Physiology Flashcards
(316 cards)
1
Q
what is osmolarity?
A
concentration of osmotically active particles present in a solution
2
Q
what are the units of osmolarity?
A
osmol/l or mosmol/l
3
Q
what 2 factors are needed to calculate osmolarity?
A
- the molar concentration of the solution
- the number of osmotically active particles present
4
Q
what are the units of osmolality?
A
osmol/kg water
5
Q
when can the terms osmolarity and and osmolality be used interchangeably?
A
for weak salt solutions including body fluids
6
Q
what is tonicity?
A
the effect a solution has on a cell volume
7
Q
what affect does a hypertonic solution have on a cell?
A
fluid moves out of the cell- the cell shrinks
8
Q
what affect does a isotonic solution have on a cell?
A
there is no change
9
Q
what affect does a hypotonic solution have on a cell?
A
water moves into the cell, cell bursts
10
Q
what are the 2 major components of total body water?
A
intra cellular fluid and extracellular fluid
11
Q
why do males have 60% of body weight made up of water and woman only have 50%?
A
woman have more fat. fat cells dont contain a lot of water
12
Q
what does extracellular fluid consist of?
A
plasma, interstitial fluid, other (negligible)
13
Q
what are all body cells bathed in?
A
interstitial fluid
14
Q
how can we measure body fluid compartments?
A
with ‘tracers’
15
Q
what is insulin a useful tracer for?
A
ECF
16
Q
what is a useful tracer of plasma?
A
labelled albumin
17
Q
useful tracer of total body water?
A
3H20
18
Q
how do you calculate the distribution volume (in litres)?
A
- add a known quantitty of tracer X (Qx: mol or mg) to the body
- measure the equilibration volume of X in the body ([X])
distribution of volume = Qx (mol) / [X] (mol/litre)
19
Q
what is meant by insensible loss of water?
A
loss of water from somewhere when there is no physiological control over this water loss eg water loss from the skin, lungs
20
Q
where is there sensible loss of water in the body?
A
- in sweat
- faeces
- urine
21
Q
3 ways in which water can be put into the body?
A
- fluid intake
- food intake
- metabolism
22
Q
what changes when there is water imbalance?
A
body fluid osmolarity
23
Q
are sodium ions more abundant in ECF or ICF?
A
always more sodium on the outside of the cell in the ECF
24
Q
where is chloride ions more abundant?
A
ECF
25
where are potassium ions more abundant?
in the cell (ICF)
26
what are the main ions in the ICF?
potassium, magnesium
27
what is the difference in osmotic concentrations of ECF and ICF?
they are identical
28
what is the osmotic concentration of the ECF and ICF?
around 300 mosmol/l
29
what is meant by fluid shift?
movement of water between the ICF and ECF in response to an osmotic gradient
30
if the ECF loses water, what will happen to its osmolarity?
it will go up
31
an increase in osmolarity in the ECF will cause what?
it to become hypertonic and cells are now in hyperotonic solution so they will begin to loss water from the ICF and water will go into ECF to restore volume and osmolarity
32
if there is a gain of NaCl in the ECF, what is the fluid shift response?
ECF goes up and ICF goes down
33
if there is a loss if NaCl from the ECF, what is the fluid shift response?
ECF goes down and ICF goes up
34
what affect does a gain or loss of isotonic fluid have?
- no change in fluid osmolarity
| - change in ECF volume only
35
what gives rise to electrolyte balance?
when the rates of loss equal the rates of gain
36
what are the 2 reasons why electrolyte balance is important?
1- total electrolyte concentrations can directly affect water balance (via changes in osmolarity)
2. the concentrations of individual electrolytes can affect cell function
37
what is the balance of sodium and potassium particularly important?
1. they are major contributors to the osmotic concentrations of the ECF and ICF, respectively
2. they directly affect the functioning of all cells
38
the presence of what makes up >90% of the osmotic concentration of the ECF?
sodium salts
39
what do potassium ions play a key role in?
establishing the membrane potential
40
what percentage of the bodys potassium is intracellular?
