The Urinary System

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Urinary System
Ch 25
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Function

• Remove nitrogenous wastes
• Maintain electrolyte, acid-base, and fluid
  balance of blood
• Homeostatic organ
• Acts as blood filter
• Release hormones calcitriol erythropoietin

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Kidneys as Filters

• Diuretic- lose water coffee, alcohol
• Antidiuretic- retain water ADH
• Aldosterone- sodium water reabsorption, and K
  excretion
• GFR 180 liters (50 gal) of blood/day
• 178-179 liters are reabsorbed back into blood
• Excrete a protein free filtrate

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Nephron

• consist of a long tubule a ball of capillaries
  called a glomerulus
• the end of the tubule that surrounds the
  glomerulus is called Bowmans capsule
• the remaining parts of the tubule are called the
• proximal tubule
• loop of Henle
• distal tubule
• the tubule empties into a collecting duct that
  leads to the renal pelvis
• the renal pelvis opens to the ureter

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Nephron
Each kidney contains over 1 million nephrons and
thousands of collecting ducts
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• Nephrons functions
• glomerular filtration
• tubular reabsorption
• tubular secretion

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Histology of a renal corpuscle
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Pressures that drive glomerular filtration
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The filtration membrane
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Nephron
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Composition of Glomerular Filtrate

• Water
• Small Soluble Organic Molecules
• Mineral Ions

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Bomans Capsule

• filtration occurs as blood pressure in the
  capillaries of the glomerulus forces filtrate
  into Bowmans capsule
• the process is passive (diffusion)
• the filtrate includes
• water, salts, bicarbonate (HCO3), H, urea,
  glucose, amino acids

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Proximal Convoluted Tubule
Reabsorbs water, glucose, amino acids, and
sodium.

• 65 of Na is reabsorbed
• 65 of H2O is reabsorbed
• 90 of filtered bicarbonate (HCO3-)
• 50 of Cl- and K

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Loop of Henle
Creates a gradient of increasing sodium ion
concentration towards the end of the loop within
the interstitial fluid of the renal pyramid.

• 25 Na is reabsorbed in the loop
• 15 water is reabsorbed in the loop
• 40 K is reabsorbed in the loop

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Loop of HenleDescending Limb

• is impermeable to salts but permeable to water
• as filtrate moves through the descending limb,
  water steadily moves out making the filtrate more
  more concentrated
• this occurs because the osmolarity (salt
  concentration) of the interstitial fluid in the
  renal medulla becomes increasingly greater the
  further down you go

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Loop of HenleAscending Limb

• is permeable to salts but impermeable to water
• as filtrate moves through the ascending limb,
  NaCl moves out making the filtrate more more
  dilute
• basically, the purpose of the loop of Henle is to
  keep the renal medulla region of the kidney at a
  high osmolarity so water can move passively out
  of the filtrate in the collecting duct (as well
  see shortly

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Distal Convoluted Tubule
Under the influence of the hormone aldosterone,
reabsorbs sodium and secretes potassium. Also
regulates pH by secreting hydrogen ion when pH of
the plasma is low.

• only 10 of the filtered NaCl and 20 of water
  remains

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ADH

• Antidiuretic hormone
• Produced by posterior pituitary
• Targets collecting ducts to be more permeable to
  water
• Results in more concentrated urine

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Collecting Duct
Allows for the osmotic reabsorption of water.

• the collecting duct carries the remaining
  filtrate back through the renal medulla which is
  now very high in salt (high osmolarity)
• as the filtrate passes through the collecting
  duct, water can passively move out
• how much water moves out depends on the amount of
  water needed by the body
• this is controlled by the hormone ADH

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Urine

• Water- 95
• Nitrogenous waste
• urea
• uric acid
• creatinine
• Ions
• sodium
• potassium
• sulfate
• phosphate

