Physiology Flashcards
1
Q
What is the function of the kidney?
A
To maintain the composition and volume of extracellular fluid
2
Q
What are the primary ions in the ECF?
A
Na+, Cl-, HCO3-, Ca2+
3
Q
What are the primary ions in the ICF?
A
K+, (PO4)3-, Mg2+, proteins
4
Q
What does “ECF fluid” include and exclude?
A
Fluid outside of cells but within body boundaries. Does not include water in the bladder, GI tract, and lungs.
5
Q
What is the typical volume of the ICF?
A
27 L
6
Q
What is the typical volume of the ECF?
A
15 L
7
Q
What is the function of the ECF?
A
To create a supportive environment for the cells
8
Q
What are the two components of the ICF?
A
Non-circulating cells (24 L), and circulating blood cells (3 L)
9
Q
What are the two components of the ECF?
A
Interstitial fluid (12 L), and plasma (3 L)
10
Q
What is the function of the mobile portion of the ECF (plasma)?
A
To carry nutrients and waste to and from the stationary portion.
11
Q
What are the important water intakes and their quantities?
A
Ingestion (2 L) Metabolic processes (0.5 L)
12
Q
What are the important water outputs and their quantities?
A
Sweat and feces (0.1 L)
Respiration, skin “leak” (0.9 L)
Urine (1.5 L)
13
Q
What happens to the ECF when water input equals output?
A
The volume does not change (homeostasis)
14
Q
What values are behavior dependent?
A
Ingestion, sweat
15
Q
How are behavior dependent changes compensated for?
A
Changes in urinary output
16
Q
What values are regulated by the renal system?
A
Volume, osmolarity, electrolyte composition, pH, waste, foreign substances (first 4 are ECF characteristics)
17
Q
What is the basic structural components of the kidney?
A
The nephron
18
Q
How many nephrons are in a kidney?
A
One million
19
Q
What are the two major components of a nephron?
A
A blood supply and an epithelial tube (tubule)
20
Q
What are the two components of a nephron’s blood supply?
A
Glomerular capillary bed and peritubular capillaries in series
21
Q
Describe glomerular filtration
A
Free passage of water and solutes into the initial portion of the tubule while retaining large colloids and blood cells
22
Q
Describe tubular reabsorption
A
Filtered components are reabsorbed as part of regulation via highly selective transporters.
23
Q
Describe excretion
A
Excesses of regulated substances pass through the tubule and are excreted in the urine
24
Q
Describe tubular secretion
A
Reabsorbed substances are secreted back into the filtrate
25
How much of the cardiac output goes to the kidneys?
25% (2nd largest requirement)
26
What is the quantity of renal blood flow?
1.3 L/min
27
What is the renal plasma flow?
0.65 L/min
28
What is the normal filtration fraction?
0.2 (20% of the flow enters a tubule)
29
What is the typical glomerular filtration rate?
0.13 L/min
30
How much of the filtrate flow is reabsorbed?
99%
31
What portion of body energy is used in kidney functions?
10%
32
Why does the kidney remove so much into the filtrate only to reabsorb it?
This excess is a safety measure which is built in to account for large additions to the ECF (i.e. from the GI tract). The kidney is always ready to correct for any large imbalancing additions
33
What are the non-ECF functions of the kidney?
Erythropoietin production
Gluconeogenesis (emergency glucose production)
Vitamin D production
BP regulation
34
Describe hormonal BP regulation
Low BP -> Renin secretion -> conversion of angiotensinogen to angiotensin I -> conversion of Ag I to Ag II in lungs -> vasoconstriction -> increased BP
35
What is the normal plasma level of HCO3-?
18-23
36
What is the normal plasma level of CL-?
98-106
37
What is the normal plasma level of creatinine?
0.6-1.2
38
What is the normal plasma level for osmolarity?
280-296
39
What is the normal plasma level of K+?
3.5-5.0
40
What is the normal plasma level of protein?
6.0-8.4
41
What is the normal plasma level of Na+?
135-145
42
What is the normal plasma level of BUN?
7-18
43
What are the components of the glomerulus?
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Afferent and efferent arterioles (blood to and from)
Capillary loops (site of glomerular filtration)
Bowman's capsule (tubule portion interacting with capillary loops)
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44
What is the function of granular cells?
Smooth muscle cells in afferent arteriole responsible for renin secretion.
