Urinary 2

Question 1

The volume of filtrate formed by both kidneys per minute is termed the …
* At rest, the heart pumps ~… litres of blood/minute
* ~…% (~… litre) enters the kidneys to be filtered
* ~… ml/min filtrate produced in men and ~… ml/min in women
* filtrate volume of ~… litres/day in men and ~… litres/day in women
* >…% of this filtrate is returned to the circulation by reabsorption
* This results in only ~… liters of urine produced /day

Answer 1

The volume of filtrate formed by both kidneys per minute is termed the glomerular filtration rate (GFR)
* At rest, the heart pumps ~5 litres of blood/minute
* ~20% (~1 litre) enters the kidneys to be filtered
* ~125 ml/min filtrate produced in men and ~105 ml/min in women
* filtrate volume of ~180 litres/day in men and ~150 litres/day in women
* >99% of this filtrate is returned to the circulation by reabsorption
* This results in only ~1–2 liters of urine produced /day

Question 2

Glomerular filtration occurs when glomerular … exceeds the … of Bowman’s capsule
Glomerular filtration also needs to take into account … pressure

The osmotic pressure inside the glomerular capillary (~… mmHg) is … than the osmotic pressure in Bowman’s capsule (~… mmHg)
* The absence of … in the lumen within Bowman’s capsule results in …

The only pressure moving fluid across the capillary wall into the lumen of Bowman’s space is … pressure

NFP = … – … – …
(NFP) of ~… mmHg

With ~… liters of filtrate passing through the nephrons of the kidney each day, and just … litres of urine being produced, the kidney’s must be very efficient at reabsorption

Answer 2

Glomerular filtration occurs when glomerular hydrostatic pressure exceeds the capsular (luminal) hydrostatic pressure of Bowman’s capsule
Glomerular filtration also needs to take into account osmotic pressure

The osmotic pressure inside the glomerular capillary (~30 mmHg) is higher than the osmotic pressure in Bowman’s capsule (~0 mmHg)
* The absence of proteins in the lumen within Bowman’s capsule results in no osmotic pressure gradient to pull water into Bowman’s capsule

The only pressure moving fluid across the capillary wall into the lumen of Bowman’s space is hydrostatic pressure

NFP = GBloodHydrostaticP – CHP – BCOP
(NFP) of ~10 mmHg

With ~180 liters of filtrate passing through the nephrons of the kidney each day, and just 1-2 litres of urine being produced, the kidney’s must be very efficient at reabsorption

Question 3

The low net pressure across the filtration membrane, a minor change in either the osmolarity of the blood or the capillary blood pressure can result in major changes in the amount of filtrate formed at any given point in time
* To cope with this narrow range of filtration pressures, the kidney employs autoregulatory processes

• When smooth muscle is stretched, it … to minimize this change (… Effect)
  Thus, as blood pressure goes up, the smooth muscle in the afferent arterioles … while efferent arterioles… to limit any increase in blood flow and filtration rate
  Vice versa

The net result of this autoregulatory system is a relatively steady flow of blood into the glomerulus and a relatively steady filtration rate over a wide range of alterations to systemic blood pressure

This holds true as long as mean arterial pressure is >… mmHg
* When blood pressures fall … this level renal function … and can cause systemic disorders that are severe enough to threaten survival

The kidneys are also innervated by the … neurons. Para or Symp?
* Reduction of sympathetic stimulation results in … and … blood flow through the kidneys during resting conditions
* Sympathetic stimulation increases, the arteriolar smooth muscle …, resulting in … glomerular flow which produces … filtrate

Answer 3

As a result of the low net pressure across the filtration membrane, a minor change in either osmolarity of the blood or capillary blood pressure can result in major changes in the amount of filtrate formed at any given point in time
* To cope with this narrow range of filtration pressures, the kidney employs autoregulatory processes

• When smooth muscle is stretched, it contracts to minimize this change (Bayliss Effect)
  Thus, as blood pressure goes up, the smooth muscle in the afferent arterioles contract while efferent arterioles slightly dilate to limit any increase in blood flow and filtration rate

The net result of this autoregulatory system is a relatively steady flow of blood into the glomerulus and a relatively steady filtration rate over a wide range of alterations to systemic blood pressure

This holds true as long as mean arterial pressure is >60 mmHg
* When blood pressures fall below this level renal function is impaired and can cause systemic disorders that are severe enough to threaten survival

The kidneys are also innervated by the sympathetic neurons. ONLY SYMP
* Reduction of sympathetic stimulation results in vasodilation and increased blood flow through the kidneys during resting conditions
* Sympathetic stimulation increases, the arteriolar smooth muscle constricts (vasoconstriction), resulting in diminished glomerular flow which produces less filtrate

Question 4

Vasoconstriction - stimulation?
glomerular capillary blood pressure
net filtration pressure
GFR

Vasodilate - stimulation?
glomerular capillary blood pressure
net filtration pressure
GFR

Answer 4

Vasoconstriction - Sympathetic
glomerular capillary blood pressure - DOWN
net filtration pressure - DOWN
GFR - DOWN

