L29 & 30: Control of Fluid, Electrolyte, and Acid-base Homeostasis Flashcards
1
Q
What is the general role of the lymphatic system?
A
Acts as a drain to collect the fluid back from the tissues.
2
Q
How much of your body is water?
A
45-75%
3
Q
Of the extracellular fluid in your body, 80% is interstitial fluid. Where is the remaining 20%?
A
Plasma
4
Q
What barrier separates interstitial fluid from intracellular fluid?
A
Cell plasma membrane
5
Q
What barrier separates interstitial fluid from plasma?
A
Blood vessel wall
6
Q
Define “fluid balance”
A
When required amounts of water and solutes are present and correctly proportioned among compartments
7
Q
In the body, what are the sources of water gain?
A
- Ingested liquids
- Ingested foods
- Metabolic water
8
Q
What is metabolic water?
A
Water derived from chemical reactions in the body (condensation reactions…etc.)
9
Q
What are the sources of water loss from the body?
A
- Kidneys
- Skin
- Lungs
- GI tract
10
Q
Body water volume is mainly governed by which source?
A
How much we drink
11
Q
What governs how thirsty we feel?
A
The thirst centre of the hypothalamus
12
Q
How much water loss results in dehydration?
A
2% decrease
13
Q
Fill in the gaps:
Dehydrations stimulates the __1__ (which stands for: __2__ __3__ __4__ System), which stimulates the __5__.
A
- RAAS
- Renin
- Angiotensin
- Aldosterone
- thirst centre
14
Q
Describe how fluid escapes from the capillaries to bathe surrounding tissue.
A
- Most is forced out by blood hydrostatic pressure (BHP). BHP pushes water and small ions out through the walls of the arterial end of capillaries.
- A small amount is lost by osmosis (interstitial fluid osmotic pressure, IFOP)
15
Q
After it is forced out of the arterial end of the capillary, where does fluid go?
A
It bathes the cells, delivering ions and nutrients. Some water is drawn back in to the capillary, via osmosis (blood colloid osmotic pressure, BCOP). The rest is drained through the lymphatic system and goes back into the blood plasma.
16
Q
Why is blood colloid osmotic pressure (BCOP) constant throughout the vessel?
A
BCOP is a result of large proteins in the blood plasma, and they don’t leave the vessel. Because the concentration of proteins doesn’t change, their osmotic pressure stays constant.
17
Q
Fill in the gaps:
In capillaries, net filtration pressure results in a net reabsorption at the __1__ end, and net filtration at the __2__ end.
A
- venous
2. arterial
18
Q
What is osmolarity?
A
The concentration of a solution expressed as the total number of solute particles per litre
19
Q
What is the effect of increasing osmolarity of the interstitial fluid?
A
Water is drawn out of cells, causing them to shrink
20
Q
What is the effect of decreasing osmolarity of the interstitial fluid?
A
Cells absorb more water, causing them to swell
21
Q
Does drinking too much water increase or decrease osmolarity of interstitial fluid?
A
Decreases
22
Q
True or false: Water intoxication can lead to convulsions, coma, or death.
A
True
23
Q
Other than water consumption, what else can cause changes in osmolarity?
A
Changes in Na+ concentration
24
Q
In RAAS, what is the major effect of aldosterone?
A
Reabsorption of Na+ and water. K+ and H+ secreted into urine.
25
In RAAS, what is the major effect of angiotensin II?
Vasoconstriction of arterioles (increases BP). Also stimulates release of aldosterone.
26
How do ACE inhibitors reduce blood pressure?
Stop conversion of angiotensin I to angiotensin II, preventing vasoconstriction.
27
What would be the effects of having a persistent elevated renin level?
Massively high BP: More angiotensinogen is converted to angiotensin I, and so more angiotensin I is converted by ACE's into angiotensin II. This causes prolonged vasoconstriction and increased aldosterone (increases sodium reabsorption).
28
What changes activate the RAA system?
Dehydration, Na+ deficiency, or haemorrhage decrease blood volume and pressure.
29
In the RAA system, what detects the decreased blood pressure, and responds by releasing renin?
Juxtaglomerular cells of kidneys.
| 'Juxta-' means near; so these cells are near the glomerulus of the kidney
30
Where is angiotensinogen produced?
Liver
31
What two factors can stimulate the adrenal cortex to produce more aldosterone?