>95%
41
what are the 2 things that can happen if small leakages or increased cellular uptake of potassium occurs?
1. muscle weakness --- paralysis
| 2. cardiac irregularities --- cardiac arrest
42
what does salt imbalance manifest as?
changes in ECF volume
43
what is bilirubin a breakdown of?
haemoglobin
44
what hormone stimulates the kidney to produce erythropoitin?
EPO
45
what does erythropoitin do?
increase red blood cell production
46
what percentage of the cardiac output does the kidneys receive?
20-25%
47
what kind of appearance does the medulla have?
granulated appearance
48
what kind of appearance does the cortex have?
striated
49
what does the afferent arteriole subdivide to form?
the glomerulus
50
where does blood from the glomerulus pass to?
the efferent arteriole
51
where does blood flow to from the efferent arteriole?
into the peritubular capillaries
52
following the peritubular capillaries, where does the blood go?
the renal vein
53
what are the 2 types of nephron?
juxtramedullary and cortical
54
what percentage of nephrons are juxtamedullary nephrons?
20%
55
what are the 2 differences between juxtamedullary and cortical nephrons?
1. juxtamedullary nephron has a very long loop of Henle compared to cortical nephron
2. cortical nephron has a network of capillaries, whereas the juxtamedullary only has one vessel
56
what is the vessel in the juxtamedullary nephron called and what is its flow like?
vasa recta, sluggish flow
57
what is the function of the juxtamedullary nephrons?
enable us to make concentrated urine
58
if the smooth muscle of the afferent arteriole contracts, how will this affect the flow downstream to the glomerular capillary?
less blood will flow downstream
59
what percentage of plasma that flows through the capillary makes up the initial tubular fluid?
20%
60
how does the initial tubular fluid differ from the plasma?
almost identical except tubular fluid does not contain large proteins or red blood cells
61
what do the macula densa cells of the juxtaglomerular apparatus detect?
amount of salt in tubular fluid as it passes through this region of the nephron
62
for any substance: rate of excretion = ?
rate of filtration + rate of secretion - rate of reabsorption
63
for a freely filterable substance: rate of filtration = ?
rate of filtration of
X = [X]plamsa x GFR
GFR= glomerular filtration rate
64
what is the normal GFR in a healthy adult?
125 mil/min
65
how do you calculate rate of excretion?
rate of excretion of X:
X = [X]urine x Vu
Vu = urine flow rate
66
how do you calculate the rate of reabsorption?
Rate of reabsoption of X
| = rate of filtration of X - rate of excretion of X
67
how do you calculate the rate of secretion of a substance?
Rate of secretion of X:
| rate of excretion of X - rate of filtration of X
68
what does is mean if the rate of filtration of a substance exceeds the rate of excretion of that substance?
net reabsorption of the substance has occured
69
what are the 3 filtration barriers in glomerular filtration?
1. glomerular capillary endothelium
2. basement membrane (basal lamina)
3. slit processes of podocytes
70
what is the glomerular capillary endothelium a barrier to?
to RBC
71
what is the basement membrane a barrier to?
plasma protein barrier
72
what is the slit processes of podocytes a barrier to?
plasma protein barrier
73
what charge does the basement membrane have and how is the useful?
has a net negative charge, this helps to repel negatively charged plasma proteins to prevent filtration of these
74
what 4 things contribute to net filtration pressure?
1. glomerular capillary blood pressure
2. capillary oncotic pressure
3. Bowman's capsule hydrostatic pressure
4. Bowman's capsule oncotic pressure
75
how is the net filtration pressure calculated?
(glomerular capillary BP + Bowman's Capsule oncotic pressure) - (Bowman's capsule hydrostatic pressure + capillary oncotic pressure)
76
what 2 forces that compromise net filtration favor filtration?
glomerular capillary BP and Bowmans capsule oncotic pressure
77
what 2 forces that compromise net filtration oppose filtration?
Bowman's capsule hydrostatic pressure and capillary oncotic pressure
78
will a build up of fluid in the lumen of Bowman's capsule act to oppose or promote filtration?
oppose filtration
79
what is another term for oncotic pressure?
colloid osmotic pressure
80
what are the 4 forces that compromise net filtration pressure often known as collectively?
