Download Chapter 21: Blood Vessels and Circulation

Document related concepts

Organ-on-a-chip wikipedia , lookup

Animal nutrition wikipedia , lookup

Metabolic network modelling wikipedia , lookup

Homeostasis wikipedia , lookup

Allometry wikipedia , lookup

Transcript
Chapter 27: Fluid, Electrolyte and
Acid-base Balance
BIO 211 Lecture
Instructor: Dr. Gollwitzer
1
• Today in class we will discuss:
– The importance of water and its significance to fluid
balance in the body
– Definitions and the importance of:
• Fluid Balance
• Electrolyte balance
• Acid-base balance
– Extracellular fluid (ECF) and intracellular fluid (ICF)
and compare their composition
– Fluid and electrolyte balance
• Hormones that regulate them
• Importance of key electrolytes
2
Introduction
• Water critical to survival
– 50-60% total body weight
– 99% of extracellular fluid (ECF)
– Essential component of cytosol (intracellular
fluid, ICF)
• All cellular operations rely on water
– Diffusion medium for gases, nutrients, waste
products
3
Body Fluid Compartments
• Body must maintain normal volume and
composition of:
– ICF
– ECF = all other body fluids
• Major - IF, plasma
• Minor - lymph, CSF, serous and synovial fluids
• ICF > total body water than ECF
– Acts as water reserve
4
Body Fluid Compartments
Figure 27–1a-2
5
Body Fluid Balance
• Must maintain body fluid:
– Volume (fluid balance)
– Ionic concentration (electrolyte balance)
– pH (acid-base balance)
• Gains (input) must equal loss (output)
• Balancing efforts involve/affect almost all
body systems
6
Fluid (Water) Balance
• = amount of H20 gained each day equal to
amount of H2O lost
• Regulates content and exchange of body
water between ECF and ICF
• Gains
– GI (from food, liquid)*
– Catabolism
• Losses
– Urine*
– Evaporation (from skin, lungs)
– Feces
* Primary route
7
Fluid Gains and Losses
Figure 27–3
8
Electrolyte (Ion) Balance
• Balances gains and losses of all electrolytes
(ions that can conduct electrical current in solution)
• Gains
– GI (from food, liquid)
• Losses
– Urine
– Sweat
– Feces
9
Acid-base (pH) Balance
• Balances production and loss of H+
• Gains
– GI (from food and liquid)
– Metabolism
• Losses
– Kidneys (secrete H+)
– Lungs (eliminate CO2)
10
Fluid Components
• ECF components (plasma and IF) very similar
• Major differences between ECF and ICF
• ICF very different because of cell membrane
– Selectively permeable
– Specific channels for ions
– Active transport into/out of cell
• Water exchange between ECF and ICF occurs across
cell membranes by:
– Diffusion
– Osmosis
– Carrier-mediated transport
11
Cations in Body Fluids
Figure 27–2 (1 of 2)
12
Anions in Body Fluids
Figure 27–2 (2 of 2)
13
Cations and Anions in Body
Fluids
• In ECF
– Na+
– Cl– HCO3-
• In ICF
– K+ (98% of body content)
– Mg2+
– HPO42– Negatively charge proteins
14
Principles of Fluid and Electrolyte
Regulation
• All homeostatic mechanisms that monitor and
adjust body fluid composition respond to
changes in ECF, not ICF
– Because:
• A change in ECF spreads throughout body and affects
many or all cells
• A change in ICF in one cell does not affect distant cells
15
Principles of Fluid and Electrolyte
Regulation
• No receptors directly monitor fluid or
electrolyte balance
– Electrolyte balance = electrolytes gained equals
the electrolytes lost
• Monitor secondary indicators
– Baroreceptors – for plasma volume/pressure
– Osmoreceptors – for osmotic (solute)
concentration
• Solutes = ions, nutrients, hormones, all other materials
dissolved in body fluids
16
Principles of Fluid and Electrolyte
Regulation
• Cells cannot move water by active transport
– Passive in response to osmotic gradients
• Fluid balance and electrolyte balance are
