Renal Physiology Flashcards
1
Q
What are the functions of the kidneys?
A
Regulates blood volume and pressure
Maintaining pH
Excrete urea, uric acid, creatinine, bilirubin, and removal of foreign chemicals
Synthesizes glucose
Secretes EPO, renin, and 1,25-dihydroxy Vitamin D
2
Q
Why do fluid volume changes occur?
A
During various health disorders
By rapid movement of water (osmosis)
3
Q
Where is 40% of the body’s water content found?
A
Intracellular fluid
4
Q
Where is 20% of the body’s water content found?
A
Interstitial fluid
5
Q
What fluid compartment do the kidneys regulate?
A
Extracellular fluid
- fluid outside of cell
- plasma
- interstitial fluid
- CSF
6
Q
What fluid compartment is [Na+] higher?
A
Extracellular fluid compartment
7
Q
What fluid compartment is [K+] higher?
A
Intracellular fluid compartment
8
Q
What fluid compartment is [Cl-] higher?
A
Extracellular fluid compartment
9
Q
What fluid compartment is [HCO3-] higher?
A
Extracellular fluid compartment
10
Q
What fluid compartment is [PO4-] higher?
A
Intracellular fluid compartment
11
Q
What are aquaporins?
A
Water channels
12
Q
What is water concentration measured in?
A
Osmoles = 1 osm is equal to 1 mole of solute particles
13
Q
What is osmolarity?
A
Number of solutes per unit volume of solution expressed in moles per litre
14
Q
What is the water concentration when there is low osmolarity?
A
High water concentration
15
Q
What is the water concentration when there is high osmolarity?
A
Low water concentration
16
Q
What is osmosis?
A
Net diffusion of water across a selectively permeable membrane from a region of high water concentration to one with a lower water concentration
17
Q
What is osmotic pressure?
A
The pressure necessary to prevent solvent movement (osmosis)
18
Q
What is tonicity?
A
Determined by the concentration of non-penetrating solutes of an extracellular solution relative to the intracellular environment of the cell
The solute concentration may influence changes in cell volume
19
Q
What does isotonic mean?
A
Same osmolarity inside and outside of the cell
20
Q
What does hypertonic mean?
A
Higher osmolarity outside than inside of the cell
21
Q
What does hypotonic mean?
A
Lower osmolarity outside than inside of the cell
22
Q
Which way does water flow?
A
From low osmolarity to high osmolarity
23
Q
What is absorption?
A
Movement of solute/water into the blood (plasma)
24
Q
What is filtration?
A
Movement of solute/water out of the blood (plasma)
25
What happens when the net filtration is positive?
Favours filtration
26
What happens when the net filtration is negative?
Favours absorption
27
What is homeostasis?
The total body balance of any substance
28
What are the associated organs in the urinary system?
Ureters
Bladder
Urethra
29
Where is the location of the kidneys?
Retroperitoneal
30
What is the function of the ureters?
Drain the formed urine from the kidneys and empty it into the bladder
31
What is the function of the bladder?
Stores urine and empties out of the body via the urethra
32
What is micturition?
Urination
33
What is the nephron?
The functional unit of the kidneys
34
What are the parts of the nephron?
Renal Corpuscle
| Renal tubule
35
What is the renal corpuscle composed of?
Glomerulus
| Bowman's capsule
36
What are the parts of the renal tubule?
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting ducts
37
What is the proximal convoluted tubule?
Close to the renal corpuscle
| Twisted
38
What is the loop of Henle?
Divided into the descending limb and ascending limb
39
What is the distal convoluted tubule?
Far away from the renal corpuscle
| Drains its contents into the main tube called the collecting duct
40
What is the collecting duct?
Nephrons drain into the collecting ducts which collect all formed processed contents and empty into the renal pelvis of the kidney
41
What does the renal corpuscle do?
The initial blood filtering component
| Blood enters from the afferent arteriole and leaves through the efferent arteriole
42
What does Bowman's capsule do?
The filtrate enters Bowman's space once the blood has been filtered
Has podocytes that come in contact with the glomerulus
Has epithelial cell layer that continues on to form the tubule
43
How is the renal corpuscle developed?