Starling forces
81
why is the oncotic pressure of the Bowman's capsule zero?
since there should be no plasma proteins within the lumen
82
is filtration at the glomerulus active or passive?
passive
83
what is the normal GFR?
125 ml/min
84
what is the major determinant of GFR?
glomerular capillary fluid (blood) pressure
85
what is the extrinsic regulation of GFR?
sympathetic control via baroreceptor reflex
86
other than extrinsic regulation of GFR, what else controls it?
autoregualtion (intrinsic) control
87
what are the 2 parts to the autoregulation (intrinsic) of GFR?
1. myogenic mechanism
| 2. tubuloglomerular feedback mechanism
88
how does blood pressure affect GFR?
because it affects glomerular filtration pressure
89
what happen to GFR is there is vasoconstriction of the afferent arteriole?
reduced GFR
90
what affect does an increase in sympathetic activity have on the GFR and urine output?
causes constriction of afferent arterioles which causes a reduction in glomerular capillary fluid pressure which causes a fall in GFR and decreased urine volume
91
what prevents short term changes in systemic arterial pressure affecting GFR?
autoregulation
92
what happens in the myogenic response?
if vascular smooth muscle is stretched (ie arterial pressure increased), it contracts thus consticting the arteriole
93
what is the tubuloglomerular feedback mechanism? what does it do if GFR rises?
- involved the juxtaglomerular apparatus
| - if GFR rises, more NaCl flows through the tubule leading to constriction of afferent arterioles
94
give an example when extrinsic control to the kidneys can override intrinsic control?
haemorrhage
95
what part of the juxtaglomerular apparatus senses NaCl content of tubular fluid?
macula densa
96
how does a kidney stone decrease GFR?
blockage increases hydrostatic fluid pressure in Bowman's capsule which opposes filtration and decreases GFR
97
what affect does severe diarrhoea have on GFR?
decreases it
98
how does severe diarhhoea decrease GFR?
dehydration which increases plasma protein concentration which increases capillary oncotic pressure which opposes filtration: decreased GFR
99
what affect does severe burns have on GFR?
increases GFR
100
how do severe burns increase GFR?
lose plasma proteins from site of burns, decreases plasma protein conc, decreases capillary oncotic pressure which normally would oppose filatration but since it is decreased GFR goes up
101
how does damage to the kidneys lead to a decreased GFR?
makes glomerular membrane less permeable which leads to reduced GFR
102
what is plasma clearance a measure of?
of how effectively the kidneys can 'clean' the blood of a substance
103
what is the plasma clearance equal to?
the volume of plasma completely cleared of a particular substance per minute
104
what are the units of plasma clearance?
ml/min
105
how do you calculate clearance of a substance?
clearance of substance X =
| (conc of X in urine) x (rate of urine flow) divided by plasma conc of X
106
why does inulin clearnance = GFR?
it is freely filtered at glomerulus and is neither absorbed nor secreted and not metabolised by kidney
107
what can measurements of inulin clearance be used to determine?
GFR
108
what is inulin?
exogenous compound- a polysaccharide
109
what else other than inulin can be used as a rough determinant of GFR?
creatinine clearance
110
why is creatine clearance not as reliable as inulin clearnace in determining GFR?
undergoes some tubular secretion
111
what should the clearance of glucose be?
should be zero, should be no glucose in urine
112
how is urea handled in the kidney?
filtered, partly reabsorbed and not secreted
113
should the clearance of urea be higher or lower than GFR?
clearance of urea should be lower than GFR
114
what percentage of filtered urea is reabsorbed?
50%
115
for a substance that is filtered, secreted but not reabsorbed, is its clearance more or less than GFR?
more than GFR
116
what is used clinically to calculate renal plasma flow (RPF)?
para-amino hippuric acid (PAH)
117
what is para-amino hippuric acid?
an exogenous organic anion
118
how is para-amino hippuric acid dealt with in the kidney?
freely filterated at glomerulus, secreted into the tubule, not reabsorbed and completely cleared from the plasma
119
what should the renal plasma flow of a healthy individual be?