Part of the juxtoglomerular apparatus
45
What is filterability?
Ability to enter the filtrate, dependent on concentration in filtrate and plasma and molecular size. (0 unfiltered to 1 free filter)
46
What is the size limit of ultrafiltration?
60,000 daltons
47
What is the size limit for free filtraion
Less than 1000 daltons
48
What are the three layers of the filtration barrier?
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Capillary endothelium (fenestrated)
Basal lamina (slit membranes)
Podocytes (tubular epithelium)
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49
What is the function of the endothelium?
Exclude RBCs, generally non-selective
50
What is the function of the basal lamina?
Mucoproteins, regularly sized holes (slit membrane) and negative charge to perform ultrafiltration
51
What is the function of the podocytes?
Pedicles intertwine to act as a sieve. Help create the basal lamina.
52
What are the forces contributing to GFR?
Capillary hydrostatic force (positive flow)
Tubule hydrostatic "back-flow" (negative flow)
Tubule osmotic force (negative flow)
53
What is the Starling equation for GFR?
GFR= K(Pgc-Pt-Pi(gc))
54
What is the typical value of capillary hydrostatic force (Pgc)?
46 mm
55
What is the typical value of tubule hydrostatic "back-flow" (Pt)?
10 mm
56
What is the typical value of tubule osmotic force (Pi(gc))?
30 mm
57
What is the typical value of net filtration pressure (NFP)?
(Pgc-Pt-Pi(gc)), 6 mm
58
How is a high filtration rate achieved with a small NFP?
K is very large.
59
What is K and its contributing factors?
Total hydraulic conductivity.
| Product of specific hydraulic conductivity and SURFACE AREA
60
What is autoregulation?
Afferent arteriole contraction to decrease GFR to normal level when MAP is increased.
61
What is the range of autoregulation?
75-150 mmHg
62
How is the hypovolemia response different from autoregulation?
Hypovolemic response constricts both the afferent and efferent arterioles.
63
What is the effect of autoregulation's contraction?
Afferent constriction increase resistance to flow (decreasing RBF and GFR)
64
What is the effect of hypovolemic response's contraction?
Efferent constriction acts as a flow diverter to restore Pgc and GFR by increasing resistance to RBF. This increases filtration fraction
65
How are the autoregulation and hypovolemic responses different when MAP is low?
Autoregulation would dilate in response to low MAP.
| Hypovolemic response would constrict the afferent an efferent arterioles.
66
What are the three baroreceptors in hypovolemic response?
1) usual baroreceptors sense low MAP and cause sympathetic nerve stimulation and renal vasoconstriction.
2) external baroreceptors cause hormone mediated constriction by renin release.
3) intrarenal baroreceptors in granular cells sense low MAP and stimulate renin axis, systemic vasoconstriction to increase renal blood flow.
67
What are renal prostaglandins?
Secreted by renal interstitial cells in the medulla in response to AgII.
68
What is the function of renal prostaglandins?
Local dilation of afferent arterioles to maintain renal blood flow and prevent ischemia (blunts other responses)
69
What tubule structures are in the medulla?
Collecting duct and loop of Henle
70
What tubule structures are in the cortex?
Proximal and distal tubules
71
What is the appearance of the medulla?
Parallel tubes
72
What is the appearance of the cortex?
Circles and glomeruli
73
What is the branching of arteries in the kidney?
Renal artery -> Ant. and Post. segments -> Interlobar artery -> Arcuate artery -> Interlobular artery -> Afferent arteriole
74
What is the branching of veins in the kidney?
Efferent arterioles -> Vasa recta -> Interlobular veins -> Arcuate veins -> Interlobar veins -> renal vein
75
What is the function of mesangial cells?
Secrete matrix continuous with basal lamina, phagocytic, contractile.
76
What is unique about juxtamedullary nephrons?
Key to urine concentration
77
Describe the epithelium of the proximal tubule
Cuboidal with extensive microvilli
78
Describe the epithelium of the thin Loop of Henle
Simple squamous
79
Describe the epithelium of the thick Loop of Henle
Cuboidal with lots of mitochondria
80
Describe the epithelium of the distal tubule
Cuboidal with short sparse microvilli
81
Describe the epithelium of the collecting duct
Principal and intercalated celles, cuboid transitioning to columnar
82
What is the primary function of the proximal tubule?
Na/K ATPase to pump Na to basolateral side, drives the uptake of water, sodium, glucose, and AA's by facilitated diffusion.
