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Physiology (books) > Elements of renal function (berne Ch. 32) > Flashcards

Elements of renal function (berne Ch. 32) Flashcards

1
Q

The pH is maintained by buffers within the body fluids and by the coordinated action of what organs

A

Lungs, liver, and kidneys

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2
Q

The kidneys excrete a number of the end products of metabolism. These waste products include…
Amino acids:
Nucleic acids:
Muscle creatine

A

Amino acids: Urea
Nucleic acids: Uric acid
Muscle creatine: creatinine

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3
Q

The kidneys regulate (3)

A
  1. Body fluid osmolality and volumes
  2. Electrolyte balance
  3. Acid-base balance
    * * In addition, the kidneys excrete metabolic products and foreign substances and produce and secrete hormones
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4
Q

Kidneys are important endocrine organs that produce (3)

A

Renin, calcitriol, and erythropoietin

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5
Q

Renin-angiotensin-aldosterone system helps regulate what? (2)

A

Blood pressure and Na and K balance

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6
Q

In patients with renal disease, the kidneys’ ability to produce calcitriol is impaired, and levels of this hormone are reduced. What is the result of calcitriol reduction?

A

Ca absorption by the intestine is decreased
**This reduced intestinal Ca absorption contributes to the bone formation abnormalities seen in patients with chronic renal disease

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7
Q

True or false

Chronic renal failure may also manifest anemia

A

True
** Another consequence of many kidney diseases is a reduction in erythropoietin production and secretion. Erythropoietin stimulates red blood cell formation by the bone marrow

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8
Q

Patients in whom the glomerular filtration rate (GFR) is less than 10% of normal are said to have _____

A

End-stage renal disease (ESRD)

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9
Q

The medial side of each kidney contains an indentation. What structures pass through this indentation?

A

Renal artery and vein, nerves, and pelvis

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10
Q

The medulla in the human kidney is divided into conical masses called ____

A

Renal pyramids

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11
Q

The base of each renal pyramid originates at what structure?

A

Corticomedullary border

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12
Q

The apex each renal pyramid terminates in what structure?

A

Papilla – lies within a minor calyx (collect urine from each papilla)

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13
Q

Numerous minor calyces expand into two or three open-ended pouches called _____

A

Major calyces

** The major calyces in turn feed into the pelvis

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14
Q

Blood flow to the two kidneys is equivalent to about what percent of the cardiac output in resting individuals?

A

25% (1.25 L/min)

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15
Q

Renal artery branches progressively to form what structures? (4)

A

Interlobar artery, the arcuate artery, the interlobular artery, and the AFFERENT arteriole

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16
Q

The nephron consists of a what structures (4)

A

renal corpuscle, proximal tubule, loop of Henle, distal tubule

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17
Q

It is composed of the straight part of the proximal tubule, the descending thin limb (which ends in a hairpin turn), the ascending thin limb and the thick ascending limb

A

Loop of Henle

** Ascending thin limb – present in nephrons with long loop of Henle

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18
Q

The renal corpuscle consists of what structures? (2)

A

Glomerular capillaries and Bowman’s capsule

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19
Q

Near the end of the thick ascending limb, the nephron passes between the afferent and efferent arterioles of the same nephron. This short segment of the thick ascending limb is called ____

A

Macula densa

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20
Q

The distal tubule begins a short distance beyond the macula densa and extends to the point in the cortex where two or more nephrons join to form what structure?

A

Cortical collecting duct

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21
Q

Brush border is present only in (a) proximal tubule (b) distal tubule

A

a. Proximal tubule

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22
Q

True or false

In proximal tubule cells, apical membrane is highly invaginated. These invaginations contain many mitochondria

A

False – basolateral membrane

    • Proximal tubule cells have an extensively amplified apical membrane (the urine side of the cell) called brush border
    • In contrast, the descending and ascending thin limbs of Henle’s loop have poorly developed apical and basolateral surfaces and few mitochondria
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23
Q

The collecting duct is composed of two cell types:

A

Principal cells and intercalated cells

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24
Q

This cell type of collecting duct has a moderately invaginated basolateral membrane and contains few mitochondria and plays an important role in reabsorption of NaCl

A

Prinicipal cells

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25
Q

This cell type of collecting duct plays an important role in the regulation of acid-base balance and has many mitochondria

A

Intercalated cells

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26
Q

All cells in the nephron, except _____, have in their apical plasma membrane a single nonmotile primary cilium that protrudes into the tubule fluid