1. Increased angiotensin II
| 2. Increased K+ in extracellular fluid
32
What are the 2 main solutes in extracellular fluid?
Na+ and Cl-
33
Why is hormonal regulation of solute and fluid concentration vital?
Diet is in constant flux, so concentrations need constant regulation
34
What are the 3 most important substances for regulating ion concentrations?
1. Angiotensin II
2. Aldosterone
3. Atrial natriuretic peptide (ANP)
35
What stimulus causes ANP release?
Stretching of the heart atria due to increased blood volume
36
Which hormone is most important for regulating water loss?
Antidiuretic hormone (ADH)
37
What is vasopressin?
It is another name for ADH
38
Where is ADH produced and secreted?
Produced in the hypothalamus, released from the posterior pituitary
39
What effect does ADH have?
Promotes insertion of aquaporin-2 into principal cells of collecting duct, increasing permeability to water. Produces concentrated urine.
40
What stimuli result in ADH release?
1. Increase in blood osmolarity
| 2. Severe haemorrhage
41
When osmoreceptors detect an increase in blood osmolarity, what happens next?
a. Hypothalamus produces ADH
| b. Thirst receptors in hypothalamus activated to encourage drinking
42
Which receptor does ADH bind to?
V2
43
In the V2-mediated pathway, what is the first messenger and what is the second messenger?
First messenger is ADH; second messenger is cAMP
44
What molecule can prevent cAMP from progressing the pathway?
Phosphodiesterase
45
What molecule activates cAMP?
Adenylyl cyclase - makes ATP into cAMP
46
What molecule is activated by cAMP?
Protein kinase A
47
What do kinases generally do?
Stick phosphate groups on other molecules
48
What does protein kinase A do?
PKA can either:
1. Activate proteins directly in the cytoplasm; or,
2. Activate CREB (cAMP response element-binding protein) inside the nucleus.
49
What is CREB?
CREB (or cAMP response element-binding protein) is a molecule that binds to CRE, activating protein synthesis
50
What are electrolytes?
Substances that dissociate to form ions
51
What are the four general functions of electrolytes?
1. Control osmosis of water between body fluid
2. Help maintain the acid-base balance
3. Carry electrical current
4. Serve as cofactors (Mg and Ca)
52
In what units are electrolytes typically expressed?
milliequivalents per litre (mEq/L)
Na+ or Cl-: mEq/L = mmol/L
Ca2+ or (HPO4)2-: mEq/L = 2 x mmol/L
53
Which is the most prevalent electrolyte in extracellular fluid?
Sodium
54
Which is the most prevalent electrolyte in intracellular fluid?
Potassium
55
Which is the most prevalent anion in extracellular fluid?
Chloride
56
Why does sodium play a pivotal role in fluid and electrolyte balance?
Because it accounts for almost half of the osmolarity of ECF
57
How are blood sodium levels regulated?
1. Aldosterone (increases renal reabsorption of Na+)
2. ADH (controls water levels: if Na+ levels are low, ADH release stops so more water is excreted)
3. Atrial natriuretic peptide (increases renal excretion of Na+)
58
How can physical exercise affect renal water reabsorption?
Physical exercise promotes sweating, which takes water from the blood. This increases the osmolarity of the blood. Osmoreceptors in the hypothalamus detect the rise on osmolarity and stimulate the posterior pituitary to release ADH. ADH acts on the kidney tubules and collecting ducts to increase renal reabsorption of water.
Plasma volume increases, blood osmolarity decreases.
59
How can physical activity cause an increase in sodium reabsorption?
Sweating reduces blood volume, detected by the juxtaglomerular cells of the kidneys. Kindeys release renin, which forms angiotensin I. This is then converted to angiotensin II, which stimulates release of aldosterone from adrenal cortex.
Aldosterone causes kidneys to reabsorb more Na+ and water.
60
Why can chloride anions move relatively easily between extracellular and intracellular fluid?
Because most plasma membranes contain Cl- leakage channels and antiporters
61
How are chloride levels regulated?
- ADH
| - Processes that affect renal reabsorption of Na+ also affect reabsorption of Cl-
62
What organ(s) regulates bicarbonate levels?
The kidneys
63
How is bicarbonate formed?
