Physiology Flashcards
(175 cards)
1
Q
What is osmolarity?
A
Concentrated solution of osmotically active particles present in a solution
2
Q
What are the units used for osmolarity?
A
osmol/l or mosmol/l
3
Q
What needs to be known to calculate osmolarity?
A
Molar concentration of the solution and the number of osmotically active particles present
e.g.
150mM NaCl (150mmol/l)
No. of osmotically active particles = 2 (Na + Cl-)
Osmolarity = 2x150 = 300 mosmol/l
4
Q
What is the difference between osmolality and osmolarity?
A
Osmolality has units of osmol/kg water
Osmolarity has units of osmol/l
For weak salt solutions (incl. body fluids) these 2 terms are interchangable
5
Q
What is the osmolarity of body fluids?
A
300 mosmol/l
6
Q
What is tonicity?
A
Effect a solution has on cell volume
Can be hypo, hyper and iso tonic
7
Q
What is an isotonic solution?
A
No change in cell volume (no net movement of water)
8
Q
What is a hypotonic solution?
A
More water; dilute salt solution
Increase in cell volume due to movement of water via osmosis from the ECF to the ICF
9
Q
What is a hypertonic solution?
A
Less water; concentrated salt solution
Decrease in cell volume, cell losing fluid via osmosis from the ICF to the ECF
10
Q
What, aside from the salt concentrations, has an impact on osmolarity?
A
Ability of a solute to cross the cell membrane
11
Q
What percentage of the body weight is due to total body water in males and females?
A
Males - 60%
Females - 50% (due to more fat present)
12
Q
What are the 2 compartments to total body water?
A
ICF (67% of TBW)
ECF (33% of TBW)
13
Q
What is included in the extracellular fluid?
A
Plasma
Interstitial fluid
Lymph and transcellular fluid (negligible)
14
Q
How can body fluid compartments be measured?
A
Tracers to obtain the distribution volume of a tracer
15
Q
What are useful tracers?
A
TBW: 3H20
ECF: Inulin
Plasma: labelled albumin
16
Q
How is the volume of distribution measured?
A
V (litres) = dose (D) / sample concentration (C)
17
Q
How much fluid intake is there of a given day?
A
2500 ml
18
Q
How much fluid is lost per day and where from?
A
Insensible: skin (350), lungs (350)
Sensible loss: sweat (100), faeces (200), urine (1500)
TOTAL: 2500
19
Q
How is water imbalance manifested?
A
Body fluid osmolarity
20
Q
What is the ionic composition of the ICF?
A
Sodium: 10
Potassium: 140
Chloride: 7
HCO3-: 10
21
Q
What is the ionic composition of the ECF?
A
Sodium: 140
Potassium: 4.5
Chloride: 115
HCO3-: 28
22
Q
What is fluid shift?
A
Movement of water between the ICF and ECF in response to an osmotic gradient
23
Q
What would happen if the osmotic concentration of the ECF increases?
A
ICF will lose water to ECF to maintain fluid balance
24
Q
What would happen if the osmotic concentration of the ECF decreases?
A
ICF will gain water from the ECF to maintain the fluid balance
25
What will happen if there is a gain or loss of NaCl?
Change in fluid osmolarity - Na+ excluded from ICF, causing osmotic water movements
26
What will happen if there is a gain or loss of isotonic fluid (0.9% NaCl)?
No change in fluid osmolarity
| Change in ECF volume only
27
What organ alters the composition and volume of the ECF?
Kidneys
28
Why is electrolyte balance important?
Total electrolyte concentrations can directly affect water balance (via changes in osmolarity)
The concentrations of individual electrolytes can affect cell function
29
Describe sodium balance?
>90% of the osmotic concentration of the ECF results from the presence of sodium salts
The total amount in the ECF represents a balance between 2 factors (input and output)
Sodium is mainly present in ECF - major determinant of ECF volume - water follows salt
VITAL to regulate Na+
30
Describe potassium balance?
Minor fluctuations in plasma potassium can have detrimental consequences
Potassium plays a key role in establishing membrane potential
>9% of K+ is ICF, small leakages can lead to paralysis and cardiac arrhythmias
K+ plasma must be closely monitored and regulated
31
What are the functions of the kidney?
```
Water and salt balance
Maintenance of plasma volume
Maintenance of plasma osmolarity
Acid-base balance
Excretion of metabolic waste products
Excretion of exogenous foreign compounds
Secretion of renin
Secretion of erythropoietin
Conversion of vitamin D to active form (calcitrol)
```
32
What are the functional mechanisms of the nephron?