Vasodilate - less sympathetic
glomerular capillary blood pressure - UP
net filtration pressure - UP
GFR - UP

Question 5

• Majority (~90%) of the water in the filtrate is recovered in the …, loop of Henle, and …, and only ~…% (~18L) reaches the …
• Majority of the Na+, K+, AND 100% of …, …, and other organic substances (e.g. vitamins) are normally recovered in the PCT

The collecting ducts are heavily influenced by … and regulate the volume of water reabsorbed based on … levels:
* If plasma osmolarity rises, … water is recovered and urine volume … (dehydrated)
* If plasma osmolarity decreases, … water is recovered and urine volume … (well-hydrated)

Aldosterone is secreted by the adrenal cortex in response to … stimulation
* Aldosterone stimulates principal cells to manufacture … on the basal membrane of the cells
* As more Na+ is reabsorbed, there is also … water reabsorbed which … blood volumes and augments blood pressure

Answer 5

• Majority (~90%) of the water in the filtrate is recovered in the PCT, loop of Henle, and DCT, and only ~10% (~18L) reaches the collecting ducts
• Majority of the Na+, K+, glucose, amino acids, and other organic substances (e.g. vitamins) are normally recovered in the proximal convoluted tubule

The collecting ducts are heavily influenced by ADH and regulate the volume of water reabsorbed based on hydrations levels:
* If plasma osmolarity rises, more water is recovered and urine volume decreases (dehydrated)
* If plasma osmolarity decreases, less water is recovered and urine volume increases (well-hydrated)

Aldosterone is secreted by the adrenal cortex in response to angiotensin II stimulation
* Aldosterone stimulates principal cells to manufacture luminal Na+and K+ channels as well as Na+/K+ ATPase pumps on the basal membrane of the cells
* As more Na+ is reabsorbed, there is also more water reabsorbed which increases blood volumes and augments blood pressure

Question 6

Question 7

… is actively pumped out of the PCT into the interstitial spaces
As … moves back into the blood stream, … follows passively
* This is called …
* Facultative water reabsorption occurs in the … through the activation (and inactivation) of …, as previously mentioned. ADH

• The apical surface is the one facing the … or open space of a cavity or tube
• The basal surface of the cell faces the … to which the cell attaches (… membrane)
• A few of the substances transported with Na+ (… mechanism) on the apical membrane include: …–, …+, … acids, …, and PO43−
• One of the substances transported against Na+ (… mechanism) is … (in turn regulates HCO3- levels

Recovery of bicarbonate (HCO3–) is vital to the maintenance of … balance
* In the lumen of the PCT, HCO3– combines with H+ to form carbonic acid (H2CO3)
* In turn, this is enzymatically catalyzed(CA) into CO2 and water, which then diffuse across the apical membrane into the cell

Inside the cell, the … reaction occurs to produce bicarbonate ions (HCO3–)
These … ions are co-transported with Na+ across the basal membrane to the interstitial space around the PCT
* At the same time the … antiporter excretes … into the lumen as it recovers Na+, enabling this cycle to keep going

Answer 7

Na+ is actively pumped out of the PCT into the interstitial spaces
As Na+ moves back into the blood stream, water follows passively
* This is called obligatory water reabsorption
* Facultative water reabsorption occurs in the collecting ducts through the activation (and inactivation) of aquaporins, as previously mentioned

• The apical surface is the one facing the lumen or open space of a cavity or tube
• The basal surface of the cell faces the connective tissue base to which the cell attaches (basement membrane)
• A few of the substances transported with Na+ (symport mechanism) on the apical membrane include: Cl–, Ca2+, amino acids, glucose, and PO43−
• One of the substances transported against Na+ (antiport mechanism) is H+ (in turn regulates HCO3- levels

Recovery of bicarbonate (HCO3–) is vital to the maintenance of acid–base balance
* In the lumen of the PCT, HCO3– combines with H+ to form carbonic acid (H2CO3)
* In turn, this is enzymatically catalyzed (by carbonic anhydrase) into CO2 and water, which then diffuse across the apical membrane into the cell

Inside the cell, the reverse reaction occurs to produce bicarbonate ions (HCO3–)
These bicarbonate ions are co- transported with Na+ across the basal membrane to the interstitial space around the PCT
* At the same time the Na+/H+ antiporter excretes H+ into the lumen as it recovers Na+, enabling this cycle to keep going

Question 8

At bottom of loop of henle, what is the concentration?
* These changes are accomplished by osmosis via … in the descending loop and … in the ascending loop

The thick portion of the ascending loop is made of … epithelium and is … to water (due to the absence of aquaporin proteins)
Instead, … out of the loop

• By removing Na+ from the filtrate and retaining water results in a … filtrate
• The additional Na+ in the interstitial space contributes to the hyperosmotic medulla

structure of the loop of Henle and associated vasa recta create a … multiplier system
* The descending and ascending loops are next to each other and their fluid flows in … directions (…current)
* The action of solute pumps increase (multiply) the concentrations of urea and Na+ the deeper they project into the medulla

