THE URINARY SYSTEM

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THE URINARY SYSTEM

• Excretion
• Introduction to the urinary system
• External anatomy of the kidney
• Internal anatomy of the kidney
• Nephron
• Endothelial-capsular membrane
• Renal tubule histology
• Renal blood supply and nerve supply
• Juxtaglomerular apparatus
• Basic functions of the nephron
• Three processes in urine formation
• Glomerular filtration
• Net filtration pressure (NFP)
• Glomerular filtration rate (GFR)
• Renal autoregulation
• Hormonal regulation RAA system
• Tubular reabsorption of solutes
• Tubular reabsorption of water
• Negative feedback control of ADH

• Summary of nephron functions
• Urine drainage from the kidneys
• Urinary bladder
• Urethra
• Micturition reflex

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EXCRETION
What is excretion? How is it different from
secretion? Why do we need a urinary system?
protein catabolism yields toxic nitrogenous wastes
-NH2 groups converted to ammonia ?
urea creatinine and uric acid also formed
water and essential ions tend to accumulate
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INTRO TO THE URINARY SYSTEM
The urinary system consists of
kidneys (2) ureters (2) urinary bladder urethra
General functions of the kidneys
regulate blood volume and composition regulate
blood pressure renin regulate RBC numbers with
erythropoietin synthesize vitamin D (calcitriol)
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EXTERNAL ANATOMY OF THE KIDNEY
Location
liver
spleen
adrenal gland
posterior body wall at T12 L3 retroperitoneal
10th rib
right kidney
left kidney
Gross appearance Hilus Coverings
ureters
aorta
urinary bladder
pubic symphysis
left kidney
renal fascia adipose capsule renal capsule
adipose capsule
renal fascia
parietal peritoneum
peritoneal cavity
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INTERNAL ANATOMY OF THE KIDNEY
Renal cortex
cortex
renal columns nephrons
minor calyces
renal columns
Renal medulla
major calyx
renal pyramids renal papillae
Renal sinus
Renal pelvis
minor calyces major calyx
ureter
renal pyramids
renal papillae
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NEPHRON
Functional unit of kidneys
filtration reabsorption secretion
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ENDOTHELIAL-CAPSULAR MEMBRANE
Bowmans capsule
capsular space
proximal tubule
afferent arteriole
parietal layer
parietal and visceral layers capsular space
visceral layer
distal tubule
Endothelial-capsular membrane
fenestrated endothelium (restricted formed
elements) fused basement membranes
(restricts plasma proteins) visceral layer
podocytes
efferent arteriole
podocyte cell body
pedicels and filtration slits
pedicels filtration slits
glomerular capillary with fenestra
capsular space
filtration slit
glomerulus with visceral layer
podocyte
pedicel
basement membrane
capsular space
glomerular capillary
parietal layer
fenestra
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RENAL TUBULE HISTOLOGY
Proximal tubule simple cuboidal brush
border Loop of Henle simple squamous Distal
tubule simple cuboidal basal
foldings Collecting ducts simple cuboidal
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RENAL BLOOD SUPPLY and NERVE SUPPLY
25 of cardiac output via aorta ? renal
arteries ?
interlobular artery
arcuate arteries
segmental artery
segmental arteries ? interlobular arteries
? arcuate arteries ? afferent arteriole
? glomerular capillaries ? efferent arteriole ?
peritubular capillaries and vasa recta
capillaries ? ultimately the renal veins
? inferior vena cava
renal artery
renal vein
glomerulus
peritubular capillaries
efferent arteriole
afferent arteriole
arcuate artery
interlobular artery
Nerve supply sympathetic fibers
vasa recta capillaries
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JUXTAGLOMERULAR APPARATUS
Location
juxtaglomerular apparatus
junction of distal tubule and afferent
arteriole
distal convoluted tubule
glomerulus
Macula densa cells
afferent arteriole
special cells of the distal tubule measure
tubular flow rate and NaCl in filtrate
secretes paracrine message
Juxtaglomerular cells
special cells of afferent arteriole respond to
paracrine message by causing vasoconstriction
macula densa cells
efferent arteriole
juxtaglomerular cells
distal convoluted tubule
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BASIC FUNCTIONS OF THE NEPHRON
Control blood concentration and volume Regulate
blood pH Remove toxic wastes from the blood
So what do nephrons accomplish?
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GLOMERULAR FILTRATION
What is the principle of filtration? Endothelial-c
apsular membrane Blood hydrostatic pressure is
the driving force Filtrate all blood components
except
formed elements plasma proteins
Filtrate 180 Liters/day
urine 1 2 Liters/day filtrate reabsorbed
178 179 Liters/day
Renal corpuscle adaptations that enhance
filtration
glomerular capillaries are long endothelial-capsul
ar membrane is porous glomerular blood
hydrostatic pressure is higher than normal
blood pressure
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NET FILTRATION PRESSURE (NFP)
NFP GBHP (CHP BCOP) 60 (1832) 10
mmHg
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GLOMERULAR FILTRATION RATE (GFR)
GFR 125 ml filtrate produced every minute GFR
is directly related to the NFP Homeostasis
requires a relatively constant GFR
if GFR is too high, then what do you want to
happen if GFR is too low, then what do you want
to happen?
