18.1.1 Hormones

Maintaining a Balance
Topic 18: Hormones
Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis
 Outline the role of the hormones, aldosterone and ADH
(anti-diuretic hormone) in the regulation of water and salt
levels in blood.
Hormones are chemical control substances that are secreted
by endocrine (ductless) glands, directly into the bloodstream.
They travel via the general circulation to parts of the body and
when they reach their target cells, these cells (in our case,
cells within the kidney nephrons) respond.
The passage of the filtrate from
Bowman’s capsule to the distal
parts of the nephron occurs
without variation.
Adjustments to the
concentration of water and
salts within the urine takes
place mainly in the distal parts
of the tubules and the
collecting tubules, by
alterations to the permeability
of the membranes of cells
lining the nephron walls.
These changes in permeability are brought about by two main
 Aldosterone: brings about retention (conservation) of salts
within the body.
 ADH (anti-diuretic hormone): brings about water
reabsorption (conservation) within the body.
A decrease in the
concentration of sodium ions
in the bloodstream leads to a
decrease in blood volume and
this stimulates cells in the
cortex of the adrenal gland
(above the kidney) to secrete
the hormone aldosterone.
When aldosterone reaches the
kidney (via the bloodstream),
it increases the permeability
of the nephron to sodium,
particularly in the ascending
limb of the loop of Henle.
Reabsorption of sodium ion
from the nephron into the
surrounding kidney tissue and
capillaries occurs, resulting in
the retention (conservation)
of salt by the body. (less salt is
lost in urine)
Anti-diuretic hormone (ADH)
When a mammal begins to dehydrate, blood volume drops and
this is detected in the hypothalamus of the brain. It stimulates
the pituitary gland to release the hormone ADH, which acts on
the nephrons of the kidneys to increase the reabsorption of
Anti-diuretic hormone (ADH)
The presence of ADH increases the permeability of the
membranes of the cells lining the distal tubules and collecting
tubules to water. As a result, water is reabsorbed from these
tubules into the kidney tissue and bloodstream and so water is
conserved within the body (less water is lost in urine).
Anti-diuretic hormone (ADH)
The name of the hormone describes its function – a diuretic is
a substance that causes the loss of water from the body
(alcohol, tea and coffee are diuretics), so ‘anti-diuretic’ refers
to a substance that reduces water loss.
Both ADH and aldosterone therefore play an important role in
helping the kidney to carry out its homeostatic functions of
 Regulation of the solute concentration of the blood:
regulating the amount of sodium and other ions that are
reabsorbed or secreted in urine.
 Regulation of blood volume: maintaining a constant fluid
volume of dilute urine or a small concentration of
concentrated urine.
Technology and Kidney Function
An understanding of how the kidney functions to remove
wastes, as well as the hormonal regulation of kidney
functioning to maintain homeostasis has played a key role in
the development of technologies such as:
 Renal dialysis for people suffering from reduced kidney
 Hormone replacement therapy for patients suffering
from abnormally low levels of the hormone aldosterone.
Technology and Kidney Function
These applications of the use of biology have helped to improve
the lifestyle and increase the life expectancy of people who
suffer from these diseases.
Renal Dialysis
The kidneys are responsible for filtering our blood, removing
metabolic wastes so that they may be excreted via urination. If
a person suffers from kidney failure, there is no natural means
by which these wastes can be removed and their toxic effect
eventually leads to death.
Renal Dialysis
The process of renal dialysis has been developed to carry out
the function of failed kidneys so that blood may be effectively
filtered. There are two types of renal dialysis:
 Haemodialysis
 Peritoneal dialysis
Renal Dialysis
The main function of a dialysis machine is to remove metabolic
wastes that have built up in the persons blood. The patient is
connected to a dialysis machine, which pumps their blood
through a system of tubes (coiled to increase their surface area
and therefore the rate of diffusion) which have artificial semipermeable membranes.
Renal Dialysis
The tubes are submerged in dialysis fluid (dialysate), which
flows in the opposite direction to the blood in order to
maximise diffusion.
Renal Dialysis
Dialysis has the same
concentration as blood plasma
without the metabolic wastes,
and since the concentration of
metabolic wastes is higher in
the blood than in the dialysing
fluid, the waste materials
move through the semipermeable membrane into the
dialysing fluid by diffusion.
Renal Dialysis
Since dialysis relies on passive transport for the removal of
wastes from the blood, the dialysis fluid must constantly be
replaced so that the concentration gradient is maintained away
from the blood.
Renal Dialysis
Renal dialysis must be carried out
for 3 to 4 hours, two or three times
per week. As well as its timeconsuming nature, another
disadvantage is that only limited
amounts of fluid/wastes can be
removed from the blood. Other
substances such as sodium
phosphate and potassium ions do
not diffuse quickly enough and
therefore may accumulate in the
Renal Dialysis
Patients have to follow a specific diet to prevent the build up of
such substances, as renal dialysis is not effective in regulating
the concentration of these ions in the blood.
Hormone Replacement Therapy
Aldosterone increases the amount of salt reabsorbed from
kidney tubules and as a result it also helps regulate blood
pressure. Some people lack aldosterone. Addison’s disease
results from abnormally low levels of aldosterone in the body.
The causes are not always known, but include:
 Damage to the adrenal glands that produce aldosterone, due
to accident, surgery or disease (such as bacterial infections
or cancer of the gland)
 Damage to the pituitary gland that controls the adrenal gland
(for example, because of a tumor)
Hormone Replacement Therapy
Hormone replacement therapy involves restoring the balance
of the hormones at levels that are normal for the body, by
giving the patients hormones. When applied appropriately, it
can increase fluid retention, raise blood pressure and remove
the danger of heart failure, allowing sufferers to lead normal
Hormone Replacement Therapy
Since 1927, when the first hormone
replacement therapy began (using an
extract from the adrenal cortex of
cattle), hundreds of human lives
which would have been lost to
Addison’s disease in the past have
been saved. Modern day hormone
replacement therapy involves
administering a genetically
engineered hormone called
-Students to complete activity 3.8 Renal Dialysis and 3.10
ADH Replacement Therapy

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