Urinary System
Our Goals This Section....
• Identify and explain the functions of each of the following:
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kidney
ureter
urethra
urinary bladder
renal cortex
renal medulla
renal pelvis
nephron
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glomerulus
Bowman’s capsule
afferent and efferent arterioles
peritubular capillary network
proximal and distal convoluted tubules
collecting duct
loop of Henle
• Identify and explain the functions of the following components
of the nephron:
Wastes
Excretion
Main wastes: carbon dioxide and ammonia
Ammonia comes from the digestion of amino acids
Ammonia goes to liver and is converted to UREA
Digestion of nucleic acids produce URIC ACID
Must be secreted so they don’t become toxic
Some wastes and water are excreted when you
exhale
• Water is also excreted in sweat
• Kidneys are the primary organ of waste excretion –
they take urea, uric acid, excess H+, water soluble
vitamins, etc from the blood and excrete as urine
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Urinary System
Kidneys
• Renal arteries deliver blood to kidneys to
“clean it”
• Blood leaves the kidneys via the renal
vein
• Nephrons
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Functional unit of the kidney
Remove wastes
Make Urine
Millions/kidney
• Urine collects in the pelvic region of the
kidney where peristalsis moves it to the
ureters and then the urinary bladder
Nephron
Nephron
• Tubules
• All the same pattern
• Start in the cortex of the kidneys with
the Bowman’s capsule
• Then loop down into the renal medulla
• Bowman’s capsule →proximal convoluted
tubule → loop of Henle → distal convoluted
tubule → collecting duct
Blood Flood
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Renal Artery
Afferent Arterioles
Glomerulus
Efferent Arterioles
Peritubular Capillaries
Venule
Renal Vein
Remember Our Goals Today....
• Identify and explain the functions of each of the following:
–
–
–
–
–
–
–
–
kidney
ureter
urethra
urinary bladder
renal cortex
renal medulla
renal pelvis
nephron
–
–
–
–
–
–
–
glomerulus
Bowman’s capsule
afferent and efferent arterioles
peritubular capillary network
proximal and distal convoluted tubules
collecting duct
loop of Henle
• Identify and explain the functions of the following components
of the nephron:
Our Goals Today...
• Describe the production of urine with reference to the
following terms:
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pressure filtration
selective reabsorption
reabsorption of water following an osmotic gradient
tubular excretion
metabolic waste (e.g., nitrogenous waste, urea, ammonia)
• Describe how the kidneys maintain blood pH
• Compare urea and glucose content of blood in the renal
artery with that of the renal vein
• Identify the source glands for antidiuretic hormone (ADH) and
aldosterone
• Describe how the hypothalamus, posterior pituitary, ADH, and
the nephron achieve homeostasis of water levels in the blood
• Describe how the adrenal cortex, aldosterone, and the
nephron achieve homeostasis of water and sodium levels in
the blood
Urine Formation
• Interaction between the tubules of
nephrons and the blood capillaries
• Modified version of blood capillary
fluid exchange
• There are 3 stages of urine formation
1. Pressure Filtration
2. Selective Reabsorption
3. Tubular Secretion
Pressure Filtration
• Blood slows down when it enters the
cortex (enters the capillaries of the
glomerulus)
• Structure allows blood pressure to force
small parts of the blood plasma into the
spaces surrounding the glomerulus
• Bowman’s capsules cup around each
glomerulus
• Substances removed from blood are
forced into the beginning of the nephron
tubules by constant blood pressure
Pressure Filtration
• Fluid entering tubules is called FILTRATE
• Large components like blood cells and
globulins are too big therefore stay in
the blood
• Creates an osmotic gradient between
the blood and extracellular fluid
Selective Reabsorption
• Filtrate contains useful materials that the body
needs (eg. Glucose, amino acids, nutrients,
etc.)
