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Excretionremoval of metabolic waste
Protein and nucleic acid metabolism nitrogen containing compounds
does not include feces
Excretion is an example of homeostasisPrevent build up of toxic
wastes within our bodyContribute to water
balance in our body
Composition of Urine
solution of metabolic wasteWater (mostly)urea and uric acidsaltsorganic compounds
deamination – removal of amine group
Occurs in the liverByproducts are sent to
the kidneys for further processing
Ureaproduct of two other waste molecules
ammonia, NH3 (very toxic)
carbon dioxide, CO2
ammonia released when liver breaks down proteins0.005 mg NH3 is lethal
reacts with CO2 to produce less toxic urea100 000x less toxic than NH3
Ammonia
Role of Kidneys1. Removal of wastes
Urea, uric acid and other materials are filtered through the kidney and excreted
2. Water balanceaverage person loses
2L of liquids a daysuggested to consume
2L H2O / day
Role of Kidney
1. blood filtration
2. waste excretion
3. acid / base balance
4. blood pressure regulation
5. hormone secretion
Kidney Structurerenal cortex – outside of
kidney; location of Bowman’s capsule
renal medulla (lobes) – middle of kidney; location of loop of Henle
renal pelvis – location of the ends of collecting ducts
Kidney Blood FlowBlood enters the kidney through
the renal artery.renal arteries stem from the
aortaCarry oxygenated blood
Filtered blood exits the kidney through the renal vein.renal veins flow into the inferior
vena cavaCarry de-oxygenated blood
NephronFunctional unit
of the kidneyResponsible
for the formation of urine
A million nephrons make up the kidney
Blood and the Nephron
Blood from renal artery is filtered through nephrons.
Nephrons collect liquid to be excreted
Filtered blood is returned to renal vein
The renal artery is split into afferent arterioles.blood brought to glomerulus; a capillary bed.blood leaves through the efferent arterioles
no veins involved
Efferent arterioles are the beginning of a network of peritubular capillaries, that wrap around the nephron.
Renal artery
From the bowman’s capsule:fluids to become urine flow to narrow proximal tubuleurine flows through loop of Henleurine flows through distal tubule
Urine from multiple nephrons flow into the collecting duct.
Urine FlowUrine leaves the renal pelvis
through the ureters and travels to the bladder. Fluid leaves the body through the urethra.
When ~200 mL of urine has collected in the bladder, the walls stretch and signals are sent to the brain.
At ~600 mL, urine will involuntarily be released. ureters
afferent arteriole
efferent arteriole
glomerulus
Bowman’s capsule
proximal tubule
Loop of Henle
distal tubule
collucting duct
aortainferior vena
cavarenal artery
renal vein
kidney
ureter
bladder
urethra
renal cortex
renal medulla
renal pelvis
nephrons
ureter
QuestionAthletes now undergo random
urine testing for drugs.
Describe the pathway of drugs through the urinary system, from the time they enter the glomerulus until they are excreted in the urine.
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
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
protein transporters move nutrients into interstitial fluid and blood
kidney tissue will only reabsorb a certain level of nutrients – threshold level
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.
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
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