Physiology Flashcards
(115 cards)
1
Q
Define osmolarity
A
Concentration of osmotically active particles present in a solution
2
Q
What is the osmolarity of most body fluids?
A
300mosmol/l
3
Q
Define tonicity
A
Effect a solution has on cell volume
4
Q
What is the effect of a hypotonic solution?
A
Causes a cell to swell and increases cell volume
5
Q
What is the effect of a hypertonic solution?
A
Causes a cell to shrink and decreases cell volume
6
Q
What percentage of the body weight is total body water?
A
50-60%
7
Q
What are the two components of total body water?
A
Intracellular and extracellular
8
Q
What makes up the extracellular fluid?
A
Plasma
Interstitial Fluid
9
Q
What separates the intra/extracellular fluid?
A
Cell membrane
10
Q
How can the distribution volume be calculated?
A
By use of a tracer - titrated water, inulin, labelled albumin
11
Q
Describe the ionic differences between ICF and ECF
A
ICF - high potassium
ECF - high sodium, chloride, bicarbonate, magnesium, negative proteins
12
Q
Define fluid shifts
A
Movement of water between ICF and ECF in response to an osmotic gradient
13
Q
What is the effect of water loss from ECF?
A
Increase in ECF osmotic concentration water will move out of the ICF and into the ECF so cells will shrink
14
Q
What is the effect of water gain to the ECF?
A
Decrease in ECF osmotic concentration water will move out of the ECF into the ICF so cells will swell
15
Q
Describe the effect of gain/loss of NaCl
A
Sodium excluded from ICF, if ECF gains salt osmolarity will increase so water will leave ICF to ECF
Loss of salt will increase ICF volume as ECF osmolarity will decrease
16
Q
Other than salt/water changes what else can cause a fluid shift?
A
Change in volume - gain/loss of isotonic fluid, only change in ECF volume
17
Q
Define an electrolyte
A
Any substance that dissociates into free ions when dissolved
18
Q
Name two key ions that contribute to osmotic concentrations
A
Sodium - ECF
Potassium - ICF
19
Q
What detrimental changes can occur due to changes in potassium?
A
Muscle weakness and paralysis
Cardiac irregularities and arrest
20
Q
What is the recommended salt allowance?
A
6g/day
21
Q
Name the function of the kidneys
A
- water balance
- salt balance
- maintain plasma volume
- maintain plasma osmolarity
- acid base balance
- excretion of metabolic waste
- excretion of exogenous compounds
- secretion of renin
- secretion of erythropoietin
- conversion of vit D to its active form
22
Q
What percentage of blood is filtered by the glomerulus?
A
20%
23
Q
Name the three components of the glomerular filter
A
- glomerular capillary endothelium
- basement membrane
- slit processes of podocytes
24
Q
Name the four forces that result in glomerular filtration
A
Glomerular capillary BP 55mmHg towards tubule
Capillary oncotic pressure 30mmHg towards capillary
Bowman’s capsule hydrostatic pressure 15mg towards capillary
Bowman’s capsule oncotic pressure towards tubule 0mmHg
25
What is the net filtration pressure?
10mmHg
26
Define GFR
Rate at which protein free plasma is filtered from the glomeruli in to Bowmans capsule per unit time
27
What is the normal GFR?
125ml/min
28
How is GFR regulated extrinsically?
Changes to vessel shape alter the GFR
29
Describe the effect of a fall in blood volume
1. Decreased blood pressure
2. Detected by baroreceptors
3. Increase in sympathetic activity
4. Vasoconstriction
5. Decreased GFR
6. Decreased urine volume (compensates for reduced blood volume)
30
What is the effect of auto regulation on GFR?
Prevents short term changes in systemic arterial pressure affecting GFR
31
Describe myogenic auto regulation
If vascular smooth muscle is stretched it contracts, constricting the arteriole
32
Describe tubuloglomerular auto regulation
Involves juxtaglomerular apparatus
| If GFR rises more salt will through flow the tubule leading to constriction of afferent arterioles
33
What senses NaCl content in the tubular fluid?
