Regulation of Respiration

Question 1

neural regulation

Answer 1

normally the rate and depth of respiration (pulmonary ventilation) are regulated in accordance with the needs of the body and to maintain the arterial pco2, po2 and ph constant

there are two seperate neural control mechanisms - voluntary and automatic control

• the centers for voluntary control are located in the cerebral cortex. the cortex controls resp muscles via corticospinal tract
• the centers for autonomic control are located in brain stem. the neurons of brainstem resp areas converge on spinal cord motor neurons

Respiratory Centers - Is a group of neurons situated bilaterally in reticular formation of brain stem which
control respiration

• medullary resp center - composed of several groups of neurons and located bilaterally in the medulla oblongata and pons of the brain stem.
• controls basic rhythm of respiration.

1) Dorsal Respiratory group - dorsal portion of medulla
- located bilaterally in and around the nucleus tractus solitarius (nts)
- primarily contains inspiratory neurons
- receive sensory inputs via the vagal (10th) and glossopharangeal nerves (9th) from
a) peripheral chemoreceptors
b) baroreceptors
c) several types of receptors in the lungs
- inspiratory ramp signal - in normal Respiration - weakly and steadily increases in a ramp manner for about 2 seconds. then for 3 secs the signals cease and muscles relax causing expiration.

2) Ventral Respiratory Group - located in the ventrolateral part of medulla. in the region of the nucleus ambiguous (retroambiguous and paraambiguous) and retrofacialis.
- contains both inspiratory and expiratory neurons.
- remains almost totally inactive during normal quiet breathing
- imp in providing the powerful expiratory signals to the abdominal muscles during very heavy expiration

• Pontine Respiratory centers
  two Respiratory centers - pneumotaxic and apneustic. modulate the output from medullary resp centers

1) pneumotaxic center -
- located dorsally in the nucleus parabrachialis of the upper pons
- neurons active during both inspiration and expiration
- normally, inhibits apneustic center
- therefore, stimulation of PNC shortens inspiration, leading to shallow and more rapid Respiration.
function - primarily to limit inspiration
- Sends afferent impulses to DRG neurons and cause early switch off of inspiratory ramp signal. It therefore limits the phase of inspiration and secondarily increases the rate of respiration
- strong stimulation- dec the duration of inspiration thus increasing the rate
2) apneustic center -
- located bilaterally in the lower part of pons
- prevents the switch off of the inspiratory ramp signals. this increases the tidal volume and duration of inspiration resulting in a deeper and more prolonged inspiratory effort termed as apneusis
- inhibited by vagus nerve and also by the activity of pneumotaxic center.

1) afferent impulses from pulmonary stretch receptors
(hering breuer inflation reflex)
- walls of bronchi and bronchioles
- transmit impulses through vagus nerve
- when lungs are overstretched, the stretch receptors activates an appropriate feedback response that switches off the inspiratory ramp and thus stops further inspiration
- activated when tidal volume increases more than 3 times than normal
- therefore this reflex appears to be mainly a protective mechanism for preventing excess lung inflation rather than an imp ingredient in normal control of ventilation.

2) afferent impulses from j receptors juxtacapillary
- constitute the j reflex located very close to the pulmonary capillaries
- j receptors are primarily sensitive to increase in the content of interstitial fluid between the capillary endothelium and alveolar epithelium
- stimulation of j receptors produces a reflex response which is characterised by apnoea followed by hyperventilation
- more useful in infants than adults

impulse from irritant receptors of lungs

• bronchi and bronchioles
• stimulation causes reflex

proprioreceptors
- muscles, tendons and joints
stimulated during change in the position of diff. parts
- afferent impulses from proprioreceptors stimulate the inspiratory neurons to increase rate and depth od respiration

reflexes from baroreceptors - inc arterial bp –> stimulates baroreceptors —-> inhibition of Respiration —> dec in rate and depth of breathing

reflexes from chemoreceptors - dec po2 and inc pco2 —> chemoreceptors —-> inc the rate and depth of breathing

deglutition apnoea - reflex inhibition of Respiration during swallowing.

somatic pain sensation - inc rate and depth of Respiration

pain sensation in the internal organs - dec rate and depth of Respiration.

if enviornment temp inc - rate and depth of Respiration increase

Question 2

chemical regulation

Answer 2

the ultimate goal of respiration is to maintain proper conc of oxygen, carbon dioxide and hydrogen ions in the tissues.
-excess carbon dioxide or excess hydrogen ions mainly act greatly (directly) on the respiratory centers.

two sets of receptors detect these chemical changes in the blood - peripheral and central chemoreceptors

1) central chemoreceptors -
- a neuronal area chemosensitive located bilaterally lying only 0.2 mm beneath ventral surface of neurons.
- sensitive to pco2, h+ ions and po2
- monitor h ion concentration of csf
- co2 stimulates the chemosensitive area by indirect effect

co2 + h2o — h2co3 —- h+ + hco3-

• bbb is not permeable to hydrogen ions but is to co2 so when the blood pco2 increases so does the pco2 of the interstitial fluid and cerebrospinal fluid.
• stimulation increases the rate and depth of Respiration.

2) peripheral chemoreceptors -
- located in the carotid and aortic bodies.
- only sites that detect changes in arterial po2
- send signals to the dorsal Respiratory group of neurons in medulla to increase ventilation.
- carotid body - glossopharangeal nerve supply
- aortic bodies - vagus nerve
- they are especially imp for detecting changes in oxygen but can also detect co2 and hydrogen ions to a lesser extent
- carotid bodies - located at the bifurcation of the carotid artery.
- blood flow through these bodies is extreme, 20 times the weight of the bodies themselves each minute
- the impulse rate is particularly sensitive changes in arterial pco2 ( 60-30 mm hg)
- these bodies contain two types of cells -
a) type I cells - glomus cells - have k+ channels which are sensitive to hypoxia

b) type II - glia like cells - supportive in function.