Step 1: nephrons develop as blind-ended tubules composed of a single layer of simple epithelium
Step 2: A growing tuft of capillaries penetrate the expanded end of the tubules
-epithelial layer differentiates into the parietal and visceral layers
Step 3: Parietal layer eventually flattens to become the wall of Bowman's capsule, the visceral layer becomes podocyte layer
44
What are the 3 layers of the glomerular capillary?
Endothelial layer
Basement membrane
Podocytes with filtration slits
45
Where are all renal corpuscles found?
In the cortex
46
What are the two types of nephrons?
Cortical
| Juxtamedullary
47
What are cortical nephrons?
Do basic functions (filtration, reabsorption, secretion)
| Most of the nephron is found in the cortex
48
What are juxtamedullary nephrons?
Do basic functions, regulate the concentration of urine
The renal corpuscle is found in the cortex closer to the medulla, the loop of Henle and the ascending limb are found in the renal medulla
49
What are the 3 types of capillaries around the nephron?
Glomerular
Peritubular
Vasa recta
50
Where are vasa recta capillaries found?
Mostly associated with juxtamedullary nephrons in the medullary portion of the kidney
51
What are the 3 basic renal processes?
Glomerular filtration
Tubular secretion
Tubular reabsorption
52
What is glomerular filtration?
Fluid in the blood is filtered across the capillaries of the glomerulus and into Bowman's space
53
What is tubular reabsorption?
The movement of a substance from inside the tubule into the blood
54
What is tubular secretion?
Movement of nonfiltered substances from the capillaries into the tubular lumen
55
What is the amount excreted equal to?
Amount filtered + amount secreted - amount reabsorbed
56
What can't move out of the glomerular capillaries into Bowman's space
Large proteins and albumin
Why?
pores are not large enough and the pores and basement membrane have negative charges and repel negatively charged proteins
57
What is filtered through the glomerulus?
Water, electrolytes, glucose, amino acids, fatty acids, vitamins, waste products (urea, uric acid, creatinine)
58
What is ultrafiltrate?
The concentration of substrate filtered through the filtration layers is the same in plasma and in the filtrate
cell-free fluid
59
What is proteinuria?
A condition where some of the proteins that are not supposed to pass through the filtration barrier show up in the filtrate and ultimately in the urine
60
Is the net glomerular filtration pressure always positive or negative?
Positive
61
How does glomerular filtration pressure initiate urine formation?
By forcing protein-free filtrate from plasma out of the glomerulus and into Bowman's space
62
What forces favour filtration?
Glomerular capillary blood pressure
63
What forces oppose filtration?
Fluid pressure in Bowman's space
| Osmotic force due to protein in plasma
64
What factor would contribute to an increase in the glomerular filtration rate?
High blood pressure
65
What factor would contribute to a decrease in the glomerular filtration rate?
An increase in the protein concentration in the plasma would increase the protein content in the glomerular capillaries, decreasing the glomerular filtration rate
66
What is the fraction of the volume entering the glomerular capillaries that are filtered?
20%
67
What is the final volume of fluid that is excreted?
1%
68
What is the definition of glomerular filtration rate?
The volume of fluid filtered from the glomerulus into the Bowman's space per unit time
69
How much GF happens per day?
180 L/day
| Rate is not fixed
70
What are some factors influencing GFR?
Net glomerular filtration pressure
Neural and endocrine control
Permeability of the corpuscular membrane
Surface area available for filtration
71
What is GFR autoregulation?
GFR remains fairly constant despite large changes in arterial pressure or renal blood flow
Regulated by changes in the myogenic reflex
Occurs by changing renal blood vessel resistance to compensate for any changes in pressure
72
How is a constant GFR rate maintained?
Autoregulation of GFR takes place over a wide range of blood pressures
73
How does constriction of the afferent arteriole affect the GFR?
