Respiratory control and arterial blood gases

Question 1

The medulla in respiratory control

Answer 1

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.

Question 2

Pneumotaxic centre

Answer 2

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.

Question 3

Dorsal respiratory group

Answer 3

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.

Question 4

Ventral respiratory group

Answer 4

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

Question 5

Efferent nerves in ventilation

Answer 5

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.

Question 6

Peripheral chemosensors in respiration

Answer 6

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%.

Question 7

Nervous control of sternocleidomastoid

Answer 7

Cranial nerve 11 (CNXI)

Efferent nerve that controls the accessory muscle in inspiration.

Question 8

Nervous control of scalene muscles

Answer 8

Cranial nerves 3-8 (CNIII-VIII)

Control the accessory muscles involved in inspiration.

Question 9

Expiratory nerves

Answer 9

Thoracic nerves: supplies internal thoracic muscles and the abdominal wall.

Question 10

Lung stretch receptors

Answer 10

Connected to vagus nerves.

Sense when lungs (alveoli) are over stretching and terminates that.

Question 11

C-fibre neurones

Answer 11

Neuron activated by oedema and senses bradykinin.

Involved in controlling respiratory behaviour

Question 12

Irritant receptors

Answer 12

Detect punctuate mechanical stimuli- objects that push on the tissue of the respiratory tract.

Stimulates coughing reaction.

Question 13

Normal pH range

Answer 13

7.38-7.42

Question 14

Normal PaCO2

Answer 14

36-44 mm Hg

Question 15

Normal HCO3-

Answer 15

22-26 mmol/L

Question 16

Respiratory acidosis

Answer 16

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.

Question 17

Acidaemia

Answer 17

Blood pH below 7.38

Question 18

Alkalaemia

Answer 18

Blood pH above 7.42

Question 19

Metabolic acidosis

Answer 19

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-.

Question 20

Respiratory alkalemia

Answer 20

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.

Question 21

Metabolic alkalemia

Answer 21

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.

Question 22

Anion gap metabolic acidosis

Answer 22

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.

Question 23

Causes of anion gap in metabolic acidosis

Answer 23

GOLD MARK

G-lycols (ethylene and propylene)
O-xoproline
L-lactate
D-lactate

M-ethanol
A-sprin
R-enal failure
K-eto acidosis

Question 24

Non-anion gap metabolic acidosis

Answer 24

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

Question 25

Base excess

Answer 25

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

Question 26

Renal tubular acidosis (RTA)

Answer 26

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