Filtration
Reabsorption
Secretion
33
Describe the blood supply to the nephron
```
Renal artery
Afferent arteriole
Glomerulus at the bowman's capsule
Efferent arteriole
Peritubular capillaries
Venule
Renal vein
```
34
What are the 2 different types of nephron?
Juxtamedullary - has vasa recta instead of peritubular capillaries
Cortical - smaller loop of helne
35
What makes up the glomerular membrane?
Endothelial cells
Basement membrane
Podocyte foot processes
36
What do the granular cells within the juxtaglomerular apparatus produce?
Produce and secrete renin
37
What is the function of the macula densa cells?
Salt sensitive cells, monitor salt levels in the tubular fluid passing through the juxtaglomerular apparatus
38
How much of plasma that enters the glomerulus is initially filtered to the kidney tubule?
20%
39
How is the rate of excretion calculated?
[X[ urine X Vu (Vu is urine production rate)
40
How is the rate of filtration calculated?
[x]plasma x GFR
41
What is the GFR of a normal, healthy kidney?
125 ml/min
42
How is the rate of reabsorption of a substance calculated?
Rate of filtration - rate of excretion
43
How is the rate of secretion calculated?
Rate of excretion - rate of filtration
44
How is GFR calculated?
Kf x net filtration pressure (Kf = filtration coefficient of glomerular membrane)
45
Why is the basement membrane of the glomerulus negatively charged?
To repel the negatively charged plasma proteins, they will therefore stay in the capillary and will not filter through
46
What are the forces that comprise net filtration pressure?
Glomerular capillary blood pressure
Bowman's capsule hydrostatic (fluid) pressure
Capillary oncotic pressure
Bowman's capsule oncotic pressure
47
What force does glomerular capillary blood pressure exert?
55 mmHg into the bowman's capsule
48
What force does bowman's capsule hydrostatic pressure exert?
15 mmHg into the capillary
49
What force does the capillary oncotic pressure exert?
30 mmHg into the capillary
50
What force does bowman's capsule oncotic pressure exert?
0 mmHg into the bowman/s capsule
51
What are starling forces?
Balance of hydrostatic pressure and osmotic forces
52
What is the net filtration rate of a normal kidney?
10 mmHg, pushes fluid and small molecules to form the initial tubular fluid
53
What force has the largest impact on the net filtration rate and subsequent GFR?
Glomerular capillary BP
54
How does the glomerular capillary BP remain constant along the length of the capillary?
Due to the larger diameter of the afferent arteriole compared to the efferent arteriole
55
What is oncotic pressure?
Plasma proteins that will drug fluid along with it
56
What is the GFR?
The rate at which protein free plasma is filtered from the glomeruli into the bowman's capsule per unit time
57
What is the extrinsic regulation of the GFR?
Sympathetic control via baroreceptor reflex
58
What is the intric regulation of the GFR?
Myogenic mechanism
| Tubuloglomerular feedback mechanism
59
Describe the direct effect of arterial BP on GFR
Increased arterial BP increases blood flow into the glomerulus
Increased glomerular capillary BP
Increased net filtration pressure
Increased net filtration pressure
60
How will vasoconstriction and vasodilation affect GFR?
Vasoconstriction will reduce GFR
| Vasodilation will increased GFR`
61
How is renal blood flow and GFR protected from changes in MABP?
Intrinsic (autoregulation) factors
| Helps to prevent unwanted shifts in salt
62
What is the myogenic autoregulation?
If vascular smooth muscle is stretched (i.e. arterial pressure is increased), it contracts thus constricting the arteriole
63
What is the tubuloglomerular feedback autoregulation?
Involves the juxtaglomerular apparatus via macula densa cells whereby if GFR rises, and subsequently there is a rise in NaCl flowing through the tubule, there will be a constriction of the afferent arterioles
64
Describe what occurs to GFR in the case of a kidney stone
Increased bowman's capsule fluid pressure, leading to a decreased GFR
65
Describe what occurs to GFR in the case of diarrhoea?
Increased capillary oncotic pressure due to a loss of water but not proteins, leading to a decreased GFR
66
Describe what occurs to GFR in the case of severe burns
Decreased capillary oncotic pressure due to a loss of plasma proteins, resulting in an increased GFR
67
What is plasma clearance
A measure of how effectively the kidneys can clean the blood of a substance
Equals the volume of plasma completely cleared of a particular substance per minute
68
How is clearance calculated?
[X] urine x V urine / [X] plasma
69
What unit is used in the clearance of a substance?
ml/min
70
Describe the properties of inulin
```
Freely filtered at the glomerulus
Neither absorbed nor secreted
Not metabolised by the kidney
Not toxic
Easily measured in urine and blood
```
71
What does inulin clearance tell you?
