Transcript Reading Part 4: The Urinary System

Reading
Part 4: The Urinary System
Concepts: Chapter 25
 Tortora: Chapter 26
 Coloring Book: pp146-150
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The Urinary System

Urinary system
contains:
Kidneys (2)
 Ureters (2)
 Bladder
 Urethra

The Urinary System

Most of the work in the urinary system is
done by the kidneys. They are responsible
for:

Regulating
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ionic composition of blood (Na+, K+, Ca++, Cl-,
HPO4--)
blood pH (excrete H+ & conserve HCO3-)
blood volume (via H2O)
blood pressure (via H2O & the hormone renin)
blood glucose level (by using the aa glutamine to
make glucose—called gluconeogenesis)
blood osomolarity (total # of solutes/liter)
The Urinary System
Production of hormones (calcitriol, the
active form of vit. D & erythropoietin which
stimulates RBC production)
 Excretion of wastes & foreign substances
(ammonia & urea from aa breakdown,
bilirubin from hemoglobin breakdown, uric
acid from nucleic acid breakdown, drugs &
toxins)
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The rest of the urinary system is
responsible for urine transport & storage.
The Urinary System--anatomy

Kidneys are reddish kidney-bean shaped
organs.
 Size of a bar of soap.
 Btwn peritoneum & posterior wall of
abdomen.
 At level of T12-L3 (some protection from
ribs 11-12).
 Concave side faces vertebral column.
 Blood vessels, nerve & lymph enter kidney
at renal hilum.
The Urinary System--anatomy
Smooth outer region is called renal
cortex.
 Inner region is called renal medulla.

Within medulla are regions called renal
pyramids.
 Base of pyramid faces cortex, apex (called
renal papilla) faces hilum.
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Within medulla are the functional units of
the kidney, called nephrons.
The Urinary System--anatomy

Urine formed in
nephron drains into
papillary duct, then
minor calyxmajor
calyx  renal
pelvis  ureter 
bladder  urethra
& out.
The Urinary System--anatomy
Kidneys receive 25% of cardiac output
via right & left renal arteries.
 These arteries branch several times until
they form afferent arterioles.
 Each afferent arteriole ends as a tangled
ball of capillaries called a glomerulus at
the nephron.
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The Urinary System--anatomy
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Glomerular capillaries reunite to form
efferent arterioles that carry blood out of
glomerulus.
 Efferent arterioles branch to form
peritubular capillaries which surround some
of the tubular parts of the nephron.
 Some of these vessels form long loops
called vasa recta.
 Eventually all these vessels reunite to form
renal vein.
The Urinary System--anatomy
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Each nephron has 2 parts:

Renal corpuscle
Blood plasma filtered here
 Consists of glomerulus & Bowman’s capsule
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The Urinary System--anatomy
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Renal tubule
Filtered fluid passes into here
 Consists of:
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Proximal convoluted tubule (PCT)
Loop of Henle (descending limb, thin & thick
ascending limbs)
Distal convoluted tubule (DCT)
Distal convoluted tubules from several
nephrons empty into a single collecting
duct. Many of these will unite to form
papillary ducts.
The Urinary System--anatomy
The Urinary System--physiology
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To produce urine, nephrons & collecting
ducts do 3 basic things:
1.
2.
3.
Glomerular filtration—water & most blood solutes
move across glomerular wall into Bowman’s
capsule.
Tubular reabsorption—Most water & solutes are
moved back into blood stream from the tubules.
Tubular secretion—Some materials (water, drugs,
wastes) from blood are moved back into the
tubules.
The Urinary System--physiology
The Urinary System--physiology
By filtering, reabsorbing & secreting,
nephrons help to maintain homeostasis
of blood volume & composition.
 1 million nephrons/kidney
 Filters 150-180 liters/day
 99% of that returns to bloodstream
 1-2 liters excreted as urine

