Renal Physiology Flashcards
1
Q
What are the three functions of the kidneys?
A
- Regulation of blood volume and composition.
- Regulation of blood pressure.
- Contribution to metabolism.
2
Q
What is the renal hilus?
A
Deep vertical fissure near the center of the concave renal border. The ureter emerges from the hilus along with lymphatic vessels, blood vessels, and nerves.
3
Q
What are the three layers of tissue around the kidney?
A
- Renal capsule.
- Adipose capsule.
- Renal fascia.
4
Q
What is the renal capsule?
A
Deepest layer of the kidney, clear and irregular connective tissue that is continuous with the shiny outer lining of the ureter.
5
Q
What is the function of the renal capsule?
A
Serves as a barrier against trauma that also maintains the shape of the kidney.
6
Q
What is the adipose capsule?
A
Mass of fatty tissue surrounding the renal capsule.
7
Q
What is the function of the renal capsule?
A
Barrier against trauma and holds the kidneys firmly placed in the abdominal cavity.
8
Q
What is the renal fascia?
A
The superficial layer of the kidney.
9
Q
What is the function of the renal fascia?
A
Defence layer, anchors the kidneys to the surrounding structures and to the peritoneum.
10
Q
What is the renal cortex?
A
Smooth-textured, reddish area of the kidney, comprises the outer-rind of the kidney.
11
Q
What is the renal medulla?
A
The inner section of the kidney, contains cone-shaped renal pyramids.
12
Q
What are renal pyramids?
A
Cone-shaped structures within the renal medulla that point toward the renal hilus for renal emptying/clearance.
13
Q
What are renal papila?
A
Segments of pyramidal cones in the renal medulla, narrower/apical end
14
Q
What are the two zones of the renal cortex?
A
The cortical zone and the juxtamedullary zone.
15
Q
What is a renal column?
A
Portion of the renal cortex that extends between renal pyramids.
16
Q
What is a renal lobe?
A
Portion of the kidney consisting of one pyramid and half of adjacent columns.
17
Q
What is the parenchyma?
A
Functional portion of the kidney consisting of the renal cortex and the pyramids of the renal medulla.
18
Q
What are the functional units of the kidney? Where are they located?
A
The nephrons; are located within the parenchyma.
19
Q
Where does urine formed by nephrons drain?
A
Into the papillary duct.
20
Q
What are the papillary ducts?
A
Ducts that collect urine formed by nephrons, extend through the renal papillae.
21
Q
Where do papillary ducts drain?
A
Into minor calyx.
22
Q
Where do minor calyces drain?
A
Into a major calyx.
23
Q
Where do the major calyces drain?
A
Into the renal pelvis.
24
Q
What blood vessel supplies the kidneys?
A
Right and left renal arteries.
25
List the branching of renal circulation from IN to OUT:
1. Renal artery.
2. Segmental arteries.
3. Interlobar artieries.
4. Arcuate arteries.
5. Interlobular arteries.
6. Afferent artieries.
7. Glomerular capillaries.
8. Efferent arterioles.
9. Pertitubular capillaries.
10. Interlobular veins.
11. Arcuate veins.
12. Interlobar veins.
13. Renal vein.
26
What is a renal lobule?
Group of nephrons that empty into the same collecting duct.
27
What is unique about the glomerular capillaries?
They are positioned between two arterioles.
28
What is the vasa recta?
Loop-shaped capillaries supply the tubular sections of the nephron in the renal medulla.
29
Where does the blood leave the kidney from?
Renal vein that exits the renal hilus.
30
What is the renal corpuscle?
Glomerular capsule and the glomerular capillary system.
31
What is the function of the renal corpuscle?
To filter blood plasma into the nephron.
32
What is the renal tubule?
Consists of the proximal tubule, descending loop of Henle, ascending loop of Henle, and the distal tubule.
33
What is the function of the renal tubule?
Conducts filtered fluid through the nephron.
34
What comprises the visceral layer of the glomerular capsule?
Podocytes with footlike projections that wrap around a single layer of endothelial cells of the glomerular capillaries.
35
What comprises the parietal layer of the glomerular capsule?
Simple squamous epithelium that forms the outer wall of the capsule.
36
What are the urethral differences between male and female systems?
Male: passes through prostate, longer.
Female: shorter in length.