interrelated
• Body’s content of water and electrolytes:
– Increases if gains exceed losses
– Decreases if losses exceed gains
17
Primary Hormones for Fluid and
Electrolyte Balance
• ADH
• Aldosterone
• Natriuretic peptides (e.g., ANP)
18
ADH
• Produced by osmoreceptor neurons in
supraoptic nuclei in hypothalamus (and released
by posterior pituitary)
– Osmoreceptors monitor osmotic concentrations in
ECF
– Osmotic concentration increases/decreases when:
• Na+ increases/decreases or
• H2O decreases/increases
• Increased osmotic concentration  increased
ADH
19
ADH
•  Water conservation
– Increases water absorption  decreased osmotic
concentration (by diluting Na+)
– Stimulates thirst center in hypothalamus 
increased fluid intake
20
Figure 27–4
21
Aldosterone
• Mineralocorticoid secreted by adrenal cortex
• Produced in response to:
– Decreased Na+ or increased K+
– In blood arriving at:
• Adrenal cortex
• Kidney (renin-angiotensin system
22
Renin-Angiotensin System
• Renin released in response to:
– Decreased Na+ or increased K+ in renal circulation
– Decreased plasma volume or BP at JGA
– Decreased osmotic concentration at DCT
• Renin   angiotensin II activation in lung
capillaries
• Angiotensin II 
– Adrenal cortex  increased aldosterone
– Posterior pituitary  ADH
– Increased BP (hence it’s name)
23
Aldosterone
• In DCT and collecting system of kidneys 
– Increased Na+ absorption (and associated Cl- and
H2O absorption)
– Increased K+ loss
•  Increased sensitivity of salt receptors on
tongue  crave salty foods
24
Natriuretic Peptides
• Released by cardiac muscle cells stretched by:
– Increased BP or blood volume
• Oppose angiotensin II and cause diuresis
–  Decreased ADH  increased H2O loss at kidneys
–  Decreased aldosterone  increased Na+ and
H2O loss at kidneys
– Decreases thirst  decreased H2O intake
• Net result = decreased stretching of cells
25
Figure 27–5, 7th edition
26
Fluid and Electrolyte Balance
• When body loses water:
– Plasma volume decreases
– Electrolyte concentrations increase
• When body loses electrolytes:
– Electrolyte concentrations decrease
– Water also lost
27
Disorders of Fluid and Electrolyte
Balance
• Dehydration = water depletion
– Due to:
• Inadequate water intake
• Fluid loss, e.g., vomiting, diarrhea
• Inadequate ADH (hypothalamic/pituitary malfunction)
– Leads to:
•
•
•
•
Too high Na+ = hypernatremia
Thirst, wrinkled skin
Decreased blood volume and BP
Fatal circulatory shock
28
Disorders of Fluid and Electrolyte
Balance
• Overhydration = water excess
– Due to:
• Excess water intake (>6-8 L/24 hours)
– Seen in hazing rituals (water torture)
– Marathon runners/paddlers
– Ravers on ecstasy who overcompensate for thirst
• Chronic renal failure
• Excess ADH
– Leads to
• Too low Na+ = hyponatremia
• Increased blood volume and BP
• CNS symptoms (water intoxication); can proceed to
convulsions, coma, death
29
Disorders of Fluid and Electrolyte
Balance
• Hypokalemia
– Too low K+
– Caused by diuretics, diet, chronic alkalosis (plasma
pH >7.45)
– Results in muscle weakness and paralysis
• Hyperkalemia
– Too high K+
– Caused by diuretics (that block Na+ reabsorption)
– Renal failure, chronic acidosis (plasma pH<7.35)
– Results in severe cardiac arrhythmias
30
Summary: Disorders of Electrolyte
Balance
• Most common problems with electrolyte
balance
– Caused by imbalance between gains/losses of Na+
• Uptake across digestive epithelium
• Excretion in urine and perspiration
• Problems with potassium balance
– Less common, but more dangerous
31
• Today in class we will discuss:
– Acid-base balance and
• Three major buffer systems that balance pH of ECF and ICF
• Compensatory mechanisms involved in maintaining acidbase balance
