1
Q
List the functions of the kidney.
A
- Regulation of water concentration and fluid volume
- Regulation of inorganic ion concentrations
- Regulation of acid-base balance
- Some gluconeogenesis & synthesis of hormones
- Excretion of metabolic waste products and xenobiotics
2
Q
List the 4 essential renal processes in the nephron.
A
- Filtration
- Reabsorption
- Secretion
- Excretion
3
Q
Define renal filtration.
A
Water and small solutes are forced under pressure to flow from the glomerulus into the Bowman’s space
4
Q
Define renal reabsorption.
A
Substances reclaimed from lumen to blood
5
Q
Define renal secretion.
A
Substances move from peritubular capillary to lumen
6
Q
Define renal excretion.
A
Substances are removed in the urine
7
Q
How many kidneys do humans have? Location?
A
2 kidneys located at either side of the vertebral column at posterior/dorsal wall outside main visceral cavity (retroperitoneal)
8
Q
Define retroperitoneal.
A
Outside main visceral cavity
9
Q
How many ureters do we have? Function?
A
- 2 ureters connecting each kidney to the urinary bladder
- Collects major calices
10
Q
How many urethras do we have? Function?
A
1 urethra connecting the bladder to the exterior for excretion
11
Q
What is the function of the fibrous capsule of the kidney? What tissue does it work with?
A
Works w/ adipose layer to protect outside of each kidney
12
Q
What 2 major layers is kidney tissue organized into?
A
Cortex and medulla
13
Q
What are the pyramids of the kidney? Appearance? Characteristics?
A
- Cone-shaped
- Arranged w/ tips (papilla) pointing inward
14
Q
Describe the diff calices of the kidneys. Function, location of each?
A
- Minor calices collect each pyramid
- Major calices collect groups of minor calices
15
Q
What is the significance of the hilum of the kidney?
A
Vessels and ureter enter the kidney here
16
Q
What is a nephron? How many do we have? Location?
A
- Functional unit of the kidney
- 1 million total
- Extends through both cortex and medulla
17
Q
What is the function of juxtamedullary nephrons? What % of nephrons do these make up?
A
- Contribute to medullary osmotic gradient
- 15%
18
Q
What type of nephrons make up 85% of the total amount of nephrons in the kidneys?
A
Cortical nephrons
19
Q
What does the renal corpuscle include?
A
- Glomerulus
- Bowman’s capsule
20
Q
What is the glomerulus?
A
Capillary filtration unit
21
Q
What is Bowman’s capsule? Location?
A
- Site where filtrate passes from the vascular system into the tubule system
- Surrounds glomerulus
22
Q
What are the functions of the renal corpuscle?
A
- Connects to proximal convoluted tubule to pass on filtrate
- Creates a filtrate similar to plasma, free of blood cells and proteins
23
Q
What is the input and output of the renal corpuscle?
A
- Input = afferent arteriole
- Output = efferent arteriole
24
Q
What does it mean to be fenestrated? Which cells are fenestrated?
A
Endothelial cells have holes in them
25
What comprises the basement membrane of the glomerulus? Function?
- Composed of gel-like acellular network of collagen and glycoproteins
- Surrounds endothelial cells
26
What are podocytes? Function? Location?
Interdigitate around the basement membrane, leaving gaps for flow-thru
27
What kinds of molecules pass through the basement membrane? Which are repelled?
- Large, negatively charged proteins are repelled
| - Small solutes pass through
28
What drives glomerular filtration of plasma?
Pressure differences
29
What is the equation for net filtration? Define each component and give typical values.
P (NFP) = [P(gc) + π(bc)] -
[P(bc) + π(gc)]
-P(gc): hydrostatic pressure in glomerular capillaries (~50 mmHg)
-π(gc): oncotic pressure in Bowman's capsule (very small, negligible)
-P(bc): hydrostatic pressure in Bowman's capsule caused by the fluid collecting there (~10 mmHg)
-π(bc): oncotic pressure in glomerular capillaries since there are proteins in the blood, but not in the filtrate (~25 mmHg)
30
What are the characteristics of tubules?
- Lined w/ epithelial cells
| - Have differing channels and pumps all along the length of the tubule
31
What are peritubular capillaries?
Second capillary bed that comes off the efferent arteriole and surrounds the tubule system
32
What happens to substances that are not filtered at the glomerulus? What is this process called?
Tubular secretion: substances secreted into the tubule by the peritubular capillary
33
What substances are secreted vis tubular secretion?
K+, H+, NH4+, urea, some creatinine, some hormones, some drugs
34
What is the mechanism by which tubular secretion occurs?
Active transport across epithelial cell membranes
35
What is tubular reabsorption?
Tubular epithelial cells transport certain substances back across into the peritubular capillary
36
What are the mechanisms by which tubular reabsorption occurs?
- Can be passive (using flux down gradients)
| - Active transport (using pumps or exchangers)
37
Where does potassium secretion occur? What does it depend on?
