Nephrology Flashcards
How can solute exchange occur?
1) Passive exchange
2) Bulk flow
What is passive exchange?
Exchange of glucose, O2, and CO2 between interstitial fluid and plasma membranes of cells
What is bulk flow?
Movement of water and a number of solutes across the capillary wall via pores
What does bulk flow determine?
The distribution of ECF volume between vasculature and IF compartments
What are the main components of the body fluid?
ICF and ECF (plasma and IF)
What percent of body fluid does ICF make up?
67%
What percent of body fluid does ECF make up?
33%
What percent of ECF is made up of plasma?
20%
What percent of ECF is made up of IF?
80%
What is interstitial fluid?
An intermediary between the fluids in capillaries and the fluids within the cells of the tissues
True or false: H2O and all plasma constituents are actively exchanged across the capillary wall
False, H2O and all plasma constituents are continuously and freely exchanged passively
True or false: plasma and IF are nearly identical in composition
True
What is different between IF and plasma?
Plasma contains plasma proteins while IF does not
What happens if a change occurs in plasma and why?
A change in IF will also occur because they are constantly mixing
True or false: ICF and ECF are nearly identical in composition
False, their compositions differ greatly due to the highly selective plasma membrane
What statement can be made about any control mechanism that operates on plasma?
It in effect regulates the entire ECF
True or false: ICF is influenced by changes in the ECF
True
To what extent is ICF influenced by changes in ECF?
To the extent permitted by the permeability of membrane barriers surrounding the cells
Why must ECF volume be regulated?
To maintain blood pressure
Why must ECF solute concentration be regulated?
To prevent swelling or shrinking of cells
What are negligible compartments of body fluid?
Lymph and transcellular fluids
What are transcellular fluids?
Fluid that is secreted by specific cells into a particular body cavity to perform a specialized function
What are 4 examples of transcellular fluids?
1) CSF
2) Synovial fluid
3) Serous fluids (peritoneal, pericardial)
4) Digestive juices
True or false: transcellular fluids reflect changes in the body’s fluid balance
False, they do not reflect changes in the body’s fluid balance
When would transcellular fluids reflect fluid imbalances?
Under pathological conditions
What occurs in glaucoma?
Too much intraocular fluid pressure that pushes against the inner neural layer of the retina causing retina and optic nerve damage
How is glaucoma treated?
Any means that can decrease fluid pressure
What is dehydration?
Fluid loss, either loss of water or loss of water and solutes together
What is hypotonic hydration?
- Cellular overhydration or renal deficiency
- ECF is diluted causing low solute concentration promoting net osmosis into tissue cells
- Increased amount of fluid in all compartments
What can hypotonic hydration cause?
Nausea, vomiting, muscular cramping, and cerebral edema ultimately leading to death
How is hypotonic hydration treated?
Administration of IV hypertonic saline solution
What is edema?
An atypical accumulation of fluid in the IF leading to tissue (not cell) swelling
What does edema cause?
Increased distance that fluids must diffuse between the blood and cells
What can cause edema?
- Increase in ultrafiltration
- Decrease in absorption
- Decrease in lymphatic return
What percentage of most tissues is made up of water?
70-80%
What percentage of plasma does water make up?
93%
What percentage of fat is made up of water?
10%
What percentage of bone is made up of water?
22%
How can body composition be estimated?
1) Bioelectrical impedance analysis
2) Hydrostatic weighing
3) Magnetic resonance imaging (MRI)
4) Mirror
True or false: once urine is formed by the kidneys it can be altered in composition or volume
False, it cannot be altered
What can prostatic hypertrophy cause?
Partial or complete occlusion of the urethra
How do kidneys contribute to homeostasis?
1) Maintain plasma volume
2) Regulate H2O and ion concentrations
3) Acid-base balance
4) Eliminate all metabolic wastes (except CO2)
5) Endocrine
What is also regulated when the kidneys regulate plasma volume?