A

Intercalated cells
**Primary cilia are mechanosensors and
chemosensors and they initiate Ca- dependent signaling pathways, including those that control kidney cell function, proliferation, differentiation, and apoptosis

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27
Q

Expressed in the membrane of primary cilia and mediate entry of Ca into cells

A 
Polycystin 1 (encoded by the PKD1 gene) and polycystin 2 (encoded by the PKD2 gene)
**PKD1 and PKD2 are thought to play an important role in flow-dependent K secretion by principal cells of the collecting duct.
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28
Q

Afferenet arteriole leads into _____; efferent arteriole leads into _____

A

Glomerolus; peritubular capillaries
**The glomerulus consists of a network of capillaries supplied by the afferent arteriole and drained by the efferent arteriole

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29
Q

When compared with superficial nephrons, juxtamedullary nephrons differ anatomically in two important ways:

A
  1. The loop of Henle is longer and extends deeper into the medulla
  2. The efferent arteriole forms not only a network of peritubular capillaries but also a series of vascular loops called the vasa recta
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30
Q

The vasa recta descend into the medulla, where they form capillary networks that surround what structures?

A

Collecting ducts and ascending limbs of the loop of Henle

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31
Q

Passive movement of an essentially protein-free fluid from the glomerular capillaries into Bowman’s space

A

Ultrafiltration

**First step of urine formation

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32
Q

Forms the visceral layer of Bowman’s capsule

A

Podocytes – epithelial cells that cover the capillaries

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33
Q

Structures making up the filtration barrier

A

The capillary endothelium, basement membrane, and foot processes of podocytes

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34
Q

This part of the glomerolus function primarily as a charge-selective filter

A

Glomerular basement membrane

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35
Q

Anatomy of podocyte foot processes

Organizes nephrin and NEPH1 in specific microdomains in the plasma membrane, which is important for signaling events that determine the structural integrity of podocyte foot processes

A

Podocin

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36
Q

This complex structure function primarily as a size-selective filter

A

Filtarion-slit
** The processes of the podocytes interdigitate to cover the basement membrane and are separated by apparent gaps called filtration slits. Each filtration slit is bridged by a thin diaphragm

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37
Q

The filtration slit diaphragm, which appears as a continuous structure when viewed by electron microscopy, is composed of several proteins:

A

nephrin (NPHS1), NEPH-1, podocin (NPHS2), a-actinin 4 (ACTN4) and CD2-AP

38
Q

These cells possess many properties of smooth muscle cells which surround the glomerular capillaries and provide structural support for the glomerular capillaries secrete the extracellular matrix, exhibit phagocytic activity by removing macromolecules from the mesangium, and secrete prostaglandins and proinflammatory cytokines

A

Mesangial cells

39
Q

IN THE CLINIC
Characterized by an increase in permeability of the glomerular capillaries to proteins and by loss of normal podocyte structure, including effacement (i.e., thinning) of the foot processes

A

Nephrotic syndrome

  • *The augmented permeability to proteins results in an increase in urinary protein excretion (proteinuria). Thus, the appearance of proteins in urine can indicate kidney disease. Hypoalbuminemia often develops in individuals with this syndrome as a result of the proteinuria
    • Generalized edema is commonly seen in individuals with nephrotic syndrome
40
Q

Nephrins from opposite foot processes interdigitate in the center of the slit. In the slit, nephrin interacts with what proteins?

A

NEPH1 and NEPH2, FAT1 and FAT2 and P-cadherin

41
Q

IN THE CLINIC
Characterized by hematuria (i.e.,blood in urine) and progressive glomerulonephritis
(i.e., infl ammation of the glomerular capillaries) and accounts for 1% to 2% of all cases of ESRD

A

Alport’s syndrome

42
Q

IN THE CLINIC

Alport’s syndrome is caused by defect in ____

A

Type IV collagen (encoded by the COL4A5 gene), a major component ofthe glomerular basement membrane

43
Q

Structures that make up the juxtaglomerular apparatus include the following: (3)

A
  1. The macula densa of the thick ascending limb
  2. Extraglomerular mesangial cells
  3. Renin- and angiotensin II–producing granular cells of the afferent arteriole
44
Q

The nerve supply to the kidneys consists of sympathetic nerve fibers that originate in what plexus?

A

Celiac plexus

** There are no parasympathetic innervations

45
Q

Adrenergic fibers that innervate the kidneys release norepinephrine and dopamine. The adrenergic fibers lie adjacent to what structure?