CO2 released from metabolism combines with water to form carbonic acid, which dissociates into H+ and bicarbonate (HCO3-)
64
What effect does exhalation have on bicarbonate levels?
Decreases bicarbonate levels as CO2 is exhaled, as water and CO2 cannot combine
65
# Fill in the gaps:
Potassium plays a key role in establishing __1__ __2__ potential in __3__ and __4__ fibres.
1. resting
2. membrane
3. neurons
4. muscle
66
How is potassium regulated?
By aldosterone - stimulates principal cells in renal collecting ducts to secrete excess K+
67
How does hyperkalemia cause death?
Ventricular fibrillation (which leads to cardiac arrest)
68
What is the most abundant mineral in the body?
Calcium, Ca2+
Most of it is stored in the skeleton and teeth
69
In what functions does calcium play an important role?
- Blood clotting
- Neurotransmitter release
- Muscle tone
- Excitability of nervous and muscle tissue
70
How is calcium regulated?
Regulated by parathyroid hormone - stimulates osteoclasts to release calcium from bone extracellular fluid and enhances calcium reabsorption from glomerular filtrate.
71
True or false:
In adults, the majority of total body magnesium is found in intracellular fluid.
False. 54% of Mg is in the bone as magnesium salts. The remaining 46% is found in ICF (45%) or ECF (1%).
72
# Fill in the gaps:
Magnesium is a cofactor for certain enzymes and __?__.
sodium-potassium pump
73
For which functions is Mg essential?
Normal neuromuscular activity, synaptic transmission, myocardial function, and secretion of parathyroid hormone
74
How is Mg regulated?
Varying rate excreted in urine
75
How is phosphate regulated?
1. Parathyroid hormone - stimulates resorption of bone by osteoclasts, releasing calcium and phosphate into the blood, but inhibits reabsorption of phosphate ions in kidneys (PTH increases urinary excretion & lowers plasma levels)
76
What is the link between phosphate and calcitrol?
Calcitrol promotes absorption of phosphates and calcium from GI tracts
77
What are the 3 important ionized phosphates?
1. (H2PO4)-
2. (HPO4)2-
3. (PO4)3-
78
Which phosphate molecule is an important buffer of H+ in body fluids and urine
(H2PO4)-
79
Why is it important to maintain fluid pH?
Proteins are denatured by excessively high/low pH
80
# Fill in the gaps:
Arterial blood pH should be between __1__ and __2__.
1) 7.35
| 2) 7.45
81
What mechanisms help keep arterial blood pH between 7.35 and 7.45?
Buffer systems
Exhalation of CO2
Renal excretion of H+
82
What type of buffer is most abundant in intracellular fluid and plasma?
Protein buffer
83
How does a protein respond to an increase in pH?
Increased pH means the medium has become more alkaline (i.e. there are too few H+ floating around). To compensate, the carboxyl end of a protein will give up a H+. Because it is donating H+, the protein acts as an acid.
84
How does a protein respond to a decrease in pH?
Decreased pH means the medium has become more acidic (i.e. there are too many H+ floating around). To compensate, the amine end of a protein will adopt a H+. Because it is accepting H+, the protein acts as a base.
85
Which phosphates are involved in the phosphate buffer system?
Dihydrogen phosphate (H2PO4)-
Monohydrogen phosphate (HPO4)2-
86
What does the phosphate buffer system regulate?
pH in cytosol
87
Name the receptors, control centre, and effectors that are involved with regulating blood pH through respiration.
Blood pH change is detected by chemoreceptors in medulla oblongata (CNS) and chemoreceptors in aortic and carotid bodies (PNS).
Nerve impulses send this to the control centre (inspiratory area in medulla oblongata), which send nerve impulses to the effector, the diaphragm.
88
How does the diaphragm alter the pH of blood?
It can speed up or slow down respiration, determining how much or how little bicarbonate is allowed to form. Speeding up breathing rate exhales more CO2, meaning less bicarbonate can form. Less bicarbonate = pH increase
89
How can your body regulate pH changes as a result of non-volatile acids?
Excrete H+ in urine
90
How does H+ get into the urine?
1. Na+/H+ antiporters in the proximal convoluted tubule secrete H+ as they reabsorb Na+
2. Intercalated cells of collecting duct include proton pumps that secrete H+ into tubule fluid
91
With all this acid being secreted into urine, how does your body stop the urine becoming too acidic to handle?