- In cortical and medullary collecting ducts
| - Depends on balance
38
What does potassium secretion require?
- H-K-ATPase channel in Type A intercalated cells
| - H+ secretion to reabsorb K+
39
What stimulates potassium secretion?
Aldosterone, hypernatremia, volume depletion, ACTH
40
What substances reduce potassium secretion?
Dopamine, ANP
41
Where does sodium reabsorption occur? What % of reabsorption occurs there? Mechanism of each?
- Proximal convoluted tubule reabsorbs ~65% via uncontrolled active transport
- Loop of Henle reabsorbs ~25% via uncontrolled passive transport
- Distal tubules and collecting ducts reabsorb the remainder
42
What factors increase sodium reabsorption?
- Aldosterone
| - Antidiuretic hormone
43
What inhibits reabsorption? How?
ANP inhiits reabsorption by increasing sodium excretion
44
What kind of drugs affect sodium reabsorption?
Diuretics
45
Where does water reabsorption occur? What % of reabsorption occurs there?
- Proximal tubule reabsorbs ~65%
- Loop of Henle reabsorbs ~10%
- Distal tubules and collecting ducts reabsorb ~5-25% depending on fluid need
46
What molecule follow sodium and water?
Chloride
47
What follows sodium reabsorption? Why?
Water follows to keep osmotic balance
48
Where is bicarbonate reabsorbed? What % does each location account for?
- Proximal tubule reabsorbs 80%
| - Loop of henle reabsorbs 10-20%
49
What is the equation for glomerular filtration rate?
```
GFR = Kf x Pnet
Kf = filtration coefficient
Pnet = net filtration pressure
```
50
What is the typical adult GFR?
125 mL/min
51
Why is there no way to directly measure GFR?
Due to small size of the renal corpuscle
52
Define clearance.
Volume of plasma that is completely "cleaned" of a substance
53
Does clearance every equal GFR?
No natural substance in the body where Cx = GFR
54
Equation for clearance.
Cx = (Ux x Vurine) / Px
Ux: [x] in urine
V(urine) = urine flow rate
Px: [x] in plasma
55
What does it mean if clearance is equal to GFR? Greater than? Less than?
- Cx = GFR --> substance is only filtered
- Cx > GFR --> net secretion of substance
- Cx net absorption of substance
56
By how much does creatinine overestimate GFR?
Overestimates GFR by 10-20%
57
Why is creatinine easily monitored?
B/c produced at a relatively constant rate
58
What is GFR proportional to?
- Creatinine clearance
| - Urine creatinine
59
What is GFR inversely proportional to?
Plasma creatine
60
What is specific gravity? Equation?
- Ratio of density of a material to the density of water
| - P(material) / P(water)
61
What is specific gravity used as an index for?
Total solute w/in the urine (osmolarity)
62
What is the juxtaglomerular apparatus?
Area where the distal convoluted tubule comes up b/t the afferent and efferent arterioles
63
What make up the juxtaglomerular apparatus?
- Extraglomerular matrix cells
- Macula densa cells
- Granular cells
64
What is the function of macula densa cells?
- Sense [NaCl] in arterioles and signal granular cells to low conc
- Secrete vasodilator/vasoconstrictor chemicals onto arterioles
65
What is the function of granular cells?
Secrete renin in response to macula densa cells
66
What does renin do?
Activates angiotensinogen (in liver) to produce angiotensin I
67
What does angiotensin I stimulate?
- Adrenals to produce aldosterone
- Hypothalamus to produce arginine vasopressin
- Hypothalamic thirst drive
- Arteriolar vasoconstriction
68
What does aldosterone stimulate?
Na+ reabsorption by the renal distal tubule
69
What is arginine vasopressin also known as?
Antidiuretic hormone
70
Where is ADP made? Stored?
- Made in the hypothalamus
| - Stored in the posterior pituitary
71
What is ADP release controlled by?
- BP
- Plasma osmolarity
- Angiotensin II
72
What inhibits the release of antidiuretic hormone? What happens consequently?
- Ethanol (alcohol)
| - You'll pee more --> get dehydrated --> contributes to hangover
73
What synthesizes and secretes atrial natriuretic peptide?
Cardiac atria
74
When is atrial natriuretic peptide released?
When pressure or stretch in the atrium gets too high (high BP)
75
What does atrial natriuretic peptide cause?
Relaxation of afferent arterioles into the renal corpuscle
76
What does atrial natriuretic peptide inhibit?
Release of renin
77
What is the RAAS system? Function?
Renin-Angiotensin-Aldosterone system stimulates Na+ reabsorption by the distal and collecting tubules
78
What is ANP? Function?
Atrial Natriuretic Peptide inhibits Na+ absorption at the distal nephron --> allows Na+ and water retention in the urine --> causes increased excretion of Na+ and water by the kidney --> reduces blood volume
79
What does ADH do?
Tubule and ductal cells become more permeable to water --> increase Na+ absorption
80
Define hypotonic.