650 ml/min
120
critea for a GFR marker?
should be filtered freely, not secreted or reabsobed
121
critea for a RPF marker?
should be filtered and completely secreted
122
what is filtration fraction?
is the fraction of plasma flowing through the glomeruli that is filtered into the tubules
123
how do you calculate filtration fraction?
GFR divided by renal plasma flow
124
what is the normal filtration fraction?
20%
125
how do you calculate renal blood flow?
renal plasma flow x (1/1-Hct)
| where Hct = haematocritt
126
what percentage of CO does the kidneys receieve?
around 24%
127
approximately how many times a day is plasma filtered?
65 times per day
128
how much of filtered fluid is reabsorbed in the proximal tubule per minute?
80ml/min
129
is the fluid that is reabsorbed in the proximal tubule hypo/hyper or iso-osmotic with filtrate?
iso-osmotic
130
what is meant by iso-osmotic?
salt and water reabsorption is equal
131
what substances are reabsorbed in the proximal tubule?
sugars, amino acids, phosphate, sulphate, lactate
132
what is secreted in the proximal tubule?
hydrogen ions, hippurates, neurotransmitters, bile pigments, uric acid, drugs, toxins
133
what are the 2 types of reabsorption that can take place in the nephron?
transcellular and paracellular
134
when does paracellular reabsorption occur?
if the cells dont have such tight junctions
135
what do substances from the filtrate need to go through to get into the peritubular capillary?
luminal membrane then tubular epithelial cells then interstitial fluid then the capillary wall (endothelia)
136
what are the 3 types of carrier-mediated membrane transport?
- primary active transport
- secondary active transport
- facilitated diffusion
137
primary active transport?
energy is directly required to operate the carrier and move the substrate against its concentration gradient
138
secondary active transport?
the carrier molecule is transported coupled to the concentration gradient of an ion (usually Na+)
139
facilitated diffusion?
passive carrier-mediated transport of a substance down its concentration gradient
140
how does oxygen and carbon dioxide move into/out of the cell?
diffusion through the lipid bilayer
141
how does sodium enter the cell?
diffusion through channels
142
how does glucose enter the cell?
facilitated diffusion
143
what type of transport occurs at a sodium/potassium pump?
primary active transport
144
what type of transport occurs at a sodium/glucose pump?
secondary active transport
145
if one ATP is hydrolysed, what affect does this have in the sodium/potassium pump?
3 Na are kicked out of the cell and 2 potassium are taken in
146
what is the isoosmotic fluid reabsorption across 'leaky' PT epithelium due to?
1. standing osmotic gradient
| 2. oncotic pressure gradient
147
what percentage of filtrate glucose is reabsorbed at the PT?
usually 100%
148
over what membrane can glucose easily pass down its gradient?
over basolateral membrane
149
what membrane can glucose not easily diffuse across, what does it need ti help?
the cell membrane - needs co-transporter or facilitated diffusion
150
why is there a transport maximum for glucose?
co-transport requires conformational changes in the proteins and therefore only so many molecules can be moved per unit time
151
what causes glucose in the urine in DM?
high glucose concentration in the plasma leads to high amount of glucose filtered and the transport mechanisms become saturated so not all glucose can be reabsorbed.
152
what is the renal threhold for plasma glucose concentration?
10-12 mmol/l
153
what percentage of all salt and water is reabsorbed in the PT?
67%
154
what is Na+ reabsorption driven by?
the basolateral Na+ - K+- ATPase
155
what does sodium reabsorption drive?
chloride reabsorption through the paracellular pathway
156
how is water reabsorbed?
by osmosis
157
what is the function of the loop of Henle and what does this enable?
