CHAPTER 4: RENAL FUNCTION Flashcards
They make up approximately 85% of nephrons, and are situated primarily in the cortex of the kidney
Cortical nephrons
They are responsible
primarily for the removal of waste products and reabsorption of
nutrients
They have longer loops of Henle
that extend deep into the medulla of the kidney. Their primary function is concentration of the urine
Juxtamedullary nephrons
What supplies blood to the kidney
renal artery
The human kidneys receive approximately ______ of the blood pumped through
the heart at all times
25%
Blood enters the capillaries of the nephron through the?
It then flows through
the _______and into the ____________
afferent arteriole; glomerulus; efferent arteriole
The varying sizes of these arterioles help create the _______________ that is important for glomerular filtration and to maintain consistency of glomerular capillary pressure and renal blood flow within the glomerulus
hydrostatic pressure differential
Before returning to the renal vein, blood from the efferent
arteriole enters the ___________ and the _________ and flows slowly through the cortex and medulla of the kidney
close to the tubules.
peritubular capillaries; vasa recta
These provide for the
immediate reabsorption of essential substances from the fluid in the proximal convoluted tubule and the final adjustment of the urinary composition in the distal convoluted tubule.
Peritubular capillaries (that surround the proximal and distal convoluted tubule)
_________ are located adjacent to the ascending and descending
loops of Henle in juxtamedullary nephrons
Vasa recta
In this area, the major exchanges of water and salts take place between the blood and the medullary interstitium
Ascending and Descending loop of Henle
The exchange in the Ascending and Descending loop of Henle maintains the ___________ in the medulla, which is necessary for renal concentration
osmotic gradient (salt concentration)
average body size
1.73 m2 of surface
Based on an average body size of 1.73 m2 of surface, the
total renal blood flow is approximately
1200 mL/min
The total renal plasma flow ranges from
600 to 700 mL/min
Normal values for renal blood flow and renal function tests depend on?
Body size
The glomerulus consists of a coil of approximately ______ capillary lobe
eight
The walls of the glomerulus are referred to as the
glomerular filtration barrier
The glomerulus is located within __________, which forms the beginning of the renal tubule.
Bowman capsule
The glomerulus serves as a ________ filter of plasma substances with molecular weights less than __________.
nonselective; 70,000
Factors that influence the actual (glomerular) filtration process
- Cellular structure of the capillary walls and Bowman
capsule
-Hydrostatic pressure and oncotic pressure
-Feedback mechanisms of the renin–angiotensin–aldosterone
system (RAAS)
The three glomerular filtration
barrier cellular layers
- The capillary wall membrane
- The basement membrane (basal lamina), and the
- Visceral epithelium of
the Bowman capsule
The endothelial cells of the capillary wall differ from those in other capillaries by containing pores and are referred to as
Fenestrated endothelium
The thin membranes covering the filtration slits are formed by the intertwining foot processes of the _______ of the inner layer of the Bowman capsule
podocytes
T/F: The fenestrated pores increase capillary permeability but do not allow the passage of large molecules and blood cells
TRUE
In addition to the structure of the glomerular filtration barrier that prohibits the filtration of large molecules, the barrier contains a ___________ that repels molecules with a negative charge even though they are small enough to pass through the three layers of the barrier
shield of negativity
This is very important because it is the place where albumin (the primary protein associated with renal disease) has a negative charge and
is repelled
shield of negativity
This enhances filtration
hydrostatic pressure
This pressure is necessary to overcome the opposition of pressures from the fluid
within the Bowman capsule and the oncotic pressure of unfiltered plasma proteins in the glomerular capillaries
hydrostatic pressure
Renal Blood Flow
- Renal artery
- Afferent arteriole
- Glomerulus
- Efferent arteriole
- Peritubular capillaries
- Vasa recta
- Renal vein
Urinary Filtrate Flow
- Bowman capsule
- Proximal convoluted tubule
- Descending loop of Henle
- Ascending loop of Henle
- Distal convoluted tubule
- Collecting duct
- Renal calyces
- Ureter
- Bladder
- Urethra
This prevents a marked
decrease in blood flowing through the kidney, thus preventing an increase in the blood level of toxic waste products.
