1- control of respiration

Question 1

what are the names of the sections of brian stem?

Answer 1

closest to brain is pons then middle is medulla oblongata and the turns to spinal cord

Question 2

where is rhythm of breathing generated?

Answer 2

by a network of neurons called pre-Botzinger complex in the upper end of medullary respiratory centre in medulla oblongata

Question 3

what is process that gives rise to inspiration?

Answer 3

rhythm generated by pre-botzinger complex in upper medulla oblongata - this excites dorsal respiratory group neurons which fire in bursts, this firing leads to contraction of inspiratory muscles

*when firing stops = passive expiration

Question 4

what process makes active expiration when hyperventilating?

Answer 4

increased firing by dorsal neurons excites a second group which are ventral respiratory group neurons (both these groups in medulla oblongata) and these excite internal intercostals and abdominals which cause the forceful expiration

Question 5

what terminates inspiration?

Answer 5

pneumotaxic centre stimulation = when stimulated, inspiration is inhibited

Question 6

what leads to prolonged inspiration?

Answer 6

apneustic centre being stimulated = impulses excite inspiratory area of medulla

Question 7

what happens without pneumotaxic centre?

Answer 7

apneusis = prolonged inspiratory gasps without brief expiration (as no inhibition of inspiration)

Question 8

what release stimuli that influence respiratory centres?

Answer 8

• higher brain centres (cerebral cortex, limbic system, hypothalamus)
• stretch receptors in walls of bronchi & bronchioles, the inflation of hering-breuer reflex (guard against hyperinflation)
• juxtapulmonary receptors
• joint receptors
• baroreceptors

also chemical parts like central chemoreceptors & peripheral chemoreceptors

Question 9

what stimulates juxtapulmonary capillary receptors?

Answer 9

pulmonary capillary congestion & pulmonary oedema and pulmonary emboli
= leads to rapid shallow breathing as influences respiratory centres

Question 10

what are examples of involuntary modifications of breathing?

Answer 10

• pulmonary stretch receptors hering-breuer reflex
• Joint Receptors Reflex in Exercise (impulses from moving limbs)
• Stimulation of Respiratory Centre by Temperature, Adrenaline, or Impulses from Cerebral Cortex
• Cough Reflex

Question 11

what is hering-breuer reflex?

Answer 11

• when pulmonary stretch receptors (sensory receptors in smooth muscle of airways & lungs) are activated during inspiration when muscle stretches.
• activation triggers afferent discharge which travel to respiratory centres in brain and inhibits inspiration (preventing over inflation of lungs)

Question 12

do pulmonary stretch receptors inhibit inspiration in normal respiratory cycle?

Answer 12

• unlikely, they don’t switch off inspiration during normal respiratory cycle - only at large >1 L volumes.
  
  • they play a more important role in newborns to prevent over inflation. may prevent over inflation during hard exercise

Question 13

what factors may increase ventilation during exercise?

Answer 13

• Reflexes originating from body movement (joint receptors)
• Adrenaline release
• Impulses from the cerebral cortex
• Increase in body temperature
• Later: accumulation of CO2 and H+ generated by active muscles

Question 14

what is purpose of cough reflex?

Answer 14

vital part of body defence mechanism that helps clear airways of dust, dirt or excessive secretion

Question 15

what happens in cough reflex?

Answer 15

activated by irritation of airways or tight airways (asthma) = centre in medulla activated and afferent discharge stimulates short intake of breath followed by closure of larynx then contraction of abdominal muscles to increase intra-alveolar pressure then finally opening of larynx & expulsion of air at high speed

Question 16

what do chemoreceptors sense?

Answer 16

they sens the values of gas tensions = example of negative feedback system (have controlled variables of blood gas tensions)

Question 17

what do peripheral chemoreceptors sense?

Answer 17

sense tension of oxygen & carbon dioxide and [H+] in blood

Question 18

where are central chemoreceptors stimulated?

Answer 18

stimulated near surface of medulla of brainstem

Question 19

what do central chemoreceptors respond to and what’s the function?

Answer 19

respond to changes in H+ concentration in cerebrospinal fluid - CO2 mostly determines pH as it’s conversion to carbonic acid & H+

carbonic acid & H+ are impermeable to blood brain barrier but CO2 diffuses readily

since cerebral fluid has less protein than blood it’s less buffered and more sensitive to CO2 changes. when accumulation of CO2 in blood it diffuses in cerebral fluid and when in fluid turns into H+ which stimulate the central chemoreceptors →triggers nerve impulses that transported to respiratory centre and respond by increasing rate & depth of breathing (ventilation) to remove excess CO2 from blood and restore pH homeostasis

Question 20

what is relationship between pH and CO2?

Answer 20

low pH = high H+ concentration and increase in CO2 = increase in H+ concentration due to CO2 to carbonic acid (H2CO3) and H+

Question 21

what explains why you have to take a breath after stop breathing for a while?

Answer 21

the increased CO2 building up and diffusing into cerebral fluid which turns into H+ and stimulates central chemoreceptors making body breathe to get rid of excess CO2

Question 22

what chemoreceptors drive respiration through hypoxaemia?

Answer 22

hypoxaemia = low oxygen

via peripheral chemoreceptors - they are stimulated when arterial partial pressure of oxygen falls to low levels (below 8 kPA)
= becomes important when patients in chronic CO2 retention like COPD

Question 23

why can giving excessive oxygen to patients with chronic hypoxaemia and chronically elevated CO2 lead to worsening hypercapnia and acidosis?

Answer 23

1. increases the ventilation/perfusion mismatch - you might start to divert blood flow to poorly ventilated alveoli resulting in CO2 accumulation
2. increase release of CO2 from oxygenated haemoglobin (halden effect) - since COPD patients unable to increase their exhalation to match increase in CO2 release so CO2 accumulates

Question 24

in acute exacerbations, what is the aim to give patients?

Answer 24

give oxygen to raise the PaO2 without worsening the hypercapnia so not excessive oxygen

= most patients you aim to lower saturation of oxygen 88-92% when in normal people it’s 94-98%

Question 25

what causes hypoxia at high altitudes and what is the acute response + symptoms?

Answer 25

caused by decreased partial pressure of oxygen
acute response = hyperventilation & increased cardiac output

symptoms: headache, fatigue, nausea, tachycardia, dizziness, sleep disturbance, exhaustion, shortness of breath, unconsciousness

Question 26

what are chronic adaptations to high altitude?

Answer 26

effect is via peripheral chemoreceptors: they adjust for acidosis caused by non-carbonic acid H+ to blood e.g. lactic acid in exercise & diabetic ketoacidosis

stimulation by H+ causes hyperventilation and increases elimination of CO2 from body

Question 27

when are each of the chemoreceptors important?

Answer 27

peripheral chemoreceptors only important in certain circumstances

central chemoreceptors are always important

Question 28

what effect does severe hypoxia have on respiratory centre?

Answer 28

depresses it