Urinary System
Functions
• Maintains homeostasis in blood by:
1.
Regulating :
– blood pressure by
blood volume
+, K+, & 2+
– ion
, e.g.
– blood
by maintaining concentration of H+ & HCO3-
2.
Remove nitrogenous waste from metabolism, e.g. urea,
, & creatinine
– recall: most ammonia (NH3) from amino acid
converted into less toxic urea by liver
3.
Remove other
excess vitamins
compounds, e.g. hormones &
– must conserve nutrients, e.g. water, glucose, & amino acids
• cv
renal artery
• both branch off aorta
• each artery
blood to one kidney to be
filtered
• also supplies
blood to one
kidney
renal vein
• both join with posterior vena cava
• each vein
filtered blood from one
kidney, which contains substances
reabsorbed during
formation
ureters:
• tubes that carry urine from renal pelvis to
urinary bladder
urethra:
• tube that carries urine from urinary bladder
to
of body
urinary bladder:
• muscular
sac that stores urine prior
to urination
• when sac stretches to certain point, sends
messages to
to notify need to urinate
Kidney
• organ that filters blood
to remove
wastes and regulates
of blood
plasma
• contains nephrons: functional
unit of
that forms urine
Parts of the Kidney
Cortex
•
layer of kidneys (renal =
kidneys,
= outer
layer)
Renal medulla
• inner
of kidneys
• has higher
concentration than cortex
+ and
because contains
urea
Renal pelvis
• inner
chamber of
kidneys, where urine from
collecting ducts
before entering
Urine Formation
Nephron
• Approximately one
million
per a
kidney
• Blood supply enters
the
in the
renal artery and
branches into
capillaries
• Blood is filtered as it
passes
the
capillaries where
wastes (filtrate) is
out as urine
and nutrients are kept
in the
to be used
throughout the body
Bowman’s Capsule
• Located at the “end” of
the nephron
• In the
of the
kidney
• Surrounds the
(a knot of capillaries)
Peritubular capillaries
Glomerulus - Pressure Filtration
•
•
•
•
•
blood from renal artery enters through
afferent
and exits through
efferent
efferent arteriole has smaller diameter than
afferent arteriole, which
pressure
in glomerulus
blood
forces fluids & small
dissolved
in blood through pores in
capillary walls from glomerulus into
in Bowman’s capsule
substances that:
1.
remain in capillaries:
,
,
platelets, blood proteins (e.g.
globulins),
, & certain
drugs (e.g. penicillin)
2.
enters filtrate: water, glucose, amino
acids, ions (e.g. Na+, Cl–, H+, K+, &
HCO3–), vitamins, & nitrogen waste
(e.g. uric acid, urea, & NH3)
filtrate from Bowman’s capsules enters
tubular system, where substances exchange
with blood in
capillaries
Proximal Convoluted Tubule - Tubular
(Selective) Reabsorption
•
•
In the
of the kidney
nutrients actively transported back
into blood in
capillaries, e.g. glucose & amino
acids
– NOTE: all glucose
from filtrate, but some glucose used
for active transport
•
•
•
less glucose in efferent arteriole
than afferent arteriole
Most
ions (Na+) actively
transported back into blood, which
causes
transport
–
of negative ions (Cl ) by diffusion
and water by
back into
blood
substances remaining in filtrate:
–, &
water, Na+,
nitrogenous waste
peritubular capillary
proximal convoluted tubule
Loop of Henle: Tubular Reabsorption
•
as filtrate
down descending
limb, increasing solute concentration
of renal
causes
water to diffuse out of filtrate by
osmosis, i.e.
becomes
more concentrated as water content
of filtrate decreases as it passes
through
– descending limb permeable to water,
but impermeable to ions
•
as filtrate moves up ascending limb,
Na+ actively
out of
filtrate, i.e.
becomes less
concentrated
– ascending limb impermeable to water,
which prevents water from diffusing
back into filtrate by
In renal medulla
Distal Convoluted Tubule - Tubular
Secretion
• Takes place in the renal cortex
• More Na+ actively reabsorbed
from
back into blood in
peritubular capillaries, which
causes more Cl– and water to
move out
• Hormones,
,
creatinine, & excess K+ in
blood actively transported
from
into filtrate for
excretion
• Blood
increased by
secreting excess H+ into filtrate
&
HCO3– from
filtrate
Collecting Duct - Tubular Excretion
• Takes place in the renal
medulla
• As
moves through
higher concentration
gradient in renal medulla,
water
out by
osmosis
• Some urea also diffuses out
of the
duct to
contribute to the high
solute concentration of the
inner medulla
• Urine
nephron
merges in renal pelvis
pH
• Essentially, the kidneys are
bicarbonate ions and excreting hydrogen ions
as the blood
a normal pH
– If the blood is acidic, H+ ions are excreted and
HCO3- ion are reabsorbed into blood
– If the blood is basic, H+ ions are not excreted and
HCO3- ions are not reabsorbed and are passed into
the filterate
Pathway of Urine
•
As the urine passes through the
ducts, it is drained
into the pelvis of the kidney, then
the ureters and to the
– Stretch receptors signal internal
sphincters to relax for urination
– Sphincters close the urethra until
the urge becomes necessity (at
approximately 600mL)
– voluntary (external) sphincters
can be controlled to prevent
urination until convenient
Pathway:
1. blood:
artery afferent arteriole
glomerulus efferent
peritubular capillary network renal vein
2. urine: renal pelvis in kidney ureter
urinary bladder
Regulation
Salt Regulation by Kidneys
Blood volume, pressure, & salt concentration
regulated by stimulating or inhibiting secretion
of
to control water content of
blood
Aldosterone
• Is a
that increases the blood
volume by increasing reabsorption of Na+
ions at the distal
tubule, which
increases reabsorption of water by osmosis
– i.e.