Dilation of the afferent arterioles and constriction of the
efferent arterioles
This prevents over-filtration or damage to the glomerulus
an increase in blood pressure results in constriction of the
afferent arterioles
What would possibly happen if the glomerular filtration barrier does not contain a shield of negativity?
All routine urines would have positive readings on reagent strips for protein and albumin.
Regulates the flow of blood to and within the glomerulus
Renin–Angiotensin–Aldosterone System (RAAS)
This responds to changes in blood pressure and
plasma sodium content
RAAS
This monitors the changes in blood pressure and
plasma sodium content
juxtaglomerular apparatus (which consists of the juxtaglomerular cells in the afferent arteriole and the macula densa of the distal convoluted tubule)
An enzyme produced by the juxtaglomerular cells
Renin
This detects the changes in the plasma sodium content and subsequent changes in blood pressure
Macula dennsa
This reacts with the bloodborne substrate angiotensinogen to produce the inert hormone angiotensin I.
Renin
As angiotensin I passes through the ______ of the lungs, __________________ changes it to the active form angiotensin II
alveoli; angiotensin-converting enzyme (ACE)
Does the following to correct the renal blood flow:
- Causing vasodilation of the afferent arterioles and
constriction of the efferent arterioles
- Stimulating reabsorption of sodium and water in the
proximal convoluted tubules
- Triggering the release of the sodium-retaining hormone
aldosterone by the adrenal cortex and antidiuretic hormone by the hypothalamus
Angiotensin II
This corrects renal blood flow
Angiotensin II
The actions of _________ produce a constant pressure within the nephron.
angiotensin II
As systemic blood pressure and plasma sodium content
increase, the secretion of renin _________
decreases
T/F: Every minute, approximately 3 to 5 million glomeruli filter approximately 120 mL of water-containing low-molecular-weight
substances
FALSE. Every minute, approximately 2 to 3 million glomeruli filter approximately 120 mL of water-containing low-molecular-weight substances
What is the only difference between the compositions of the filtrate and the plasma?
the absence of plasma protein, any protein-bound substances, and cells
Analysis of the fluid as it leaves the glomerulus shows the filtrate to have a specific gravity of?
1.010
Stimulates sodium reabsorption in the proximal convoluted tubule
RAAS
Dilates the afferent arteriole and constricts the efferent arteriole
RAAS
How many mL of water-containing essential substances does the body cannot lose every minute?
120 mL
Triggers the hypothalamus to release antidiuretic hormone to stimulate water reabsorption in the collecting duct
RAAS
Triggers the adrenal cortex to release the sodium-retaining hormone aldosterone to cause sodium reabsorption and potassium excretion in the distal convoluted tubule and collecting duct
RAAS
Passive transport is responsible for the reabsorption of?
- Water in the PCT, Descending loop of Henle, and Collecting duct
- Urea in the PCT and Ascending loop of Henle
- Sodium in the Ascending loop of
Henle
Movement of molecules across a
membrane as a result of differences in their concentration or electrical potential on opposite sides of the membrane.
Passive transport
For this to occur, the substance to be reabsorbed must combine with a carrier protein contained in the membranes of the renal tubular epithelial cells
Active transport
Active transport is responsible for the reabsorption of?
- Glucose, amino acids, and salts in the proximal convoluted tubule
- Chloride in the ascending loop of Henle
- Sodium in the distal convoluted tubule
The cellular mechanisms involved in tubular reabsorption are?
Active and passive transport
Passive reabsorption
of water takes place in all parts of the nephron except the __________, because its walls are impermeable to water.
