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Chapter 26
The Urinary System
Three major functions:
excretion:
removal of organic wastes from
body fluids
elimination:
discharge of waste products into
the environment
regulate blood plasma:
volume and
solute concentration
Major organs
kidneys (2)
produce urine
water, soluble compounds
urinary tract:
ureters (2)
kidney to urinary bladder
urinary bladder (1)
temporary storage of urine
urethra (1)
urinary bladder to exterior
Other important functions:
regulate blood volume and pressure
regulate [ions] in blood
Na+, K+, Cl-, etc.,
stabilize blood pH
conserve nutrients
while getting rid of wastes
detoxify compounds
kidney location
fig. 26-2
fig. 26-2a
The Kidneys
location
on either side of vertebral column
around T12 to L3
capped by adrenal gland
retroperitoneal
supported by CT
surrounded by adipose (cushioning)
to here 4/4/07
lec# 35
The Kidneys
anatomy:
hilum
indentation
entry/exit
ureters
renal artery, vein, nerves
fig. 26-4a
The Kidneys
anatomy:
renal cortex
renal medulla
renal pyramids
minor calyx
major calyx
renal pelvis
nephrons
tubular
functional
numerous
vascular
The Kidneys
blood supply
20-25% of cardiac output
renal artery
segmental artery
interlobar artery
arcuate artery
kidney vasculature
fig. 26-5a
fig. 26-5a
The Kidneys
blood supply
coming off of arcuate arteries
interlobular arteries
afferent arteriole
glomerulus
efferent arteriole
peritubular capillary
interlobular veins
arcuate veins
fig. 26-5a
The nephron overview
renal
corpuscle
renal
tubule
renal
tubule
fig 26-6
renal
corpuscle
The nephron: parts
Bowman’s
capsule
loop of
Henle
distal
convoluted
tubule
fig. 26-6a
Bowman’s
capsule
dct
pct
loop of Henle
proximal
convoluted
tubule
fig. 26-9
The nephron: blood supply
efferent
arteriole
glomerulus
(capillary bed)
afferent
arteriole
fig. 26-6a
?
The nephron: blood supply
peritubular
capillaries
efferent
arteriole
glomerulus
(capillary bed)
afferent
arteriole
fig. 26-6a
The nephron: Bowman’s capsule
hollow structure
two layers
visceral (inner)
parietal (outer)
surrounds glomerulus
fig 26-6a
The nephron: Bowman’s capsule
fig. 26-8
What is between blood and space?
podocytes and filtration slits
lamina densa (connective tissue)
fenestrated endothelium (capillary)
pedicel
pedicel
podocyte 1
filtration slits
podocyte 2
The nephron: Bowman’s capsule
fig. 26-8
endothelium
lamina densa
filtration slits
blood
capsular space
= filtration
membrane
fig. 26-10
blood
pressure
forces water
and small
solutes
across
“membrane”
into
Bowman’s
capsule
fig. 26-10
wastes
but also
water
glucose
amino acids
vitamins
fatty acids
etc.
= glomular
filtrate
fig. 26-10
but not:
cells
large plasma
proteins
fig. 26-10
The nephron: proximal convoluted tubule
proximal
convoluted
tubule
fig. 26-6a
pct
The nephron: proximal convoluted tubule
cuboidal cells
microvilli
reabsorption
remove water, nutrients etc., from the
glomerular filtrate and release them into
the peritubular fluid
loop of
Henle
fig. 26-6a
loop of Henle
The nephron: loop of Henle
The nephron: loop of Henle
descending limb
thick pumps Na+ Cl- out of fluid
thin
permeable to H2O
ascending limb
thin
thick
The nephron:
distal convoluted tubule
dct
distal
convoluted
tubule
fig. 26-6a
The nephron: distal convoluted tubule
active secretion (ions, acids, drugs)
selective reabsorption of Na+ and Ca2+
selective reabsorption of H2O
The nephron: distal convoluted tubule
also part of the jg apparatus (JGA)
(juxtaglomerular)
macula densa (DCT)
juxtaglomerular cells (afferent arteriole)
secrete EPO, renin
juxtaglomerular apparatus
The collecting system
DCT
collecting duct
papillary duct
minor calyx
…
100 keys (pg. 959)
“The kidneys remove waste products from
the blood; they also assist in the
regulation of blood volume and blood
pressure, ion levels, and blood pH.
Nephrons are the primary functional units
of the kidneys.”
