Acid-Base Balance

Week 3

What is intracellular fluid called

Cytosol

What is extracellular fluid called

Interstitial fluid

What is an electrolyte

Inorganic compound that dissociates into ions in H2O

What is an ion

Atom or molecule with electrical charge due to loss/gain of an electron

What are two sources of water gain

• Ingestion - 2300mL/day

• Metabolic water during aerobic respiration n dehydration synthesis - 200mL/day

What are four sources of water loss

• Urine - 1500mL

• Skin evaporates by insensible n regular perspiration - 600mL

• Lungs exhale water vapour - 300mL

• Feces - 100mL

What does insensible mean

You can’t feel it

What is important to note about metabolic water

More ATP produced = more H2O produced

What does dehydration result in

Decreased volume n increased osmolarity

Where is the thirst centre

Hypothalamus

What are the five triggers of the thirst centre

• Increased activity from osmoreceptors in hypothalamus

• Volume receptors in atria

• Baroreceptors in BVs

• Angiotensin II

• Neurons in mouth detect decreased salivary flow

What is the primary hormone involved in regulating water loss

Antidiuretic hormone (ADH)

Where is ADH produced n stored

Produced in hypothalamus n stored in PPG

How is ADH triggered

Thirst centre triggered by increased osmolarity in blood, increasing synthesis n release of ADH (others include atria volume receptors, nausea, baroreceptors in BVs, pain, stress, etc)

How does ADH promote water reabsorption | 2

• Increases H2O permeability in principal cells of tubule n duct of DCT

• Promotes peripheral vasoconstriction

What triggers aldosterone

Decreased blood volume or Na+ deficiency in plasma trigger RAAS

What does aldosterone do

Increases Na+ reabsorption in DCT n ducts

What triggers the release of atrial natriuretic peptide (ANP)

Stretch receptors in atria trigger release of ANP

What does atrial natriuretic peptide (ANP) do | 2

• Promotes Na+ excretion in urine (H2O follows Na+)

• Slows release of renin (n therefore aldosterone)

What helps limit changes to tonicity in the body

Functional kidneys

What is water intoxication

Excessive body water causes cells to swell dangerously

What causes water intoxication | 2

• Renal impairment

• Massive water consumption faster than kidneys can excrete it

What is ion concentration measured in

Milli-equivalents per litre (mEq/L)

Blood plasma contains a higher

Amount of protein anions

Intracellular fluid has a higher concentration of

K+, HPO4 n proteins

What are the most abundant ions in extracellular fluid

Na+ n Cl-

What is the normal blood plasma concentration of Na+

135-145mEq/L

What is hyponatremia

Na+ is <135mEq/L

What is hypernatremia

Na+ is >145mEq/L

What is Na+ responsible for in the body

Generation of action potentials in neurons n muscle fibres

What helps regulate Cl- in body

ADH, Cl+ follows Na+

What is the intracellular fluid concentration of K+

140mEq/L

What is the normal blood plasma concentration of K+

3.5-5mEq/L

What is important to note about K+ n aldosterone

Aldosterone encourages K+ secretion in collecting ducts

What is hyperkalemia

K+ >5mEq/L

What is hypokalemia

K+ <3.5mEq/L

What is the normal blood plasma concentration of bicarbonate

22-26mEq/L

How is bicarbonate regulated

Kidneys synthesize n release HCO3 into blood

Where is Ca2+ mostly found in fluids

Extracellular fluid

What is Ca2+ responsible for | 4

• Blood clotting

• Neurotransmitter release

• Muscle tone n contractility

• Excitability of nervous n muscle tissue

How is Ca2+ regulated

Parathyroid hormone (PTH)

How does PTH regulated Ca2+ | 2

• Promotes renal reabsorption

• Ca2+ releases from bones n increases absorption from food in GI

What is important to note about phosphate in the body

3 different phosphate ions r intracellular anions that regulated pH

What is important to note about Mg | 2

• Aids in metabolism of carbs n proteins

• Involved in synaptic transmission, cardiac function n neuromuscular activity

What is an acid

Substance that dissociates into hydrogen ion(s) n anion(s) (proton donor)

What is a base

Substance that dissociates into hydroxide ion(s) n cation(s) (removes H+ from solution - proton acceptor)

What is important to note about strong acids/bases

Dissociate easier in H2O - easily give up H+/OH- ions

What is important to note about weak acids/bases

Contain strong chemical bonds n don’t dissociate as easily in H2O (strong hold on H+/OH- ions)

What is the normal pH in the body

7.35-7.45 (7.4 mainly)

What are the 3 mechanisms used to regulate pH in body

• Buffer systems

• Exhalation of CO2

• Kidney excretion of H+

What are protein buffers | 3

• Can buffer acids n bases

• Proteins composed of amino acids

• Release or pick up H+

What is the carbonic acid-bicarb equation

H2O + CO2 <=> H2CO3 <=> H+ + HCO3-

What is important to note about the bicarb n carbonic acid buffer system

Depending on the conditions H2CO3 n HCO3- can act as weak or strong acids/bases

What is the ratio of bicarb ions to carbonic acid molecules

20:1

What about phosphate buffers | 3

• Involves H2PO4- n HPO2-2

• Intracellular pH regulation

• Can buffer acids n bases

Phosphate buffers regulating bases

OH+ + H2PO4- = H2O + HPO4-2

Phosphate buffers regulating acids

H+ + HPO4-2 = H2PO4-

What detects low pH/increased CO2 levels

Chemoreceptors in medulla oblongata (central) n carotid n aortic arteries (peripheral)

What do the chemoreceptors do

Stimulates respiratory centre in medulla to change rate n depth of breathing

What about the kidney in regulating pH | 2

• Can excrete excess H+/HCO3

• H+ that is excreted into tubules is buffered/combined w/other ions to prevent reabsorption of H+

What are the symptoms of acidosis | 3

Physiological effects - CNS depression via depression of synaptic transmission (disorientation, lethargy, coma, death)

What are the symptoms of alkalosis

Physiological effects - over-excitability of CNS n PNS (repeated impulses w/o stimulation)

Acidosis causes a build up of

CO2, H2CO3 n H+

What causes respiratory acidosis | 4

• COPD

• Pulmonary edema

• Brainstem trauma

• Respiratory muscle disorder

What causes respiratory alkalosis | 3

• Oxygen deficiency conditions

• Strokes

• Severe anxiety

What is the treatment for respiratory acidosis | 2

• Increase exhalation of CO2 - assisted ventilations

• Administer IV HCO3 in hospital

What is the treatment for respiratory alkalosis

Decrease respiratory rate n depth

What are the three causes of metabolic acidosis

• Loss of HCO3- due to severe diarrhea or renal dysfunction

• Accumulation of acid other than carbonic acid (ketosis)

• Failure of kidneys to excrete H+

What is the treatment for metabolic acidosis | 2

IV sodium bicarb n correcting the cause

What are the causes of metabolic alkalosis | 6

• Excessive vomiting of stomach acid

• Gastric suctioning

• Certain diuretics

• Endocrine disorders

• Excessive intake of alkaline drugs

• Severe dehydration

What is the treatment for metabolic alkalosis | 2

Electrolyte IV fluid n correcting the cause