Exam 3 Britton Renal Physiology II Flashcards
(129 cards)
1
Q
Movement of solutes and H2O is via either ____ or ____
A
Paracellular transport or transcellular transport
2
Q
What is paracellular transport?
A
Between cells and across tight junctions
3
Q
What is transcellular transport?
A
Across both the luminal (apical) and the basolateral membrane
4
Q
What primarily provides the driving force for solute movement?
A
Na+/K+-ATPase pump in the basolateral membrane
5
Q
What are some mechanisms by which substances move across membranes for reabsorption or secretion?
A
- Diffusion
- Active transport (pumps)
- Facilitated diffusion
- Co-transport
- Counter transport (exchangers)
- Osmosis
6
Q
Reabsorption can be ____ or ____
A
Active or passive
7
Q
The mechanisms for reabsorption involve transporters where?
A
In the membranes of the nephron
8
Q
Reabsorption depends mostly on ____
A
Active transport
9
Q
Active transport of Na+ from tubule to blood creates a ____
A
Transepithelial electrical gradient
10
Q
What is the transepithelial electrical gradient?
A
- Active transport of Na+ from tubule into blood
- Anions follow Na+ out of lumen
- Water leaves tubule via osmosis
- K+ reabsorption is due to solvent drag
11
Q
____ is a hallmark of proximal tubular function
A
Isosmotic reabsorption
12
Q
During isosmotic reabsorption, ____ and ____ are coupled to each other and are ____ to each other
A
Solute and H2O; Proportional
13
Q
Glucose reabsorption in the proximal tubule requires what transporters?
A
- Na+/K+ ATPase pump
- SGLT2
- GLUT2
14
Q
What is SGLT2?
A
Sodium glucose co-Transporter 2
15
Q
____ establishes the concentration gradient for Na+
A
Na+/K+ ATPase pump
16
Q
Normally, ___ of filtered glucose is reabsorbed
A
100%
17
Q
The SGLT2 and GLUT2 mechanism in the _____ is responsible for ___ of glucose reabsorption. The remaining ____ is reabsorbed in the ____ involving SGLT1 and GLUT1
A
Early proximal tubule; 90%; 10%; Late proximal tubule
18
Q
Where is SGLT2 located on the proximal tubule?
A
Apical membrane
19
Q
Where is Na+/K+ ATPase pump located on the proximal tubule?
A
Basolateral membrane
20
Q
Where is the GLUT2 transporter located on the proximal tubule?
A
Basolateral membrane
21
Q
____ enables glucose to leave the cell down a concentration gradient
A
GLUT2
22
Q
____ transports Na+ and glucose into the cell simultaneously
A
SGLT2
23
Q
As plasma glucose increases, the filtered load will increase ____
A
Linearly
24
Q
When the plasma concentration of glucose is less than 200 mg/dL, ____ is reabsorbed
A
All filtered glucose
25
When the plasma concentration of glucose is less than 200 mg/dL, why is reabsorption = filtration?
Because SGLT2 transporters are plentiful
26
When the plasma concentration of glucose is greater than 200 mg/dL, what happens?
Some of the filtered glucose is not reabsorbed, since the number of SGLT2 transporters is limited
27
At P>350 mg/dL, what happens? (glucose)
SGLT2 transporters are completely saturated and thus reabsorption levels off at maximal value (transport maximum)T
28
True or false: For glucose, when [P] < 200 mg/dL, all filtered glucose is reabsorbed and none is excreted
True
29
For glucose, when [P] > 200 mg/dL, the SGLT2 carriers are near ____. Glucose that is not reabsorbed is ____
Saturation; excreted
30
What is renal threshold for glucose?
[P]glucose at which glucose is first excreted in the urine (glucosuria)
31
At [P] glucose > 350 mg/dL, Tm is reached and SGLT carriers are ____. Glucose excretion in urine _____
Fully saturated; Now increases linearly
32
Excess glucose in diabetes: Tm occurs as ___ are saturated. Excess glucose in nephron tubule will ____. What symptoms will the patient experience?