Ascending loop of Henle
This is passively reabsorbed in the proximal convoluted tubule and the ascending loop of Henle
Urea
Passive reabsorption of ______ accompanies the active transport of ________ in the ascending loop
sodium; chloride
When the plasma concentration of a substance that is normally completely reabsorbed reaches a level that is abnormally high, the filtrate concentration exceeds the____________ of the tubules, and the substance begins to appear in the urine.
maximal reabsorptive
capacity (Tm)
Glucose appearing in the urine of a person with a normal blood glucose level is the result of?
Tubular damage and not diabetes mellitus
For glucose, the plasma renal threshold is?
160 to 180 mg/dL
The plasma concentration at which active transport stops is termed the?
renal threshold
Water is removed by
osmosis in the ___________, and sodium and chloride is reabsorbed in the __________
descending loop of Henle; ascending loop of Henle
This serves to maintain the osmotic gradient of the medulla and is a selective reabsorption process
Countercurrent mechanism
Reabsorption of sodium continues in the distal convoluted tubule and is controlled by the hormone?
Aldosterone
↑ Body Hydration =
↓ Body Hydration =
↑ Body Hydration = ↓ ADH = ↑ Urine Volume
↓ Body Hydration = ↑ ADH = ↓ Urine Volume
This renders the walls of the distal convoluted tubule and collecting duct permeable or impermeable to water.
antidiuretic hormone (ADH
Reabsorption depends on the?
Osmotic gradient in the medulla and hormone vasopressin antidiuretic hormone (ADH)
A high level of _______ increases permeability, resulting in increased water reabsorption, and a low-volume concentrated urine.
ADH
The production of ADH is determined by the?
state of body hydration
The major site for the removal of the nonfiltered substances
proximal convoluted tubule
To maintain the normal blood pH of 7.4, the blood must buffer and eliminate the excess acid formed by?
dietary intake and body metabolism
Many foreign substances, such as _________, cannot be filtered by the glomerulus because they are bound to plasma proteins.
medications
This prevents the filtered bicarbonate from being excreted in the urine and causes the return of a bicarbonate ion to the plasma.
Secretion of hydrogen ions (H+) by the renal tubular cells
The buffering capacity of the blood depends on?
bicarbonate (HCO3–) ions
The actual excretion of excess hydrogen ions also depends on?
tubular secretion
To ensure that glomerular filtration is being measured accurately, the substance analyzed must be one
that is?
neither reabsorbed nor secreted by the tubules
The standard tests used to measure the filtering capacity of the glomeruli are termed as?
clearance tests
What are the primary substances used in clearance test?
creatinine, beta2-microglobulin (B2M), cystatin C, and, possibly, radioisotopes
The earliest glomerular filtration tests measured urea because of its presence in all urine specimens, as well as the existence of routinely used methods of chemical analysis.
Urea Clearance
The original reference method for clearance tests
Inulin Clearance
A polymer of fructose, is an extremely stable substance that is neither reabsorbed nor secreted by the
tubules
Inulin
A test that requires an infused substance and is seldom the method of choice if a suitable test substance is already present in the body _______
exogenous procedure; endogenous procedure
Measurement of this is not a reliable indicator in patients suffering from muscle-wasting diseases or those involved in heavy exercise or athletes
supplementing with creatine.
Creatinine clearance
A waste product of muscle metabolism that is produced enzymatically by creatine phosphokinase from creatine
Creatinine
By far, the greatest source of error in any clearance procedure using urine is the use of urine specimens that are?
improperly timed
The GFR is reported in
milliliters cleared per minute;
The standard formula used to calculate the milliliters of plasma cleared per minute (C) is:
C = UV/P
The formula used most frequently for eGFR
Modification of Diet in Renal Disease (MDRD)
At present, the formula recommended by the National Kidney Disease Education Program (NKDEP) is?
