Urinary System
Consists of:
•
•
•
•
Kidney(s)
Ureters
Urinary Bladder
Urethra
Functions:
• Filter gallons of fluid
from bloodstream
– Filter plasma 60
times/day
• Responsible for
removing:
– Toxins
– Metabolic Wastes
– Excess ions
• Regulates volume and
chemical make up of
blood
• Maintains the proper
pH between water,
salts, acids and bases
– Maintains blood pH
between 7.35 – 7.45
Functions
• Regulatory functions
include:
– Produce hormones Renin
and erthropoietin
– Renin helps regulate BP
and kidney function
– Erthropoietin stimulates
RBC production in bone
marrow
– Assists in metabolizing
Vitamin D to its active
form.
Kidney Anatomy
• Kidneys are covered by
fatty tissue; anchors
kidneys to posterior
wall
• Internal Anatomy – 3
distinct regions
– Pelvis – where kidneys
join ureters; responsible
for collecting urine
– Renal Cortex – outer
region; most of
nephrons are found here
– Medulla – Middle
region; Renal pyramids
Medulla
• Nephron – Working Unit of Kidney; Carry out processes
that form urine
Nephron
• Glomerulus – tuft of
capillaries
• Parts of Nephron
–
–
Bowman’s capsule
Renal Tubule - 3 cm in
length
•
•
•
–
Proximal Convoluted tubule
(PCT)
Loop of Henle
Distal Convoluted tubule
(DCT)
Collecting Duct
Urine Formation
Involves 3 processes
• Filtration
glomerulus and
Bowman’s capsule
• Renal
Reabsorption
Carried out by
renal tubules
• Secretion
Carried out by
renal tubules
• Glomerular Filtration
– Blood enters via afferent
arteriole (larger
diameter) and leaves via
the efferent arteriole
– Difference in vessel
diameter increases BP in
glomerulus and assists
with filtration
• Podocytes (Bowman’s
capsule) – surround
capillaries
• Passive, nonselective
process where fluids
and solutes are passed
through a membrane
• Force is cause by
hydrostatic pressure
– What caused pressure
increase?
• GFR (Glomerular
filtration rate) is the
amount of filtrate
produced in the kidneys
in one minute.
• Renin regulates GFR by
causing an increase in
blood volume and
blood pressure
(Constricts blood
vessels)
• Filtration Pressure –
Increase in BP at
glomerulus forces water
and solutes out of
blood and into capsule.
• What passes through?
What remains in the blood?
Filtrate is not Urine
• Filtrate contains both
wastes and needed
water and solutes
• Reabsorption begins as
soon as nutrients enters
the PCT
• All water can’t be
excreted, so tubules
claim what it needs
• Why is it called
reabsorption and not
absorption?
What is reabsorbed?
• 100 % of organic nutrients
• Most electrolytes by
facilitated diffusion
• Water is passively
reabsorbed
– 60 – 70 % of fluid is reaborbed
by PCT
Rate and degree of
reabsorption is regulated by
hormones
Problems: Hyperglycemia
Where does Reabsorption occur in the nephron?
• PCT are most active
reabsorbers
• The descending loop of
Henle is permeable to
water but not solutes
• The ascending loop of
Henle is impermeable
to water and most
solutes
– Na and Cl are actively
reabsorbed into the
blood stream
• DCT is impermeable to
solutes
• Reabsorption of Na, K,
and water is controlled
by hormones
Na+ (65%)
Glucose
Amino acids
H2O (65%) and
many ions (e.g.