in blood
water by increasing Na+
• Produced and secreted by adrenal cortex
(outer layer of
glands, which
sits above kidney)
• Secretion controlled by juxtaglomerular
apparatus between afferent arteriole &
distal convoluted tubule in nephron, which
blood volume
• When juxtaglomerular
apparatus detects
blood flow
caused by low blood
volume, then stimulates
of enzyme
renin from kidneys that
catalyzes production of
angiotensin II from
angiotensinogen
•
II
stimulates secretion of
aldosterone from the
adrenal cortex
– NOTE: angiotensin II
also causes blood
vessels to constrict
raising blood pressure
Antidiuretic Hormone (ADH)
•
Is a hormone that increases water content of blood
by increasing permeability of distal
tubule and the collecting duct to increase
reabsorption of water by
– i.e. conserves water by increasing urine
concentration and
volume of
urine produced
– produced by
& stored/secreted by
posterior pituitary gland
– secretion controlled by hypothalamus &
on solute concentration in blood,
i.e. more water reabsorbed into blood plasma
when water
in blood decreases
– when
in hypothalamus
detect increased solute concentration in
blood, stimulates secretion of ADH from
posterior
gland
– reabsorbing more water causes increased
blood
, which increases
blood pressure &
salt
concentration
Water Regulation by Kidneys
•
The water content of the body can vary depending on various factors:
–
–
–
–
–
•
•
•
•
water intake
diarrhea
vomiting
sweating
drinking alcohol (inhibits ADH production)
This means that
the body has too little water and needs to conserve it
and sometimes too much water and needs to get rid of it.
Most of the
of water conservation takes place in the distal and collecting
tubules of the nephrons under the control of anti-diuretic hormone (ADH)
If the
contains too little water (indicating dehydration) then more ADH is
released so that the kidneys can reabsorb more water, thereby decreasing urine
volume and increasing urine concentration (urine color = dark yellow).
If the blood
too much water (indicating over-hydration) then less ADH is
released into the blood stream so that the kidneys don`t reasborb as much water,
increasing urine volume and
urine concentration (urine colour = less
yellow)
By the end of this section, you should
be able to:
• dentify and explain the
functions of each of the
following:
– kidney
– ureter
– urethra
– urinary bladder
– renal cortex
– renal medulla
– renal pelvis
– nephron
• identify and explain the
functions of the following
components of the
nephron:
– glomerulus
– Bowman’s capsule
– afferent and efferent
arterioles
– peritubular capillary network
– proximal and distal
convoluted tubules
– collecting duct
– loop of Henle
• describe the production of urine with
reference to the following terms:
– pressure filtration
– selective reabsorption
– reabsorption of water following an osmotic
gradient
– tubular excretion
– metabolic waste (e.g., nitrogenous waste, urea,
ammonia)
• describe how the kidneys maintain blood pH
• compare urea and glucose content of blood in the
renal artery with that of the renal vein
• identify the source glands for antidiuretic
hormone (ADH) and aldosterone
• describe how the hypothalamus, posterior
pituitary, ADH, and the nephron achieve
homeostasis of water levels in the blood
• describe how the adrenal cortex, aldosterone,
and the nephron achieve homeostasis of water
and sodium levels in the blood
Mandatory Vocabulary
antidiuretic hormone (ADH), adrenal cortex,
afferent and efferent arterioles, aldosterone,
ammonia, Bowman’s capsule, collecting duct,
glomerulus, glucose, homeostasis, hypothalamus,
kidney, loop of Henle, metabolic waste, nephron,
nitrogenous waste, osmotic gradient, peritubular
capillary network, pH, posterior pituitary, pressure
filtration, proximal and distal convoluted tubules,
reabsorption of water, renal artery, renal cortex,
renal medulla, renal pelvis, renal vein, selective
reabsorption, tubular excretion, urea, ureter,
urethra, urinary bladder, urine