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Homeostasis of the kidney (The Kidneys' Role in, Homeostasis, Acid…
Homeostasis of the kidney
The Kidneys' Role in
Homeostasis
Acid Base Balance
Decreased Body pH (more acidic)
Reabsorption of Bicarbonate happens
mainly in the Proximal Convoluted Tubule
(90%), and partially in the Distal
Convoluted Tubule (10%) through a
process called "Bicarbonate Trapping."
The body uses carbonic anhydrase
produced by the brush border of the
convoluted tubules as a catalyst to break
down Bicarbonate into CO2 and H2O.
The CO2 is then diffused into tubular
cells where it rejoins with H2O to form
bicarbonate that is then released into the
blood circulation.
Excess hydrogen ions are secreted into the
proximal and distal tubules and excreted in
urine to prevent the body from becoming
too acidic, (pH too low) for example, after
ingestion of a high protein meal
Increased Body pH (moer acidic)
Bicarbonate is freely filtered in the
glomerulus and excreted in urine when
plasma bicarbonate concentration is
elevated, thus preventing from the body
from becoming too basic (pH too high)
Blood Pressure
Changes in blood pressure are directly
related to changes in blood volume which
is controlled by a hormonal cascade known
as the Renin- Angiotensin- Aldosterone-
System, or RAAS. Cells located in the distal
tubule called macula densa cells, along with
renin-releasing cells in the arterioles of the
glomerulus make up what's known as the
juxtaglomerular apparatus (JGA). The JGA
detects increases and decreases to the
amount of blood flow to the glomerulus, or
the GFR. Changes in blood pressure
typically directly affect the GFR
Decreased Blood Pressure
Cells in the JGA sense a decrease in the
GFR in the glomerulus and stimulate the
renin-releasing cells to release renin, thus
initiating the RAAS.
Renin stimulates the release of
angiotensinogen which stimulates the
release of angiotensin I which is activated
by ACE and converted to angiotensin II.
Angiotensin II causes vasoconstriction of
the efferent arteriole of the glomerulus,
increasing GFR, as well as peripheral
vasoconstriction, raising systemic BP by
decreasing the space within the blood
vessels which exerts more pressure.
Angiotensin II also stimulates the release of
aldosterone from the adrenal cortex.
Aldosterone promotes the reabsorption of
both sodium and water from the distal
tubule, thus increasing blood volume and
blood pressure. This is done by exchanging
potassium or hydrogen for sodium
Increased Blood Pressure
Cells in the JGA sense increased GFR and
send a negative feedback signal to the
stop the release of renin, thus halting the
RAAS system which leads to increased
blood pressure. The excretion of sodium
and water is permitted freely to decrease
blood volume, and no vasoconstriction
occurs.
Body Fluid Osmolarity
Antidiuretic Horomone (ADH) is directly
influenced by blood osmolality.
Increased Blood Osmolarity
Osmoreceptors in the hypothalamus
detect increased blood osmolality and
relay a signal to the posterior pituitary
gland to secrete more ADH. ADH then
travels to the ADH receptors in the
collecting ducts of nephrons and
cause the water channels to open
allowing more water to be reabsorbed
out of the filtrate and into the blood
stream to decrease blood osmolality.
Decerased Blood Osmolarity
Osmoreceptors in the hypothalamus detect
decreased blood osmolarity and relay a
signal to the posterior pituitary gland to
stop secreting ADH. This is part of a
negative feedback loop. The water channels
in the collecting ducts remain closed and
more water is excreted in the urine,
increasing blood osmolality.
Body Fluid Volume
Extracellular fluid volume is largely
influenced by sodium, the main
extracellular ion. An increase in sodium will
usually lead to an increase in body fluid
volume and inversely, a decrease in sodium
will usually lead to a decrease in body fluid
volume. Body fluid volume and sodium
levels are regulated by ADH and
Aldosterone
Increased Body Water
Urine output is increased in order to
prevent fluid overload in the body,
for example, in the case of increased
or excessive fluid ingestion. Less
water is reabsorbed from the loop of
henle into the medulla and water
channels remain closed in the
collecting duct. A less concentrated
urine with lower specific gravity is
produced since generally, the total
amount of solutes excreted is less
variable. The maximum urine output
that can be produced is 23000mL
Decreased Body Water
Urine output is decreased when the body
is lacking water, such as with decreased
intake or excessive losses through
vomiting, diarrhea, or sweating. ADH acts
on the ADH receptors in the collecting
ducts and water channels open allowing
more water to be reabsorbed from the
filtrate into the bloodstream. More water
is also reabsorbed from the loop of Henle
. A more concentrated urine with higher
specific gravity is produced in order to
still eliminate the required solutes and
waste products. The least amount of
urine that can be produced daily in order
to still eliminate the necessary waste is
approximately 300mL
Electrolyte Balance
Phosphate
Phosphate levels are linked to calcium
levels. Phosphate and calcium are freely
filtered at the glomerulus. Phosphate is a
significant part of the buffering system
which maintains the pH balance of the
blood. Inorganic phosphate may exist as
either an acid-phosphate (H2PO4-) or an
alkaline phosphate (HPO4-)
Increased Serum Phosphate
When plasma phosphate levels rise
above 1 mmol/L, some phosphate
remains in the filtrate to be excreted in
urine.
An increase in PTH also promotes the
excretion of phosphate in exchange for
retained calcium
Decreased Serum Phosphate
When serum phosphate is below 1
mmol/L, all phosphate that enters the
filtrate is reabsorbed in the proximal
convoluted tubule.
Calcium
Calcium levels are related to both
phosphate levels and magnesium levels.