A

Smooth muscle cells of the major branches of the renal artery (interlobar, arcuate, and interlobular arteries) and the afferent and efferent arterioles

46
Q

The coordinated actions of the nephron’s various segments determine the amount of a substance that appears in urine. This represents three general processes:

A
  1. Glomerular filtration
  2. Reabsorption of substance from tubular fluid back into blood
  3. Secretion of substance from blood to tubule fluid
47
Q

Based on the Fick principle (i.e., mass balance or conservation of mass)

A

Renal clearance

48
Q

Mass balance relationship of a kidney

Input:
Output:

A

Input: Renal artery: Pax X RPFa
Output: Renal vein + ureter: (Pvx X RPFv) + (Ux X V)
** Pax and Pvx are the concentrations of substance x in the renal artery and renal vein plasma, respectively
** RPFa and RPFv are renal plasma flow rates in the artery and vein, respectively
**Ux is the concentration of substance x in urine
**V is the urine flow rate

49
Q

The principle of renal clearance emphasizes what function of the kidney?

A

Excretory function of the kidneys
**it considers only the rate at which a substance is excreted into urine and not its rate of return to the systemic circulation in the renal vein

50
Q

In terms of mass balance, the urinary excretion rate of substance x (Ux X V) is proportional to _____

A

Plasma concentration of substance x (Pax)

51
Q

Pax X Cx is equal to _____

A

Ux X V

**Cx is the rate at which substance x is removed from plasma by the kidneys (RENAL CLEARANCE)

52
Q

Sum of the filtration rates of all functioning nephrons

A

Glomerular filtration rate (GFR)

53
Q

Renal handling of creatinine
Amount filtered:
Amount excreted:

A

Amount filtered: PCr X GFR
Amount excreted: UCr X V
**Amount filtered is equal to amount excreted

54
Q

IN THE CLINIC
Used to estimate the GFR in clinical practice. It is synthesized at a relatively constant rate, and the amount produced is proportional to the muscle mass

A

Clearance of Creatinine
** Because measurements of GFR are cumbersome, kidney function is usually assessed in the clinical setting by measuring PCr, which is inversely related to GFR

55
Q

GFR

A

(UCr X V)/PCr

  • *UCr = urine concentration of creatinine
  • *PCr = plasma concentration of creatinine
56
Q

Renal clearance (Cx)

A

(Ux X V)/Px

  • *Ux = urine concentration of substance x
  • *Px = plasma concnetration of substance x
57
Q

Any substance that meets these following criteria can serve as an appropriate marker for the measurement of GFR

A
  1. Be freely filtered across the glomerulus into Bowman’s space
  2. Not be reabsorbed or secreted by the nephron
  3. Not be metabolized or produced by the kidney
  4. Not alter the GFR
58
Q

The portion of filtered plasma

A

Filtration fraction

59
Q

Filtration Fraction

A

GFR divided by RPF
**Under normal conditions the filtration fraction averages 0.15 to 0.20, which means that only 15% to 20% of the plasma that enters the glomerulus is actually filtered. The remaining 80% to 85% continues on through the glomerular capillaries and into the efferent arterioles and peritubular capillaries. It is finally returned to the systemic circulation in the renal vein

60
Q

In normal adults, the GFR ranges from

A

Male: 90 to 140 mL/min
Female: 80 to 125 mL/min

61
Q

IN THE CLINIC

Reduction of the negative charges on the glomerular wall results in the filtration of proteins based on ______

A

Size only

  • *In this situation the relative filterability of proteins depends only on the molecular radius. Accordingly, excretion of polyanionic proteins (20 to 42 A) in urine increases because more proteins of this size are filtered
  • *In a number of glomerular diseases the negative charges on the filtration barrier are reduced because of immunological damage and inflammation. As a result, the filtration of proteins is increased, and proteins appear in urine (proteinuria).
62
Q

The glomerular filtration barrier determines the composition of the plasma ultrafiltrate. It restricts the filtration of molecules on the basis what properties?

A

Size and electrical charge

63
Q

Force that promote the movement of fluid from the glomerular capillary into Bowman’s space

A

The hydrostatic pressure in the glomerular capillary (PGC)

  • *PGC is the only force that favors filtration because oncotic pressure in Bowman’s space (πBS) is near zero
  • *The hydrostatic pressure in Bowman’s space (PBS) and the oncotic pressure in the glomerular capillary (πGC) oppose filtration
64
Q

A net ultrafiltration pressure (PUF) of 17 mm Hg exists at what end of the glomerolus?