- generates a cortico-medullary solute concentration gradient
- enables the formation of hypertonic urine
158
what is opposing flow in the 2 limbs of loop of Henle referred to as?
countercurrent flow
159
what does the loop of Henle work with to establish a hyper-osmotic medullary interstitial fluid?
vasa recta
160
what is being reabsorbed the entire length of the ascending limb of loop of henle?
sodium and chloride
161
how is sodium and chloride reabsorbed in the thick (upper) ascending limb?
active transport
162
how is sodium and chloride reabsorbed in the thin (lower) acending limb?
passive
163
why does little or no water follow salt reabsorption in the ascending limb?
it is relatively impermeabel to water
164
what does the descending limb of loop of Henle absorb?
does not reabsorb NaCl and it highly permeable to water
165
what does the selective permeabilities of the ascending and descending limbs of the loop of Henle enable?
an osmotic gradient to be established in the medulla
166
what do loop diuretics block?
the triple co-transporter
167
what happens at the triple co-transporter?
recycling of potassium and NaCl is absorbed into the interstitial fluid
168
where does the triple co-transporter pump solute from?
the thick ascending limb of loop of Henle
169
as you move further into the medulla, what happens to the concentration of interstitial fluid?
it increases
170
what happens to the concentration of the tubular fluid as it moves down the descending limb and then up the ascending limb?
increasingly concentrated as it moves down the descending limb and becomes increasingly dilute as it ascends the ascending limb
171
the tubular fluid is iso osmotic as it leaves the PT, what is it when it enters the DT?
hypo osmotic
172
what contributes to approx half of the medullary osmolality?
the urea cycle
173
how does urea enter the loop of Henle?
diffuses passively
174
what does urea add to the interstitium?
adds solute
175
is the distal tubule permeable to urea?
no
176
what is the purpose of countercurrent multiplication?
to concentrate the medullary interstitial fluid
177
why does a concentrated medullary interstitial fluid enable the kidney to do?
to produce urine of different volume and concentration according to the amounts of circulating ADH
178
essential blood flow through the medulla tends to wash NaCl and urea away. what features of the vasa recta minimise this?
1. vasa recta capillaries follow hairpin loops
2. vasa recta capillaries are freely permeable to NaCl and water
3. blood flow in vasa recta is low
179
what preserves the medullary gradient?
passive exchange across the endothelium
180
what does preservation of the medullary gradient ensure?
that the solute is not washed away
181
what does the high medullary osmolarity allow in the presence of ADH?
production of hypertonic urine
182
what is the osmolarity of the tubular fluid leaving the Loop of Henle?
hypo-osmotic, 100 mosmol/l
183
what causes the osmotic gradient at the end of the loop of Henle/start of distal tubule?
tubular fluid is 100 mosmol/l and the surrounding interstitial fluid of the renal cortex is 300 mosmol/l.
184
what is the collecting duct bathed in?
progressively increasing concentrations (300-1200 mosmol/l) of surrounding interstitial fluid
185
what is the distal tubule and collecting duct a major site for?
the regualtion of ion and water balance
186
what percentage of filtered ions are left by the time it gets to distal tubule?
less than 5%
187
what is fluid and NaCl regualtion mainly influenced by?
hormomes
188
what parts of the nephron are affected by hormones?
only the distal tubule and collecting duct
189
what are the 4 hormones that influence the distal tubules and collecting duct in the regulation of ion and water balance?
1. Antidiuretic hormone (ADH)
2. Aldosterone
3. Atrial natriuretic hormone
4. Parathyroid hormone (PTH)
190
what affect does ADH have on the regulation of water?
causes increased water reabsorption
191
what affect does aldosterone have on ion regulation?
increased sodium reabsorption and and increased potassium and hydrogen excretion
192
what affect does atrial natriuretic hormone have on ion regulation?
decreased sodium reabsorption
193
what affect does PTH have on ion regulation?
increased calcium reabsorption and decreased phosphate ion reabsorption
194
what 2 segments can the distal tubule be split into?
the early and late
195
what is the function of the early distal tubule?
NaCl reabsorption
196
what does the early distal tubule contain that allows it to undertake NaCl reabsorption?
the triple co-transporters
| Na+-K+-2Cl- transport
197
what is the late distal tubule responsible for?
- calcium reabsorption
- H+ secretion
- sodium reabsorption and potassium reabsorption in the basal state but in presence of aldosterone potassium secretion
198
what hormones is the late distal tubule sensitive to?
