Download H 2 O - Mr. Shanks` Class

III] KIDNEY and WASTE EXCRETION
A] Macronutrients & wastes
1. Carbohydrates
a. formula is [CH2O]n
b. break down into CO2 and
H20 which are exhaled
2. Lipids
a.
formula involves C,H and a few O
b.
converted to glucose or pyruvate
& breakdown into CO2 and H20  exhaled
3. Proteins
a. formula involves C, H, O and N
b. breakdown into amino acids & then amino group
is removed before converted to pyruvate or
oxaloacetate which breakdown into CO2 and H2O
c. the -NH2 or amino group is a problem  it is toxic
d. amine wastes are combined with carbon dioxide as
follows to form urea
O
//
-NH2 + -NH2 + CO2  H2N – C – NH2
amine + amine + CO2  urea
B] Goals of the kidney
1. filter as much blood as possible
– 1.2 L per minute
2. conserve the glucose and amino acids in the blood
3. retain sodium in the body
4. retain as much water as possible
5. eliminate the urea and other wastes from the blood
6. be able to adjust system to account for changes in
dietary water, proteins, minerals
C] The parts of the system
kidney
ureter
bladder
urethra
switch to website
http://www.sumanasinc.com/webcontent/anisamples/majors
biology/kidney.html
D] The parts of the nephron
GLOMERULUS
BOWMAN’S
CAPSULE
PROXIMAL
TUBULE
DISTAL
TUBULE
RENAL
ARTERY
RENAL
VEIN
COLLECTING
DUCT
DESCENDING
ARM of
LOOP of HENLE
ASCENDING
ARM
E] Concept of Countercurrent System
1. the countercurrent system is similar to an
uncontrolled positive feedback loop
2. it depends on the fact that as water is pulled out of
the decending arm of the Loop of Henle by the
NaCl gradient, the concentration of the
remaining solution changes
3. The development of a countercurrent system is
shown below in 3 steps.
A
Loop of Henle is at equillibrium
No pumping or diffusion is occuring
300mmol/L
300
300
300
300
300
300
300
B.
Ascending arm is pumping out sodium
The interstitial tissue surrounding the nephron
now has a higher sodium concentration than the
nephron
300mmol/L
400
200
300
400
350
250
300
350
C.
The higher concentration of sodium outside the
nephron descending arm causes water to diffuse out
of the descending arm of the nephron.
300mmol/L
400
200
H2O
300
400
350
250
H2O
300
350
D.
As water diffuses out of the descending arm, the
concentration of sodium remaining increases
This means that sodium pumping by the ascending
arm creates a larger gradient outside the nephron
300mmol/L
450
300
H2O
400
450
400
450
H2O
500
400
4. This countercurrent eventually builds up to a
maximum level of 1400 mmol/L
300
300
300
H2O
H2O
H2O
H2O
450
750
900
700
700
900
900
1100
1400
1150
900
1100
1100
1400
1400
1400
H2O
500
700
600
H2O
500
500
F. The value of the counter current system
1. Most of the water will be removed at the
proximal tubule [85%]
2. More water will be removed at the
descending arm [5 %]
3. The counter current system is designed to recover
additional water from the collecting duct [10 %]
4. It does this by creating a concentration gradient
in the tissues outside the collecting duct and
then water will move from the area of high
concentration in the urine to an area of low
water concentration in the interstitial fluids.
G.
Achieving the goals of the kidney
1. Filtering
a. The blood from the renal artery enters the
glomerulus under high pressure.
b. All large molecules and cells stay in the blood,
all dissolved molecules pass through.
c. The Bowman’s capsule therefore receives plasma +
dissolved molecules now called urine.
d. The NaCl concentration is 300 mmol/L.
2. Retaining glucose and amino acids
a. The cells in the proximal tubule actively transport
glucose & amino acids out of urine
b. Water follows these molecules out of urine due to the
concentration gradient.
c. The NaCl concentration of the urine is still 300 mmol/L.
[because NaCl is also pumped out of the nephron
here]
glucose
NaCl
H2O
amino
H2O
acid
3. Retaining sodium
a. Pumps in the ascending arm of the Loop of Henle
pump out NaCl.
b. Due to the countercurrent system this means that
the level of [NaCl rises] to as high as 1400 mmol/L
in the urine and surrounding tissue.
c. By the top of the ascending arm, there is 300 mmol/L
in the urine.
d. Sodium / potassium pumps in the distal tubule and
the collecting duct will pump additional sodium
out of the urine.
glucose
NaCl
K+
H2O
amino
acid
H2O
H20
area
with
extra
sodium
NaCl
NaCl
NaCl
Na+
area very high
in sodium
NaCl
NaCl
Na+
K+
4. Retaining water
a.
About 85% of the water leaves the urine in the
proximal tubule due to glucose & amino acid
gradients.
b. 5 % of the water leaves the urine in the
descending arm due to the sodium gradient.
c. 0 – 10 % water leaves the urine in the
collecting duct due to the sodium gradient.
d. Remember water can never be pumped
It moves due to a concentration gradient
other wastes
glucose
NaCl
K+ Na+
H2O
amino
acid
H2O
area high
in sodium
H20
NaCl
NaCl
NaCl
H2O
Na+
NaCl
K+
H2O
NaCl
urea
H2O
urea +
some H2O
some Na & K
5. Removing urea and wastes from the body
a. The urea is dissolved in the plasma and
therefore enters through the Bowman’s capsule.
b. Some additional wastes are added at the distal
tubule by exocytosis.
c. In cases of severe dehydration, the urea diffuses
out of the urine
d. Water moves out of the urine due to the [gradient]
6. Controlling the system over a range of conditions
.........hormones
Now work on………..
“Problems in the urinary system”