37
Are the majority of nephrons cortical or juxtamedullary?
Majority (80%) is cortical, 20% are juxtamedullary.
38
What are peritubular capillaries?
Long, specialized capillaries that align alongside the juxtamedullary nephron tubules.
39
What is the juxtaglomerular complex?
Comprised of the ascending limb of the loop of Henle and glomerulus and afferent/efferent arterioles.
40
What is the morphology of the tubular epithelium?
Epithelial cells are connected mostly by tight junctions; the apical surface faces the lumen while the basolateral surface faces the renal interstitium by resting on the basement membrane.
41
What kind of fluid enters the tubules through glomerular filtration?
Protein-free plasma like fluid.
42
What two processes is the filtrate subject to?
Reabsorption and secretion.
43
What filtrate contents are reabsorbed?
Water and solutes.
44
Where is filtrate reabsorbed?
Through vasa recta or peritubular capillaries.
45
What is secretion?
Selective removal of substances from the circulation into the tubular filtrate.
46
What is the function of the loop of henle?
Descending limb: facilitates water reabsorption.
| Ascending limb: facilitates active solute reabsorption.
47
What kind of filtrate leaves the loop of henle?
Diluted.
48
What is the function of the distal & convoluted tubule?
Salt and water regulation, varies in permeability based on body needs (in response to hormones)
49
How is the amount of solute excreted calculated?
Based on the amount of solute filtered minus the amount reabsorped plus the amount secreted into tubules.
50
What is the filtration fraction?
Proportion of plasma volume that filters into the tubule.
51
What are the three filtration barriers in the renal corpuscle?
Glomerular capillary endothelium.
Basal lamina (basement membrane)
Epithelium of bowman's capsule.
52
What is the morphology of the glomerular capillary endothelium? How is it a filtration barrier?
Contains fenestrated capillaries with pore sizes that permit most solutes but not plasma proteins.
The surface is negatively charged to repel proteins.
53
What is the function of the glomerular basement membrane? How is it a filtration barrier?
It is the extracellular matrix of the glomerular membrane, separates glomerular capillary endothelium from Bowman's epithelium.
Negatively charged to repel proteins.
54
What is bowman's capsule epithelium? How is it a filtration barrier?
Layer of podocytes with foot processes that wrap around glomerular capillaries with slits for siltration; contain contracile mesangial cells that contribute to blood flow control.
55
What two Starling forces dictate glomerular filtration?
1. Glomerular capillary hydrostatic pressure favors filtration (high pressure wants to move INTO bowman's space)
2. Proteins remaining in the capillaries oppose filtration (lower than glomerular hydrostatic pressure)
56
What is GFR?
Volume of fluid entering Bowman's capsule per unit time.
57
What is GFR influenced by?
Net filtration pressure (altered by renal blood flow)
Filtration coefficient (total surface area, permeability)
58
What does increased renal nerve activity cause?
Decreased RBF and GFR.
59
How do RBF and GFR remain stable in face of fluctuating arterial pressures?
Constant operation of renal autoregulatory mechanisms.
60
What two mechanisms is renal autoregulation composed of?
Myogenic response
| Tubuloglomerular feedback mechanism
61
What is the function of renal autoregulation?
To keep RBF and GFR between 80-180mmHg,
62
What is the myogenic response?
When RBF increases, hydrostatic pressure against walls of the afferent arteriole also increase.
Stretch receptors in vascular smooth muscle cells nitiate vasoconstriction
RBF decreases, causing pressure in glomerular capsule to decrease, which in turn idecreases the GFR
63
What is the tubuloglomerular feedback mechanism?
1. GFR increases
2. Increased tubular flow past macula densa (early distal tubule)
3. Paracrine factor released from macula densa.
4. Afferent arteriole constricts, resistance increased.
5. Glomerular hydrostatic pressure decreased
6. decreased GFR
64
What other system does feedback from the macula densa activate? (Other than constriction of afferent arterioles?)
The RAAS system.
65
How is water reabsorped?
Sodium is actively transported from the lumen to the interstitium, this creates an electrochemical gradient that drives anion reabsorption. Water moves by osmosis, following solute reabsorption.
66
What is transcellular reabsorption?
Transport through tubular epithelial cells (via receptors or transporters)
67
What is paracellular reabsorption?