PTH, aldosterone
199
what is the early collecting duct similar to?
the late distal tubule
200
what are the properties of the late collecting duct and what is it influenced by?
a low ion permeability and permeability to water (and urea). influenced by ADH
201
Where is ADH secreted from?
posterior pituitary
202
what kind of peptide is ADH?
an octapeptide
203
where is ADH synthesied?
by the supraoptic and paraventricular nuclei in the hypothalmus
204
how is ADH transported from the hypothalmus to posterior pituitary and how is it stored?
down nerves to terminals where it is sorted in granules in posterior pituitary
205
what triggers the release of ADH?
when action potentials down the nerves lead to calcium dependent exocytosis
206
what is the plasma half-life of ADH?
10-15 minutes
207
what effect does increased ADH have on the water permeability of the collecting duct?
increased water permeability
208
what does ADH bind to in the tubule/collecting duct?
type 2 vasopressin receptor
209
where do you find the type 2 vasopressin receptor?
basolateral membrane
210
what type of receptor is a type 2 vasopressin receptor?
G-protein coupled receptor
211
what does binding of ADH to type 2 vasopressin receptor cause an increase in?
in cyclic AMP
212
what does the increase in cyclic AMP cause?
increased permeability of the luminal membrane
213
how does the luminal membrane increase its permeability to water?
by inserting new water channels (aqauporins)
214
what happens to the aquaporins on the luminal membrane when we are over-hydrated?
the become internalized back into vesicles and stored in the cytoplasm
215
how do the aquaporins on the basolateral membrane differ from those on the luminal membrane?
the ones of the basolateral membrane are always present (do not internalize) and they are not influenced by ADH
216
in the presence of high ADH, what type of urine is produced?
small amounts if hypertonic (concentrated) urine
217
what is the main stimuli for the release of ADH?
an increase in plasma osmolarity
218
what senses an increase in osmolarity?
hypothalamic osmoreceptors
219
where does the hypothalmic osmoreceptors send signals to and what does the lead to?
the hypothalamic neurons, leads to an increased thirst which increases fluid and decreases plasma osmolarity
220
a significant decrease in what can also activate hypothalamic neurons?
decrease in ECF
221
what senses a significant drop in ECF ?
left atrial volume receptors
222
if the left atrial volume receptors activates the hypothalamic neurons, what does this cause?
an increase in ADH, water reabsortion and decreased urine output so increased plasma volume
223
what are the 2 types of diabetes insipidus?
central diabetes insipidus and nephrogenic diabetes insipidus
224
main symptoms of DI?
- large volumes of dilute urine
| - constant thirst
225
what is the problem in central DI?
posterior pituitary unable to produce or secrete ADH
226
what is the problem in nephrogenic DI?
ADH production is normal but it does not exert its affects on tubules - problem with the receptors
227
treatment for central DI?
ADH replacement
228
what drug has a 25% risk of giving the patient DI?
long term lithium
229
what is the most important stimuli for ADH release?
hypothalamic osmoreceptors
230
what affect does decreased atrial pressure have on ADH release?
increased ADH release
231
what affect does stimulation of stretch receptors in upper GI tract have on ADH release?
feed-forward inhibition of ADH
232
what affect does nictotine and alcohol have on ADH release?
nicotine stimulates ADH release and alcohol inhibits ADH release
233
most reabsoption happens at proximal tubule so why is there not a change is osmolarity?
salt and water is reabsorbed in equal proportions
234
what is aldosterone released in response to?
-to rising potassium or falling sodium conc in the blood
235
what system activates aldosterone release?
rennin-angiotensis system
236
what does aldosterone cause?
stimulates sodium reabsorption and potassium secretion
237
most of potassium is reabsorbed in the proximal tubule, when aldosterone is absent what happens to the rest of it?
it is reabsorbed in the distal tubule, no potassium is excreted in urine
238
a change in what ion directly stimulates the adrenal cortex?
an increase in potassium
239
how does a decrease in plasma sodium cause aldosterone secretion?
promotes indirect secretion of aldosterone by means of the juxtaglomerular apparatus
240
what are the 3 ways in which rennin release can be stimulated?