Constriction increases resistance to flow through the afferent arteriole
Renal blood flow to the glomerulus has decreased due to an increase in the resistance in the afferent arteriole
A decrease in renal blood flow reduces the hydrostatic pressure of the glomerular capillary resulting in a decrease in GFR
74
What are the 4 scenarios that alter GFR?
Constrict afferent arterioles
Constrict efferent arterioles
Dilate efferent arterioles
Dilate afferent arterioles
75
What 2 scenarios decrease GFR?
Constricting the afferent arteriole
| Dilating the efferent arteriole
76
What 2 scenarios increase GFR?
Constricting the efferent arteriole
| Dilating the afferent arteriole
77
How is GFR regulated?
Myogenic response
Hormones and autonomic neurons
Tubuloglomerular feedback
78
What is the juxtaglomerular apparatus?
A specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole
79
What are the 3 types of cells that control the GFR?
Macula densa
Juxtaglomerular cells
Mesangial cells
80
What is the macula densa?
Cells on the wall of the distal tubule
Can sense increase fluid flow through the distal tubule
Secretes vasoactive compounds
Changes afferent arteriole resistance and signals to JG cells
81
What are juxtaglomerular cells?
On the wall of the afferent arteriole
| Secrete renin which controls afferent arteriole resistance
82
What are the mesangial cells?
Not part of the JGA
| Contraction of these cells reduces surface area of the glomerular capillaries so GFR is reduced
83
What is the filtered load?
The total amount of non-protein or non-protein bound substance filtered into Bowman's space
84
What is the filtered load equation?
GFR x [substance in plasma]
85
What happens when the substance excreted in urine is less than the filtered load?
Reabsorption occurs
86
What happens when the substance excreted in urine is greater than the filtered load
Secretion occurs
87
What are the 3 ways that the renal system handles different substances?
Filtration + secretion
Filtration + partial reabsorption
Filtration + complete reabsorption
88
How are inulin and creatinine handled by the renal system?
Filtration only - what is filtered is excreted completely in the urine
No secretion or reabsorption
89
How are electrolytes handled by the renal system?
Filtered and partially reabsorbed
90
How are glucose and amino acids handled by the renal system?
Filtered and completely reabsorbed
91
How are organic acids and bases handled by the renal system?
Filtered and secreted
| The substance is completely secreted in urine
92
What percent of water is reabsorbed every day?
99%
93
What percent of sodium is reabsorbed every day?
99.5%
94
What percent of glucose is reabsorbed every day?
100%
95
What percent of urea is reabsorbed every day?
44%
96
What is reabsorption mediated by?
```
Diffusion across tight junction (paracellular) = minor
Mediated transport (transepithelial) = major
```
97
What is the pathway of transepithelial transport for the reabsorption of sodium?
Across luminal or apical membrane
| Across basolateral membrane
98
How do sodium move across the apical side and the basolateral membrane?
```
Apical = passive diffusion
Basolateral = active transport on basolateral membrane by Na+/K+ ATPase
```
99
How is sodium reabsorbed?
Sodium enters the cell through membrane proteins moving down its electrochemical gradient
Sodium is then pumped out of the basolateral side of the cell by the Na+/K+ ATPase
100
How is glucose reabsorbed?
Sodium moving down its electrochemical gradient using the SGLT protein pulls glucose into the cell against its concentration gradient
Glucose diffuses out of the basolateral side of the cell using the GLUT protein
Sodium is pumped out by Na+/K+ ATPase
101
What is glucose reabsorption linked to?
Sodium-linked glucose reabsorption in the proximal tubule
102
What is glucosuria?
When above threshold glucose appears in the urine
103
What is the transport maximum?
Limit of substance that can be transported per unit time
Binding sites of transport proteins become saturated
Filtered load exceeds the limit of reabsorption
104
What is diabetes mellitus?
The capacity to reabsorb glucose is normal, but the filtered load is greatly increased and is beyond the threshold level to reabsorb glucose by the tubules
105
What is renal glucosuria?
Genetic mutation of the Na+/glucose cotransporter, which normally mediates active reabsorption of glucose in the proximal tubules
106
What is urea reabsorption dependent on?
Water reabsorption
107
What is urea reabsorbed?