Systemic blood pressure
How do the kidneys regulate ion and H2O concentrations?
- Adjust for wide variations in ingestion of water, salt, and other electrolytes
- Adjust to adnormal losses through heavy sweating, vomiting, diarrhea, or hemorrhage
What 2 sections is the kidney divided into?
1) Renal cortex
2) Renal medulla
What is found in the renal medulla?
Renal pyramids
What is a nephron?
The basic functional unit of the kidney that forms urine
How many nephrons are found in one kidney?
More than 1 million
What does the nephron regulate and how?
Water and solutes by filtering the blood under pressure and then reabsorbing necessary fluid and molecules back into the blood while secreting other unneeded molecules
What is the main function of a nephron?
Maintain consistency in the ECF composition, which produces urine
What 2 basic components can a nephron be divided into?
1) Tubular component
2) Vascular component
What is a nephron composed of?
1) Renal corpuscle
2) Renal tubules
Where is the renal corpuscle found?
In the renal cortex
What does the renal corpuscle do?
Filters blood (first step in urine formation)
What type of fluid does the renal corpuscle filter?
Fluid that is almost identical in composition to plasma
What is the renal corpuscle composed of?
1) Glomerulus
2) Bowman’s capsule
3) Filtration membrane
What is the glomerulus?
A capillary bed
Where is the Bowman’s capsule found?
Surrounding the glomerulus
What does the Bowman’s capsule do?
Collects filtrate from the glomerulus
What are the 2 layers of the Bowman’s capsule?
1) Outer layer
2) Inner layer
What is found in the inner layer of the Bowman’s capsule?
Podocytes wrapped around the glomerular capillaries
What does the filtration membrane consist of?
1) Glomerular endothelium
2) Basement membranes
3) Podocytes (of Bowman’s capsule)
What type of cells are found in the glomerular endothelium?
Simple squamous with pores (fenestrations)
What are podocytes?
Projections that “cling” to the glomerulus
What are the 4 parts of a renal tubule?
1) Proximal convoluted tubule
2) Loop of Henle
3) Distal convoluted tubule
4) Collecting ducts
Where is the proximal convoluted tubule found?
Renal cortex
Where is the Loop of Henle found?
Renal medulla
Where is the distal convoluted tubule found?
Renal cortex
Where are collecting ducts found?
Renal cortex and renal medulla
How many nephrons drain into one collecting duct?
About 8
What do collecting ducts do?
Drain to the renal pelvis
What are the 2 types of nephrons?
1) Cortical (80%)
2) Juxtamedullary (20%)
Describe cortical nephrons
- Renal corpuscle near kidney surface in cortex
- Short loop of Henle in outer medulla
Describe juxtamedullar nephrons
- Renal corpuscle in cortex near medulla
- Long loop of Henle that penetrates deep into medulla
With respect to the renal blood supply, what does the aorta branch into?
Renal arteries
With respect to the renal blood supply, what do the renal arteries branch into?
Segmental arteries
With respect to the renal blood supply, what do the segmental arteries branch into?
Interlobar arteries
With respect to the renal blood supply, what do the interlobar arteries branch into?
Arcuate arteries
What is significant about the arcuate arteries?
Medulla-cortex junction
With respect to the renal blood supply, what do the arcuate arteries branch into?
Cortical radiate arteries
With respect to the renal blood supply, what do the cortical radiate arteries branch into?
Afferent arterioles
With respect to the renal blood supply, what do the afferent arterioles feed into?
Glomeruli
With respect to the renal blood supply, what exits the glomeruli?
Efferent arterioles
What is significant about the efferent arterioles of the glomeruli?
They are the only arterioles that drain from capillaries
With respect to the renal blood supply, what do the efferent arterioles branch into?
Peritubular capillaries and vasa recta
What are peritubular capillaries?
Cortical nephrons in renal cortex
What are vasa recta?