SGLT; Osmotically hold water; Excess urination and thirst
33
What is splay?
Where reabsorption is approaching saturation but is not fully saturated
34
Of all functions of the kidney, ____ is the most important
Reabsorption of Na+
35
Na+ is the major cation of the ____
ECF compartment
36
What occurs during positive Na+ balance?
Hypernatremia
37
What is hypernatremia?
Abnormal increase of blood Na+
38
Hypernatremia can be caused by:
Hormonal imbalances
39
Describe what happens during hypernatremia
- Increased Na+ content in ECF
- Increased ECF volume (termed ECF volume expansion, attracts more water)
- Increased blood volume and MAP
- May be edema in the limbs
40
What happens in negative Na+ balance?
Hyponatremia
41
What is hyponatremia?
An abnormal decrease of blood Na+
42
Describe what happens during hyponatremia
- Decreased Na+ content in ECF
- Decreased ECF volume (ECF volume contraction)
- Decreased blood volume and MAP
43
What diseases/situations can lead to hyponatremia?
- Sweating
- Vomiting
- Diarrhea
- Diuretics
- Diabetes
44
___% of the filtered load of Na+ is subsequently reabsorbed in various segments throughout the nephron. ___% is excreted
99%; 1%
45
What % of Na+ is reabsorbed in the proximal tubule?
~65%
46
What % of Na+ is reabsorbed in the thick limb of the ascending loop of Henle?
~25%
47
What % of Na+ is reabsorbed in the early distal tubule?
5-10%
48
What % of Na+ is reabsorbed in the principal cells of the late distal tubule and collecting duct?
1-5%
49
In the early proximal tubule, Na+ is co-transported with:
- Glucose
- Amino acids
- Phosphate
50
In the early proximal tubule, Na+ is exchanged for:
H+ (via Na+/H+ exchanger)
51
Na+ co-transporters and exchangers are located on what surface of the PT cell?
Apical
52
On which membrane is the Na+/K+ ATPase located? (early PT)
Basolateral
53
The late proximal tubule allows for additional Na+ movement across the membrane through what mechanism?
Cl- gradient (paracellular transport)
54
In the proximal tubule, ____ reabsorption is always linked to Na+ reabsorption. This mechanism is described as ____
H2O; isosmotic
55
How is Na+ reabsorbed in the thick ascending limb of LoH?
Via the Na+-K+-2Cl- co-transporter (NKCC) on apical membrane
56
NKCC is inhibited by:
Loop diuretics
57
How is Na+ reabsorbed in the early distal tubule?
Via the NaCl co-transporter (NCC) on the apical membrane
58
NCC is inhibited by:
Thiazide diuretics
59
How is Na+ reabsorbed in the principal cells of the late DT and collecting duct?
- Via epithelial Na+ channels (EnaC) on the apical membrane
- Na+ diffuses through these channels down its electrochemical gradient
60
The nephron Na+ reabsorption at the late DT and collecting duct is regulated by what hormone?
Aldosterone
61
ENaC are inhibited by:
K+-sparing diuretics
62
What mechanisms regulate renal Na+?
- Sympathetic nerve activity
- Atrial Natriuretic peptide (ANP)
- Starling forces in peritubular capillaries
- Renin-angiotensin-aldosterone system
63
Describe how sympathetic nerve activity regulates renal Na+
- Decreased MAP activates the baroreceptor mechanism
- Causes vasoconstriction of afferent arterioles
- Leads to decreased GFR and increased Na+ reabsorption in PT
64
Describe how atrial natriuretic peptide (ANP) regulates renal Na+
- Increase in ECF volume
- ANP secreted by atria
- Vasodilation of afferent arterioles and vasoconstriction of efferent arterioles
- Increases GFR, decreases Na+ reabsorption
65
ANP secretion leads to ____ Na+ reabsorption
Decreased
66
Sympathetic nerve activity leads to ____ Na+ reabsorption
Increased
67
Increase in ECF volume leads to ____ Na+ reabsorption in the PT
Decreased
68
Decrease in ECF volume leads to ____ reabsorption in the PT
Increased
69
RAAS system is activated in response to:
Decreased MAP (decreased renal perfusion pressure)
70
Na+ reabsorption is governed by what 2 hormones?
