Making Connections
8.
Renal hypertension is high blood pressure caused by a narrowing of the arteries that carry blood to the kidneys. Salt
increases the movement of fluids from cells into capillaries, thereby raising the volume of body fluids. The increase in
body fluids increases blood pressure. People with renal hypertension have to avoid high levels of salts to avoid a further
increase in blood pressure.
7.6 WATER BALANCE
Section 7.6 Questions
(Page 356)
Understanding Concepts
1.
2.
3.
4.
5.
6.
7.
ADH is antidiuretic hormone, a hormone that regulates water balance. ADH is produced in the hypothalamus and stored
in the pituitary.
As solute concentration in the blood increases (when water intake is decreased or increase water loss), osmotic pressure
changes, and the cells of the hypothalamus shrink. This stimulates osmoregulators, which send a nerve message to the
pituitary to release ADH.
The thirst centre is located in the hypothalamus.
When osmotic pressure increases, the cells of the hypothalamus shrink, osmoregulators are stimulated, and the pituitary
releases ADH. ADH is carried in the blood to the kidney. ADH enters the kidney and acts on the collecting duct and
upper regions of the distal tubule, making them permeable to water. Greater volumes of water are reabsorbed. This helps
prevent additional water loss. The shrinking of the cells of the hypothalamus also initiate a thirst response and you begin
drinking.
In humans, the shrinking of the cells of the hypothalamus also initiates a thirst response and you begin drinking.
Low blood pressure in the kidneys or reduced blood flow to the kidneys causes the release of renin from the glomerulus
area of the kidney. Renin activates angiotensinogen and converts it into angiotensin, which in turn causes the release of
aldosterone from the adrenal cortex. Aldosterone is released into the blood and causes an increased Na+ reabsorption from
the nephron. The Na+ will increase osmotic pressure of the extracellular fluid and, therefore, increase water reabsorption.
Angiotensin also causes constriction of blood vessels, increasing blood pressure.
An acid–base balance is maintained by buffer systems that absorb excess H+ ions or ions that act as bases. Excess H+ ions
from metabolism are buffered by bicarbonate ions in the blood. Carbonic acid, a weak acid, is produced. In turn, the
carbonic acid breaks down to form carbon dioxide and water. The carbon dioxide is then transported to the lung, where
much of it is exhaled.
The buffer system removes the H+ ions, but the system must be restored to protect the body. The kidneys restore the
buffer by reversing the reaction. CO2 is actively transported from the peritubular capillaries into the cells that surround the
nephron. CO2 combines with water to produce bicarbonate and H+ ions. The bicarbonate diffuses into the blood, restoring
the buffer, and the H+ combines either phosphate or ammonia ions and is excreted.
8.
H+ + HCO3– →
bicarbonate ion
H2CO3 →
carbonic acid
H2O + CO2
The kidney restores the buffer system of the blood by reversing the buffer system reaction. CO2 is transported from the
peritubular capillaries to the cells of the nephron, where the CO2 combines with water to form bicarbonate and H+ ions.
The bicarbonate ions go back into the blood, restoring the buffer. If the H+ remained in the blood, the pH would increase.
Fluctuations in pH can lead to death. Instead, the H+ combines with either phosphate ions or ammonia ions and is excreted
with the filtrate from the nephron.
Copyright © 2003 Nelson
Chapter 7 Maintaining An Internal Balance 159
Applying Inquiry Skills
9.
The solution should resemble section 7.6, Figure 1, on page 353 of the Student Text. See below also.
releases
ADH
kidneys increase
water reabsorption;
thirst response is
initiated
negative
feedback
pituitary
gland
regulator
osmoreceptors
detect increase in
blood pressure
change in blood pressure
hypothalamus
coordinating centre
10.(a) Proteins are not filtered. Proteins are found in the plasma but not in the glomerular filtrate.
(b) Urea is secreted. The concentration of urea is greatest in the urine. It is secreted in the upper segment of the distal
tubule.
(c) Glucose is reabsorbed from the proximal tubule. No glucose remains in the nephron after the proximal tubule. No
glucose is found in the urine.
Making Connections
11. Follow links from the Nelson Biology 12 Web site, section 7.6. A possible answer follows.
Water is an important, yet very limited, resource on the space station Mir (no longer in use) and on the International
Space Station (ISS). Water is extremely heavy, so it is not practical or economical to have the Space Shuttle transport
water to the space station as needed. To fulfill water requirements, water aboard the space station is recycled. This
includes water used for washing, condensation due to humidity, and urine.
To recycle urine, the urine goes through distillation and evaporation processes to remove the high level of salts. This
process involved a phase change (from liquid to gas for instance). This is done using vapour compression distillation
(VCD) or thermoelectric integrated membrane evaporation subsystem (TIMES). A urine distillate is produced, which
goes to the next stage of the process, multifiltration. Activated charcoal, iodine, ion-exchange resin, and organic
oxidations are used in this process to remove particulate matter, additional salts, ammonia, and organic material from the
distillate. On Mir, urine was recycled to produce oxygen via electrolysis. However, on the ISS, this filtrate will be treated
to become water used for washing or even drinking.
7.7 KIDNEY DISEASE
Explore an Issue
Debate: Xenotransplants
(Page 360)
Some points and counterpoints students may encounter:
Point
Not enough organs are donated from
people—this becomes a substitute.
Hemodialysis is very expensive and
difficult for patients.
160 Unit 3
Homeostasis
Counterpoint
Success has been limited. Patients rarely lead
a healthy life.
The procedure is expensive and transfer of
genes is not without risks. Aberrant DNA could
enter the human’s body—leading to new
diseases.
Copyright © 2003 Nelson