Water reabsorption occurs in the proximal tubule
The concentration of urea increases inside the tubular lumen
Urea diffuses down the concentration gradient
108
What is tubular secretion?
Involves active transport
Tubular secretion is also coupled to the reabsorption of Na+
Mostly H+ and K+, also choline creatinine and penicillin
109
What is renal clearance?
A way of quantifying kidney function in removing substances from the plasma
The measure of the volume of plasma from which a substance is completely removed by the kidney/unit time
Clearance of S = Mass of S excreted per unit time / plasma concentration of S
110
How is inulin cleared?
Readily filtered but not reabsorbed, secreted, or metabolized by the tubule
Can be used to measure GFR
111
How is creatinine cleared?
Product of muscle metabolism
Filtered, not absorbed, but undergoes slight secretion
Clearance of creatinine slightly overestimates GFR but can be used clinically
112
What must happen if the clearance of substance X is greater than GFR?
X must undergo secretion
113
What must happen if the clearance of substance X is less than GFR?
X must undergo reabsorption
114
How is sodium transported in the nephron?
Actively reabsorbed
115
How is chloride transported in the nephron?
Transported passively when sodium is pumped out of the cell
116
How is potassium transported in the nephron?
Secreted into the tubules mainly by cells of the distal and collecting ducts
117
What labour does the proximal convoluted tubule do?
Reabsorbs majority of the water and non-waste plasma solutes
The major site of solute secretion, except potassium
118
What labour does the loop of Henle do?
Creates an osmotic gradient in the interstitial space
119
What labour does the distal convoluted tubule do?
Site of major physiological control for water reabsorption
| Major homeostatic mechanisms of fine control of water and solute to produce urine
120
What is reabsorbed and secreted?
Proximal tubules = 80% reabsorptive and secretory activities
Loop of Henle = little water, but large amounts of ions are reabsorbed
Distal tubules = 12-15% reabsorption happens here
121
What are sources of water gain?
Ingested liquid
| Water from oxidation of food
122
What are some avenues of water loss?
Skin, respiratory airways
Sweat
GI tract, urinary tract, menstrual flow
123
What is water absorption dependent on?
Na+ reabsorption
| The osmotic gradient set up by Na+ reabsorption acts as the driving force
124
Which hormone regulates water reabsorption?
Vasopressin or antidiuretic hormone
125
What does vasopressin regulate?
A specific type of aquaporin
126
Where in the tubule does vasopressin regulation occur?
In the collecting ducts
127
Does the distal tubule reabsorb water?
No, there are no aquaporins
128
What does the thin descending portion of the loop of Henle reabsorb?
Water
129
What does the thick ascending portion of the loop of Henle reabsorb?
Salt, the ascending limb is impermeable to water
130
What are the structure-function relationships of the loop of Henle?
A single tubule with two sides closely juxtaposed
| Fluid streams in the opposite directions and different transport capabilities of each side of the tubule
131
How is the hyperosmolar interstitial fluid in the renal medulla generated?
The ascending limb actively transports NaCl into the interstitial fluid and is impermeable to water
The result is a gradient difference of 200 mOsm
132
What is happening in the descending loop of Henle?
A net movement of water occurs out of the descending limb and the ascending limb continues to actively pump out solute
133
What is the counter-current multiplier?
Multiplication of the gradient down the length of the loop of Henle
134
How is the fluid that flows along the tube?
The fluid becomes concentrated in the descending limb
| Dilutes fluid again as it climbs up the ascending limb and enters the distal tubule
135
What happens to the fluid at the collecting duct?
ADH works on the collecting duct and the fluid inside the tubule becomes isoosmotic with the interstitial space
More water is reabsorbed from the cortical collecting due to the ADH effect
The high osmolarity that is established in the interstitial space helps the water to permeate out of the medullary collecting tubule
136
What does a short loop mean?
Does not need to conserve water
137
What does a long loop mean?
Needs to conserve more water
138
What is the vasa recta?
Blood vessels that run parallel to the loop of Henle
139
What is counter-current blood flow?