GFR
72
What is an alternative to inulin?
Creatinine
73
What is a substance that has a clearance of 0?
Glucose - it is completely reabsorbed by the peritubular capillaries
Therefore if there is any glucose in the urine, it is abnormal
74
What is a substance that is partly filtered by the kidneys and not secreted?
Urea
| Clearance < GFR
75
What is a substance that is filtered and secreted but NOT reabsorbed?
H+
All of the filtered plasma is cleared of H+
Clearance > GFR
76
What does para-amino hippuric acid give an indication of?
Renal plasma flow - all PAH in plasma that escapes filtration is secreted from the peritubular capillaries
77
What is the clearance value of inulin and creatinine?
125 ml/min
78
What is the clearance value of PAH?
650 ml/min (value of renal plasma flow)
79
How is filtration fraction calculated?
GFR/ renal plasma flow
80
What is filtration fraction a measure of?
Fraction of plasma flowing through the glomeruli that is filtered into the tubules
81
How is renal blood flow calculated?
RPF x 1/1-haematocrit
82
Describe what the kidneys reabsorb?
```
99% of fluid
99% salt
100% glucose
100% amino acids
50% urea
0% creatinine
```
83
What cannot get through the glomerular filtrate?
RBC
| Large plasma proteins
84
How much of filter fluid is reabsorbed in the proximal tubule?
80 ml/min
85
What is the flow of filter fluid in the loop of henle?
45 ml/min
86
Does the osmolarity of tubular fluid change as you move through the proximal tubule?
It does not - enters at 300 and leaves at 300
87
What is reabsorbed in the PT?
```
Glucose
Amino acids
Phosphate
Sulphate
Lactace
```
88
What is secreted into the PT?
```
H+
Hippurates
Neurotransmitters: ACh, noradrenaline, adrenaline
Bile pigments
Uric acid
Drugs: atropine, morphine, penicillin
Toxins
```
89
Describe the route of a substance that is reabsorbed transcellular?
Apical membrane
Cytoplasm
Lateral space (interstitial fluid)
Peritubular capillary
90
What is paracellular transport?
In-between adjacent epithelial cells
91
What is primary active transport?
Energy is directly required to operate the carrier and move the substrate against its concentration gradient
92
What is an example of primary active transport?
Na+/K+ ATPase - moves 3 sodium out for 2 potassium in for every ATP that is hydrolysed
93
What is secondary active transport?
The carrier molecule is transported coupled to the concentration gradient of an ion (usually Na+)
94
What is facilitated diffusion?
Passive carrier-mediated transport of a substance down its concentration gradient
95
What is a symporter?
Moving ions/substances in the same direction
96
What is an antiporter?
Substance/ion moves in the opposite direction of sodium
97
Where is the sodium potassium pump found for all epithelial cells?
On the basolateral membrane
98
What does the sodium potassium pump help to maintain?
The low concentration of sodium within the cell, allowing for an ion gradient to be formed allowing for the transport of other ions/substances into the cell
99
What will follow sodium?
Chloride ions - via paracellular route
100
Is the PT tight junctions tight or leaky?
Leaky - allows for paracellular transport of water and chloride ions
101
In the PT, what transport membranes are present?
Na+ glucose symporter
Na+ amino acid symporter
Na+ H+ antiporter
102
Why is there no change in osmolarity as you move through the proximal tubule?
Salt and water are reabsorbed in equal concentrations
103
How will salt and water get from the lateral space (interstitial fluid) to the peritubular capillary?
Via oncotic drag of the peritubular plasma
104
How much of glucose is reabsorbed in the proximal tubule?
100%
105
How will glucose get from the tubular filtrate to the lateral space?
Na+/glucose symporter into the tubular cell
| Facilitated diffusion at the basolateral membrane into the interstitial fluid
106
Will water follow glucose?
Yes
107
What is the renal threshold for glucose?
10-12 mmol/l
| More than this and you will excrete glucose in the urine
108
What drives sodium reabsorption?
The basolateral Na+/K+ ATPase pump
109
What is the function of the loop of henle?
Generates a cortico-medullary solute concentration gradient allowing the formation of hypertonic urine
110
Describe fluid flow in the loop of henle
Opposing flow in the 2 limbs is termed countercurrent flow
The entire loop functions as a countercurrent multiplier
Together, the loop and vasa recta establish a hyper-osmotic medullary interstitial fluid
111
What is reabsorbed in the ascending limb of the loop of henle?