Juxtaglomerular nephrons in the renal medulla
With respect to the renal blood supply, what do the peritubular capillaries and vasa recta form when they join?
Cortical radiate veins
With respect to the renal blood supply, what do the cortical radiate veins become?
Arcuate veins
With respect to the renal blood supply, what do the arcuate veins become?
Interlobar veins
With respect to the renal blood supply, what do the interlobar veins become?
Renal veins
With respect to the renal blood supply, what do the renal veins become?
Inferior vena cava
What is the function of the juxtaglomerular complex?
Regulates filtrate formation
What does the ascending limb of the juxtaglomerular complex pass through?
The fork formed by the 2 afferent and efferent arterioles
What is special about the juxtaglomerular complex?
Is the point of contact between the end of the ascending limb and the afferent and efferent arterioles at the renal corpuscle of the same nephron
What are the 2 portions of the juxtaglomerular complex?
1) Tubular portion
2) Vascular portion
What does the tubular portion of the juxtaglomerular complex contain?
Macula densa, which are modified (tall and narrow) ascending limb cells
What does the vascular portion of the juxtaglomerular complex contain?
Granular juxtaglomerular cells, which are the afferent and efferent arteriolar portion
What is the function of granular juxtaglomerular cells?
- Monitor BP
- Contain renin
At rest, what percent of cardiac output is going to the kidneys?
About 20%
What 3 basic processes occur in the nephron to form urine?
1) Glomerular filtration
2) Tubular reabsorption
3) Tubular secretion
Where does glomerular filtration occur?
Glomerular capillaries
What percent of plasma in glomerulus is filtered into the Bowman’s capsule?
20%
How is plasma in the glomerules filtered into the Bowman’s capsule?
Bulk flow (pressure gradient) across the filtration membrane
How much filtrate is collectively formed per minute?
125 mL
How many times is the entire plasma volume filtered per day?
About 65 times per day
What is filtrate?
Plasma minus large proteins
What makes up filtrate?
Water, glucose, amino acids, vitamins, ions, urea, and small amounts of small proteins
What is the pH of filtrate?
About 7.45
What is albuminuria
- When the filtration membrane allows excessive albumin into the urine
- Occurs in some renal disease
What are the 4 types of pressure that occur in glomerular filtration?
1) Glomerular hydrostatic pressure
2) Plasma-colloid osmotic pressure
3) Capsular hydrostatic pressure
4) Capsular osmotic pressure
What is the normal value of glomerular hydrostatic pressure and does it favour or oppose filtration?
- 55 mmHg
- Favoured
What is the normal value of plasma-colloid osmotic pressure and does it favour or oppose filtration?
- 30 mmHg
- Opposed
What is the normal value of capsular hydrostatic pressure and does it favour or oppose filtration?
- 15 mmHg
- Opposed
What is the normal value of capsular osmotic pressure and does it favour or oppose filtration?
- 0 mmHg
- Favoured
What is value of net filtration pressure?
(55 + 0) - (30 + 15) = 10 mmHg
What is the normal glomerular filtration rate?
About 180 L/day of filtrate
What happens to about 1% of filtered volume?
It remains at the end of collecting duct
Why must GFR be regulated?
To keep GFR from changing when MAP changes
How is GFR regulated?
1) Autoregulation (intrinsic regulation), which is aimed at preventing spontaneous changes in GFR
2) Extrinsic symp. control, which is aimed at long-term regulation of MAP
How do both control mechanisms work to regulate GFR?
Adjust glomerular blood flow by regulating the radius and thus the resistance of the afferent arteriole
How does autoregulation work to regulate GFR?