Blood flows through in one direction and goes out the other direction
140
Why is the hyperosmotic interstitial gradient created?
To absorb water into the interstitial space
141
What are the nephrons that create the gradient?
Juxtamedullary nephrons
142
How does blood in the vasa recta flow as compared to how fluid flows in the loop of Henle?
Opposite directions
143
What is the vasa recta permeable to?
Both solute and water
144
What are 3 ways that the vasa recta helps countercurrent exchange?
1. Blood flow in the vasa recta serves as countercurrent exchangers
- helps in maintaining the Na+ and the Cl- gradient
- gradient is not washed away
2. Blood flow is the medulla is low
- less than 5% of the trial renal blood flow and is sluggish
- prevents solute loss
3. The capillaries are freely permeable to ions, urea, and water, and they move in and out of the capillaries in response to the concentration gradients
- vasa recta does not create medullary hyperosmolarity, but prevents it from being washed out, and therefore maintains it
145
What is the countercurrent exchange of the vasa recta?
NaCl moves out of the ascending limb, interstitium, to enter the descending limb as blood enters the descending limb of the vasa recta
Water diffuses out of the descending limb into the ascending limb
This mechanism reinforces the gradient created by renal tubules by the exchange of salt and water which leads to an increase in sodium and urea concentration in the renal medulla interstitial space
146
How much urea is excreted?
Only 15% of the original amount
147
What helps maintain high osmolarity in the medulla?
Minimal uptake of urea by vasa recta and recycling urea in the interstitial space
148
Why is there a need for concentrated urine?
Kidneys save water by producing hyperosmotic urine
149
What are the mechanisms used to maintain the hyperosmotic environment of the medulla?
1. Counter-current anatomy and opposing fluid flow through the loop of Henle of the juxtamedullary nephrons
2. Reabsorption of NaCl in ascending limb
3. Impermeability of ascending limb to water
4. Trapping of urea in the medulla
5. Hairpin loops of vasa recta maintains the hyperosmotic interstitium in the medulla
150
What do changes in total body [Na+] cause?
Changes in blood volume and blood pressure
151
What is blood osmolarity determined by?
Measuring the plasma [Na+]
152
What does the volume of water reabsorption dictate?
How much water will be excreted
153
What exerts physiological control of water reabsorption and excretion?
ADH (vasopressin)
154
What is the site of action of vasopressin?
Collecting duct cells
155
What is the mechanism of action of vasopressin?
Alters water permeability of the luminal membrane of the collecting duct cells
156
Where is vasopressin made and secreted?
Produced by cells of the SON of the hypothalamus
| Secreted by the posterior pituitary
157
Where are aquaporins 2,3,4 located?
Collecting ducts
158
What is aquaporin 2 insertion on the luminal side regulated by?
ADH (vasopressin) via AQP2 gene transcription
159
What is the mechanism of ADH action?
ADH binds to a receptor on the cell and through G-protein coupled mechanism, transcription factors are activated and AQP-2 is up-regulated
Water moves across the apical membrane through AQP-2 and out of the basolateral membrane through AQP-3 and 4
AQP-2 is under the control of ADH but the others are not
160
What happens if ADH levels are really low?
AQP-2 channels will be recycled or taken back by endocytosis
161
What happens in the absence of ADH?
Collecting ducts cells are almost impermeable to water
| Extreme loss of large fluid = water diuresis
162
What is central diabetes insipidus?
Failure to release ADH from the posterior pituitary
163
What is nephrogenic diabetes insipidus
ADH is secreted by doesn't function right
164
When is ADH increased (pee less)?
Shock, pain, warm, hot weather, and water deprivation
165
When is ADH decrease (pee more)?
Cold, humid environment, alcohol
166
What is the relationship between water deprivation and thirst?
Water deprivation leads to high plasma osmolarity which stimulates hypothalamic osmoreceptors
This increases ADH release which leads to thirst and water intake as well as renal water retention and antidiuresis
167
What is the relationship between water intake and thirst?