- Angiotensin II
- Aldosterone
71
Angiotensin II stimulates Na+ reabsorption in the ___ via ___
PT; Na+-H+ exchange
72
Aldosterone stimulates Na+ reabsorption in the ____
Late DT and collecting duct
73
The actions of Angiotensin II cause:
Increased total body Na+, total body H2O, and vascular tone
74
Aldosterone is a steroid hormone secreted by:
Zona glomerulosa of the adrenal cortex
75
Aldosterone release is stimulated by:
Angiotensin II
76
- Aldosterone is delivered to the ____ via the circulation and diffuses into cells across the ____
- Aldosterone transfers to the ____, where it stimulates the synthesis of mRNA involved in Na+ reabsorption, including ____ and ___
- Principal cells; Basolateral cell membrane
- Nucleus; ENaC and Na+/K+ pump
77
What is the function of the principal cells in the late distal tubule and collecting duct?
- Reabsorb Na+ from tubular filtrate
- Secrete K+ into the filtrate
(thus aldosterone causes increased Na+ reabsorption and H2O)
77
____ increases K+ secretion
Aldosterone
78
How much K+ is reabsorbed in the proximal convoluted tubule?
67%
79
How much K+ is reabsorbed in the thick ascending limb of LoH?
20%
80
What is responsible for fine tuning K+ excretion that occurs when dietary K+ varies?
- Distal tubule
- Collecting duct
81
True or false: Principal cells in the DT reabsorb K+
False - secretes K+
82
____ reabsorb K+ in the DT and CD
alpha-intercalated cells (also H+ secretion)
83
What are the 4 renal effects of aldosterone?
- Decreased Na+ excretion in urine
- Decreased Cl- excretion in urine
- Increased K+ excretion in urine
- Increased NH4+ excretion in urine
84
A number of sensors detect changes in the blood volume or plasma Na+ concentrations, such as:
- Carotid baroreceptors
- Juxtaglomerular cells (intrarenal baroreceptirs)
- Macula densa
- Stretch receptors in atria (ANP release)
85
The release of renin ultimately leads to ____ production, increased ____ reabsorption and ____ retention
ANG II; Na+; H2O
86
H2O reabsorption occurs mainly in the ____. Reabsorption is by ____
Proximal tubule; osmosis
87
What are the different segments of the loop of Henle? What are these segments responsible for?
- Thin descending limb, thin and thick ascending limb
- Responsible for countercurrent multiplication
88
Countercurrent multiplication is essential for:
The concentration and dilution of urine
89
Where does H2O reabsorption occur?
In the descending limb of the LoH and at the collecting duct via aquaporins in the membrane
90
The structure of the ___ and associated ____ create a countercurrent multiplier system
LoH and vasa recta
91
In the countercurrent multiplier system, where does the term countercurrent come from?
The fact that the descending and ascending limbs of the LoH are next to each other and their fluid flows in opposite directions
92
In the countercurrent multiplier system, where does the term multiplier come from?
Due to the action of solute pumps that increase (multiply) the concentrations of urea and Na+ deep in the medulla
93
There is ____ osmolality as you go deeper into the medulla
Increased
94
In the countercurrent multiplier system:
____ concentrates the filtrate
____ dilutes the filtrate
Descending loop; Ascending loop
95
Is the descending loop permeable to water?
Yes, aquaporin channels are present and is impermeable to Na+ and Cl-
96
Is the ascending loop permeable to water?