There are 2 more buffers in the collecting duct
(HPO4)2- and NH3
92
How is H+ expelled from intercalated cells in the collecting duct?
CO2 and water combine to form carbonic acid, which dissociates into H+ and (HCO3)-. The H+ is expelled into the tubule lumen via an ATP-activated proton pump (active transport). The bicarbonate is expelled via antiporter, as chloride is drawn in (facilitated diffusion).
93
If you hold your breath for a minute, what happens to blood pH?
pH drops (acidic) as CO2 rises, forming more carbonic acid
94
How would your body respond to a rise in pH that occurs as a result of you holding your breath?
Hypothalamus will take over and compel you to breathe
95
What would be the effect of a drug that inhibits carbonic anhydrase in the kidneys?
Prevents buffer forming, so pH can't be mopped up. pH lowers.
96
What are the CNS symptoms of acidosis?
```
Headache
Sleepiness
Confusion
Loss of consciousness
Coma
```
97
What are the respiratory symptoms of acidosis?
Shortness of breath
| Coughing
98
What are the cardiac symptoms of acidosis?
Arrhythmia
| Tachycardia
99
What are the muscular symptoms of acidosis?
Seizures
| Weakness
100
What are the GI symptoms of acidosis?
Nausea
Vomiting
Diarrhoea
101
What are the CNS symptoms of alkalosis?
Confusion
Light-headedness
Stupor
Coma
102
What are the PNS symptoms of alkalosis?
Hand tremor
| Numbness/tingling in face, hands, feet
103
What are the muscular symptoms of alkalosis?
Twitching
| Prolonged spasms
104
What are the GI symptoms of alkalosis?
Nausea
| Vomiting
105
A patient comes in with nausea, tingling hands and muscle spasms. Are these symptoms of acidosis, alkalosis, or do you need more information?
Alkalosis.
Both acid- and alkalosis can cause nausea, but numbness or tingling in the hands, and prolonged muscle spasms are signs of alkalosis.
106
Define acidosis
Arterial pH drops below 7.35
107
If bicarbonate levels drop below 24 mM, the patient has:
```
A) Metabolic alkalosis
B) Metabolic acidosis
C) Respiratory alkalosis
D) Respiratory acidosis
E) Need more info
```
E) Need more info
Without knowing the arterial pH, you cannot know if this is metabolic acidosis or if bicarbonate (base) has dropped to compensate for respiratory alkalosis.
108
If CO2 partial pressure rises above 40 mm Hg, and arterial pH is 7.32 the patient has:
A) Metabolic alkalosis
B) Metabolic acidosis
C) Respiratory alkalosis
D) Respiratory acidosis
D) Respiratory acidosis
109
You perform an ABG on a patient. It shows blood pH: 7.28, CO2 is raised. What might you expect to see from the bicarbonate levels?
Bicarbonate would be raised (above 24 mM) as the renal system attempts to compensate for the respiratory acidosis
110
Define alkalosis
Arterial blood pH more than 7.45
111
Which system compensates for a drop in bicarbonate?
Respiratory.
Decreases levels of bicarbonate lead to metabolic acidosis. Respiratory system compensates by lowering the level of CO2 (below 40 mm Hg)
112
Name some causes of respiratory acidosis
Emphysema, pulmonary oedema, injury to respiratory centre of the medulla, airway obstruction
113
True or false: The kidneys can compensate for mild respiratory acidosis
True
114
How can you treat respiratory acidosis?
Ventilation therapy and IV of bicarbonate
115
What causes respiratory alkalosis?
Hyperventilation due to overstimulation of inspiratory centre
116
True or false: Kidneys can compensate for mild respiratory alkalosis, and a paper bag can help
True
117
How can diarrhoea case metabolic acidosis?
Lose bicarbonate
118
What are some causes of metabolic acidosis?
Diarrhoea, renal dysfunction, acid accumulation (e.g. ketosis)
119
How can your body compensate for mild metabolic acidosis?
Hyperventilation
120
How might you treat a patient with metabolic acidosis?
IV sodium bicarbonate solution
121
How can metabolic alkalosis occur?
Loss of acid (mainly vomiting) or excessive intake of alkaline drugs (e.g. diuretics or antacids)
122
How might you treat metabolic alkalosis?
Replace electrolytes (increase bicarb)
