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Questions? Homework due in lab 6
PreLab #6
HW 15 & 16 (follow directions, 6 points!)
Part 3
Variations in Urine Formation Composition varies
Fluid volume
Solute concentration
Variations in Urine Formation Water intake must equal water loss
Kidney regulates water loss by producing:
Hypotonic urine (dilute)
Hypertonic urine (concentrated)
Countercurrent Mechanism Role of countercurrent mechanisms
Establish and maintain an osmotic gradient
Creates hypertonic interstitial fluid within kidney medulla
Hypertonic interstitial fluid allows the kidneys to vary urine concentration
Figure 25.16a
Loop of Henle
Osmolality
of interstitial fluid (mOsm)
Inner
medulla
Outer
medulla
Cortex Active transport
Passive transport
Water impermeable
Countercurrent multiplier
The long loops of Henle of the
juxtamedullary nephrons
create the medullary
osmotic gradient.
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCI
NaCI
NaCI
NaCI
NaCI
Formation of Concentrated Urine Depends on the medullary osmotic gradient and the
ability to alter permeability of the collecting tubules ADH triggers reabsorption of H2O in the collecting
tubules
Osmotic gradient drives water from filtrate into blood
Figure 25.17b
Active transport
Passive transport
Small volume of
concentrated urine
Cortex
NaCI
NaCI
NaCI Urea
Urea
H2O
H2O
H2O
H2O
H2O
H2O
H2O
Outer
medulla
Inner
medulla
(b) Maximal ADH
DCT
Descending limb
of loop of Henle
Collecting duct
H2O
H2O
Formation of Dilute Urine Filtrate is diluted in the ascending Loop of Henle
In the absence of ADH, dilute filtrate continues into the renal pelvis as dilute urine
Figure 25.17a
Active transport
Passive transport
(a) Absence of ADH Large volume
of dilute urine
Collecting duct
Cortex
NaCI
NaCI
NaCI
Urea
Outer
medulla
Inner
medulla
DCT
H2O
H2O
Descending limb
of loop of Henle
Regulation of Water Output Influence of ADH
Water reabsorption in collecting tubules is dependent upon ADH release
ADH dilute urine and volume of body fluids
ADH concentrated urine
Figure 26.6
Osmolality
Na+ concentration
in plasma
Stimulates
Releases
Osmoreceptors
in hypothalamus
Negative
feedback
inhibits
Posterior pituitary
ADH
Inhibits
Stimulates
Baroreceptors
in atrium and
large vessels
Stimulates Plasma volume
BP (10–15%)
Antidiuretic
hormone (ADH)
Targets
Effects
Results in
Collecting ducts
of kidneys
Osmolality
Plasma volume
Water reabsorption
Scant urine
Acid-Base Balance pH affects all functional proteins and biochemical
reactions in the body Regulation prevents changes in body’s internal environment
Alkalosis or alkalemia: arterial blood pH >7.45
Acidosis or acidemia: arterial pH < 7.35
Acid-Base Balance Concentration of hydrogen ions is regulated by
1. Chemical buffer systems
Rapid, first line of defense
2. Brainstem respiratory centers
Acts within 1–3 minutes
3. Renal mechanisms
Most potent
Requires hours to days to affect pH changes
Acid-Base Balance Lungs
Regulate carbonic acid levels by CO2 manipulation
Kidneys
Selectively secrete and reabsorb to maintain pH
Acid-Base Balance Most important renal mechanisms:
Conserving (reabsorbing) HCO3–
Excreting HCO3–
Secretion of H+ H+ secretion occurs in the PCT and in collecting tubules
Acid-Base Balance Examples
Respiratory Acidosis Kidneys
Respiratory Alkalosis Kidneys
More on Compensation… Uncompensated
pH abnormal and either CO2 or HCO3- is off
The other system has not started to compensate at all
Partially compensated pH is abnormal and both CO2 and HCO3
- are off
The other system is trying to compensate
Fully compensated pH is normal and both CO2 and HCO3
- are off
The other system has corrected the pH but there is still and acid base imbalance since CO2 and HCO3
- are abnormal
Lets practice…Urinary 31 #21 - 24
Variations in Blood Pressure Activity of kidney related to variations in blood pressure
Blood pressure and blood volume are related
Blood volume is controlled by
Solute concentration
Water regulation
Variations in Blood Pressure Renal mechanisms influencing blood pressure
ADH
Water
Renin-angiotensin mechanism
Sodium
Potassium
Antidiuretic Hormone (ADH) Plasma osmolarity
Increase → osmoreceptors stimulated → thirst & ADH secretion →
water reabsorption (decreased urine output) →
increased blood volume → increased blood pressure
Causes?