Answer 8

very hypertonic solution (~1200 mOsmol/kg)
* These changes are accomplished by osmosis via permanent aquaporins in the descending loop and active transport in the ascending loop

The thick portion of the ascending loop is made of simple cuboidal epithelium and is completely impermeable to water (due to the absence of aquaporin proteins)
Instead, ions (mainly Na+) are actively pumped out of the loop

• By removing Na+ from the filtrate and retaining water results in a hypotonic filtrate
• The additional Na+ in the interstitial space contributes to the hyperosmotic medulla

structure of the loop of Henle and associated vasa recta create a countercurrent multiplier system
* The descending and ascending loops are next to each other and their fluid flows in opposite directions (countercurrent)
* The action of solute pumps increase (multiply) the concentrations of urea and Na+ the deeper they project into the medulla

Question 9

In general, blood flows slowly in the vasa recta particularly for 3 reasons:
* Maintenance of the … multiplier system
* Allows blood cells to lose and regain water without …
* A rapid flow would remove too much Na+ and urea, in turn destroying the … gradient necessary for the recovery of solutes and water

As urine is formed, it drains into the … of the kidney, which merge to form the funnel-shaped renal … in the … of each kidney
* The hilum narrows to become the ~30 cm long … of each kidney
As urine passes through the ureter, it is propelled by waves of …
A physiological sphincter (one-way valve) allows urine to enter the bladder and prevents reflux of urine from the bladder back into the ureter

The urinary bladder collects urine from both ureters
The bladder is a highly distensible organ comprised of irregular crisscrossing bands of smooth muscle collectively called the …
The interior surface is made of transitional epithelium structurally suited for the large volume fluctuations of the bladder
* Volumes in adults can range from nearly zero to …

Answer 9

In general, blood flows slowly in the vasa recta particularly for 3 reasons:
* Maintenance of the countercurrent multiplier system
* Allows blood cells to lose and regain water without crenating or bursting
* A rapid flow would remove too much Na+ and urea, in turn destroying the osmolar gradient necessary for the recovery of solutes and water

As urine is formed, it drains into the calyces of the kidney, which merge to form the funnel-shaped renal pelvis in the hilum of each kidney
* The hilum narrows to become the ~30 cm long ureter of each kidney
As urine passes through the ureter, it is propelled by waves of peristalsis
A physiological sphincter (one-way valve) allows urine to enter the bladder and prevents reflux of urine from the bladder back into the ureter

The urinary bladder collects urine from both ureters
The bladder is a highly distensible organ comprised of irregular crisscrossing bands of smooth muscle collectively called the detrusor muscle
The interior surface is made of transitional epithelium structurally suited for the large volume fluctuations of the bladder
* Volumes in adults can range from nearly zero to 500–600 ml

Question 10

When bladder volume reaches about … ml, an urge to void is sensed but is easily overridden
Voluntary control of urination (…) relies on consciously preventing relaxation of the … sphincter to maintain urinary continence
* Ultimately, voluntary constraint fails with resulting …, which will occur as bladder volume approaches 300-400 ml

Normal micturition is a result of … in the bladder wall that transmit nerve impulses to the sacral region of the spinal cord to generate a … reflex

• The resulting parasympathetic neural outflow causes contraction of the … and relaxation of the involuntary …
• Voiding is regulated voluntary skeletal muscle of the …

Answer 10

When bladder volume reaches about 150 ml, an urge to void is sensed but is easily overridden
Voluntary control of urination (micturation) relies on consciously preventing relaxation of the external urethral sphincter to maintain urinary continence
* Ultimately, voluntary constraint fails with resulting incontinence, which will occur as bladder volume approaches 300-400 ml

Normal micturition is a result of stretch receptors in the bladder wall that transmit nerve impulses to the sacral region of the spinal cord to generate a spinal reflex

• The resulting parasympathetic neural outflow causes contraction of the detrusor muscle and relaxation of the involuntary internal urethral sphincter
• Voiding is regulated voluntary skeletal muscle of the external urinary sphincter

Question 11

Urine Transport
In females, the bladder lies … to the uterus, posterior to the pubic bone and anterior to the rectum
* During late pregnancy, its capacity is … due to compression by the enlarging uterus, resulting in increased frequency of urination
In males, the anatomy is similar, minus the uterus, and with the addition of the prostate inferior to the bladder and longer urethra

The external urethral orifice in females is embedded in the anterior vaginal wall … to the clitoris, … to the vaginal opening and medial to the labia minora

• Its short length (~4 cm) is the best explanation for the greater incidence of … in women

Answer 11

Urine Transport
In females, the bladder lies anterior to the uterus, posterior to the pubic bone and anterior to the rectum
* During late pregnancy, its capacity is … due to compression by the enlarging uterus, resulting in increased frequency of urination
In males, the anatomy is similar, minus the uterus, and with the addition of the prostate inferior to the bladder and longer urethra

The external urethral orifice in females is embedded in the anterior vaginal wall inferior to the clitoris, superior to the vaginal opening and medial to the labia minora

• Its short length (~4 cm) is the best explanation for the greater incidence of UTI in women