Respiratory system: chemical and neuronal control mechanisms

Question 1

neural control of respiration

Answer 1

central rhythm generator in medulla (automatic)
Receptors in respiratory tract causing sneezing, coughing and hyperpnoea (incr rate and depth of breathing)
Nociceptors- detect noxious substances

Question 2

Chemical control of respiration

Answer 2

central and peripheral chemoreceptors

Question 3

Medulla control

Answer 3

ventral and dorsal respiratory group:

• discharge rhythmically
• efferent (output) neurones to respiratory motor nerves
• receives afferent input from periphery and pons

Question 4

Pons control

Answer 4

Apneustic centre:
prolongs medullary centre firing
so depth of breathing incr

Pneumotaxic centre:
Inhibits apneustic centre
Controls rate of breathing

Question 5

Pre-Botzinger complex

Answer 5

Region of ventral respiratory group
Spontaneous rhythmic discharge
stimulates rhythmic discharge of motor nerves, resulting in contraction of diaphragm
Key in regulation of breathing- without it there is a loss of regular rhythm and CO2 responsiveness

Question 6

Are cortical/higher centres essential for breathing

Answer 6

No, but no longer voluntary control without them

Question 7

Transection above pons

Answer 7

loss of voluntary control

Question 8

Transection above medulla

Answer 8

loss of feedback regulation from pons (above medulla)

breathing continues

Question 9

Transection of spinal cord

Answer 9

breathing abolished

Question 10

Voluntary control of breathing

Answer 10

via cerebral cortex

sends signals direct to respiratory motor neurones

Question 11

lung transplant

Answer 11

Motor innervation is to skeletal muscle, so ventilation carries on
Preservation of cough
from tracheal stimulation
But loss of cough stimulation in lower airway
Loss of Hering-Breuer reflex (prevents over inflation of the lung)

Question 12

chemoreceptors

central and peripheral

Answer 12

Central (medullary)- H+, CO2

Peripheral- cartoid and aortic bodies. Primary peripheral signal is O2, but also input from H+

Question 13

PO2

Answer 13

partial pressure of oxygen

Question 14

PCO2

Answer 14

partial pressure of CO2

Question 15

PaO2

Answer 15

partial pressure of arterial oxygen

Question 16

PaCO2

Answer 16

Partial pressure of arterial CO2

Question 17

PAO2

Answer 17

partial pressure alveolar oxygen

Question 18

Central control of respiration

Answer 18

HCO3- and H+ don’t easily cross BB
CO2- uncharged- does cross BBB and dissociates in CSF
Hence CO2 larger influence on ventilation than pH

Question 19

carbon dioxide effect

Answer 19

has little effect in stimulating neurones in the chemosensitive area, but does have a potent indirect effect by reacting with H2O in tissues to from H2CO3, dissociates into HCO3- and H+ ions, and H+ have direct effect on respiration
Hence whenever blood PCO2 incr, so does PCO2 of ISF in medulla and CSF, and H+ ions incr when CO2 reacts with water , so respiratory center activity incr by changes in blood CO2

Question 20

How does H+ act on respiratory center

Answer 20

Stimulate central chemo receptors (CO2 can’t)
Incr ventilation
Reduction in blood PCO2

Question 21

Regulation of CO2 during sustainable exercise

Answer 21

Ventilation incr prior ro rise in blood CO2- due to anticipatory stimulation in the higher CNS
Arterial PCO2 levels fall
As exercise goes on, more CO2 generated and arterial CO2 returns to normal
CO2 passes from muscles into venous blood and efficiently removed in the lung

Question 22

Peripheral control respiration- O2

Answer 22

Fall in o2 stimulates glomus cells in cartoid and aortic bodies
Contains O2 sensitive K+ channels and dopamine

Question 23

O2 falling sequence

Answer 23

O2 falls
K+ channels close
Depolarisation
DA release which stimulates afferent fibres, signals to medulla
Nerve firing increases at low PaO2

Question 24

Doxapram

Answer 24

Closes K+ channels on glomus cell (cartoid body)
Glomus cell depolarises and sends afferent signals to medullary respiratory centre
used in respiratory failure

Question 25

Caffeine

Answer 25

Non-specific CNS stimulation, including respiratory centre | bronchodilator

Question 26

Acetazolamide

Answer 26

respiratory stimulant carbonic anhydrase inhibitor Stimulates respiration by creating mild metabolic acidosis via decr renal absorption of bicarbonate and hence reduced acid buffering Cartoid bodies respond to decr in pH

Question 27

Respiratory depressants?