Decreased Serum Calcium
Calcium-sensing cells in the parat
The Kidneys' Role in
Homeostasis
Acid Base Balance
Decreased Body pH (more acidic)
Reabsorption of Bicarbonate happens
mainly in the Proximal Convoluted Tubule
(90%), and partially in the Distal
Convoluted Tubule (10%) through a
process called "Bicarbonate Trapping."
The body uses carbonic anhydrase
produced by the brush border of the
convoluted tubules as a catalyst to break
down Bicarbonate into CO2 and H2O.
The CO2 is then diffused into tubular
cells where it rejoins with H2O to form
bicarbonate that is then released into the
blood circulation.
Excess hydrogen ions are secreted into the
proximal and distal tubules and excreted in
urine to prevent the body from becoming
too acidic, (pH too low) for example, after
ingestion of a high protein meal
Increased Body pH (moer acidic)
Bicarbonate is freely filtered in the
glomerulus and excreted in urine when
plasma bicarbonate concentration is
elevated, thus preventing from the body
from becoming too basic (pH too high)
Blood Pressure
Changes in blood pressure are directly
related to changes in blood volume which
is controlled by a hormonal cascade known
as the Renin- Angiotensin- Aldosterone-
System, or RAAS. Cells located in the distal
tubule called macula densa cells, along with
renin-releasing cells in the arterioles of the
glomerulus make up what's known as the
juxtaglomerular apparatus (JGA). The JGA
detects increases and decreases to the
amount of blood flow to the glomerulus, or
the GFR. Changes in blood pressure
typically directly affect the GFR
Decreased Blood Pressure
Cells in the JGA sense a decrease in the
GFR in the glomerulus and stimulate the
renin-releasing cells to release renin, thus
initiating the RAAS.
Renin stimulates the release of
angiotensinogen which stimulates the
release of angiotensin I which is activated
by ACE and converted to angiotensin II.
Angiotensin II causes vasoconstriction of
the efferent arteriole of the glomerulus,
increasing GFR, as well as peripheral
vasoconstriction, raising systemic BP by
decreasing the space within the blood
vessels which exerts more pressure.
Angiotensin II also stimulates the release of
aldosterone from the adrenal cortex.
Aldosterone promotes the reabsorption of
both sodium and water from the distal
tubule, thus increasing blood volume and
blood pressure. This is done by exchanging
potassium or hydrogen for sodium
Increased Blood Pressure
Cells in the JGA sense increased GFR and
send a negative feedback signal to the
stop the release of renin, thus halting the
RAAS system which leads to increased
blood pressure. The excretion of sodium
and water is permitted freely to decrease
blood volume, and no vasoconstriction
occurs.
Body Fluid Osmolarity
Antidiuretic Horomone (ADH) is directly
influenced by blood osmolality.
Increased Blood Osmolarity
Osmoreceptors in the hypothalamus
detect increased blood osmolality and
relay a signal to the posterior pituitary
gland to secrete more ADH. ADH then
travels to the ADH receptors in the
collecting ducts of nephrons and
cause the water channels to open
allowing more water to be reabsorbed
out of the filtrate and into the blood
stream to decrease blood osmolality.
Decerased Blood Osmolarity
Osmoreceptors in the hypothalamus detect
decreased blood osmolarity and relay a
signal to the posterior pituitary gland to
stop secreting ADH. This is part of a
negative feedback loop. The water channels
in the collecting ducts remain closed and
more water is excreted in the urine,
increasing blood osmolality.
Body Fluid Volume
Extracellular fluid volume is largely
influenced by sodium, the main
extracellular ion. An increase in sodium will
usually lead to an increase in body fluid
volume and inversely, a decrease in sodium
will usually lead to a decrease in body fluid
volume. Body fluid volume and sodium
levels are regulated by ADH and
Aldosterone
Increased Body Water
Urine output is increased in order to
prevent fluid overload in the body,
for example, in the case of increased
or excessive fluid ingestion. Less
water is reabsorbed from the loop of
henle into the medulla and water
channels remain closed in the
collecting duct. A less concentrated
urine with lower specific gravity is
produced since generally, the total
amount of solutes excreted is less
variable. The maximum urine output
that can be produced is 23000mL
Decreased Body Water
Urine output is decreased when the body
is lacking water, such as with decreased
intake or excessive losses through
vomiting, diarrhea, or sweating. ADH acts
on the ADH receptors in the collecting
ducts and water channels open allowing
more water to be reabsorbed from the
filtrate into the bloodstream. More water
is also reabsorbed from the loop of Henle
. A more concentrated urine with higher
specific gravity is produced in order to
still eliminate the required solutes and
waste products. The least amount of
urine that can be produced daily in order
to still eliminate the necessary waste is
approximately 300mL
Electrolyte Balance
Phosphate
Phosphate levels are linked to calcium
levels. Phosphate and calcium are freely
filtered at the glomerulus. Phosphate is a
significant part of the buffering system
which maintains the pH balance of the
blood. Inorganic phosphate may exist as
either an acid-phosphate (H2PO4-) or an
alkaline phosphate (HPO4-)
Increased Serum Phosphate
When plasma phosphate levels rise
above 1 mmol/L, some phosphate
remains in the filtrate to be excreted in
urine.
An increase in PTH also promotes the
excretion of phosphate in exchange for
retained calcium
Decreased Serum Phosphate
When serum phosphate is below 1
mmol/L, all phosphate that enters the
filtrate is reabsorbed in the proximal
convoluted tubule.
Calcium
Calcium levels are related to both
phosphate levels and magnesium levels.
Decreased Serum Calcium
Calcium-sensing cells in the parat