Aldosterone Aldosterone stimulates K+ secretion and Na+
reabsorption
Changes in plasma sodium levels affect
Plasma volume, blood pressure
Aldosterone Regulation of sodium balance
Na+ reabsorption
65% is reabsorbed in the proximal tubules
25% is reclaimed in the Loops of Henle
Aldosterone active reabsorption of remaining Na+ in DCT and collecting ducts
Water follows Na+
Aldosterone Renin-angiotensin mechanism is the main trigger for
aldosterone release
Specialized cells of JGA secrete renin in response to
Sympathetic nervous system stimulation
Filtrate osmolality (decreased sodium)
Stretch (due to blood pressure)
Figure 25.8
Glomerulus
Glomerular capsule
Afferent arteriole
Efferent arteriole
Red blood cell
Podocyte cell body (visceral layer)
Foot processes of podocytes Parietal layer
of glomerular capsule
Proximal tubule cell
Lumens of glomerular capillaries
Endothelial cell of glomerular capillary
Efferent arteriole
• Macula densa cells
of the ascending limb of loop of Henle
• Granular cells
• Extraglomerular
mesangial cells
Afferent arteriole
Capsular space
Renal corpuscle Juxtaglomerular
apparatus
Mesangial cells between capillaries
Juxtaglomerular
apparatus
Aldosterone Renin catalyzes the production of angiotensin II
Prompts aldosterone release from the adrenal cortex
Targets cells of DCT and collecting ducts
Initiates sodium reabsorption
Causes systemic vasoconstriction
Figure 26.8
K+ (or Na+) concentration
in blood plasma*
Stimulates
Releases
Targets
Renin-angiotensin
mechanism
Negative
feedback
inhibits
Adrenal cortex
Kidney tubules
Aldosterone
Effects
Restores
Homeostatic plasma
levels of Na+ and K+
Na+ reabsorption K+ secretion
Figure 26.10
Stretch in afferent
arterioles
Angiotensinogen
(from liver)
Na+ (and H2O)
reabsorption
Granular cells of kidneys
Renin
Posterior pituitary
Systemic arterioles
Angiotensin I
Angiotensin II
Systemic arterioles
Vasoconstriction Aldosterone
Blood volume
Blood pressure
Distal kidney tubules
Adrenal cortex
Vasoconstriction
Peripheral resistance
(+)
(+)
(+)
(+)
Peripheral resistance
H2O reabsorption
Inhibits baroreceptors
in blood vessels
Sympathetic
nervous system
ADH (antidiuretic
hormone)
Collecting ducts
of kidneys
Filtrate NaCl concentration in
ascending limb of loop of Henle
Causes
Causes
Causes
Causes
Results in
Secretes
Results in
Targets
Results in
Releases
Release
Catalyzes conversion
Converting enzyme (in lungs)
(+)
(+) (+)
(+)
(+)
(+)
(+) stimulates
Renin-angiotensin system
Neural regulation (sympathetic
nervous system effects)
ADH release and effects
Systemic
blood pressure/volume
Renin-Angiotensin System Increases blood volume
Vasoconstriction
Aldosterone produced in response to:
Decreased blood volume
Decreased BP
Low plasma sodium
High plasma potassium
Increase BP
Factors Affecting Urine Volume Increased temperature
Increases vasodilation and perspiration
Decreases blood flow to kidneys
Decreased temperature
Increases blood flow to kidneys
Diuretics Chemicals that increase urine output
Osmotic diuretics
Substances not reabsorbed
Glucose in a diabetic patient
ADH inhibitors
Alcohol and water
Substances that inhibit Na+ reabsorption
Caffeine, thiazides, loop inhibitors
Potassium levels are affected by some diuretics
Factors Affecting Urine Output
↑ blood pressure
↑ blood solute concentration
↓ plasma proteins
Psychological factors
Anxious increased frequency and urge
Fright decreases urine output volume
Activities Regulation of Sodium Balance Worksheet
Urinary 26 – Complete 1, 2, 4, & 5
Urinary 27 – Complete 2, 3, & 5
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