Renal Physiology
what is the kidney doing
how does it accomplish these tasks
Goal
regulate volume and
composition of the blood
involves excretion of wastes
Renal Physiology
three major organic wastes
urea
21g / day
from amino acid breakdown
creatinine
1.8 g / day
from CP breakdown
uric acid
480 mg / day
recycling RNA N-bases
Renal Physiology
three major organic wastes
can be eliminated only when
dissolved in urine (H2O loss)
production of hyperosmotic urine
restrict excessive H2O loss
reabsorb useful molecules
Renal Physiology: steps
1.
filtration
blood pressure forcing water
and small solutes (good and
bad) from capillaries into
capsular space
Renal Physiology: steps
2.
reabsorption
remove water and many solutes
from filtrate by:
diffusion, osmosis
channel-mediated diffusion
carrier-mediated transport
Renal Physiology: steps
2.
reabsorption
many different proteins involved
a cell may have many functions
differential distribution of proteins
transport can be saturated
Renal Physiology: steps
3.
secretion
transport of solutes from body
fluids into the tubular fluid (or
filtrate)
table 26-2
to here 4/11/07
lec# 36
Filtration
filtration membrane
lets water and small
solutes through
cells and plasma
proteins stay in
capillaries
100 keys (pg. 969)
“Roughly 180 L of filtrate is produced at
the glomeruli each day, and that
represents 70 times the total plasma
volume. Almost all of that fluid volume
must be reabsorbed to avoid fatal
dehydration.”
Filtration: hydrostatic pressure
glomerular hydrostatic pressure (GHP)
push fluid out of vessels (bp)
capsular hydrostatic pressure (CsHP)
push fluid back into vessels
net hydrostatic pressure (NHP)
NHP = GHP - CsHP
35 =
50
- 15
mm Hg
Filtration: colloid pressure
blood colloid osmotic pressure (BCOP)
proteins in blood (hyperosmotic)
draw water back into blood
~ 25 mm Hg
Filtration: filtration pressure (FP)
FP = NHP - BCOP
10 = 35 - 25
mm Hg
importance of blood pressure
20% drop in blood pressure
50mm Hg to 40mm Hg
filtration would stop
Filtration: filtration rate (GFR)
glomerular filtration rate (GFR)
amount of fluid pushed into the
capsular space each minute
GFR ~ 125 ml / min
180 liters (~50 gallons)/ day
Filtration: filtration rate (GFR)
affected by filtration pressure (FP)
change FP
change GFR
significant factor in FP is…
… blood pressure
Filtration: filtration rate (GFR)
control of GFR
adequate blood flow to glomerulus
adequate filtration pressure
autoregulation
hormonal regulation
autonomic regulation
Filtration: filtration rate (GFR)
autoregulation
lower bp
afferent arteriole
glomerulus
efferent arteriole
dilate
dilate
constrict
Filtration: filtration rate (GFR)
autoregulation
higher bp
afferent arteriole
contract
less blood in
lower GHP
Filtration: filtration rate (GFR)
hormonal regulation
renin-angiotensin system
renin is released when:
drop in bp
JG cells stimulated by sym.
lower osmolarity of tubular fluid
Filtration: filtration rate (GFR)
hormonal regulation
bp
renin
angiotensin II
bp
constrict afferent art.
secretion of aldosterone
thirst
secretion of ADH
general vasoconstriction
Filtration: filtration rate (GFR)
hormonal regulation
bp
GFR
fluid loss
bp
ANP
BNP
GFR
Na+ reabsorption
urine production
fig. 26-11
Filtration: filtration rate (GFR)
autonomic (ANS) regulation
bp
sympathetic stimulation
powerful vasoconstriction
of afferent arteriole
GFR
bp
Filtration: filtration rate (GFR)
maximal physical exertion
(ie., marathon, etc.,)
blood to muscle
less blood to kidney
damage to glomerulus
proteinuria
hematuria
Renal Physiology: reabsorption/secretion
PCT reabsorbs 60-70% of filtrate
peritubular
fluid
peritubular
capillaries
Renal Physiology: reabsorption/secretion
PCT
reabsorb organic nutrients
active reabsorption of ions
reabsorption of H2O
passive reabsorption of ions
secretion
Renal Physiology: reabsorption/secretion
PCT
reabsorb organic nutrients
99% absorbed before reaching
the loop of Henle
facilitated transport
cotransport
(carrier proteins)
Renal Physiology: reabsorption/secretion
PCT
active reabsorption of ions
Na+
K+
HCO3-
active transport
(carrier proteins and ATP)
Renal Physiology: reabsorption/secretion
PCT
reabsorption of H2O
filtrate
solutes
H 2O
fig. 26-12
Renal Physiology: loop of Henle
countercurrent exchange (multiplication)
fluids moving in opposite directions
descending
limb
ascending
limb
Renal Physiology: loop of Henle
thin descending limb
permeable to H2O
impermeable to solutes
thick ascending limb
impermeable to both
contains Na+ + Cl- pumps