– Respiratory compensation
– Renal compensation
• Causes, effects, and the body’s response to acid-base
disturbances that occur when pH varies
– Respiratory acid-base disorders
» Respiratory acidosis
» Respiratory alkalosis
– Metabolic acid-base disorders
» Metabolic acidosis
» Metabolic alkalosis
32
Acid-Base Balance
• Control of pH
– Acid-base balance = = production of H+ is precisely
offset by H+ loss
• Body generates acids (H+) during metabolic
processes
– Decrease pH
• Normal pH of ECF = 7.35 – 7.45
– <7.35 = acidosis (more common than alkalosis)
– >7.45 = alkalosis
• <6.8 or >7.7 = lethal
33
Acid-Base Balance
• Deviations outside normal range extremely
dangerous
– Disrupt cell membranes
– Alter protein structure (remember hemoglobin?)
– Change activities of enzymes
• Affects all body systems
– Especially CNS and CVS
34
Acid-Base Balance
• CNS and CVS especially sensitive to pH
fluctuations
– Acidosis more lethal than alkalosis
– CNS deteriorates  coma  death
– Cardiac contractions grow weak and irregular 
heart failure
– Peripheral vasodilation  decreased BP and
circulatory collapse
35
Acid-Base Balance
• Carbonic acid (H2CO3)
– Most important factor affecting pH of ECF
• CO2 + H2O  H2CO3  H+ + HCO3-
36
Relationship between PCO2 and pH
• PCO2 inversely related to pH
Figure 27–9
37
Acid-Base Balance
• H+
– Gained
• At digestive tract
• Through cellular metabolic activities
– Eliminated
• At kidneys by secretion of H+ into urine
• At lungs by forming H2O and CO2 from H+ and HCO3-
– Sites of elimination far from sites of production
– As H+ travels through body, must be neutralized to
avoid tissue damage
– Accomplished through buffer systems
38
Buffers
• Compounds dissolved in body fluids
• Stabilize pH
• Can provide or remove H+
39
Buffer Systems in Body Fluids
• Phosphate buffer system (H2PO4-)
– In ICF and urine
• Protein buffer systems
– In ICF and ECF
– Includes:
• Hb buffer system (RBCs only)
• Amino acid buffers (in proteins)
• Plasma protein buffers (albumins, globulins…)
• Carbonic acid-bicarbonate buffer system
– Most important in ECF
40
Figure 27–7
41
Carbonic Acid–Bicarbonate
Buffer System
Figure 27–9
42
Maintenance of Acid-Base Balance
• For homeostasis to be preserved:
– H+ gains and losses must be balanced
• Excess H+ must be:
– Tied up by buffers
• Temporary; H+ not eliminated, just not harmful
– Permanently tied up in H2O molecules
• Associated with CO2 removal at lungs
– Removed from body fluids
• Through secretion at kidneys
• Accomplished by:
– Respiratory mechanisms
– Renal mechanisms
43
Conditions Affecting Acid-Base Balance
• Disorders affecting buffers, respiratory or
renal function
– Emphysema, renal failure
• Cardiovascular conditions
– Heart failure or hypotension
– Can affect pH, change glomerular filtration rates,
respiratory efficiency
• Conditions affecting CNS
– Neural damage/disease that affects respiratory
and cardiovascular reflexes that regulate pH
44
Disturbances of Acid-Base Balance
• Serious abnormalities have an:
– Acute (initial) phase
• pH moves rapidly out of normal range
– Compensated phase
• If condition persists
• Physiological adjustments move pH back into normal
range
• Cannot be completed unless underlying problem
corrected
• Types of compensation
– Respiratory
– Renal
45
Respiratory Compensation
• Changes respiratory rate
– Increasing/decreasing respiratory rate changes pH
by lowering/raising PCO2
– Helps stabilize pH of ECF
• Occurs whenever pH moves outside normal
limits
• Has a direct effect on carbonic acidbicarbonate buffer system
46
Respiratory Compensation
• Increased PCO2 
– Increased H2CO3  increased H+  decreased pH
(acidosis)
– Increased respiratory rate  more CO2 lost at lungs