1) Myogenic mechanism
2) Juxtaglomerular apparatus
Describe the myogenic mechanism of GFR regulation
- Increased MAP = stretch = afferent arteriole smooth muscle contracts = prevents increased BP in glomerular caps = GFR stays normal
- Vice versa
Describe the juxtaglomerular apparatus of GFR regulation
- Changes in GFR = changes in flow of flitrate past macula dense cells that detect changes in salt levels of fluid flowing past them
- Increased GFR = more fluid is filtered = more salt delivery to macula densa cells = release ATP = extracellular degradation forms adenosine = afferentarteriole v/c = increased GFR to normal
- Decreased salt delivery to macula densa cells = decreased release of ATP = decreased extracellular adenosine = afferent arteriole v/d = increased GFR to normal
True or false: intrinsic/autoregulation overrides extrinsic regulation of GFR
False, extrinsic overrides intrinsic regulation of GFR
What can extrinsic regulation do to GFR?
Can change it on purpose even when MAP is within the autoregulatory range
What mediates extrinsic control of GFR?
The sympathetic nervous system
How does extrinsic control regulate GFR?
- SNS causes arteriole v/c
- Afferent causes decreased flow into glomerules; efferent causes blood to back up in glomerulus
- Moderate SNS activation causes both to balance and GFR not to change dramatically
What can extreme stress do to GFR?
Can decrease it
What can cause changes to plasma-colloid osmotic pressure (PCOP)?
1) Dehydration causes increased PCOP, which causes decreased GFR
2) Severe burns causes decreased PCOP, which causes increased GFR
What can cause a change in capsular hydrostatic pressure (CHP)?
Urinary tract obstruction (ex: kidney stones, enlarged prostate) causes increased CHP, which causes decreased GFR
What percent of filtrate is reabsorbed?
99%
Where is filtrate reabsorbed from and where to?
- From tubules
- Into peritubular and vasa recta capillaries
True or false: all consituents are at the same concentration in the glomerular filtrate and in the plasma
False, plasma proteins are at different concentrations in filtrate and plasma
What are the 2 steps of reabsorption?
1) Active or passive transport from tubule fluid to renal IF
2) Active or passive transport from IF to blood
How many barriers must a reabsorbed substance cross?
5
When will absorption be considered active?
If any one of the steps in transepithelial transport of a substance requires energy
What is an example of active reabsorption?
An active Na/K pump in the basolateral membrane is essential for Na reabsorption
What percent of total energy spent by the kidneys is used for Na transport?
80%
What substances generally require active reabsorption?
Na, other ions, glucose, and amino acids
What substance generally require passive reabsorption?
Cl, water, and urea
What is the primary role of the proximal convoluted tubule in the process of reabsorption?
Fluid and electrolyte transport
What percent of glucose and amino acids are reabsorbed by sodium?
100%
How does sodium reabsorb glucose and amino acids?
Dependent, secondary active transport
What percent of sodium is reabsorbed by active transport?
67%
What is the final result of the proximal convoluted tubule in the process of reabsorption?
- Large amount of solute is removed and filtrate volume is decreased
- Filtrate is isotonic to plasma
What is the primary role of the loop of Henle in the process of reabsorption?
Reabsorbs into vasa recta
What is reabsorbed in the descending limb of the loop of Henle?
Water only
What is reabsorbed in the ascending limb of the loop of Henle?
25% NaCl only
What is reabsorbed in the distal convoluted tubule and collecting duct and what does this cause?
- 8% Na; causes increased aldosterone and decreased atrial natriuretic peptide (ANP)
- Facultative reabsorption of water; causes increased ADH
What 4 things do nephrons normally absorb?
- 99% of filtered water
- 99.5% of filtered NaCl
- 100% of filtered glucose
- 50% of filtered urea
What may be found in filtrate?
Trace amounts of amino acids and proteins (depending on diet)
What should never be found in filtrate?
Glucose or blood
Where does tubular secretion occur?
From peritubular blood into filtrate
What are the main substances that are secreted in tubular secretion?
- Wastes such as urea, uric acid, and some hormones
- Potassium
- H+ which helps maintain blood plasma pH
What does the countercurrent multiplier mechanism permit?
