Download EXCRETORY SYSTEM

Biology 12
EXCRETORY SYSTEM
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.
2a.
2b.
Urea is an important metabolic waste.
a) Identify the organ where it is produced.
Liver
b) Identify the molecules used to produce it.
Ammonia and carbon dioxide
c) Identify the role of the circulatory system in ridding the body of this waste.
Urea is transported from the liver to the kidneys via the circulatory system.
Draw a diagram of a dissected kidney (in longitudinal section). Colour in and label that area
represented by the cortex, medulla, renal pelvis, pyramids, ureter.
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.
Brings blood to the nephron
ii) glomerulus
network of blood vessels where pressure filtration occurs. Podocytes allow for small molecules to
pass through and enter the nephron
iii) efferent arteriole
Substances in the blood that were not filtered at the glomerulus contine on
ix) peritubular capillaries (peri = around)
Capillaries that surrounfd the nephron
v) Bowman's capsule
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Surrounds the glomerulus and gathers the filtrate
vi) proximal convoluted tubule
-equiped with villi and carrier proteins the PCT allows substances to be re-absorbed back into the
blood
vii) Henles loop (ascending and descending limb)
-descending limb- has aquaporins which allow water to leave the nephron and enter the
surrounding salty medulla
-ascending limb- carrier proteins will actively pump out sodium into the salty medulle
viii) distal convoluted tubule
pH regulation occurs here. OH- and H+ exit or enter the blood
blood pressure can be increased when aldosterone is present
substances and drugs can leave blood and enter DCT
ix) collecting duct
Water and urea can enter nephron
x) cortex
Outer layer of nephrons…where the Glomerulus, PCT and DCT would be
xi) medulla
Salty middle layer where the loop of henle would be
2c. 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)
Small molecules (urea, glucose, amino acids, salt, water) enter the nephron due to pressure build up
and squeezing through podocytes
ii) selective reabsorption (tutular reabsorption)
Most of the water, sodium, some urea and all of the glucose is reabsorbed back into the blood
iii) tubular excretion (tubular secretion).
Creatinine, potassium, drugs, penicillin H+, OH- leave the blood and enter nephron
2d.
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.
Afferent artierole-efferent arteriole- peritubular capillaries-renal vein- inferior vena cava-pulmonary
artery-pulmonary vein-aorta-renal artery-afferent arteriole
2e.
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?.
Most likely damage to the glomerulus/ podocytes
Use the following chart to answer questions 3 & 4.
Daily
SUBSTANCE
WATER
AMOUNT
ENTERING
(KIDNEYS)
100 liters
URINE
1 liter
AMOUNT
REABSORBED
(INTO BLOOD)
99 liters
%
REABSORBED
99%
3
CHLORIDE
SODIUM
GLUCOSE
POTASSIUM
UREA
PHOSPHATE
CALCIUM
SULPHATE
CREATININE
URIC ACID
3.
370 GRAMS
340 grams
70 grams
20 grams
30 grams
9 grams
10 grams
3 grams
1 gram
4 grams
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
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
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? Villia
and carrier proteins in the PCT If there was glucose in the urine, what must that mean? Too
much glucose and the carrier proteins can not keep up What disease would cause glucose to
be in the urine? Explain why this occurs. Diabetes…either the pancreas isn’t releasing
insulin or the insulin that is released isn’t binding to the liver properly
b) Why would glucose be the nutrient that is reabsorbed 100%?
Glucose is a molecule that can be boken down to release ATP. DO not want to waste any energy
molecules
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?
To create a concentration gradient that water will follow. This prevents excess water from
leaving the body
5.
The collecting duct is specially structured to allow urine concentration. Describe the
characteristics of the collecting duct.
There are aquaporins that allow water to leave the collecting duct and re-enter the blood
4
6.
Explain how and where the kidneys would correct
a) an acid blood
b) an alkaline blood
Both in the DCT
7.
The kidney condition called uremia occurs when more than 65% of the nephrons become nonfunctional. Explain how this condition affects the human body.
Urea builds up in the blood…headache, nausea, fatigue, drowsy…due to water loss and buildup of
other toxins
8.
Alcohol causes increased urination. Explain why.
Alcohol inhibits production of ADH…this closes aquaporins and water stays in nephronmore urine
9.
The Loop of Henle is organized in such a way that the descending limb is permeable to H20 but
the ascending limb is permeable to Na+ only. Show how the organization allows for a high water
reabsorption.
Sodium is pumped actively to create the concentration that water will follow into the body. Therefor
the water doesn’t leave as urin
10.
A drop in blood pressure occurs in the afferent arteriole.
a.
What will happen to pressure filtration and therefore urine production?
Lower pressure…less filtration
Less urea leaving in urine
b.
What homeostatic mechanisms act on the kidney to help to return the blood pressure to
normal?
1. Juxtaglomerular apparatus detects low BP..releases renin…causes angiotensinogen into angiotensin
which target the adrenal cortex. The AC releases aldosterone which goes to the DCT and increases
reabsorption of sodium into the blood and the excretion of potassium into the DCT. Water follows the
sodium and increases the pressure of the vessel
2. Right atrium detects high BP which then releases ANH. This stops renin production…lowers BP
3. ADH promote the production of aquaporins. This allows water to enter the blood which will
increase/ maintain the BP
ANALYSIS OF THE COMPOSITION OF PLASMA, FILTRATE & URINE
SUBSTANCE
a. Glucose
b. Protein
11.
CONCENTRATION
IN PLASMA g/100 ml.
0.100
8.00
CONCENTRATION IN
FILTRATE g/100 ml.
0.100
0.000
CONCENTRATION
IN URINE g/100 ml
0.000
0.000
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.
5
a)
glucose. Glomerulur filtration allows some glucose to enter the nephron…at the
PCT ALL of the glucose is reabsorbed
b)
protein- no proteins are allowed to enter at the glomerulus because they are too
large to fit through the podocytes. If there aren’t any in the nephron then none will be
in the urine