From the original 1800 g NaCl, only 10 g appears
in the urine
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Nitrogenous Wastes
urea
uric acid
ammonia
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Hormonal Control of Kidney Function
ADH
ANP
Renin-Aldosterone-Angiotensin
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Fig. 18.09
ADH
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Hormonal Control of Kidney Function
hypothalamus
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ANP
aldosterone
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Regulation of Aldosterone secretion by
renin-angiotensin-aldosterone (RAA) pathway
Fig. 18.16
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Hormonal Control of Kidney Function
reduced blood pressure and glomerular filtrate
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Hormonal Control of Kidney Function
renin
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Hormonal Control of Kidney Function
angiotensin II
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Urinary Bladder
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Bladder

• Mucosa (transitional epithelium)
• Muscular layer (detrusor muscle) 3 layers of
  smooth muscle
• Fibrous adventia

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Sphincter Muscles on Bladder

• Internal urethral sphincter
• Smooth muscle
• Involuntary control
• More superiorly located
• External Urethral sphincter
• Skeletal muscle
• Voluntary control
• Posteriorly located

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Diuresis (Micturition)
When bladder fills with 200 ml of urine, stretch
receptors transmit impulses to the CNS and
produce a reflex contraction of the bladder (PNS)
When is incontinence normal?
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Urinalysis
Why do doctors ask for a urine sample?       

• characteristics
• smell- ammonia-like
• pH- 4.5-8, ave 6.0
• specific gravity more than 1.0 1.001-1.030
• color- affected by what we eat salty foods,
  vitamins

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Odor
odor- normal is ammonia-like diabetes mellitus-
smells fruity or acetone like due to elevated
ketone levels diabetes insipidus-
yucky asparagus---
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pH- range 4.5-8 ave 6.0 vegetarian diet- urine
is alkaline protein rich and wheat diet- urine
is acidic
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Color
Color- pigment is urochrome Yellow color due to
metabolic breakdown of hemoglobin (by bile or
bile pigments) Beets or rhubarb- might give a
urine pink or smoky color Vitamins- vitamin C-
bright yellow Infection- cloudy
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Specific Gravity
Water s.g. 1g/liter Urine s.g. 1.001 to
1.030
Pyelonephritus- urine has high s.g. form kidney
stones Diabetes insipidus- urine has low s.g.
drinks excessive water injury or tumor in
pituitary
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Normal Constitutes of Urine
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Normal Constitutes of Urine
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Abnormal Constitutes of Urine

•  Glucose- when present in urine condition called
  glycosuria (nonpathological) glucose not
  normally found in urine
• Indicative of
• Excessive carbohydrate intake
• Stress
• Diabetes mellitus

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Abnormal Constitutes of Urine
Albumin-abnormal in urine its a very large
molecule, too large to pass through glomerular
membrane gt abnormal increase in permeability of
membrane Albuminuria- nonpathological conditions-
excessive exertion, pregnancy, overabundant
protein intake-- leads to physiologic
albuminuria Pathological condition- kidney trauma
due to blows, heavy metals, bacterial toxin
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Abnormal Constitutes of Urine
Ketone bodies- not normal in urine Ketonuria-
find during starvation, using fat
stores Ketonuria is couples w/a finding of
glycosuria-- which is usually diagnosed as
diabetes mellitus RBC-hematuria Hemoglobin- Hemogl
obinuria- due to fragmentation or hemolysis of
RBC conditions hemolytic anemia, transfusion
reaction, burns or renal disease
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Abnormal Constitutes of Urine
Bile pigments- Bilirubinuria (bile pigment in
urine)- liver pathology such as hepatitis or
cirrhosis WBC- Pyuria- urinary tract infection
indicates inflammation of urinary tract Casts-
hardened cell fragments, cylindrical, flushed out
of urinary tract WBC casts- pyelonephritus RBC
casts- glomerulonephritus Fatty casts- renal
damage
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INQUIRY

• List several functions of the kidneys.
• What does the glomerulus do?
• What are several constitutes you should not find
  in urine?
• What is specific gravity?
• What two hormones effect fluid volume and sodium
  concentration in the urine?
• Where are the pyramids located in the kidney?
• What vessel directs blood into the glomerulus?
• Where does most selective reabsorption occur in
  the nephron?

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Moment of Zen
KIDNEY
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Moment of Zen