The Urinary System--physiology
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The cells that line the glomerular
capillaries are “leaky.” They form a
filtration membrane.
Large solutes like large proteins & blood
cells can’t pass thru.
 Small molecules do pass thru the capillaries
& into Bowman’s capsule:
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Water, glucose, vitamins, amino acids ammonia,
urea, ions & some small proteins.
The Urinary System--physiology
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In addition to the permeability of the filtration
membrane, glomerular blood pressure plays a
role.
 The hydrostatic pressure of blood here is high
& helps to force fluids & solutes thru the
filtration membrane like pushing material thru
a sieve.
 The fluid that collects in Bowman’s capsule is
called filtrate.
 Amount of filtrate formed each minute
determines the glomerular filtration rate (GFR).
The Urinary System--physiology
The Urinary System--physiology
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Kidneys have mechanisms to adjust GFR:
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Renal autoregulation: if BP rises or falls, afferent
vessels to nephrons adjust to keep GFR constant.
Neural regulation: CNS responds to things like
exercise or hemorrhage to ↓ GFR (less urine & ↑
blood volume to tissues)
Hormonal regulation: Angiotensin II constricts
vessels to nephron when blood volume decreases.
The Urinary System--physiology
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Reabsorption is the next important task of the
nephron.
Almost everything that enters the kidney is
reabsorbed or put back into the blood stream.
Filtered fluid becomes tubular fluid once it
enters the PCT.
Composition of tubular fluid changes as it
passes thru nephron.
Fluid that drains from papillary duct at the end
is called urine.
The Urinary System--physiology
Substances can be reabsorbed via
active & passive transport or pinocytosis.
 Be reabsorbing (bringing substances
back into the blood stream) & secreting
(putting substances from the blood into
the tubular fluid) the kidney is able to
maintain constant fluid volume in your
body even though your intake can vary.
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The Urinary System--physiology
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When fluid intake is
low, kidney can
conserve water &
produce small
amounts of
concentrated urine.
 When fluid intake is
high, urine is more
dilute & in larger
quantities.
The Urinary System--physiology
The concentration of solutes in the
interstitial fluid surrounding the nephron
will determine how much water is
reabsorbed—i.e. urine concentration.
 Remember the rules for osmosis!
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The Urinary System--physiology
The Urinary System--physiology
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See AP section of website for tutorial.
Material entering Bowman’s capsule is called
filtrate.
 Filtrate = H2O, NaCl, HCO3-, H+, urea,
glucose, aa, some drugs.
 #1--PCT—this area actively transports NaCl
from filtrate. H2O will follow. These 2 things
are picked up by the blood vessels
surrounding each nephron & eventually end up
in renal vein.
 Skip to:
The Urinary System--physiology
The Urinary System--physiology
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#3--Ascending limb also actively reabsorbs
NaCl, but it’s NOT permeable to H2O. NaCl
conc. increases in the surrounding tissue.
 #2--Descending loop is NOT permeable to
NaCl, but IS permeable to H2O. High NaCl
conc. in tissue makes H2O diffuse out of
descending loop. As a result, fluid in tube gets
concentrated.
 Because a lot of solute leaves in #3, the fluid
in
The Urinary System--physiology
The Urinary System--physiology
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#4--(DCT) ends up being less concentrated
than tissue fluid. This causes more H2O to
leave the DCT osmotically. By now, urea is
the primary solute in the filtrate.
 #5--Collecting duct--This part is permeable to
H2O but nothing else. As tube descends thru
tissue w/ increasing conc., H2O is reabsorbed
via osmosis. At the end of collecting duct,
concentrated filtrate is called urine.
 The reabsorption of fluids can be affected by
hormones and drugs.
The Urinary System--physiology
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Hormonal regulation
Renin-Angiotensin-Aldosterone System
(RAAS)
 Antidiuretic Hormone (ADH)
 Atrial Natriuretic Peptide (ANP)

The Urinary System--physiology
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Renin-Angiotensin-Aldosterone System
(RAAS)
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When blood vol. & pressure decrease
(blood loss, diarrhea) walls of afferent
arterioles are not stretched as much.
Renin is released
 Renin is an enzyme that changes inactive
angiotensin I into active angiotensin II.

The Urinary System--physiology
Causes afferent arterioles to constrict (↓ GFR)
 ↑ reabsorption of Na+, Cl- & H2O in PCT.
 Stimulates adrenal gland to release the hormone
aldosterone. This causes ↑ reabsorption of Na+,
Cl-, plus secretion of K+. Result = H2O
excretion ↓’s.
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Blood volume increases.
The Urinary System--physiology
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ADH (aka vasopressin)
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When blood volume decreases
(dehydration, bleeding) pituitary gland
releases ADH.
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Causes DCT & collecting duct to be more
permeable to water.
Alcohol & caffeine inhibit ADH
The Urinary System--physiology
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ANP
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An increase in blood vol. promotes its
release.
Inhibits reabsorption of Na+ & water in PCT &
collecting duct.
 Suppresses secretion of ADH & aldosterone.
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Diuresis
The Urinary System--physiology
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Urinalysis
Looking at chemical, physical & microscopic
properties of urine can show problems in
other parts of body.
 Traces of substances not normally found in
urine can indicate metabolic problems.
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Constituent
Albumin
Glucose
RBC’s
Urobilirubin
Microbes
Abnormal amts may
indicate:
High BP or bacterial
infection
Diabetes
Kidney stones, trauma,
kidney disease
Anemia, liver disease,
mono
Bacterial infection
The Urinary System—storage &
elimination
From collecting ducts urine passes to the
calyces, renal pelvis, ureter, bladder &
urethra.
 Ureters from each kidney contract to
push urine into bladder. Gravity assists.
 Bladder is a hollow, distensible,
muscular organ.
 Micturition=release of urine from bladder.
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The Urinary System—storage &
elimination
The Urinary System—storage &
elimination
The Urinary System—storage &
elimination
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Urethra is terminal portion of urinary
system.

4 cm in females, 20 cm in males.
The End