Renal Physiology: loop of Henle
thick ascending limb
contains Na+ + Cl- pumps
pumps ions out of the tubular filtrate
into the peritubular fluid
makes peritubular fluid hyperosmotic
ascending limb is not
permeable, but has
pumps
Na+-K+/2Cltransporter
fig 26-13
Na+-K+/2Cltransporter
fig 26-13a
Renal Physiology: loop of Henle
thick ascending limb
contains Na+ + Cl- pumps
makes peritubular fluid hyperosmotic
as thin, descending limb passes down,
H2O diffuses out making fluid more
concentrated
permeable
to H20,
not solutes
fig 26-13
which
means
there are
more ions
to pump
out
that makes tubular fluid more
concentrated
positive feedback maintains a
hyperosmotic peritubular fluid
sets up a concentration gradient
within the medulla of the kidney
papillary
duct is only
place
permeable
to urea
to here 4/13
lec # 37
Renal Physiology: distal convoluted tubule
only 15-20% of original volume of
filtrate makes it to the DCT
final adjustments are made here:
reabsorption
secretion
Renal Physiology: distal convoluted tubule
reabsorption
remove Na+ and Cl- from filtrate
aldosterone stimulates the Na+
pumps in some parts of the DCT
fig. 26-14
Renal Physiology: distal convoluted tubule
secretion
K+
sodium-potassium exchange
H+ secreted to raise blood pH
HCO3- is produced (buffer blood)
fig. 26-14c
Renal Physiology: the collecting system
reabsorption and secretion
collecting ducts gather tubular fluid
from many nephrons and transport it
toward the ureter through the
concentration gradient set up in the
medulla
Renal Physiology: the collecting system
regulation
aldosterone
activate Na+ pumps of DCT
and collecting duct
ADH
controls permeability of
collecting duct to H2O
Renal Physiology: the collecting system
reabsorption
Na+
aldosterone controlled
exchange for K+
Bicarbonate
exchange for ClUrea
usually diffuses out of lower
portion of collecting duct
Renal Physiology: the collecting system
secretion
can secrete H+ to raise pH
or
bicarbonate to lower pH
100 keys (pg. 976)
“Reabsorption involves a combination of
diffusion, osmosis, channel-mediated
diffusion, and active transport. Many of
these processes are independently
regulated by local or hormonal
mechanisms. the primary mechanism
governing water reabsorption can be
described as “water follows salt.”
Secretion is a selective, carrier-mediated
process.”
What happens to all that stuff that has
been reabsorbed and put into the
peritubular space?
taken up by the peritubular capillaries
and returned to circulation.
Control of water reabsorption
will determine:
volume of urine
osmotic concentration of urine
Control of water reabsorption
85% will occur no matter what
PCT
descending limb of loop of Henle
osmosis
Control of water reabsorption
remaining 15% is reabsorbed (or not) by
the DCT
and the collecting duct
(27 L / day)
Control of water reabsorption
DCT and the collecting duct are usually
impermeable to H2O
except in the presence of ADH
no ADH
more, dilute urine
fig. 26-15
with ADH
less, concentrated urine
Control of water reabsorption
diabetes insipdus
underproduction of ADH
not enough water reabsorbed
(too much water lost)
Control of water reabsorption
diabetes
insipdus
flow through
>10 liters of urine / day
very thirsty
tasteless
Control of water reabsorption
ANP
BNP
natriuretic peptides
oppose action of ADH
Diuretics: drugs that promote H2O loss
reduce
blood volume
blood pressure
ECF
Normal Urine
clear
sterile
yellow
odorous
no bacteria
urobilin pigment
evaporation of small molecules
ammonia etc.,
ketones ?
urinalysis
color, appearance, taste, chemical
summary
fig. 26-16
Urine transport, storage and elimination
fig. 26-7a
fig. 26-4a
Urine transport, storage and elimination
collecting duct
minor calyx
major calyx
renal pelvis
ureter
fig. 26-17
Urine transport, storage and elimination
ureter
urinary bladder
fig. 26-18c
Urine transport, storage and elimination
ureter
urinary bladder
sphincters (2)
urethra
urethral opening
Urine transport, storage and elimination
fig. 26-18
Urine transport, storage and elimination
fig. 26-18
Urine transport, storage and elimination
micturation reflex
1. stretch bladder
2. sense
3. stimulate muscle
4. relax sphincter(s)
Urine transport, storage and elimination
micturation reflex
incontinence
inabililty to voluntarily
control urination
Aging and the urinary system
1. decline in # of functional nephrons
2. reduction in GFR
(#1, reduced blood flow)
3. less responsive to ADH
4. voiding problems
loss of muscle tone
cerebral damage
bph