Macula densa
34
Name three pathologies that can alter GFR
Kidney stones, increases bowmans fluid pressure, decreases GFR
Diarrhoea increases bowman oncotic pressure, decreases GFR
Severe burns decrease bowmans oncotic pressure and increases GFR
35
Define plasma clearance
Measure of how effectively the kidneys can clean the blood of a substance
36
Describe the clearance/GFR of inulin
Clearance = GFR as it is freely filtered and not reabsorbed or secreted
37
Describe the clearance/GFR of glucose
Filtered, completely reabsorbed and not secreted
| Clearance = 0
38
Describe the clearance/GFR of urea
Filtered and partly reabsorbed but not secreted so clearance
39
Describe H+ clearance/GFR
Filtered and secreted but not absorbed
Clearance > GFR
All filtered plasma is cleared and some peritubular plasma too
40
State three things a clearance marker should be
Non-toxic
Inert
Easy to measure
41
Name some substances that are reabsorbed
- sugars
- amino acids
- phosphate
- sulphate
- lactate
42
Name some substances that are secreted
- hydrogen ions
- hippurates
- neurotransmitters
- bile pigments
- uric acid
- drugs and toxins
43
Name two methods of reabsorption
Transcellular
| Paracellular
44
State three methods of transport of a substance
Primary active
Secondary active
Facilitated diffusion
45
Describe primary active transport
Energy directly required to move the substance against the gradient
46
Describe secondary active transport
Molecule is transported, coupled to the concentration of an ion
47
Describe facilitated diffusion
Passive carrier mediated transport down the concentration gradient
48
Describe three methods of sodium reabsorption
- Sodium potassium pump on basolateral membrane
- Co-transport with glucose/amino acids
- Sodium/hydrogen exchanger using hydrogen ions produced by carbonic anhydrase
49
How do water and chlorine leave the tubule?
Paracellular reabsorption
Standing osmotic gradient moves water by diffusion
As sodium leaves the lumen becomes more negative which causes chloride ions to leave
50
How is glucose reabsorbed?
Co-transported with sodium into the epithelial cell, it then leaves via facilitated diffusion
51
What is the renal threshold for glucose?
10-12mmol/l
52
What is the function of the loop of henle?
Generates a cortico-medullary solute concentration gradient which enables formation of hypertonic urine
53
Describe the movement of substances in the loop of henle
1. Solute is removed from the ascending limb
2. Tubular fluid is diluted and osmolality of interstitial fluid increases
3. Water leaves the descending limb via osmosis
4. Fluid in the descending limb is concentrated
54
Describe the gradient created by countercurrent multiplication
The horizontal gradient has been multiplied into a large vertical gradient
55
How is urea managed in the distal tubule?
Distal tubule is impermeable to urea so as water is removed it becomes more concentrated
56
What happens to urea in the medullary collecting duct?
It is absorbed as transporters are activated by vasopressin as a result this drives water reabsorption from the descending limb
57
What transporters are activated by vasopressin?
UTA3
| A3
58
Name the blood vessel that supplies the medulla
Vasa Recta
59
How does the vasa recta prevent all the solute being washed away?
- hairpin loops
- capillaries are permeable to NaCl and water
- low blood flow
60
Name four hormones that control body fluid
- antidiuretic
- aldosterone
- atrial natriuretic hormone
- parathyroid hormone
61
What ions are reabsorbed in the early distal tubule?
NaCl (NaK2Cl transport)
62
What ions are reabsorbed in the late distal tubule?
Calcium
Hydrogen
Sodium
Potassium
63
Describe the late collecting duct
Low ion permeability
| Permeability to water and urea influenced by ADH
64
Where is antidiuretic hormone synthesised?
Hypothalamus
65
State the shape of antidiuretic
Octapeptide
66
What signals to the hypothalamus to release ADH?
Osmoreceptors
| Atrial volume receptors
67
When is ADH released?
When action potentials down the nerves lead to calcium dependent exocytosis
68
How does ADH increase the permeability to water?
Binds to receptor to turn ATP to cAMP
| Increased the permeability by inserting new aquaporins to the luminal membrane
69
What happens to water in the presence of ADH?
Moves from the collecting duct lumen along the osmotic gradient and into the medullary interstitial fluid
70
Describe the effect of high/low ADH
High - small volume of concentrated urine
| Low - large volume of dilute urine
71
What extra-renal features can impact ADH level?
GI stretch receptors inhibit ADH
Nicotine stimulates ADH
Alcohol inhibits ADH
72
Where is aldosterone secreted?
Adrenal cortex
73
When is aldosterone secreted?
In response to increased potassium or decreased sodium in the blood
74
What is the effect of aldosterone?
Increases sodium reabsorption and potassium secretion
75
State the steps of the RAAS system in response to decreased salt, ECF or ABP
1. Angiotensinogen converted into angiotensin I by renin
2. Angiotensin I is converted into angiotensin II by ACE
3. Angiotensin II causes vasoconstriction, thirst and ADH release
Thirst increases fluid uptake
ADH increases water reabsorption
76
How does aldosterone act as part of RAAS?
Increases sodium reabsorption and chlorine follows this leads to osmotic hold of water and thus conservation of water
77
Where is renin released from?
Granular cells in the juxtaglomerular apparatus
78
What signals for renin to be released?