Cl– and K+)
Milliosmols
Cortex
(d)
(a)
300
(e)
Outer
medulla
(b)
(c)
600
Some
drugs
–
H+, HCO3
NH4+
Inner
medulla
Blood pH regulation
1200
(a) Proximal convoluted tubule:
• 65% of filtrate volume reabsorbed
• Na+, glucose, amino acids, and other nutrients actively
transported; H2O and many ions follow passively
• H+ and NH4+ secretion and HCO3– reabsorption to
maintain blood pH
• Some drugs are secreted
Active transport
(primary or
secondary)
Passive transport
Figure 25.18a
Reabsorption
(b) The descending loop of
Henle
• Freely permeable to H2O
• Not permeable to NaCl or
other solutes
• Filtrate becomes
increasingly concentrated
as H20 leaves by
____________?
Active transport
(primary or
secondary)
Passive transport
Milliosmols
Na+
Cl–
K+
Cortex
(d)
(a)
300
(e)
Outer
medulla
Urea
Na+
Cl–
(c) Ascending limb of loop of Henle
• Impermeable to H2O
• Permeable to NaCl
• Filtrate becomes
increasingly dilute as salt is
reabsorbed
(b)
(c)
600
Inner
medulla
1200
Active transport
(primary or
secondary)
Passive transport
Figure 25.18c
Osmolality
of interstitial
fluid
(mOsm)
Active transport
Passive transport
Water impermeable
Filtrate entering the
loop of Henle is
contains many
substances that
are needed in the
body
The descending limb:
• Permeable to H2O
• Impermeable to NaCl
As filtrate flows, it
becomes increasingly
concentrated as H2O
leaves the tubule by
osmosis. The filtrate
osmolality increases.
H2O
NaCI
H2O
NaCI
H2O
NaCI
H2O
NaCI
Cortex
Outer
medulla
H2O
NaCI
H2O
H2O
Inner
medulla
Loop of Henle
The ascending limb:
• Impermeable to H2O
• Permeable to NaCl
Filtrate becomes increasingly dilute as NaCl leaves, eventually becoming
hypo-osmotic to blood . NaCl leaving the ascending limb increases the
osmolality of blood.
Figure 25.16a
What’s left in the nephron?
• Non-reabsorbed
substances are:
– Urea – 50 % is reclaimed;
the rest is waste
– Creatinine – a large lipid;
insoluble molecule that
is not reabsorbed at all
– Uric Acid – 50 % is
reclaimed; waste
product of RNA synthesis
Tubular Secretion – “Reabsorption in Reverse”
• Urine is formed from
filtered and secreted
substances
• Secretion occurs in the
DCT tubules and
collecting ducts
– Hormones assist with
this process
• ADH (antidiuretic
hormone)
• Aldosterone
• ANP
Na+; aldosterone-regulated
Ca2+; PTH-regulated
Cl–; follows Na+
Milliosmols
Cortex
(d)
(a)
300
(e)
Outer
medulla
(b)
(c)
600
Inner
medulla
(d) Distal convoluted tubule
• Na+ reabsorption regulated by
aldosterone
• Ca2+ reabsortion regulated by
parathyroid hormone (PTH)
• Cl– cotransported with Na+
1200
Active transport
(primary or
secondary)
Passive transport
Figure 25.18d
Milliosmols
Cortex
H2O regulated
by ADH
(d)
(a)
300
Regulated by
aldosterone:
Na+
K+
Blood pH
regulation
H+
Urea;
increased
by ADH
(e)
Outer
medulla
(c)
600
HCO3–
NH4+
(b)
Inner
medulla
1200
(e) Collecting duct
• H2O reabsorption regulated by ADH
• Na+ reabsorption and K+ secretion regulated by aldosterone
• H+ and HCO3– reabsorption or secretion
Active transport
to maintain blood pH
(primary or secondary)
Passive transport
• Urea reabsorption increased by ADH Why?
Figure 25.18e
Substances that are not reabsorbed
• Substances that lack
carry proteins along
membrane
– Urea
– Uric acid
• Substances that are not
lipid soluble
• Substances that are too
large to pass
– Creatinine
Label the parts of the nephron
Describe what is occurring at
sections 1-6.
1.
2.
3.
4.
5.
6.
