membrane only permeable to H2O (osmosis) and impermeable to salt

Reabsorption of waterAs fluids travel down the loop

of henle, the fluids within the tube become more concentrated.

H2O

4. Loop of Henle – Ascending Limb

only permeable to salt (need ionic transporters) and not permeable to water

Reabsorption of saltAs fluids travel up the loop of

henle the fluid is becoming less concentrated

NaCl

5. Distal Tubule

Selective reabsorption of nutrients (need transporters)

Secretion of H+, ammonia and K+

pH determined by HCO3-

reabsorption and H+ secretion

H+

NH3

K+

HCO3-

Na+, Cl-

H2O

6. Collecting DuctUrine formation by concentration of

nephron fluidAny urea and urine that is reabsorbed

is less than that was filtered into nephron

Why is some urea reabsorbed?Contributes to the formation of a

hypertonic interstitial fluidcauses water to be reabsorbedCONCENTRATING THE URINE

NaClureawater

Proximal tubule

Filtrate

H2OSalts (NaCl and others)HCO3

–

H+

UreaGlucose; amino acidsSome drugs

Key

Active transport

Passive transport

CORTEX

OUTERMEDULLA

INNERMEDULLA

Descending limbof loop ofHenle

Thick segmentof ascendinglimb

Thin segmentof ascendinglimb

Collectingduct

NaCl

NaCl

NaCl

Distal tubule

NaCl Nutrients

Urea

H2O

NaCl

H2OH2OHCO3

K+

H+ NH3

HCO3

K+ H+

H2O

1 4

32

3 5

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

300

300 100

400

600

900

1200

700

400

200

100

Activetransport

Passivetransport

OUTERMEDULLA

INNERMEDULLA

CORTEX

H2O

Urea

H2O

Urea

H2O

Urea

H2O

H2O

H2O

H2O

1200

1200

900

600

400

300

600

400

300

Osmolarity of interstitial

fluid(mosm/L)

300

Osmolarity – concentration of solutes in a solution, the higher the Osmolarity, the more concentrated the solution, the better it is able to pull water towards it.

http://www.biologymad.com/resources/kidney.swf

Diabetes (Type II) Not enough insulin released from pancrease High levels of glucose in the blood

Why do you think that individuals with Type II Diabetes (untreated)

(a) Excrete a large amount of gluose in the urine?

(b) Excrete large amounts of urine?

Kidney Stonescrystallization of some

urine solutes

a 2 – 3 mm stone can obstruct flow to the ureter

Treatment:increased water

consumptionsurgery