A

Afferent

  • *whereas at the efferent end it is 8 mm Hg
  • *PUF = PGC - PBS - πGC
65
Q

True or false

PGC decreases slightly along the length of the capillary

A

True - because of the resistance to flow along the length of the capillary

66
Q

True or false

πGC decreases slightly along the length of the capillary

A

False
**πGC increases along the length of the glomerular capillary because water is filtered and protein is retained in the glomerular capillary, the protein concentration in the capillary rises, and πGC increases

67
Q

Blood flow through any organ may be represented by what equation?

A

Q = ∆P/R

  • *Q = blood flow
  • *∆P = mean arterial pressure minus venous pressure for that organ
  • *R = resistance to flow through that organ
68
Q

PGC is affected in three ways:

  1. Changes in afferent arteriolar resistance:
  2. Changes in efferent arteriolar resistance:
  3. Changes in renal arteriolar pressure:
A
  1. Changes in afferent arteriolar resistance: A decrease in resistance increases PGC and GFR, whereas an increase in resistance decreases them
  2. Changes in efferent arteriolar resistance: A decrease in resistance reduces PGC and GFR, whereas an increase in resistance elevates them
  3. Changes in renal arteriolar pressure: An increase in blood pressure transiently increases PGC (which enhances GFR), whereas a decrease in blood pressure transiently decreases PGC (which reduces GFR)
69
Q

IN THE CLINIC
A reduction in the GFR in disease states is most often due to decreases in Kf because of the loss of filtration surface area. The GFR also changes in pathophysiological conditions because of changes in PGC, πGC, and PBS.
Changes in Kf:

A

Changes in Kf: Increased Kf enhances the GFR, whereas decreased Kf reduces the GFR. Some kidney diseases reduce Kf by decreasing the number of filtering glomeruli (i.e., diminished surface area). Some drugs and hormones that dilate the glomerular arterioles also increase Kf. Similarly, drugs and hormones that constrict the glomerular arterioles also decrease Kf.
**filtration fraction

70
Q

IN THE CLINIC
A reduction in the GFR in disease states is most often due to decreases in Kf because of the loss of filtration surface area. The GFR also changes in pathophysiological conditions because of changes in PGC, πGC, and PBS.
Changes in PGC:

A

Changes in PGC: With decreased renal perfusion, the GFR declines because PGC falls. A reduction in PGC is caused by a decline in renal arterial pressure, an increase in afferent arteriolar resistance, or a decrease in efferent arteriolar resistance.

71
Q

IN THE CLINIC
A reduction in the GFR in disease states is most often due to decreases in Kf because of the loss of filtration surface area. The GFR also changes in pathophysiological conditions because of changes in PGC, πGC, and PBS.
Changes in πGC:

A

Changes in πGC: An inverse relationship exists between πGC and GFR. Alterations in πGC result from changes in protein synthesis outside the kidneys. In addition, the protein loss in urine caused by some renal diseases can lead to a decrease in the plasma protein concentration and thus in πGC.

72
Q

IN THE CLINIC
A reduction in the GFR in disease states is most often due to decreases in Kf because of the loss of filtration surface area. The GFR also changes in pathophysiological conditions because of changes in PGC, πGC, and PBS.
Changes in PBS:

A

Changes in PBS: Increased PBS reduces the GFR, whereas decreased PBS enhances the GFR. Acute obstruction of the urinary tract (e.g., a kidney stone occluding the ureter) increases PBS.

73
Q

RBF

A

(Aortic pressure-venous pressure)/(Renal vascular resistance)

74
Q

The phenomenon whereby RBF and GFR are maintained relatively constant

A

Autoregulation

75
Q

Two mechanisms are responsible for the autoregulation of RBF and GFR:

A

One mechanism that responds to changes in arterial pressure and another that responds to changes in [NaCl] in tubular fluid
**Both regulate the tone of the afferent arteriole

76
Q

Two mechanisms are responsible for the autoregulation of RBF and GFR
Myogenic mechanism:
tubuloglomerular feedback:

A

Myogenic mechanism: Related to an intrinsic property of vascular smooth muscle - the tendency to contract when stretched. When arterial pressure rises and the renal afferent arteriole is stretched, the smooth muscle contracts. Because the increase in resistance of the arteriole offsets the increase in pressure, RBF and therefore GFR remain constant

Tubuloglomerular feedback: NaCl-dependent mechanism that involves a feedback loop in which the concentration of NaCl in tubular fluid is sensed by the macula densa of the juxtaglomerular apparatus and converted into a signal or signals that affect afferent arteriolar resistance and thus the GFR

77
Q

Cellular mechanism whereby an increase in the delivery of NaCl to the macula densa causes vasoconstriction of the afferent arteriole of the same nephron

A

Tubuloglomerular feedback

    • An increase in GFR elevates [NaCl] in tubule fluid at the macula densa. This in turn enhances uptake of NaCl across the apical cell membrane of macula densa cells via the 1Na-1K2Cl (NKCC2) symporter, which leads to an increase in [ATP] and [adenosine] (ADO).
    • ATP binds to P2X receptors and adenosine binds to adenosine A1 receptors in the plasma membrane of smooth muscle cells surrounding the afferent arteriole, both of which increase intracellular [Ca]. The rise in [Ca] induces vasoconstriction of the afferent arteriole, thereby returning GFR to normal levels
78
Q

True or false

Autoregulation occurs at any arterial pressure.