Soln has a lower solute concentration than the cell --> water moves out of soln into cell
81
Why did creatinine clearance greatly increase in the hypotonic subject (water)?
Increased flow rate
82
Why did the sodium clearance greatly decrease in the hypotonic subject (water)?
Increased flow rate
83
What is the expected result for specific gravity of the hypotonic subject (water)?
Decreased from normal
84
What did creatinine clearance increase in the isotonic subject (saline)?
Increased flow rate
85
Why did the sodium clearance increase in the isotonic subject (saline)?
Increased flow rate
86
Why did the sodium clearance decrease in the hypertonic subject (bicarbonate)?
Decreased flow rate
87
Why did the creatinine clearance decrease in the hypertonic subject (bicarbonate)?
Decreased flow rate
88
Why did the pH increase in the hypertonic subject (bicarbonate)?
Bicarbonate raises the pH of water
89
Define isotonic.
Solute concentration is equal inside and outside of cell --> water moves equally in both directions
90
Define hypertonic.
Solute concentration is higher in soln than cell --> water moves out of cell into soln
91
What changes in flow rate, Cr clearance, pH, specific gravity, [Na+], and Na+ clearance occurred in the hypotonic subject?
- Increase in flow rate
- Increase in Cr clearance
- Increase/? in pH
- Decrease in specific gravity
- Decrease in [Na+]
- Decrease in Na+ clearance
92
What changes in flow rate, Cr clearance, pH, specific gravity, [Na+], and Na+ clearance occurred in the isotonic subject?
- Increase in flow rate
- Increase in Cr clearance
- Increase/? in pH
- No change in specific gravity
- No change/increase in [Na+] & Na+ clearance
93
What changes in flow rate, Cr clearance, pH, specific gravity, [Na+], and Na+ clearance occurred in the hypertonic subject?
- Huge increase in pH
- Increase in specific gravity
- Increase in [Na+]
- Increase in Na+ clearance
94
What is the role of osmoreceptors in water balance and ADH release?
Osmoreceptors are particularly sensitive to decreases in extracellular fluid osmolarity --> stimulate the pituitary to secrete ADH
95
If the room had been very hot during the exercise tests in the respiratory or cardiovascular labs, how might water balance and osmoreceptors have been effected?
Hot room would induce increased sweating --> increased water and Na+ loss --> osmoreceptors would stimulate ADH secretion
96
How does the kidney regulate plasma bicarbonate or hydrogen concentrations?
pH is controlled by the active secretion of H+ and bicarb ions by the intercalated cells in the proximal, distal, and collecting tubules
97
What is water diuresis? What pathologic states/diseases induce diuresis? How?
- Increased urinary output of water w/ little/no increase in excretion of solutes
- Normally a response to excess water ingestion, but can occur in response to an inappropriate vasopressin secretion
98
What hormone combats diuresis, and what are its pathways of function?
Vasopressin
99
What does angiotensin II do?
- Stimulates the synthesis and secretion of aldosterone by the adrenal cortex
- Increases the Na+-H+ exchange in the proximal convoluted tubule
- Increases thirst
- Causes vasoconstriction of the arterioles --> increases TPR and arterial pressure
100
What changes in GFR occurred in response to hypotonic (water) drinks? Mechanism?
Increase in GFR b/c decrease in plasma osmolarity and increase in plasma volume trigger ANP system
101
What changes in GFR occurred in response to isotonic (saline) drinks? Mechanism?
Increase in GFR b/c isotonic increase in plasma volume activates ANP system
102
What changes in GFR occurred in response to alkalytic (bicarb) drinks? Mechanism?
Decrease in GFR b/c increase in plasma osmolarity and minimal effect on volume activates RAAS system
103
What changes in Na+ clearance occurred in response to isotonic drinks?
Higher than normal
104
What changes in Na+ clearance occurred in response to hypotonic drinks?
Same or lower than normal
105
What changes in Na+ clearance occurred in response to alkalytic drinks?
Same as normal
106
What are the mechanisms controlling Na+ balance? How does each contribute?
- RAAS system compensates for reduced Na+
| - ANP compensates for elevated body Na+
107
What are the major components of gastric secretions?
Water and HCl (protons)
108
If we know the plasma concentration of a certain molecule or substance, which properties would that substance need to accurately estimate GFR?
- Freely filtered at a constant rate
| - No secretion or reabsorption
109
What is the function of the ascending loop of Henle?
Drives osmotic gradient in kidney
110
What is the function of the distal convoluted tubule?
Reabsorbs additional sodium due to aldosterone
111
What is the function of the proximal convoluted tubule?
A majority of essential ions and glucose are reabsorbed
112
What is the function of the descending loop of henle?
Mainly permeable to H2O
113
What is the function of the collecting duct?
Location of AQP2 channels
114
Constriction of the ____ arteriole and the dilation of the ____ arteriole will lead to increased filtration at the glomerulus.
- Efferent
| - Afferent
NPB 101L
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