NaCl
| IMPERMEABLE TO WATER
112
Describe the difference between the thick and thin ascending limbs of the loop of henle?
Thick AL achieves NaCl reabsorption via active transport
| Thin AL achieves NaCl reabsorption via passive transport
113
What is reabsorbed in the descending limb of the loop of henle?
HIGHLY permeable to water
| Does NOT reabsorb NaCl
114
What transporter is present in the thick ascending limb of the loop of henle?
Triple co-transporter: 1 sodium, 1 potassium, 2 chloride
115
What happens to the potassium reabsorbed in the loop of henle?
It is recycled back into the tubular fluid to allow the absorption of NaCl
116
What is the mechanism of action of loop diuretics?
Bind reversibly to the co transporter preventing the reabsorption of NaCl, decreasing interstitial hypertonicity and therefore water reabsorption
Increase the urinary K+ excretion by enhancing distal tubular K+ secretion and reducing K+ reabsorption in the loop of Henle
117
Describe the changes in osmolarity as you move around the loop of henle
Solute removed from lumen of ascending limb via triple co-transporter but water cannot follow
Tubular fluid is diluted and osmolality of interstitial fluid is raised (increase in NaCl)
Interstitial solute cannot enter the descending limb
Water leaves descending limb via osmosis due to gradient set up
Fluid in descending limb is concentrated
118
What type of fluid will the loop of henle produce?
Osmolarity of 100 mmosmol/l
Hypotonic solution: More water; dilute salt solution
Increase in cell volume due to movement of water via osmosis from the ECF to the ICF
119
What is the difference in interstitial fluid osmolarity as you move from the cortex to the medulla?
Coretx: 300
Medulla: 1,200
120
What effect does urea have on medullary osmolality?
Contributes around half of the osmolality as it adds solute to the interstitium
Collecting duct will reabsorb 50% of urea (ADH promotes)
121
What is the purpose of countercurrent multiplication?
Concentrate medullary interstitial fluid to enable the kidney to produce urine of different volume and concentration according to the amounts of circulating ADH
122
What is the osmolarity fo the interstitial fluid of the renal cortex?
300 mosomol/l
123
What is the osmolarity of the interstitial fluid surrounding the collecting ducts?
300-1200 mosmol/l
124
What is the primary action of ADH?
Increased water reabsorption - reduced urine production
125
What is the primary action of aldosterone?
Increased sodium reabsorption
| Increased hydrogen and potassium secretion
126
What is the primary action of atrial natriuretic hormone?
Decreased sodium reabsorption
127
What is the primary action of PTH?
Increased calcium reabsorption
| Decreased phosphate reabsorption
128
What is the permeability of the distal tubule?
Low permeability to water and urea - permeability is influences by the levels of ADH
129
What is the action of the early distal tubule?
Na+/K+/2Cl- transport (NaCl transport)
130
What is the action of the late distal tubule?
Ca2+ reabsorption
H+ secretion
Na+ reabsorption
K+ reabsorption
131
What is the action of the late collecting duct?
Low ion permeability
| Permeability to water (and urea) influenced by ADH
132
Where is ADH synthesised and secreted?
Supraoptic and paraventricular nuclei in the hypothalamus
Transported down nerves to terminals where it is stored in granules in the posterior pituitary
Released into blood when action potentials down the nerves lead to Ca2+ dependent exocytosis
133
What effect does ADH have on the collecting ducts?
Increases the permeability of the luminal membrane to water by inserting new aquaporins via increased cAMP within the cell
134
Describe the actions of a high ADH
High water permeability
Hypertonic urine
Presence of ADH moves water from the collecting duct lumen into the medullary interstitial fluid vi osmotic gradient forming a hypertonic urine
135
Describe low plasma ADH
```
Low water permeability
Hypotonic urine (<50 mosmol)
```
136
What are the symptoms of diabetes insipidus?
Large volumes of dilute urine (20 litres a day)
| Constant thirst
137
What can cause cranial DI?
Trauma to the hypothalamus or posterior pituitary
| DIDMOAD (DI + DM + optic atrophy + deafness)
138
What can cause nephrogenic DI?
Inherited
Lithium
CKD
139
What is the most important stimulator for ADH release?
Hypothalamic osmoreceptors
| Also via activation of left atrial stretch receptors
140
What is the action of nicotine and ADH?
Stimulates ADH release
141
What is the action of alcohol and ecstasy on ADH?
Inhibits release - high volumes of dilute urine
142
Describe tubular flows as you move through the nephron?