Diffusion between cell tight junctions.
68
How is sodium reabsorped?
Sodium concentrations in epithelial cells are low so sodium is able to pass through ENac channels and sodium hydrogen exchangers.
Excess sodium is then pumped out through Na-K-ATPase.
69
How does intracellular sodium levels remain low?
Basolateral Na-K-ATPase
70
How does glucose diffuse out of the cell and into interstitial fluid?
Via the GLUT channel (diffuses due to low gradient in interstitial fluid)
71
What is the fate of proteins that enter the tubules?
Receptor-mediated endocytosis conserves the proteins, which are transported to the renal interstitium and degraded into amino acids.
72
What occurs if all available solute transporters are occupied? What does this mean for the final filtrate?
The transport maximum for a substance has been reached and that substance will NOT be reabsorped. It will be excreted in the final urine.
73
How is capillary exchange governed by Starling equilibrium from the interstitial fluid following filtration?
Low peritubular capillary hydrostatic pressure, high capillary colloid osmotic pressure (pushes fluid into capillaries):
Favours movement of solute INTO capillaries by bulk flow.
74
What are OATs?
Organic anion transporters: transport wide variety of wastes. Moves organic wastes FROM interstital fluid into the tubule lumen for excretion.
75
What three factors does the excretion of a substance depend on?
1. Filtration rate.
2. Reabsorption.
3. Secretion.
76
How is clearance rate of a substance calculated?
Urine concentration of substance multiplied by the urine flow rate, all of this divided by the plasma concentration of the substance.
77
What is renal clearance?
The rate at which a substance is lost from the body by excretion or metabolism.
78
How much fluid can the bladder hold?
500mL
79
What is the internal sphincter?
Smooth muscle that is a part of the bladder wall, remains contracted at rest.
80
What is the external sphincter?
Skeletal muscle controlled by somatic motor neurons, CNS stimulation maintains contraction unless urination occurring.
81
What is the micturition reflex?
1. Stretch receptors fire.
2. Parasympathetic neurons fire, smooth muscle contracts and internal sphincter is pulled open.
3. Motor neurons controlling external sphincter stop firing and external sphincter relaxes to open.
82
What is total body water content divided into?
ICF, ECF.
83
What is ECF comprised of?
Interstitial fluid and plasma.
84
What systems stabilize acute fluctuations in fluid and electrolyte balances?
Cardiovascular system, behavior, kidneys.
85
What system stabilized long-term blood pressure?
The kidneys.
86
How do the kidneys stabilize long-term blood pressure?
By regulating water and salt balance which controls blood volume.
87
How is water typically lost?
Urine, feces, sweat.
88
How do the kidneys regulate output when responding to excess water?
Output large volumes of dilute urine.
89
How do the kidneys respond regulate output in response to dehydration?
Small volumes of concentrated urine.
90
Where does adjustment of sodium and water reabsorption occur?
At the renal tubules.
91
What hormone controls water balance?
Vasopressin (ADH)
92
When is vasopressin released?
In response to low blood volume/pressure or increased plasma osmolarity.
93
What is the target for ADH?
V2 receptors istal and collecting tubule, activation increases the expression and insertion of aquaporins
94
What specific aquaporins mediate renal water reabsorption in response to vasopressin?
AQP2
95
Where are AQP2 channels inserted?
Apical and basolateral membranes.
96
What is the most potent stimulus for vasopressin release?
High plasma osmolarity.
97
What is plasma osmolarity monitored by?
Hypothalamic osmoreceptors.
98
How is decreased blood volume/pressure monitored?
Arterial baroreceptors.
99
How is thirst stimulated?
Hypothalamic osmoreceptors stimulate thirst in response to high plasma osmolarity to encourage water intake.
100
Describe the passage of filtrate through the renal tubule.
Isosmotic fluid leaving the proximal tubule becomes progressively more concentrated in the descending limb due to loss of water.
Removal of solute in the thick ascending limb creates hypoosmotic fluid.
Permeability to water and solutes in the distal tubule and collecting duct is regulated by hormones (ADH)
Final urine osmolarity depends on distal tube interactions.
101
What is the countercurrent exchange in the vasa recta?
Vasa recta moves in the opposite direction as filtrate in the loop of henle, preventing water reabsorped in the descending limb from diluting the ascending limb.
