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Excretion

within them and hence more effective
Activity 4.4:
ultrafiltration. The high coiling also
Analysing the presence of metabolic creates and maintains high pressure in the
waste in urine glomerulus which causes ultrafiltration.
Materials The glomerular capillaries and tubule are
FOR ONLINE READING ONLY
Test strips (glucose, protein, pH), animal semipermeable structures to allow selective
urine samples (synthetic or real under movement of materials in and out of the
supervision), beakers droppers and nephrone. This process is called selective
standard colour chart reabsorption. The epithelium is thin and
Procedure leakier than normal capillaries to reduce
1. Pour urine sample in a beaker. diffusion distance for faster passage. This
2. Dip the glucose test strip into the in turn enhances reabsorption of materials.
sample and observe the color change. The urinary system is also connected to
3. Repeat the process using protein and a collecting duct, which channels urine
pH test strips. out to the ureter to allow continuous
4. Record the observations and compare functioning of the nephrone. Apart from
with standard color charts. that, the proximal convoluted tubule and the
Safety precaution distal convoluted tubule are coiled so as to
increase the nephrone’s length and hence
All safety gears should be properly used. more surface area for efficient reabsorption

Questions to take place. The Bowman’s capsule is cup-
1. What do the results indicate about shaped to provide maximum surface area
the body’s excretory function? for filtration. The tubule is supplied with a
2. How would abnormal test results network of blood capillaries for maximum
help diagnose kidney disease? reabsorption. The nephrones are numerous
in number for efficient excretion of waste
Adaptive features of urinary system products. Lastly, the urinary bladder has
There are several adaptations that enable sphincter muscles that remain contracted to
the kidney to perform its functions prevent urine from leaking before a certain
properly. The kidney has large afferent level is reached. When relaxed, the muscles
arteriole and narrow efferent arteriole. This allow movement of urine out of the body.
arrangement enables building-up of a very
high hydrostatic pressure in the glomerulus. Exercise 4.3
This pressure facilitates ultrafiltration of
materials. Glomerulus capillaries are highly 1. Why is selective reabsorption
coiled or convulated and semipermeable to important in urine formation?
increase surface area within a small space 2. How do structural adaptations of
to allow for a more efficient ultrafiltration. the kidney enhance its excretory
The coiling or twisting of the capillaries function?
increases more time for the blood flow

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