Respiratory control and arterial blood gases Flashcards
The medulla in respiratory control
The medulla is the centre that generates the depth and pace of breathing- contains inspiratory and expiratory groups of neurones.
Also contains- The ventral and dorsal respiratory group.
Pneumotaxic centre
A neural centre located in the pons which helps to control maintain inspiration and expiration.
It relays information to the dorsal respiratory group in the medulla.
Dorsal respiratory group
Neural centre in the medulla composed of:
Nucleus tractus solitarius (NTS)
The NTS relays information to the ventral respiratory group.
It controls muscles in ventilation through the phrenic and intercostal nerves:
Diaphragm
External intercostal muscles.
Ventral respiratory group
Neural centre in the medulla composed of:
Nucleus ambigualis
Nucleus retroambigualis
Relays information to the dorsal respiratory group
Controls accessory muscles in ventilation via the phrenic nerve:
Internal intercostal muscles
Efferent nerves in ventilation
Control inspiratory muscles:
Diaphragm controlled by the phrenic nerve (C3-5).
Internal and external intercostal muscles controlled by T1-T11
Accessory neck muscles (sternocleidomastoid and the scalene muscles) are controlled by C11, C3-8 respectively.
Peripheral chemosensors in respiration
Composed of afferent nerves connecting to chemoreceptors.
Chemoreceptors are located in the aortic and carotid bodies.
Responds to high levels of CO2 and H+. Only changes ventilation when PaO2 drop is very significant, below 90%.
Nervous control of sternocleidomastoid
Cranial nerve 11 (CNXI)
Efferent nerve that controls the accessory muscle in inspiration.
Nervous control of scalene muscles
Cranial nerves 3-8 (CNIII-VIII)
Control the accessory muscles involved in inspiration.
Expiratory nerves
Thoracic nerves: supplies internal thoracic muscles and the abdominal wall.
Lung stretch receptors
Connected to vagus nerves.
Sense when lungs (alveoli) are over stretching and terminates that.
C-fibre neurones
Neuron activated by oedema and senses bradykinin.
Involved in controlling respiratory behaviour
Irritant receptors
Detect punctuate mechanical stimuli- objects that push on the tissue of the respiratory tract.
Stimulates coughing reaction.
Normal pH range
7.38-7.42
Normal PaCO2
36-44 mm Hg
Normal HCO3-
22-26 mmol/L
Respiratory acidosis
When blood pH is below 7.38 due to high PCO2 levels.
This happens when PCO2 is above 44 mm Hg.
This resolved by the kidney absorbing more HCO3- to reduce pH.
Acidaemia
Blood pH below 7.38
Alkalaemia
Blood pH above 7.42
Metabolic acidosis
Blood pH <7.38, due to low concentrations of HCO3-.
HCO3- < 22 mmol/L
Low pH= high H+
This is resolved by decreasing CO2 inspired. This prevents more H+ being made to use up HCO3-.
Respiratory alkalemia
Blood pH> 7.42 due to low pCO2.
pCO2< 36 mm Hg
This is resolved by increasing the amount of HCO3- excreted by the kidneys.
Removing HCO3- increases H+ in the system, decreasing pH.
Metabolic alkalemia
Blood pH> 7.42 due to high HCO3 levels
HCO3- > 26 mmol/L
This is resolved by increasing CO2 inspired in order to increase H+ levels.
Anion gap metabolic acidosis
Happens when there is an addition of acid or loss of HCO3-.
Occurs when additional anion concentration exceeds 12 mEq/L.
This is when the anion concentration exceeds that of Na+, when they should be balance.
Causes of anion gap in metabolic acidosis
GOLD MARK
G-lycols (ethylene and propylene)
O-xoproline
L-lactate
D-lactate
M-ethanol
A-sprin
R-enal failure
K-eto acidosis
Non-anion gap metabolic acidosis
Addition of H+ or loss of HCO3- not showing addition of anions.
Causes: Renal tubular acidosis (RTA) GI losses Acetazolamide- carbonic anhydrase inhibitor XS NaCl fluid
Base excess
The dose of acid required to return pH back to 7.4 This base excess is due to metabolic disturbances.
Negative base excess- the concentration of base required to return pH back to 7.4
Renal tubular acidosis (RTA)
pH <7.38 due to loss of HCO3- and hyperchloremia.
Type 1: distal duct unable to secrete H+
Type 2: Proximal convoluted tube doesn’t absorb HCO3-
Type 3: Combination of type 1 and 2