Water intake leads to low plasma osmolarity which blocks hypothalamic osmoreceptors
This blocks ADH and leads to renal water excretion and large water diuresis
168
What is water diuresis?
Only excess water is excreted without excess solute in urine
169
What is osmotic diuresis?
Excess solute in urine is always associated with high levels of water excretion
Uncontrolled diabetes mellitus
170
Is sodium ever secreted into the renal tubes?
No, never
171
What is the short-term regulation of low sodium in the plasma?
Baroreceptors regulate GFR
172
What is the long-term regulation of low sodium in the plasma?
Aldosterone facilitates Na+ reabsorption
| Renin and angiotensin II are needed
173
What is the regulation of high sodium in the plasma?
Atrial natriuretic peptide
ANP regulates GFR and inhibits Na+ reabsorption
ANP also works by inhibiting aldosterone actions
174
What are baroreceptors
Used for short-term regulation of low plasma volume, nerve endings sensitive to tough
175
Where are the baroreceptors located?
Carotid sinus, aortic arch, major veins, intrarenal (JG cells of JGA)
176
How do baroreceptors work?
Can sense changes in blood volume and peripheral resistance
Increase or decrease in blood pressure causes an increase or decrease in stretch which causes an increases or decrease in nerve impulse frequency
177
Where is baroreceptor information processed?
In the medulla oblongata
| Activation of the ANS
178
What is the role of baroreceptors in plasma (Na+)?
When there is low Na+, there is low plasma volume, which means low arterial blood pressure and reduced firing of baroreceptors
This increases the activity of sympathetic renal nerves and increased afferent arteriolar constriction which decreased GFR and increases Na+ reabsorption
179
What is aldosterone?
A steroid hormone secreted from the adrenal cortex
Low plasma volume associated with low sodium triggers its release
Regulates Na+ reabsorption
Effect is long-term
180
What is the site of action of aldosterone?
Late distal tube and cortical collecting duct
181
What is the action of aldosterone?
Induces the synthesis of Na+ transport proteins
Stimulates Na+ reabsorption
Reduces Na+ excretion
182
What regulates aldosterone secretion?
Na+ content in diet
High Na+ intake = low aldosterone secretion
Low Na+ intake = high aldosterone secretion
183
How does angiotensin II relate to aldosterone?
Acts on the adrenal cortex to control the secretion of aldosterone
184
What is renin?
An enzyme that is a sensor for low NaCl in the blood and converts angiotensin to angiotensin I
185
What is ACE?
Angiotensin converting enzyme
| Converts angiotensin I to angiotensin II
186
What is an ACE inhibitor?
Drug to manage high blood pressure by blocking the ACE enzyme
187
Where is renin secreted?
From the juxtaglomerular cells of the JGA
188
What is the most important trigger for the release of aldosterone?
The renin-angiotensin mechanism
189
What does the renin-angiotensin mechanism respond to?
Sympathetic stimulation of renal nerves
Decrease in filtrate osmolarity
Decreased blood pressure
190
What do the juxtaglomerular cells do?
Mechanoreceptors
Sense circulating plasma volume
Secrete renin
191
What determines [renin] in the plasma?
Sympathetic input from external baroreceptors
Intrarenal baroreceptors
Signals from the macula densa
192
What is the macula densa?
On the wall of the distal convoluted tube
Chemoreceptors
Sense NaCl load of the filtrate
193
Where is ANP made?
Synthesized and secreted by the cardiac atria
194
What is the site of ANP action?
On cells of several tubular segments
ANP inhibits aldosterone
Inhibits Na+ reabsorption
Increases GFR and Na+ excretion
195
What stimulates ANP secretion?
Increased Na+ concentration
Increased blood volume
Arterial distension
196
What is the amount of K+ excreted?
K+ filtered - K+ absorbed + K+ secreted
197
Where is most of filtered K+ reabsorbed?
In the proximal tubule and the loop of Henle
198
Where can K+ be secreted?
The collecting duct
199
What is [K+] in the urine regulated by?
The cortical collecting duct
200
What is hyperkalemia?
Excess K+ in the blood
201
What controls the homeostasis of K+ in the body?