• Cells in the proximal convoluted tubule have
CARRIER PROTEINS designed to pump these
materials back into the peritubular capillaries
• Requires ATP
• Some Na+, Cl- and water are reabsorbed
– Na+ is pumped out of filtrate
– Cl- and water follow passively into the blood
plasma
Selective Reabsorption
• As the filtrate moves through the nephron it
makes 3 passes between the cortex and the
medulla before entering the renal pelvis
• Filtrate goes from the proximal convoluted
tubule to the descending loop of Henle
– Here the tubule is permeable to water but not
Na+
– The extracellular region of this part of the tubule
has a high solute concentration – therefore water
moves out of the tubule and into blood (osmosis)
• Filtrate is now very “salty”
Selective Reabsorption
• Permeability of the ascending loop of Henle is
different
– permeable to Na+ and not permeable to water
• Na+ diffuses out of the tubule (concentration
gradient)
• When the filtrate gets closer to the cortex
diffusion lessens so ATP is used to remove more
Na+ from the filtrate
• Once at the distal convoluted tubule in the
cortex the filtrate is iso-osmotic to the
extracellular fluids
Tubular Secretion
• Substances that are excess in the
blood are pumped out of the
peritubular capillaries around the distal
convoluted tubule (enter filtrate)
• Substances: penicillin, histamines,
vitamins
• In the distal tubule pH of the blood is
also adjusted – absorption of H+ or
HCO3-
Final Phase of Urine Formation
• Collecting duct moves the filtrate
through the medulla one last time
• Filtrate is subjected to the increasing
concentration gradient of the
extracellular fluids
• Extracellular fluid in the medulla is
hypertonic to the filtrate
• Water is withdrawn as the filtrate as
moves into the renal pelvis
Final Phase of Urine Formation
• ~99% of water in the filtrate is reabsorbed
when urine is produced
• Throughout the tubule urea is reabsorbed in
very small amounts because of its low
threshold level
– However some urea will diffuse out of the
collecting duct into the medulla (contributes to
the high solute concentration around the loop of
Henle)
– It will re-enter the tubule along the ascending
loop of Henle
• Urine is what remains in the tubule
Composition of Urine
• Mainly water even though most of the
water has been reabsorbed
• Urea – low threshold in blood therefore
stays in the nephron during urine
formation
Glucose
• Blood has a high threshold level in the plasma
so most of it is reabsorbed from the nephron
• Requires ATP and transport proteins in the
tubules
• Liver removes excess glucose and stores it as
glycogen
• Diabetes is a malfunction in this system –
higher glucose concentration in the blood
causes glucose to be excreted in the urine
(less water is reabsorbed)
– Abnormal amounts of urine can be a symptom
of diabetes
• Diuretic versus Antidiuretic
Regulation of Urine Formation
• Antidiuretic Hormone (ADH) is secreted
by the posterior pituitary gland when
blood volume is low
– ADH causes more water to be reabsorbed in
the collecting duct
– This increases blood volume (& blood
pressure)
• Alcohol is a diuretic because it inhibits
ADH
– Causes increased urine production
– Excessive consumption leads to dehydration
Aldosterone
• If the blood pressure drops the regulation
of urine is in danger
• Aldosterone is released from the adrenal
cortex
• Increases the amount of Na+ absorption
in the distal convoluted tubule
• This in turn leads causes more water to be
absorbed restoring the blood pressure
Remember Our Goals Today...
• Describe the production of urine with reference to the
following terms:
–
–
–
–
–
pressure filtration
selective reabsorption
reabsorption of water following an osmotic gradient
tubular excretion
metabolic waste (e.g., nitrogenous waste, urea, ammonia)
• Describe how the kidneys maintain blood pH
• Compare urea and glucose content of blood in the renal
artery with that of the renal vein
• Identify the source glands for antidiuretic hormone (ADH) and
aldosterone
• Describe how the hypothalamus, posterior pituitary, ADH, and
the nephron achieve homeostasis of water levels in the blood
• Describe how the adrenal cortex, aldosterone, and the
nephron achieve homeostasis of water and sodium levels in
the blood