102
What effect does excess sodium have on plasma content and blood flow?
Increases plasma osmolarity, drives renal water absorption, expansion of blood volume and increased arterial pressure.
103
How are excess sodium levels counteracted?
Vasopressin secretion and thirst activation.
104
How is sodium balance controlled hormonally?
Aldosterone.
105
What is the function of aldosterone?
Acts at renal distal tubule at principal cells to stimulate sodium reabsorption and increase potassium excretion. This increases the activity of Na-K-ATPase
106
What stimulates aldosterone release?
Low blood volume/pressure, high circulating potassium.
107
What does high potassium activate?
Adrenal cortex.
108
How is low pressure/blood volume sensed to release aldosterone?
Initiate mechanisms for salt/water reabsorption by kidneys through production of angiotensin and aldosterone via RAAS.
109
What suppresses aldosterone production?
High plasma osmolarity.
110
What effect does Ang II have on the brain?
Stimulates vasopressin release at the hypothalamus.
Stimulates thirst.
Increases sympathetic outflow (cardiac output, vasoconstriction, RAAS)
111
What effect does Ang II have on vasculature?
Vasoconstriction (short term increase in blood pressure)
112
What effect does Ang II have on the proximal tubule?
Stimulates apical Na-H-Exchanger (NHE) to stimulate salt & water reabsorption.
113
What is Atrial Natriuretic Peptide (ANP)
Hormone from cardiac cells (atria) that induce natriuresis and diuresis to increase sodium and water excretion.
114
How is ANP released?
In response to high volume conditions in response to cardiac stress.
115
What effect does ANP have on vasculature? How does this impact renal function?
Dilates afferent arterioles to increase GFR, also inhibits sodium reabsorption in collecting duct and sodium/water mediators.
116
Why are potassium levels tightly regulated?
To protect membrane potential and normal cellular function.
117
What is hypokalemia?
Low potassium in blood: muscle weakness, dysfunction of respiratory and cardiac cells.
118
What is hyperkalemia?
High potassium in blood: increase in excitability followed by depression due to impaired repolarization (cardiac arrhythmia)
119
How do kidneys contribute to potassium balance?
High levels of potassium are sensed by the adrenal cortex and excreted through the release of aldosterone.
120
What are the steps of the RAAS system?
1. Blood pressure falls.
2. Renal sympathetic nerve activity increases.
3. Renin activated.
4. Renin cleaves angiotensinogen into Ang I.
5. Angiotensin-converting enzyme (ACE) converts Ang I into Ang II.
6. Ang II acts on the adrenal cortex and also CNS to cause aldosterone release and vasopressin release as well as thirst and increased sympathetic activity.
121
What causes a shift in blood volume and osmolarity?
Disturbances in fluid and electrolyte levels.
122
What is the general outcome of increased blood volume and osmolarity?
Salt intake exceeds fluid intake, therefore ECF volume and osmolarity increase; hypertonic urine.
123
What is the general outcome of increased blood volume, with normal plasma osmolarity?
Salt and water are ingested simultaneously; only volume increases.
isotonic urine.
124
What is the general outcome of increased blood volume, but decreased osmolarity?
Pure water in ingested, ECF dilutes so urine is hypotonic (large amounts)
125
What is the general outcome when blood volume remains unchanged but plasma osmolarity increases?
Solute consumed in absence of fluid intake; thirst is triggered.
Small amounts of concentrated urine.
126
What is the general outcome when blood volume remains unchanged but plasma osmolarity decreases?
Dehydration, only ingesting pure water.
| ECF is diluted.
127
What is the general outcome when blood volume is reduced, but osmolarity is increased?
Caused by diarrhea or excessive sweating, more water is lost than solute.
128
What is the general outcome when blood volume is reduced and osmolarity remains unchanged?
Typically a hemorrhage blood transfusion or IV is required.
129
What is normal body pH?
around 7.4
130
Why must plasma pH remain stable?
To support enzyme, membrane, and protein function.
131
What is the effect of acidosis on neurons?
Less excitable, CNS depression.
132
What is the effect of alkalosis on neurons?
Highly excitable.
133
What are main sources of protons?
Food, organic acids, CO2
134
How are protons excreted?
Ventilation via CO2 and H20
| Renal excretion of protons
135
What are proton buffers?