Excretion of urine that is dilute or concentrated (100 - 1200 mOsm/L)
What does the countercurrent multiplier mechanism produce?
A vertical osmotic gradient (solute concentration increases in ISF as you move deeper into the medulla)
What produces the vertical osmotic gradient?
Juxtamedullary nephrons
What 3 things occur within the loop of Henle with respect to the countercurrent multiplier mechanism?
1) Filtrate moves down descending limb and water moves into ISF by osmosis
2) Highly concentrated filtrate enters ascending limb
3) Filtrate leaving ascending limb is lower in osmolarity than plasma
How is NaCl pumped out of the ascending limb of the loop of Henle?
Against the concentration gradient
What is the descending limb of the loop of Henle permeable and impermeable to?
- Permeable to water
- Impermeable to NaCl
What is the ascending limb of the loop of Henle permeable and impermeable to?
- Permeable to NaCl
- Impermeable to water
What is filtrate in the ascending limb lower in osmolarity than plasma?
- Ascending limb is impermeable to water
- Ascending limb NaCl pump
What occurs within the early distal convoluted tubule with respect to the countercurrent multiplier mechanism?
- More salt is removed from filtrate (reabsorbed)
- No water removed, therefore 100 mOsm/L when enters late DCT
Concentrated urine means a ______ blood pressure
Low
What happens in the distal convoluted tubule and collecting duct to make urine concentrated?
- Aldosterone increases Na reabsorption
- ADH increases facultative water reabsorption
What is the highest concentration that urine can be?
1200 mOsm/L
Dilute urine means a ______ blood pressure
High
What happens in the distal convoluted tubule and collecting duct to make urine dilute?
ANP inhibits ADH and aldosterone, making it impermeable to water and NaCl
What is the average amount of urine produced per day?
1 - 1.5 L
What are 2 regulators of urine?
1) Hormonal
2) SNS
What 4 hormonal controls regulate urine concentration?
1) Renin-angiotensin system
2) ADH
3) Aldosterone
4) ANP
How does the renin-angiotensin system regulate urine concentration?
Granular cells of the juxtaglomerular apparatus secrete renin
What causes juxtaglomerular cells to secrete renin?
- Decreased blood pressure or ECF volume
- Decreased NaCl in filtrate
- Increased SNS activity
Granular cells act as _______
Intrarenal baroreceptors
How is decreased NaCl in filtrate detected?
At the macula densa which trigger the granular cells
Granular cells are innervated by the ______ NS
Sympathetic
What are 4 general causes of increased angiotensin 2?
1) Increased NaCl reabsorption and K secretion
2) Increased systemic BP (MAP)
3) Decreased GFR
4) Increased facultative water reabsorption
What does ADH cause?
Increased facultative reabsorption of water in the DCT and collecting ducts
What percent of water reabsorption is obligatory in the proximal convoluted tubule?
65%
What percent of water reabsorption is obligatory in the distal convoluted tubule and collecting duct?
It is variable based on the secretion of ADH
What does ADH secretion do to tubule cells?
Increases the permeability of tubule cells to water
Where does an osmotic gradient exist and why?
Outside the tubules from the transport of water by osmosis
What 4 things cause ADH to increase?
1) Low blood pressure/volume
2) Increased plasma osmolarity
3) Increased angiotensin 2
4) Nicotine or nausea
What 5 things cause ADH to decrease?
1) High blood pressure/volume
2) Decreased plasma osmolarity
3) Decreased angiotensin 2
4) Increased ANP
5) Alcohol and caffeine
When does aldosterone increase?
When angiotensin 2 increases and plasma K is high
What does aldosterone do with respect to genes?
Turn on genes that increase the number of Na/K ATPase in DCT and CD, which causes increased Na reabsorption and K secretion
What is caused by Na reabsorption in late DCT and CD?
Water follows and Cl follows
What is the net result of aldosterone on regulation of urine concentration?