1. Reduced pressure in afferent arteriole
2. Macula dense cells ones the amount of NaCl in distal tubule
3. Increased sympathetic activity due to decreased ABP
79
Where does atrial natriuretic peptide come from?
Produced in heart and stored in the atrium
80
When is ANP released?
When atrial muscle cells are stretched due to increased plasma volume
81
How does ANP decrease plasma volume?
- decreases sodium reabsorption
- decreases RAAS
- vasodilation
- reduces sympathetic activity
82
What is micturition governed by?
Micturition reflex
| Voluntary control
83
What is the average pH of blood?
7.4
84
Where can hydrogen ions come form?
Carbonic acid formation
Inorganic acids produced in breakdown of nutrients
Organic acids from metabolism
85
What is the difference between a strong and weak acid?
Strong - completely dissociates in solution
| Weak - partially dissociates in solution
86
What is a buffer?
Pair of substances;
one can yield free hydrogen ions
one can bind free hydrogen ions
87
What is the key physiological buffer?
CO2, HCO2 Buffer
88
How is carbonic acid formed?
By the hydration of carbon dioxide by carbonic anhydrase
89
How does the kidney control bicarbonate concentration?
Variable reabsorption of filtered bicarbonate
| Addition of new bicarbonate to the blood
90
What does control of bicarbonate depend on?
Hydrogen ion secretion
91
Describe the reabsorption of filtered bicarbonate
Carbon dioxide moves into the epithelial cell and is hydrated to carbonic acid to produce
hydrogen ions - exchanged for sodium and move into tubule
bicarbonate - move into interstitial with sodium
92
What happens to the bicarbonate in the filtrate?
It binds to hydrogen ions forming carbonic acid which can be broken down and moved into the epithelium
93
What is the purpose of new bicarbonate formation?
Used to regenerate buffer stores depleted by an acid load
94
If bicarbonate ion decreases how is new bicarbonate produced?
Hydrogen ions combine with phosphate to form HPO42- this combines with another hydrogen ion to form HPO4-which is excreted in urine. However the bicarbonate is still formed by hydration of carbon dioxide
95
What is titratable acid?
Measure of strong bade (NaOH) added to titrate the urine back to 7.4
96
How does ammonia contribute to acid base balance?
Glutamine form the liver leads to NH3 in the tubule which mops up the hydrogen ions forming NH4+ that can be secreted in the urine
97
Define compensation
Restoration of pH irrespective of what happens to bicarbonate and carbon dioxide
98
Define correction
Restoration of pH and bicarbonate and carbon dioxide to normal
99
What is immediate buffering?
Dilution of acid/base in ECF, blood and ECF buffers respond very quickly but stores are quickly depleted
100
What is respiratory acidosis?
Retention of carbon dioxide by the body
101
What causes respiratory acidosis?
Lung diseases
102
What happens to the equilibrium in respiratory acidosis?
Driven to the right to produce hydrogen ions and bicarbonate
103
How does the body compensate for respiratory acidosis?
All bicarbonate is reabsorbed and hydrogen ions excreted with titratable acid
104
What is needed to correct respiratory acidosis?
Ventilation
105
What is respiratory alkalosis?
Excessive removal of carbon dioxide by the body
106
State the causes of respiratory alkalosis
Panic attack
Hyperventilation
Altitude
107
Describe the effect on the equilibrium of respiratory alkalosis
Moves to the left meaning both hydrogen ion and bicarbonate concentration fall
108
How does the body compensate for respiratory alkalosis?
Reduces hydrogen ion secretion and bicarbonate is excreted in urine.
No titratable acid or new bicarbonate is generated
109
What is metabolic acidosis?
Excessive hydrogen ions from any other source other than carbon dioxide
110
What can cause metabolic acidosis?
Ketoacidosis
Diarrhoea
Ingestion
111
How does the body compensate for metabolic acidosis?
Decreased pH stimulates chemoreceptors which increase ventilation to blow off CO2 and lower H+ and bicarbonate
112
How is metabolic acid corrected?
Filtered bicarbonate is low and readily reabsorbed and new bicarbonate is generated
Hydrogen ion secretion continues and acid is excreted in the urine
Ventilation can then be normalised
113
What is metabolic alkalosis?
Loss of hydrogen ions or addition of a base causes bicarbonate to rise
114
How does the body compensate for metabolic alkalosis?
Increased pH is detected by chemoreceptors which slows ventilation to retain carbon dioxide and increase hydrogen and bicarbonate ions
115
How is metabolic alkalosis corrected?
Filtered bicarbonate is so large that not all of it is reabsorbed, no titratable acid is generated so bicarbonate is secreted and falls back to normal