 CO2 decreases to normal levels
• Decreased PCO2 
– Decreased H2CO3  decreased H+  increased pH
(alkalosis)
– Decreased respiratory rate  less CO2 lost at lungs
 CO2 increases to normal levels
47
Carbonic Acid–Bicarbonate
Buffer System
Figure 27–9
48
Renal Compensation
• Changes renal rates of H+ and HCO3– Secretion
– Reabsorption
• In response to changes in plasma pH
– Increased H+ or decreased HCO3- 
• Decreased pH (acidosis)  more H+ secreted and/or less
HCO3- reabsorbed
– Decreased H+ or increased HCO3- 
• Increased pH (alkalosis)  less H+ secreted and/or more
HCO3- reabsorbed
49
The Carbonic Acid–Bicarbonate
Buffer System and
Regulation of Plasma pH
Figure 27–11a
50
The Carbonic Acid–Bicarbonate
Buffer System and
Regulation of Plasma pH
Figure 27–11b
51
Disturbances of Acid-Base Balance
• Conditions named for:
– Uncompensated or
• Compensated
– Primary source of problem
• Respiratory or metabolic
• Mixed (both)
– Primary effect
• Acidosis or alkalosis
• e.g.,
– Compensated or uncompensated
• Respiratory acidosis or alkalosis
• Metabolis acidosis or alkalosis
52
Respiratory Acid-Base Disorders
• Result from imbalance between:
– CO2 generated in peripheral tissues (ECF)
– CO2 excreted at lungs
• Cause abnormal CO2 levels in ECF
•  Respiratory
– Acidosis
– Alkalosis
53
Respiratory Acidosis
• Most common challenge to acid-base equilibrium
• Primary sign is hypercapnia (increased PCO2)
• Develops when respiratory system cannot eliminate
all CO2 generated by peripheral tissues
• Usual cause is hypoventilation
• Acute situation may be immediate, life-threatening
condition
– Requires bronchodilation or mechanical breathing
assistance (ventilator)
• pH can get as low as 7.0
54
Respiratory Acidosis
Figure 27–12a, 7th edition
55
Respiratory Alkalosis
• Relatively uncommon
• Primary sign is high pH
• Develops when increased respiratory activity
(hyperventilation) lowers plasma PCO2 to
below normal levels (hypocapnia)
• Seldom of clinical significance
• pH can get as high as 7.8 – 8.0
56
Respiratory Alkalosis
Figure 27–12b, 7th edition
57
Metabolic Acid-Base Disorders
• Result from:
– Production of acids during metabolic processes
– Conditions that affect concentration of HCO3- in
ECF
•  Metabolic
– Acidosis
– Alkalosis
58
Metabolic Acidosis
• Results from:
– Production of large numbers of acids
• H+ overloads buffer systems
– Inability to excrete H+ at kidneys
– Severe HCO3- loss
59
Metabolic Acidosis
• Production of large number of acids
– Lactic acidosis from anaerobic respiration
• After strenuous exercise
• From prolonged tissue hypoxia (O2 starvation)
– Ketoacidosis from generation of ketone bodies
during metabolism
• When peripheral tissues cannot obtain adequate
glucose from bloodstream and begin metabolizing
lipids and ketone bodies), e.g.,
– Starvation
– Complication of poorly controlled diabetes mellitus
60
Metabolic Acidosis
• Inability to excrete H+ at kidneys
– With severe kidney damage (glomerulonephritis)
– Caused by diuretics that interfere with H+
secretion into urine
• Severe HCO3- loss
– From chronic diarrhea
– Loss interferes with buffer system ability to
remove H+
61
Responses to Metabolic Acidosis
Figure 27–13
62
Metabolic Alkalosis
• Relatively rare
• Occurs after repeated vomiting
– Stomach continues to generate HCl to replace lost
acids
– Is associated with increased HCO3- in ECF
– HC03- + H+  H2CO3
• Reduces H+  alkalosis
63
Metabolic Alkalosis
Figure 27–14
64
Detection of
Acidosis and Alkalosis
• Includes blood tests for:
– pH
– PCO2
– HCO3-
• Recognition of acidosis or alkalosis
• Classification as respiratory or metabolic
65
Diagnostic Chart for Acid-Base Disorders
Figure 27–18
66
Blood Chemistry and Acid–Base Disorders
Table 27–4
67