Greater passive inward flux of Na into the tubular cells from the lumen and increased active pumping of Na out of the cells into the plasma (Increased Na reabsorption with Cl following)
What happens to nephrons in the absence of aldosterone?
Nephrons can rapidly remove excess Na from the body
How much Na can be lost with complete absence of aldosterone?
20 grams per day
How much Na can be lost with maximum secretion of aldosterone?
0 grams because all filtered Na will be reabsorbed
What 2 mechanisms can cause aldosterone secretion?
1) Increased plasma K
2) Decreased Na, ECF volume, or arterial pressure
What causes ANP to be secreted?
- Increased blood pressure
- Hypervolemia (too much fluid in the blood),
- Exercise
What does ANP cause?
- Inhibition of Na reabsorption, thus increasing Na excretion
- Inhibition of renin, angiotensin 2 and aldosterone
- Increased GFR by v/d of afferent arteriole
- Decreased CO by inhibiting symp nervous activity to heart and blood vessels
What can exacerbate a failing heart and why?
- Increased salt and water reabsorption
- Failing heart means CO is reduced and MAP is low, which means angiotensin 2 is increased
What do diuretics do?
Inhibit tubular reabsorption of Na, increasing water loss and reducing excess EFC
What else besides diuretics can inhibit salt and fluid reabsorption?
- ACE inhibitors
- Aldosterone receptor blockers
What does increased sympathetic NS impulse cause with respect to regulation of urine concentration?
Afferent and efferent arterioles constrict
What does decreased sympathetic NS impulse cause with respect to regulation of urine concentration?
Afferent and efferent arterioles relax
What happens when MAP increases with respect to regulation of urine concentration?
Flow to kidney increases causing v/c in spite of decreased SNS, renin, and angiotensin 2 and increased ANP, meaning GFR returns to resting
What does a lack of ADH and aldosterone mean for urine?
It will be dilute, so blood volume will decrease and MAP will decrease
What happens if there is a large decrease in blood pressure or volume?
V/c signals get stronger than intrinsic mechanisms, so GFR decreases
What are the normal constituents of urine?
- Water
- Nitrogenous wastes
- Regulated substances (ex: ions)
What type of nitrogenous wastes are found in urine?
- Urea
- Uric acid
- Creatinine
How is urea produced?
From amino acid metabolism
What percent of urea is reabsorbed?
About 50%
How is uric acid produced?
From nucleic acid breakdown
What percent of uric acid is reabsorbed?
About 10%
What is gout?
When uric acid accumulates between joints because it is poorly water soluble
What are kidney stones made of?
Crystallized uric acid
How is creatinine produced?
From breakdown of creatine in skeletal muscle
What percent of creatinine is reabsorbed?
None because production and excretion is constant
What are creatinine levels used to estimate?
GFR, which can indicate kidney disease before symptoms occur
What is the normal pH range of urine?
4.5 - 8
What are 3 abnormal constituents of urine?
1) Proteins
2) Glucose
What is another name for proteinuria?
Albuminuria
What causes albuminuria?
Increased permeability of glomerules due to heavy metals or glomerulonephritis
What is glycosuria?
When glucose is present in urine
What are 5 causes of renal failure?
1) Infectious organisms
2) Toxic agents
3) Inappropriate immune responses
4) Obstruction of urine flow
5) Insufficient renal blood supply
What is urinary incontinence?
Inability to prevent discharge of urine
What is renal plasma clearance?
The volume of plasma cleared of a substance in one minute
What is renal plasma clearance used for?
To estimate the time a substance remains in blood
What substance can be used to estimate GFR and why?
- Inulin
- Is filtered but not reabsorbed, secreted, or metabolized, therefore the amount in urine = amount filtered
What does it mean if plasma clearance is less than GFR of a substance and what are 2 examples of this?
- The substance is reabsorbed from filtrate
- Ex: urea and glucose
What does it mean if plasma clearance is greater than GFR of a substance and what are 2 examples of this?
