Biology 12
EXCRETORY SYSTEM
Learning Objectives: LO “O”
11th edition Mader: Chapter 16
The composition of blood serving the tissues remains relatively constant because substances required
by cells are being constantly added (O2, glucose, amino acids, lipids) and substances NOT required by
cells are being constantly removed (CO2, NH3, excesses of various ions e.g. Na+)
In this section you will learn how the organs of EXCRETION remove these unwanted substances thus
helping to maintain HOMEOSTASIS.
The excretory system is responsible for removing the wastes of cellular metabolism. These wastes are
brought to the organs of excretion, if necessary, by the circulatory system.
Complete each of the following:
1.
Urea is an important metabolic waste.
a) Identify the organ where it is produced.
b) Identify the molecules used to produce it.
c) Identify the role of the circulatory system in ridding the body of this waste.
2a.
Draw a diagram of a dissected kidney (in longitudinal section Fig. 16.3 b). Colour in and label
that area represented by the cortex, medulla, renal pelvis, pyramids, ureter.
2b.
On the supplied diagram of an enlarged nephron (or kidney tubule) with its associated capillary
beds label each of the following. Give the function of each of the parts of the nephron and any
special structures they possess to carry out their function..
i)
afferent arteriole.
ii) glomerulus
iii) efferent arteriole
ix) peritubular capillaries (peri = around)
v) Bowman's capsule
vi) proximal convoluted tubule
vii) Henles loop (ascending and descending limb)
viii) distal convoluted tubule
ix) collecting duct
x) cortex
xi) medulla
2c.
Observe the diagram carefully before coloring the circulatory system in the diagram blue or red to
indicate CO2 rich or O2 rich blood. Assume blood becomes deoxygenated ½ through the
pathway.
2d.
State clearly what is accomplished by each of the following in kidney function and label on the
diagram where each occurs. i) pressure filtration (glomerular filtration) ii) selective
reabsorption (tutular reabsorption) iii) tubular excretion (tubular secretion).
2
2e.
Name the blood vessels in order that a red blood cell would pass through from the afferent
arteriole onward to the heart and then back to the arteriole.
2f.
A soccer player receives a hard blow in the lower back (must have fallen down from boredom).
He later notices blood in his urine. Where might damage to blood vessels of the nephron have
occurred thus allowing blood cells to leak into the filtrate?.
Use the following chart to answer questions 3 & 4.
Daily
SUBSTANCE
WATER
CHLORIDE
SODIUM
GLUCOSE
POTASSIUM
UREA
PHOSPHATE
CALCIUM
SULPHATE
CREATININE
URIC ACID
3.
AMOUNT
ENTERING
(KIDNEYS)
100 liters
370 GRAMS
340 grams
70 grams
20 grams
30 grams
9 grams
10 grams
3 grams
1 gram
4 grams
URINE
1 liter
6 GRAMS
3.5 grams
0 grams
1.5 grams
20 grams
2.7 grams
0.15 grams
1.8 grams
1.0 grams
0.6 grams
AMOUNT
REABSORBED
(INTO BLOOD)
99 liters
364 grams
336.5 grams
70 grams
18.5 grams
10 grams
6.3 grams
9.85 grams
1.2 grams
0
3.5 grams
%
REABSORBED
99%
98%
99%
100%
93%
33%
70%
99%
40%
0
87%
Note that glucose is 100% reabsorbed
a) How are the nephron cells constructed to allow for complete reabsorption of glucose? If
there was glucose in the urine, what must that mean? What disease would cause glucose to
be in the urine? Explain why this occurs.
b) Why would glucose be the nutrient that is reabsorbed 100%?
4.
a) Note in the chart that urea is reabsorbed to about 33%. What is the purpose of allowing
urea to be reabsorbed instead of pumping it back into the collecting duct?
b)
5.
If urea was to be kept in the kidney tubule (nephron) to 100%, it would cost the body ATP.
Why?
The collecting duct is specially structured to allow urine concentration. Describe the
characteristics of the collecting duct.
3
6.
Explain how and where the kidneys would correct
a) an acid blood
b) an alkaline blood
7.
The kidney condition called uremia occurs when more than 65% of the nephrons become nonfunctional. Explain how this condition affects the human body.
8.
Alcohol causes increased urination. Explain why.
9.
The Loop of Henle is organized in such a way that the descending limb is permeable to H20 and
Na+ but the ascending limb is permeable to Na+ only. Show how the organization allows for a
high water reabsorption.
10.
A drop in blood pressure occurs in the afferent arteriole.
a.
What will happen to pressure filtration and therefore urine production?.
b.
What homeostatic mechanisms act on the kidney to help to return the blood pressure to
normal?
c.
Explain how the Loop of Henle contributes to the production of urine which is much saltier
than body fluids.
ANALYSIS OF THE COMPOSITION OF PLASMA, FILTRATE & URINE
SUBSTANCE
CONCENTRATION
IN PLASMA g/100 ml.
0.100
8.00
0.004
a. Glucose
b. Protein
c. Ammonia
111.
CONCENTRATION IN
FILTRATE g/100 ml.
0.100
0.000
0.004
CONCENTRATION
IN URINE g/100 ml
0.000
0.000
0.07
Note the differences between the filtrate and urine concentrations in each of the above
substances. Explain the differences by stating the part of the nephron and the process or
processes responsible for producing each of the concentration values. You must also discuss
what is occurring with each of the processes.
a)
glucose.
b)
protein
c)
ammonia