MDRD-IDMS-traceable formula
The MDRD-IDMS traceable formula is:
GFR = 175 × serum creatinine–1.154 × age–0.203 × 0.742
(if patient is female) × 1.212 (if patient is black)
The measurement of this has been shown to be a good procedure for screening and monitoring GFR
serum cystatin C
A small protein (molecular weight 13,359) produced at a
constant rate by all nucleated cells.
cystatin C
Recent studies have shown that measuring both ___________ and ________can provide even more accurate information on a patient’s GFR
serum or plasma cystatin C and
Dissociates from human leukocyte antigens at a constant rate and is removed rapidly from the plasma by glomerular filtration
Beta2-Microglobulin (molecular weight 11,800)
May be used to distinguish disorders of the kidney as either glomerular or tubular
Beta2-Microglobulin
Used to identify end-stage renal disease and early rejection of a kidney transplant.
Beta2-Microglobulin
A rise in the plasma level of ______ is a more sensitive indicator of a decrease in GFR than creatinine clearance
Beta2-Microglobulin (B2M)
Not reliable in patients who have a history of immunologic disorders or malignancy
Beta2-Microglobulin (B2M)
An exogenous procedure and more labor-intensive and costly, provides a method for determining glomerular filtration through the plasma disappearance of the radioactive material and enables visualization of the filtration in one or both kidneys
Radionucleotides
T/F: Although the GFR is a frequently requested laboratory procedure, its value does not lie in the detection of early
renal disease
TRUE
Used to determine the extent of
nephron damage in known cases of renal disease, to monitor the effectiveness of treatment designed to prevent further
nephron damage, and to determine the feasibility of administering medication
Glomerular filtration rate
Tubular Reabsorption Tests
- Osmolality
- Freezing-Point Osmometers
- Vapor Pressure Osmometers
- Free Water Clearance
This is often the first function affected in renal disease
Tubular reabsorption capability
Tubular Secretion and Renal Blood Flow Tests
- PAH Test
- Titratable Acidity and Urinary Ammonia
Under normal random conditions, the ratio of urine to serum osmolality should be at least ____; after controlled fluid intake, it should reach ____
1:1 ; 3:1
Used for initially evaluating renal concentrating ability, monitoring the course of renal disease, monitoring fluid and electrolyte therapy, establishing the differential diagnosis of hypernatremia and hyponatremia, and evaluating the secretion of and renal response to ADH.
Osmolality
Reference serum osmolality values are from
275 to 300 mOsm
The test most commonly associated with tubular secretion and renal blood flow is the?
p-aminohippuric acid (PAH) test.
Used primarily to analyze serum and sweat micro samples for disorders not related to renal function, such as
cystic fibrosis. They are used primarily in the chemistry department.
Vapor pressure osmometers
Reference values for urine osmolality are difficult to establish because of factors, such as:
Fluid intake and exercise,
can greatly influence urine concentration.
The free water clearance is determined by first calculating the
osmolar clearance
Cosm = Uosm × V/ Posm
This determines the amount of PAH excreted in the urine
volume of plasma flowing through the kidneys
Although it has the disadvantage of being exogenous, this meets the criteria needed to measure renal blood flow
chemical PAH
This nontoxic substance is loosely bound to plasma proteins, which permits its complete removal as the blood passes through the peritubular capillaries
chemical PAH
All the plasma PAH is secreted by the?
proximal convoluted tubule
Based on normal hematocrit readings, reference values for the effective renal plasma flow range from
600 to 700 mL/min
The ability of the kidney to produce an acid urine depends on the tubular secretion of ___________, as well as production and secretion of _________ by the cells of the distal convoluted tubule
hydrogen ions; ammonia
This condition may result from impaired tubular secretion of hydrogen ions associated with the proximal convoluted tubule or defects in ammonia secretion associated with the distal convoluted tubule
renal tubular acidosis
It is the inability to produce an acid urine in the presence of metabolic acidosis
renal tubular acidosis