Bicarbonate in ECF, proteins and hemoglobin, phosphates and ammonia.
136
What are the three key processes in pH homeostasis?
1. Buffer systems.
2. Ventilation.
3. Renal regulation of hydrogen & bicarbonate ions.
137
What is the function of the buffer system?
The first line of defense; rapidly prevents pH fluctuation by combining molecules with protons for transport and release.
138
Where are buffer systems located?
In cells, in plasmsa.
139
What is the function of ventilation in pH control?
Second line of defense, rapidly corrects pH disturbance by regulating rate of breathing to prevent acidosis,
140
What is the function of renal regulation of hydrogen and bicarbonate ions?
Final line of defense, slower process but most effective.
Works via direct excretion or reabsorption of protons, and indirectly by modifying bicarbonate reabsorption or excretion.
141
What is the effect of Hypoventilation?
Increases carbon dioxide concentration, acidotic state.
142
What is the effect of hyperventilation?
Carbon dioxide concentration decreases, pH increases to alkosis.
143
How does the renal system respond to acidosis?
1. Kidneys secrete protons into tubule lumen.
2. Ammonia from amino acids, HPO4 are buffers in the kidneys and trap protons.
3. Buffers increase the renal secretion of protons.
4. New bicarbonate is formed and reabsorbed into the blood to act as a buffer.
144
How does the renal system respond to alkalosis?
Bicarbonate is excreted, protons are reabsorbed to restore pH levels.
145
How long does it take to see apparent changes in pH under the response of the renal system?
24-48 hours.
146
What is the function of the apical Na-H exchanger? (NHE)
Pumps sodium INTO cell, moves protons into the lumen against concentration gradient.
147
What is the function of the basolateral Na-HCO3 symporter?
Sodium and bicarbonate moved out of cell into the interstitium.
148
What is the function of the H-ATPase (proton-pump)?
Protons pumped into lumen of distal nephron (distal tube and collecting duct) against conc gradient.
149
What is the function of the H-K-ATPase?
Protons pumped into urine in exchange for potassium.
150
What is the function of the Na-NH4 antiporter?
NH4 into the lumen in exchange for sodium.
151
What transporters are used in the nephrons to regulate acid-base balance?
1. NHE
2. Basolateral Na-HCO3 symporter
3. Proton Pump
4. H-K-ATPase
5. Na-NH4 antiporter
152
What types of cells in the collecting duct function during acidosis?
Type A intercalated cells.
153
What is the function of type A intercalated cells?
Pump out protons into lumen via proton pump, and H-K-ATPase.
| Reabsorb HCO3 and Potassium
154
What type of cells in the collecting duct are activated during alkalosis?
Type B intercalated cells.
155
What is the function of type B intercalated cells?
Excrete bicarbonate and potassium into lumen, rebasorb protons.
156
What can cause acid-base imbalance?
Metabolism, respiration
157
What does it mean is the plasma pH is altered? If the cause is respiratory, what does this mean?
The buffer system has failed. This means only kidneys can compensate.
158
What causes respiratory acidosis?
```
Hypoventilation
Drug effects
Increased airway resistance
Decreased alveolar gas exchange
Muscular dystrophy
COPD
```
159
How do the kidneys compensate for respiratory acidosis?
Hydrogen excreted, bicarbonate and potassium reabsorped.
160
What causes metabolic acidosis?
```
Dietary and metbolic input of protons exceeds excretion
Lactic acidosis
Ketoacidosis
Ethylene glycol ingestion
Loss of bicarbonate
```
161
How does the respiration system compensate for metabolic acidosis?
Hyperventilation eliminates excess carbon dioxide.
162
How do the kidneys compensate for metabolic acidosis?
Hydrogen excretion and bicarbonate reabsorption.
163
What causes respiratory alkalosis?
Hyperventilation
164
How do the kidneys compensate for respiratory alkalosis?
Excretion of bicarbonate and increased hydrogen ion.
165
What causes metabolic alkalosis?
Excessive vomiting of acidic stomach contents
Excessive ingestion of antacids
ow hydrogen ion concentration
166
How does the respiration system compensate for metabolic alkalosis?
Hypoventilation restores carbon dioxide
167
How do the kidneys compensate for metabolic alkalosis?
Bicarbonate excretion and hydrogen reaborsption