Hormonal Control of Secretion
• Osmolarity – number of
solute particles
dissolved in one liter of
water
Affects osmosis
• Kidneys are responsible
for regulating solute
concentrations in the
body; the concentration
of urine is regulated by
hormones
• Four Hormones Control
Kidney Function
– Renin
– Aldosterone
– Atrial Natiuretic
Peptide (ANP)
– Antidiuretic hormone
(ADH)
Renin
• Released when
glomerular pressure is
low
• Causes blood vessels to
constrict; raising blood
pressure in arteries
• The efferent arteriole
constricts which
increases glomerular
pressure
• Stimulates secretion of
ADH and aldosterone
Aldosterone
• Released by adrenal
glands
• When secreted causes
Na+ to be reabsorbed
from DCT
• H20 follow Na+, so both
Na+ and H2O are
reabsorbed
• Eliminates K+ into urine
• Stimuli that cause the
release of aldosterone
– Decreased blood volume
– Decreased sodium in
blood
– Increased potassium in
blood (heart block)
If too much aldosterone is secreted:
- Excessive Na+ and H20 retention (edema, hypertension
- Accelerated secretion of K ions (muscle responsiveness)
Lasix – (Diuretic) inhibits Na from being
reabsorbed; thus water is not reabsorbed.
Atrial Natiuretic Peptide (ANP)
• Works against
aldosterone
• Released by atrial
cardiac cells when
blood volume and BP
are too high.
• Why would the atrial
cells detect a change
in blood volume?
• When ANP is secreted:
– Causes Na+ to be dumped
into tubules (urine)
– H2O follows sodium into
urine
– Capillaries in glomerulus
dilate; increasing blood flow
to Bowman’s capsule;
increasing UO
– Inhibits the secretion of
renin, aldosterone and ADH
– Urine contains more Na+
H2O; blood pressure and
blood volume decrease
ADH (Antiduretic hormone)
• When ADH is secreted,
water is reabsorbed
from DCT and collecting
tubules
• Person feels thirsty
• When ADH is not
secreted, DCT and
collecting tubules are
impermeable to water,
no reabsorption occurs
here.
Concentration of Urine is controlled by ADH
• Dilute Urine
– Na and other ions
are removed from
filtrate
– Urine appears clear
in color
• Concentrated Urine
– ADH is secreted; distal
and collecting tubules
reabsorb water
– When water leaves
filtrate; urine
concentration
increases
Work of the Nephron with Hormone Secretion
Diuretics – chemicals which increase UO
• Any substance that is
not reabsorbed and
carrries water out of
body
– Alcohol – inhibits ADH
– Caffeine – Increases
filtration rate (GFR)
• Diuretic drugs are taken
for CHF, edema and to
increase UO
Active transport
Passive transport
Collecting duct
Descending limb
of loop of Henle
DCT
Cortex
NaCI
H2O
NaCI
Outer
medulla
NaCI
H2O
Urea
Inner
medulla
(a) Absence of ADH
Large volume
of dilute urine
Figure 25.17a
Maintaining a Balance
• Fluid and Electrolyte
• Other Systems assist in Balance
excretion and affect
– Water into body = Water out
kidney function
of the body
– Integumentary
– Respiratory
– Digestive
– Neither a net gain or loss of
electrolytes should occur in
body
• Acid-Base Balance
– Blood pH ranges between
7.35 – 7.45
– Kidneys will secrete H+ ions
when blood pH drops
• Acidosis – Blood pH drops
below 7.35
– Respiratory Acidosis
• Due to an increase of CO2
levels in body
– Metabolic Acidosis
• Due to cell metabolism in the
body
• Lactic acid in muscle
metabolism
• Ketone bodies by the
breakdown of fat
• Diabetics don’t use glucose
due to lack of insulin; so cells
will break down fat instead
Blood ph < 7.05 disrupts the stability of cell membrane, alters protein function (enzyme),
causes heart arrhythmias and leads to coma
Kidney Stones
• Hardened mineral
deposits that form in
kidney
• Symptoms
–
–
–
–
–
Blood in urine
Increased need to go
Nausea and vomiting
Pain during urination
Tenderness in abdomen
and kidney region
• Treatment
– Lithotripsy
– Medication
Renal Failure – Kidney Failure
• Nephrons in kidney stop
functioning
– Unable to filter or
excrete waste
– Can’t regulate
composition of body
fluids
– Can’t control
erythrocyte function
or blood pressure
– Can’t control salt
balance