- Substance is secreted into filtrate
- Ex: penicillin and H+
What does acid-base balance refer to?
Precise regulation of free H+ concentration in body fluids
What are acids?
A group of H+ containing substances that dissociate in solution to release free H+ and anions
What are bases?
A group of substances that combine with free H+ and remove it from solution
Where does most H+ in the body come from?
Metabolic activities
What is acidosis?
When the body pH is between 6.8 - 7.35
What is alkalosis?
When the body pH is between 7.45 - 8
What are 3 sources of H+ in the body?
1) Carbonic acid formation
2) Inorganic acids produced during breakdown of nutrients
3) Organic acids resulting from intermediary metabolism
How is carbonic acid formed?
CO2 + H2O
What is an example of an inorganic acid that is produced during breakdown of nutrients?
Sulphuric and phosphoric acids are produced when sulphur and phosphorus from dietary proteins are broken down
What are 3 examples of organic acids resulting from intermediary metabolism?
1) Fatty acids
2) Amino acids
3) Lactic acid
What are 3 consequences of H+ fluctuations in the body?
1) Changes in excitability of nerve and muscle cells
2) Marked influence on enzyme activity
3) Influence on K+ levels in body
What does acidosis cause to the CNS?
Depression of CNS
What does alkalosis cause to the PNS?
Overexcitability to PNS and later to the CNS
Why do H+ fluctuations have an influence on enzyme activity?
Enzymes have a narrow range of temperature and pH where their activity can be maximal, and H+ is a factor in the enzyme staying within these ranges
Why do H+ fluctuations have an influence on K+ levels in the body?
- When reabsorbing Na from filtrate, tubular cells secrete either K+ or H+ in exchange
- An increased rate of one decreases the rate of the other
What are the 3 lines of defense against changes in H+ concentration?
1) Chemical buffer systems
2) Respiratory mechanism of pH control
3) Renal mechanism of pH control
How do chemical buffer system prevent changes in H+ concentration?
- Minimize changes in pH by binding with or yielding free H+
- Act within fractions of a second
True or false: chemical buffer systems eliminate H+ from the body
False, they are removed from solution by being incorporated within one member of the buffer pair
What is the first line of defense for acid-base balance?
Chemical buffer systems
What are the 4 buffer systems of the body?
1) Carbonic acid/bicarbonate
2) Protein buffer system
3) Hemoglobin buffer system
4) Phosphate buffer system
How do carbonic acid and bicarbonate work as a buffer system?
Carbonic acid and bicarbonate are abundant in the ECF with the kidneys regulating bicarbonate and CO2 in the lungs (generating carbonic acid)
What is unique about the carbonic acid/bicarbonate buffer system?
Is the primary ECF buffer for noncarbonic acids
What is the most plentiful buffer system in the body?
Protein buffer system
What is the primary ICF buffer?
Protein buffer system
True or false: protein buffer systems contain body acidic and basic groups
True
What is unique about the hemoglobin buffer system?
Primary buffer against carbonic acid changes
What is unique about the phosphate buffer system?
Can switch Na for H+
The phosphate buffer system has a low concentration in ______
ECF
What is the most important urinary buffer and why?
- Phosphate buffer system
- There is normally excess phosphate in diet, so it remains in tubular fluid to be excreted and buffers urine as it is being formed by removing H+
True or false: there are no buffer systems present in tubular fluid
True
True or false: little to none bicarbonate and CO2 are reabsorbed
False, most or all of the filtered bicarbonate and CO2 are reabsorbed
Why must H+ be removed from the body if buffer systems exist?
Because each buffer system has a limited capacity to soak up H+
What would happen if H+ was never removed from the body?
All the body-fluid buffers would already be bound with H+ and there would be no further buffering ability
What is the second line of defense in acid-base balance?
Respiratory system
How does the respiratory system work to balance acids and bases?