Answer 27

Majority of drugs with depressant action on CNS

Question 28

Why do we breathe?

Answer 28

O2 needed for respiration- krebs can't proceed without regeneration of NAD+, ETC dependent on O2 ATP generated from respiration required for: active transport (maintaining ionic gradients, nutrient uptake), anabolic reactions, muscle contraction, phosphorylation of targets, precursor for cAMP O2 also needed to pay O2 debt after bursts of anabolic metabolism

Question 29

Pgas

Answer 29

barometric pressure x fraction of particular gas

Question 30

PAO2

Answer 30

Alveolar pressure | O2 inspired - O2 consumed

Question 31

How much O2 is consumed?

Answer 31

Estimate O2 consumption from CO2 in arterial blood | CO2 produced divided by O2 consumed is the respiratory quotient

Question 32

PAO2 also equals

Answer 32

O2 inspired - (CO2 produced/RQ)

Question 33

Uptake of oxygen in the pulmonary capillary

Answer 33

Alveolar O2 equilibrates with the blood in the capillaries | As blood in capillary gets oxygenated

Question 34

How is oxygen transported

Answer 34

Most bound to haemoglobin Binding is co-operative- 4 molecules of oxygen per haemoglobin molecule Some O2 dissolved in blood

Question 35

Myoglobin

Answer 35

O2 storage and transport in metabolically active cells Skeletal and cardiac muscle Doesn't bind co-operatively- one O2 binding site High affinity, affinity not affected by pH or CO2, so able to capture O2 released by Hb (when pH falls) Myoglobin saturated by O2 at a much lower concentration

Question 36

CO2 transport

Answer 36

Mainly as HCO3- some as dissolved CO2 Some as carbamino haemoglobin (HbCO2)

Question 37

what happens when CO2 diffuses tissues to plasma

Answer 37

Most enters RBC and converted to bicarbonate by carbonic anhydrase

Question 38

When CO2 production increased (exercise/disease)

Answer 38

Fraction of CO2 increases relative to HCO3- | Passes into CSF and detection by central chemoreceptors

Question 39

High PO2 in lungs causes the blood to release CO2

Answer 39

O2 binding to Hb makes it more acidic Less formation of HbCO2 Excess H+ bind HCO3- to form H2CO3, Co2 released

Question 40

Ventilation-Perfusion matching

Answer 40

For optimum GE ventilation must match blood perfusion | Mismatched in disease- reduced blood PO2

Question 41

Hypoxaemia

Answer 41

``` Low O2 Shunting: unventilated alveoli ventilation-perfusion mismatch Diffusion abnormalities: thickened alveolar wall Hypoventilation (ventilation inadequate) ```

Question 42

shunting

Answer 42

In shunting, venous blood enters the bloodstream without passing through functioning lung tissue. Often from blood flowing through unventilated portions of the lung

Question 43

Hypercapnia

Answer 43

Incr CO2 Incr dead space: pulmonary embolus Hypoventilation

Question 44

Physiological response to low inspired O2

Answer 44

Incr ventilation: immediate, driven by peripheral chemosensors, not sustained Pulmonary vasoconstriction: rapid, sustained, shunts blood away from poorly ventilated areas Increased hematocrit: rbc cell fraction of blood incr, HIF activation (hypoxia inducible factors) which regulate oxygen-sensitive gene transcription and EPO production by kidneys (stimulate RBC production)

Question 45

Acute mountain sickness

Answer 45

Flu-like, ahngover Breathlessness Hypoxic pulmonary vasoconstriction Pulmonary and cerebral oedema (incr fluid in the lungs)

Question 46

Chronic mountain sickness

Answer 46

``` Low PO2 cannot be matched by ventilation Incr EPO production in kidney Too high hematocrit, viscous blood Increased load on right heart Acetazolamide drug (carbonic anhydrase inhibitor) inhibits EPO production and incr ventilation ```

Question 47

Genetic adaptions for high altitude populations

Answer 47

higher hematocrit | higher myoglobin levels