83
What is the primary function of the Loop of Henle?
Creates different Na and water permeabilities in the thin and thick segments to maintain the medullary osmotic salt gradient and actively transport sodium.
84
What is the primary function of the distal tubule?
Acid/base balance, respond to aldosterone, Na/K ATPase.
85
What is the primary function of the collecting tubule?
Couple sodium uptake and potassium secretion, respond to ADH
86
What is the function of intercalated cells?
Secrete H+ and reabsorb HCO3-
87
Describe the epithelium of the bladder?
Transitional epithelium with folded elastic lamina propria allowing for stretch.
88
What percentage of filtered water is reabsorbed?
92-99.7%
89
What percentage of filtered sodium is reabsorbed?
98-99.99%
90
What portion of the unit is for bulk (obligatory) reabsorption?
Proximal tubule and loop of Henle.
91
What portion of the unit is for homeostatic (fine-tuning) reabsorption?
Distal tubule and collecting ducts
92
What ion maintains electrostatic neutrality with sodium?
Chloride (paracellular transport facilitated by sodium)
93
What percent of sodium and water is absorbed in the proximal tubule?
65%
94
What percent of sodium and water is absorbed in the loop of Henle?
15% of water (descending), and 25% of sodium (ascending)
95
Describe countercurrent multiplication
Maintenance of medullary osmotic gradient from "U-shape" tubule and variable permeability/reabsorption
96
What percent of sodium and water is absorbed in the dital tubule and collecting duct?
6% of water and 8% of sodium obligatory, remainder +/- by aldosterone and ADH (distal and collecting respectively)
97
How does aldosterone affect Na reabsorption?
Turn on genes to increase the number of Na+ transporters.
98
How does ADH affect water reabsorption?
Causes the release of preformed vesicles filled with aquaporins.
99
Define glomerulotubular balance
Ability of the proximal tubule to compensate for abnormally high GFR and keep 65% of the filtrate reabsorbed despite the value of GFR.
100
Define tubuloglomerular feedback
Regulation of GFR by sensing of NaCl at the macula densa (distal tubule) and initiate afferent arteriole constriction or dilation. Occurs when glomerulotubular balance is not sufficient to compensate for high GFR.
101
What is the primary driver of ECF volume?
Sodium
102
What is the primary driver of ECF osmolarity?
Water
103
What are the body's volume sensors?
High pressure baroreceptors (sense EABV via MAP) at aortic arch and carotid sinus
Kidneys at the juxtoglomerular apparatus in afferent arterioles and macula densa
104
What is the primary effector of body volume?
Kidney modification of sodium and water retention and secretion.
105
Describe the sequence following sodium loss
Low sodium -> water shifts into cells -> low ECF -> low MAP -> increased baroreceptor reflex -> renin release via sympathetic stimulation -> increased angiotensin II -> increased aldosterone (adrenal cortex) -> Na reabsorption (distal and collecting) -> Na addition
106
How is renin release caused?
Direct sympathetic innervation of JGA releases catecholamines
107
What is the serum osmolarity equation?
Osmo = 2*Na + Glu/18 + BUN/2.8
108
Where are the body's osmoreceptors?
Neurons in the supraoptic nucleus (SON) of the hypothalmus
109
Describe the sequence following negative and positive water balance
Negative water balance -> high osmolarity -> cell shrinking -> increased ADH production
Positive water balance -> low osmolarity -> cell swelling -> decreased ADH production
110
What serum osmolarity gives ADH release?
280
111
What serum osmolarity gives thirst stimulation?
290
112
What serum osmolarity gives the highest urine osmolarity?
290
113
Why does the serum osmolarity at which highest urine osmolarity equal that of thirst stimulation?
Because the urine is as concentrated as it can be so water can only be further added to the body by ingestion.
114
Describe the release of ADH
Synthesized in the SON, packaged into vesicles and transported to posterior pituitary for storage and release. Reaches kidney and binds Vz receptor in collecting duct, initiates cAMP signalling and aquaporin synthesis.
115
At what quantity of volume loss does the volume pathway override the sodium pathway?
10% loss
116
How does ANP affect volume regulation?
Acts as a natural diuretic hormone, activated in hypervolemia. It dilates afferent and efferent arterioles and blocks the action of ADH and aldosterone, and blocks secretion of renin and ADH.