No, but transporters such as NKCC are present for reabsorption
97
Anti Diuretic Hormone (ADH) is secreted from ____
Pituitary gland
98
What stimuli cause the release of ADH?
- Osmoreceptors
- Baroreceptors
- ANG II
99
What are the two major effects of ADH?
- Arteriole constriction in the peripheral circulation -- reduces blood flow to the kidney
- Causes epithelial cells that line the nephron collecting duct to insert aquaporins into the apical cell membrane
INCREASES water reabsorption into the blood
100
Actions of ADH in the Kidney
- ADH acts via V2 receptor
- Causes aquaporins to be inserted into the apical membrane of principal cells
- dramatically increases the reabsorption of H2O to the blood
101
Cardiovascular: ADH vascular receptor is ____
V1
102
What is the action of ADH in the cardiovascular system?
Potent vasoconstrictor and increases blood pressure
103
What is the effect of ADH on water reabsorption in the collecting duct?
- Without ADH, the late DT and CD are impermeable to water
- With ADH release, AQP-2 channels are present. Late DT and CD become permeable to H2O
104
What are the critical roles of phosphate in the body?
- Constituent of bone
- Urinary buffer for H+ (acid base balance)
105
What regulates blood phosphate concentration?
Kidneys
106
Where is phosphate localized primarily in?
- Bone matrix
- ICF
- ECF
107
In the ICF, phosphate is a component of:
- Nucleotides
- High energy molecules (ATP)
- Metabolic intermediates
108
In the ECF, phosphate is present in its ____ form and serves as a ____ for H+. ~10% phosphate in plasma is ____
Inorganic; buffer; Protein bound
109
Phosphate not bound to plasma proteins is ____
Filtered
110
What % of phosphate is reabsorbed?
85% (70% in the PCT, 15% in the proximal straight tubule)
111
Phosphate reabsorption is via what transporter in the nephron membrane?
Na+-phosphate cotransporter
112
True or false: Phosphate reabsorption is saturable and therefore exhibits a Tm
True (when Tm is reached, any phosphate not reabsorbed will be excreted)
113
What % of phosphate is excreted?
15%
114
The high level of excretion of phosphate (15%) is important because:
Unreabsorbed phosphate is a urinary buffer for H+ (titratable acid)
115
What regulated phosphate reabsorption in the PT?
Parathyroid hormone
116
Parathyroid hormone ____ Na+/phosphate co-transport which ____ the Tm for phosphate reabsorption
Inhibits; decreases
117
99% of the body's Ca2+ is contained in ____. 1% is present in ____ and ____
Bone; ICF and ECF
118
What is the total [Ca2+] in plasma?
10 mg/dL
119
Of the total plasma Ca2+:
____ is bound to plasma proteins
____ is bound to other anions such as phosphate and citrate
____ is in the free, ionized form
40%; 10%; 50%
120
Can Ca2+ bound to plasma proteins be filtered across glomerular capillaries?
No - therefore only 60% plasma Ca2+ is filtered
121
What % of filtered Ca2+ is reabsorbed?
>99%
122
Renal handling of Ca2+
____ is reabsorbed in the PT
____ is reabsorbed in the TAL
____ is reabsorbed in the DT
67%; 25%; 8%
123
Plasma [Ca2+] is regulated by ____
Parathyroid hormone
124
____ stimulates Ca2+ reabsorption at the DT
Parathyroid hormone
125
____ plasma Mg2+ is filtered
____ Mg2+ reabsorbed
80%; 95%
126
____ Mg2+ reabsorbed in the PT
____ Mg2+ reabsorbed in the DT
____ Mg2+ reabsorbed in the TAL
30%; 5%; 60%
127
What is Mg2+ reabsorption driven by?
The potential difference generated by NKCC
128
What is the major site of Mg2+ reabsorption?
Thick ascending limb of LoH