Aldosterone secreting cells in the adrenal cortex are sensitive to extracellular [K+]
202
What happens when there is an increase in extracellular [K+]?
Stimulation of aldosterone production so more K+ is excreted in the urine
203
What happens when there is a decrease in extracellular [K+]?
No aldosterone is produced so less K+ is excreted in the urine
204
Can aldosterone stimulate K+ secretion?
Yes, it stimulates both Na+ reabsorption and K+ secretion in the cortical collecting duct
205
What can small changes in pH do to enzymes?
Cause proteins to change shape
- alter their activity
- changes in neuronal activity
- coupled to K+ imbalances
- irregular cardiac beats
206
What is an acid?
Releases protons into the solution
207
What is a base?
Accepts protons in a solution
208
What is an example of a volatile acid?
Carbon dioxide
209
What are some nonvolatile acids?
Organic and inorganic acids other than CO2
Phosphoric acid
Sulfuric acid
210
What acid does the metabolism of sulfur-containing amino acids produce?
Sulfuric acid
211
What does the metabolism of lysine, arginine, and histidine produce?
Hydrochloric acid
212
What is a buffer?
Any substance that binds to H+
Composed of a weak acid and its conjugate base
Buffers modify or adjust the change in pH following the addition of acids or bases
213
What are the types of buffers?
Most of the H+ are buffered by extracellular or intracellular fluid
CO2/HCO3- is the extracellular buffer system
Phosphate ions and proteins are intracellular buffers (like hemoglobin)
214
What is the role of kidneys and lungs in acid base balance?
Both responsible for balancing hydrogen ion concentration within a narrow range
215
What homeostatic role do the lungs play?
Short-term
216
What causes respiratory imbalances?
Hyperventilation
Hypoventilation
Respiratory malfunction
217
What happens if the imbalance is non-respiratory?
Ventilation is changed by reflex to adjust the balance
- increased proton concentration stimulates ventilation
- decreased proton concentration inhibits ventilation
218
What homeostatic role do the kidneys play?
Long-term
| Ultimate balancers
219
What is the key concept about the relationship between H+ and HCO3-?
When 1 H+ ion is lost from the body, 1 HCO3- is gained by the body
220
What happens during alkalosis?
There is decreased plasma [H+]
The kidneys excrete more bicarbonate
Results in restoration of the acid-base balance
221
What happens during acidosis?
There is increased plasma [H+]
The kidney cells synthesize new bicarbonate and send it to the blood
Results in restoration of acid-base balance
222
How is HCO3- reabsorbed?
Dependent on H+ secretion and is an active process
normally most of the HCO3- is reabsorbed
Occurs in the proximal tubule, ascending loop of Henle, and cortical collecting duct
The transport mechanism is different depending on the segment
223
What is mechanism 1 of the addition of HCO3- to the plasma?
Response to acidosis
When more H+ is secreted than there is HCO3- in the lumen to bind the H+
Extra H+ binds to HPO4-
HCO3- is still generated by tubular cells and diffuses into plasma
The new gain of HCO3- in the plasma
224
What is mechanism 2 of the addition of HCO3- to the plasma?
Cells from the proximal tubule are only involved
Uptake of glutamine from glomerular filtrate or peritubular plasma
NH4+ and HCO3 are formed inside the cells
NH4+ is actively secreted via the Na+/NH4+ counter transport into the lumen
HCO3- is added to the plasma
225
What is respiratory acidosis?
Occurs as a result of decreased ventilation
Increased blood PCO2
Occurs in emphysema
Kidney compensates by secreting H+ and lowers plasma [H+]
226
What is respiratory alkalosis?
Occurs as a result of hyperventilation
Decreased blood PCO2
Happens in high altitude
Kidney compensates by excreting HCO3-
227
What is metabolic acidosis?
```
Occurs in diarrhea
Severe exercise
Diabetes mellitus
Results in increased ventilation
Results in increased H+ secretion
```
228
what is metabolic alkalosis?
Occurs after prolonged vomiting
Results in decreased ventilation
Results in increased HCO3- excretion