A

False - Autoregulation is absent when arterial pressure is less than 90 mm Hg

79
Q

Major Hormones That Influence the Glomerular Filtration Rate and Renal Blood Flow
Vasoconstrictors:

A

Sympathetic nerves
Angiotensin II
Endothelin

80
Q

Major Hormones That Influence the Glomerular Filtration Rate and Renal Blood Flow
Vasodilators:

A

Prostaglandins (PGE1, PGE2, PGI2)
Nitric oxide (NO)
Bradykinin
Natriuretic peptides (ANP, BNP)

81
Q

The afferent and efferent arterioles are innervated by sympathetic neurons; however, sympathetic tone is minimal when the volume of extracellular fluid is (a) normal (b) increased (c) decreased

A

a. Normal

82
Q

Norepinephrine and dopamine is to sympathetic nerves; epinephrine is to _____

A

Adrenal medulla
** Norepinephrine and epinephrine cause vasoconstriction by binding to a1-adrenoceptors, which are located mainly on the afferent arterioles

83
Q

Angiotensin II is produced by ____

A

Kidney
** The efferent arteriole is more sensitive to angiotensin II than the afferent arteriole. Therefore, with low concentrations of angiotensin II, constriction of the efferent arteriole predominates, and GFR increases and RBF decreases. However, with high concentrations of angiotensin II, constriction of both afferent and efferent arterioles occurs, and GFR and RBF both decrease

84
Q

A catecholamine-metabolizing hormone produced by the kidneys, facilitates the degradation of catecholamines

A

Renalase

85
Q

True or false

Prostaglandins play a major role in regulating RBF in healthy, resting people

A

False
**Prostaglandins do not play a major role in regulating RBF in healthy, resting people. However, during pathophysiological conditions such as hemorrhage, prostaglandins (PGI2, PGE1, and PGE2) are produced locally within the kidneys, and they increase RBF without changing GFR

86
Q

Synthesis of prostaglandins: dehydration and stress (e.g., surgery, anesthesia), angiotensin II, and sympathetic nerves; Inhibition of prostaglandins: ________

A

Nonsteroidal antiinflammatory drugs (NSAIDs), such as aspirin and ibuprofen

87
Q

True or false
NO is an endothelium-derived relaxing factor, is an important vasodilator under basal conditions, and it counteracts the vasoconstriction produced by angiotensin II and catecholamines

A

True

    • When blood flow increases, greater shear force acts on endothelial cells in the arterioles and increases the production of NO
    • Increased production of NO causes dilation of the AFFERENT and EFFERENT arterioles
88
Q

A potent vasoconstrictor secreted by endothelial cells of the renal vessels, mesangial cells, and distal tubular cells in response to angiotensin II, bradykinin, epinephrine, and endothelial shear stress

A

Endothelin
** Production of endothelin is elevated in a number of glomerular disease states (e.g., renal disease associated with diabetes mellitus)

89
Q

Secretion of atrial natriuretic peptide (ANP) by the _____; brain natriuretic peptide (BNP) by the _____

A

Cardiac atria; cardiac ventricle

    • increases when extracellular fluid volume is expanded
    • Both ANP and BNP dilate the afferent arteriole and constrict the efferent arteriole. Therefore, ANP and BNP produce a modest increase in GFR with little change in RBF
90
Q

True or false

The local release of histamine modulates RBF during inflammation and injury only

A

False

    • The local release of histamine modulates RBF during the resting state and during inflammation and injury
    • Histamine decreases the resistance of the afferent and efferent arterioles and thereby increases RBF without elevating GFR
91
Q

Dopamine is produced in the (a) proximal tubule (b) distal tubule

A

a. Proximal tubule

* * Dopamine has several actions within the kidney, such as increasing RBF and inhibiting rennin secretion

92
Q

NO production is stimulated by ____

A

Shear stress, acetylcholine, histamine, bradykinin, and ATP

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