1. reduced pressure in afferent arteriole
2. macula densa cells sense the amount of NaCl in distal tubule
3. increased sympathetic activity as a result of reduced arterial BP
241
what affect does reduced pressure in the afferent arteriole have on renin release and what affect does this have on blood volume?
more renin released, more sodium reabsorbed, increased blood volume, BP restored
242
what affect does a reduced NaCl conc in the distal tubule have on renin release?
more renin release so more NaCl is reabsorbed
243
what can abnormal increases in the R-A-A system cause?
hypertension
244
what do loop diuretics target and inhibit?
the triple co-transporter found in the ascending limb of loop of Henle
245
where is atrial natriuretic peptide/hormone produced and stored?
produced by the heart and stored in atrial muscle cells
246
when is ANP released?
when the atrial muscle cells are mechanically stretched due to an increase in the circulating plasma volume
247
what does ANP promote?
excretion of sodium and diuresis, decreasing plasma volume
248
what affect does ANP have on smooth muscle of afferent arteriole?
vasodilation
249
what affect does ANP have on sympathetic system?
decreases sympathetic activity
250
what affect does ANP have on kidney tubules?
decreased sodium reabsorption
251
what 2 mechanisms governs urination?
1. the micturation reflex
| 2. voluntary control
252
how much urine can the bladder accommodate before stretch receptors within its walls initiates micturation reflex?
250-400 ml
253
what happens in the micturation reflex?
involuntary emptying of the bladder by simultaneous bladder contraction and opening of both internal and external urethral sphincters
254
how is mictruation reflex over-ridden?
by voluntarily tightening the external sphincter and surrounding pelvic diaphragm
255
what is the normal pH of arterial blood?
7.45
256
what is the normal pH of venous blood?
7.35
257
average pH of blood?
7.40
258
what is a pH of 7 in terms of nmol/l?
100 nmol/l
259
what is a pH of 7.8 in terms of nmol/l?
16 nmol/l
260
what do small changes in pH reflect?
large changes in hydrogen ion concentration
261
what affect can acidosis have on the CNS?
can lead to depression of the CNS
262
changes in what can influence potassium levels in the body?
changes in Hydrogen ions
263
what affect does an increase in hydrogen ions have on potassium ions and where does this happen?
renal tubule increase hydrogen ion secretion and have a decrease in potassium ion secretion and this can lead to potassium ion retention
264
hydrogen ions are continually added to the body fluids by what 3 sources?
1. carbonic acid formation
2. inorganic acids produced during breakdown of nutrients
3. organic acids resulting from metabolism
265
how do strong acids dissociate in solution?
dissociate completely
266
how do weak acids dissociate in solution?
partially dissociate
267
what do buffer systems consist of?
a pair of substances- one can yield free hydrogen ions as the hydrgen ion concentration decreases and the other can bind free hydrogen ions when the hydrogen increases
268
at arterial PCO2 of 40mmHg what is the solubility coefficient?
0.03
269
what is the Henderson-Hasselbalch equation?
pH = pK + log [A-]/[HA]
270
what is the normal pK?
6.1
271
what is the normal bicarbonate?
24 mmol/l
272
how do you work out the rate of filtration of bicarbonate ions?
GFR x [HCO3-]plasma
273
what is the normal filtration rate of bicarbonate ions?
4320 mmol/day
274
when the concentration of bicarbonate ions is low in tubular fluid, what does secreted hydrogen ions combine with?
phosphate
275
what is tritratable acid?
the amount of hydrogen ions excreted as (largely) hydrogen phosphate
276
is ammonia a measurement of titratable acid?
no - separate ammonium determination is necessary
277
what can increase ammonium excretion in urine?
acidosis
278
what 3 things does secretion of hydrogen ions by the tubules do?
1. drives reabsorption of bicarbonate ions
2. Forms acid phosphate
3. forms ammonium ion
279
how much hydrogen ions need to be secreted to accomplish a reaborption of 4320 mmol/day of bicarbonate ions?