GFR/ proximal tubule = 125 ml/min
Loop of henle: 45ml/min to 25 ml/min
Distal tubule: 8ml... with ADH: 0.2ml/min
Without ADH: 20 ml/min
143
What is aldosterone?
Steroid hormone secreted by the adrenal cortex
144
What is the action of aldosterone?
Stimulates sodium reabsorption and potassium secretion
145
How is aldosterone initiated to reabsorb sodium and secrete potassium?
Increase in potassium acts directly on the zone glomerulosa to secrete aldosterone
Decrease in sodium will be detected by macula densa cells, activate RAAs system leading to the release of aldosterone
146
How does aldosterone increase BP?
Water follows salt; it will follow sodium, increasing circulating volume
147
What happens with a lack of aldosterone?
Salt wasting
Hypotension
ADDISON'S SYNDROME
148
What happens with too much aldosterone?
Hypernatraemia
Hypokalaemia
Hypertension
CONN'S SYNDROME
149
Where is the majority of K+ reabsorbed?
Early regions of the nephron - mainly in the proximal tubule
150
Describe the RAAS system
Decreased NaCl/ ECF/ BP
Liver produces angiotensinogen which is converted to angiotensin 1 by renin
This is converted to angiotensin 2 via ACE in the lungs which acts on the adrenal cortex to release aldosterone
151
What are the actions of angiotensin 2?
Increased ADH
Increased thirst
Increased arteriolar constriction
152
What cells release renin?
Granular cells of the juxtaglomerular apparatus
153
How is renin release from the granular cells controlled by reduced pressure in afferent arteriole?
More renin released
More Na+ reabsorbed
Increased blood vol
Increased BP
154
How is renin release from the granular cells controlled by the macula densa cells?
If NaCl reduced, more renin released, more Na+ reabsorbed
155
How is renin release from the granular cells controlled by symp activity?
Granular cells are directly innervated by sympathetic nervous system, causing renin release
156
Where will aldosterone act?
Distal and collecting tubules - will cause effects via changes in gene expression and protein synthesis causing an increase in sodium channels at the apical membrane and increased Na+/K+ ATPase pumps at the basolateral membrane
157
What is the pathophysiology of the RAAS and heart failure?
```
Failing heart
Decreased CO and BP
Stimulation of RAAS
Increased salt and water retention
Oedema
```
158
When is ANP released?
Atrial cells are physically stretched due to an increase in the circulating plasma volume
159
What are the actions of ANP?
```
Decreases:
Na+ reabsorption
RAAS
Smooth muscle of afferent arterioles
Sympathetic nervous system
```
160
What is the is purpose of ANP relaxing the smooth muscle of afferent arterioles?
Afferent arteriole vasodilation
Increased GFR
Increased sodium and water
161
What is the purpose of ANP decreasing the sympathetic nervous system output?
Decreased CO
Decreased total peripheral resistance
Decreased arterial BP
162
Describe urination
```
Bladder fills
Stretch receptors
Parasympathetics
Bladder contracts
Internal urethral sphincter opens
Stretch receptors can also tell the cerebral cortex to stimulate motor neurones closing the external urethral sphincter
```
163
Describe the relationship between osmolality and ADH?
Increased osmolality - dehydration
| Increased ADH
164
What occurs in water diuresis?
Increased urine flow but not an increased solute excretion
165
What occurs in osmotic diuresis?
Increased urine flow is as a result of a primary increase in salt excretion - a failure of normal Na+ reabsorption causes both increased sodium and increased water excretion
166
What can acidosis lead to?
Depression of the CNS
167
What can alkalosis lead to?
Overexcitability of the peripheral NS and CNS
168
What effect does hydrogen have on potassium?
Increased hydrogen secretion by cells in the tubul, will lead to potassium retention
169
How is H+ added to the body fluids?
Carbonic acid formation
Inorganic acids produced during breakdown of nutrients
Organic acids resulting from metabolism
170
Describe the difference between strong and weak acids?
Strong acids dissociate completely in a solution
| Weak acids dissociate partially in a solution
171
What is the most important physiological buffer system?
Carbonic anhydrase
Carbonic acid
Base-bicarbonate
172
What controls bicarbonate and carbon dioxide?
HCO3- kidneys
| pCO2 - lungs
173
How do the kidneys control bicarbonate?
Conserving filtrated bicarb
| Generate new bicarb to regenerate buffer stores depleted by an acid load
174
What will hydrogen ions bind to when bicarb tubular concentrations are low?
Phosphate to form phosphoric acid - this is titratable acid
175
What does hydrogen secretion in the tubule do?
Drives reabsorption of bicarb and the generation of new bicarb
Forms acid phosphate
Forms ammonium ions