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RENAL AUTOREGULATION
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HORMONAL REGULATION -- RAA SYSTEM
RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM
decreased blood pressure
renin secretion by juxtaglomerular cells
converted to
angiotensinogen
angiotensin I
angiotensin converting enzyme (ACE) in lungs
angiotensin II
increased aldosterone secretion
increased vasoconstriction of arterioles
increased ADH secretion
hypothalamus
increased vascular resistance
increased Na reabsorption
increased thirst and drinking
increased water reabsorption
increased water reabsorption
increased blood pressure
increased blood volume
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TUBULAR REABSORPTION OF SOLUTES
Tubular maximum (Tm) Active transport
peritubular capillary blood
tissue fluid
tubule epithelial cells
tubular filtrate
glucose
glucose
glucose
receptors (carriers) glucose and amino acids
(100 of the time) Na and Mg (aldosterone
controlled) Ca (PTH and CT controlled)
ATP
Na
Na
Na
exchange
K
ATP
amino acids
amino acids
Na
Na
Na
exchange
H
H
PTH
Ca
Ca
Ca
CT
Ca
Ca
Passive transport
diffusion or electrochemical Cl-, HPO4--
water following by osmosis
anions following by electrochemical gradient
urine
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TUBULAR REABSORPTION OF WATER
Obligatory reabsorption (90)
indirect control of water osmosis related to
solutes Na has major effects (aldosterone)
Facultative reabsorption (10)
direct control of water antidiuretic hormone
(ADH) aquaporins
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NEGATIVE FEEDBACK CONTROL OF ADH
CONTROLLED CONDITION
Blood osmotic pressure (decreased water
concentration) is increased in response to some
stressor
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COUNTERCURRENT MULTIPLIER AND EXCHANGER
Loop of Henle function Concentrates urine by
removing water
ECF osmolarity 300 mOsM 600 mOsM 900
mOsM 1200 mOsM
More salt continually added to ECF by PCT
The more salt pumped out, the greater the
osmolarity of the ECF in the medulla
Na
As ECF osmolarity rises, more water leaves
descending loop of Henle
K
H2O
Salt pumped out of ascending loop ascending
limb impermeable to water
H2O
Cl-
As water leaves filtrate, filtrate becomes more
concentrated
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TUBULAR SECRETION
Tubule cells extract from blood and secretes into
filtrate Serves two purposes
waste removal urea, uric acid, bile acids,
ammonia, creatinine acid-base balance hydrogen
ions or bicarbonate ions
If H secretion HCO3- filtration, then no
change in ECF pH If H secretion gt HCO3-
filtration, then ECF pH increases (more H in
urine) If H secretion lt HCO3- filtration, then
ECF pH decreases (less H in urine)
RENAL CLEARANCE
Volume of blood plasma from which a particular
waste is completely removed (cleared) in one
minute.
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SUMMARY OF NEPHRON FUNCTIONS
PROXIMAL TUBULE Reabsorbs water (osmosis)
sodium (active transport potassium
(active transport) glucose (active
transport) amino acids (active transport)
chloride (simple diffusion) bicarbonate
(simple diffusion) urea (simple
diffusion) Secretes hydrogen
ammonium urea creatinine
RENAL CORPUSCLE Filtration 125 ml/min Filtrate
includes all solutes in plasma except plasma
proteins Controlled by autoregulation,
angiotensin II, sympathetic neurons
DISTAL TUBULE Reabsorbs water (osmosis)
sodium (active transport chloride (active
transport) Secretes potassium
COLLECTING DUCT Reabsorbs bicarbonate
urea Secretes hydrogen
LOOP OF HENLE Reabsorbs water (osmosis)
sodium (active transport potassium (active
transport) chloride (active
transport) Secretes urea
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URINE DRAINAGE FROM THE KIDNEYS
Papillary ducts ? Minor calyces ? Major calyces
? Renal sinus ? Ureter ? Urinary bladder
papillary duct
minor calyx
major calyx
renal sinus
ureter
ureters
ureters
urinary bladder
pubic symphysis
ureteral openings into bladder
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URINARY BLADDER
Location Anatomy Trigone Histology
ureters
ureteral openings into bladder
urethral opening
transitional epithelium detrusor muscle ureteral
sphincters
urinary bladder
MALE
FEMALE
pubic symphysis
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URETHRA
Anatomy Location Sphincters
FEMALE
uterus
urinary bladder
rectum
pubic symphysis
internal (involuntary) external (voluntary)
pelvic diaphragm
clitoris
Female Male
urethra
vaginal introitus
prostatic membranous penile
ureter
urinary bladder
rectum
pubic symphysis
prostate gland
coccyx
prostatic urethra
penis
pelvic diaphragm
membranous urethra
penile urethra
MALE
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MICTURITION REFLEX (in the adult)
Stretch of urinary bladder (about ½ full)
stimulates stretch receptors in bladder
wall Sensory input to sacral parasympathetic
area, causing
efferent parasympathetics cause contraction of
detrusor muscle and relaxation of internal
urethral sphincter sensory input to the pons
for voluntary control
If it is an inappropriate time, pons returns
inhibitory signals to sacral spinal cord so
that the external urethral sphincter
remains contracted.
If it is an appropriate time, pons returns
excitatory signals to sacral spinal cord so
that the external urethral sphincter
relaxes, and urine is voided.
In the infant, relaxation of the external
sphincter is linked to relaxation of the
internal sphincter.
end