4300 mmol/day H+ secretion
280
how much titratable acid is secreted a day?
20 mmol/day
281
how much ammonium is secreted per day?
40 mmol/day
282
how much titratable acid is excreted each day?
20 mmol/day
283
how much ammonium ions are excreted per day?
40 mmol/day
284
what is the amount of hydrogen ion excretion equal to?
amount of "new" bicarbonate generated
285
what is the vast majority of hydrogen ion secretions used for and why?
for bicarbonate ion reabsorption to prevent generation of acidosis
286
what is the difference between compensation and correction of acid-base balance?
compensation is the restoration of pH irrespective of what happens to bicarbonate ions and Pco2.
correction of acid-base disturbance is restoration of pH and bicarb and Pco2 to normal
287
what things can cause Co2 retention?
-chronic bronchitits, chronic empyhsema, airway restriction, chest injuries, respiratory depression
288
what does co2 retention cause?
respiratory acidosis
289
what causes the acidosis in CO2 retention?
increased CO2 drives equilibrium to the right and there is an increase in hydrogen ions
290
what values indicates uncompensated respiratory acidosis?
pH 45 mmHg
291
have affect does CO2 retention have on the renal tubules?
stimulates them to secrete hydrogen ions into filtrate
292
in respiratory acidosis what happens to the bicarb ions in the renal tubules?
they are all reabsorbed
293
what does correction of respiratory acidosis require?
lowering PCO2 by restoration of normal ventilation
294
what causes respiratory alkalosis and when can this happen?
excessive removal of CO2 by the body
- low inspired P02 at altitude
- hyperventilation
295
pH is only a measure of what?
free hydrogen ions
296
why does excessive CO2 removal cause an alkalosis?
drives equilibrium to the left and there is an fall in hydrogen ions and bicarb ions (pH is only a measurement of free [H+]
297
what values indicate a respiratory alkalosis?
ph > 7.5 and
| PCO2
298
how does the kidney compensate for resp alkalosis?
reduces H+ secretion into the tubule
299
what affect does renal compensation for resp alkalosis have on bicarb concentration?
further lowers it
300
what causes metabolic acidosis?
excess H+ from any source other than CO2
301
examples of things that can cause an increase in H+?
- ingestion of acids or acid-producing foodstuffs
- excessive metabolic production of H+ (lactic acid)
- excessive loss of base from the body (e.g diarrhoea)
302
values that indicate metabolic acidosis?
ph
303
what does a decrease in plasma pH stimulate?
peripheral chemoreceptors
304
how does the respiratory system compensate for metabolic acidosis?
ventilation is increased and more CO2 is blown off, [H+]p is lowered raising pH to normal (bicarb ions are also lowered)
305
how does the renal system correct metabolic acidosis?
- filtered bicarb ions are very low and very readily reabsorbed
- H+ secretion continues and produces TA and NH4+, to generate more "new" bicarb ions
306
why is respiratory compensation essential in metabolic acidosis?
acid load cannot be excreted immediately, can take hours/days and even weeks to normalise
307
what causes metabolic alkalosis?
excessive loss of H+ from the body
308
in what ways can there be an excessive loss of H+?
- loss of HCl from the stomach (vomiting)
- ingestion of alkali
- aldosterone hypersecretion
309
how can aldosterone hypersecretion cause excessive loss of H+?
causes stimulation of Na+/H+ exchange at the apical membrane of the tubule: acid secretion
310
what values indicate metabolic alkalosis?
ph > 7.45
| bicarb ions high
311
in respiratory acidosis is the bicarb high or low?
high
312
in metabolic alkalosis is the bicarb high or low?
high
313
in metabolic acidosis, is the bicarb low or high?
low
314
in respiratory alkalosis , is the bicarb low or high?
low
315
what affect does increased pH have on breathing?
slows ventilation
316
what is the correction of metabolic alkalosis?
- filtered bicarb load is so large so not all of it is reabsorped
- bicarb excreted in urine
- no TA or NH4+ is generated