Removes CO2, therefore also removing H+
What will the respiratory system do when H+ is too high?
Hyperventilate
What will the respiratory system do when H+ is too low?
Hypoventilate
What is the third line of defense in acid-base balance?
Renal system
How does the renal system work to balance acids and bases?
Eliminates H+ from metabolically produced acids by secreting H+ into tubule
How does the majority of H+ enter urine?
Via tubular secretion
What parts of the nephron secrete H+?
Proximal convoluted tubule, distal convoluted tubule, and collecting tubules
When does the respiratory system begin to work with respect to acid-base balance?
Minutes
When does the renal system begin to work with respect to acid-base balance?
Hours to days
What can H+ energy-dependent carriers in tubular cells do?
Can secrete H+ against a concentration gradient until the tubular fluid is 800 times as acidic as the plasma
What is needed for H+ secretion to continue?
It must be buffered in the tubular fluid
What happens to make bicarbonate be considered “reabsorbed”?
One filtered bicarbonate disappears from the tubular fluid (through combination with H+), and one bicarbonate appears in the plasma (through combination of OH and CO2)
What occurs once all filtered bicarbonate has combined with secreted H+?
- Further secreted H+ is excreted in the urine, primarily in association with urinary buffers
- This is coupled with the appearance of new bicarbonate in plasma, which represent a new gain as opposed to a replacement of filtered bicarbonate
What happens once phosphate ions have soaked up H+?
The tubular cells secrete ammonia
What happens once ammonia is in the tubule?
It binds with H+ to form ammonium
True or false: ammonium is not very permeable so it remains in tubular fluid
True
What synthesizes ammonia?
The amino acid glutamate within tubular cells
What can cause acid-base inbalances?
Respiratory dysfunction of metabolic disturbances
What are the 4 general categories of acid-base imbalances?
1) Respiratory acidosis
2) Respiratory alkalosis
3) Metabolic acidosis
4) Metabolic alkalosis
What is respiratory acidosis?
Abnormal CO2 retention arising from hypoventilation
What are 4 possible causes of respiratory acidosis?
1) Lung disease
2) Depression of respiratory centre by drugs or disease
3) Nerve/muscle disorders that reduce respiratory muscle activity
4) Holding breath
What are 2 compensations to counteract respiratory acidosis?
1) Chemical buffers immediately take up additional H+
2) Kidneys
What is respiratory alkalosis?
Excessive loss of CO2 from body as a result of hyperventilation
What are 4 possible causes of respiratory alkalosis?
1) Fever
2) Anxiety
3) Aspirin poisoing (hyperstimulation of the respiratory centre)
4) Physiologic mechanisms at high altitude
What are 2 compensations to counteract respiratory alkalosis?
1) Chemical buffer systems liberate H+
2) Kidneys conserve H+ and excrete more bicarbonate
What is metabolic acidosis?
- Fall in bicarbonate concentration
- Includes all types of acidosis other than those caused by excess CO2 in body fluids
What are 4 possible causes of metabolic acidosis?
1) Severe diarrhea
2) Diabetes (ketoacidosis from fatty acid breakdown)
3) Strenuous exercise
4) Uremic acidosis (renal failure)
What are 3 compensations to counteract metabolic acidosis?
1) Buffers take up extra H+
2) Lungs blow off additional H+ generating CO2
3) Kidneys excrete more H+ and conserve more bicarbonate
What is metabolic alkalosis?
- Elevation in bicarbonate concentration
- Reduction in plasma pH caused by relative deficiency of noncarbonic acid
What are 2 possible causes of metabolic alkalosis?
1) Vomiting – loss of acidic gastric juices
2) Ingestion of alkaline drugs – extra is absorbed in the digestive system into blood plasma
What are 3 compensations to counteract metabolic alkalosis?
1) Chemical buffer systems immediately liberate H+
2) Ventilation is reduced
3) Kidneys conserve H+ and excrete excess bicarbonate in the urine
