10 regulation and 11 . disturbances of respiration

REGULATION OF RESPIRATION

1. Introduction• Respiration is a reflex process.• Voluntary control of respiration (voluntary

apnea) is possible for a short period of about 40 seconds.

• The pattern of respiration is regulated by two mechanism:

Nervous or neural mechanism Chemical mechanism

2.Nervous Mechanism• It involves respiratory centres, afferent

nerves and efferent nerves.Respiratory Centres• Adequate supply of oxygen to the tissues and

removal of carbon dioxide from the tissues is achieved by continuous exchange of gases between alveoli and blood.

• Alveoli ventilation is provided by respiratory movements.

• Respiratory movements are in turn, controlled and maintained by co-ordinated activity of some groups of neurons in trainstem.

• These collections of these nueron are called respiratory centres.

• Respiratory centres are situated in the reticular formation of the trainstem and the respiratory

Centres are classified into two groups:Medullar centresPontine centres• There are two centres in each group

Medullar Centres1. Inspiratory centre2. Expiratory centre

Pontine Centres1. Pneumotaxic centre2. Apneustic centreInspiratory Centre• Situated in upper part of medulla oblangata• It is also called dorsal group of respiratory

neurons.• It is formed by the nucleus of tractussolitarius and

some neurons surrounding this

Function• Inspiratory centre is concerned with

inspiration.• Nucleus solitarius receives sensory impulses

from peripheral baroreceptors, chemoreceptors and pulmonary receptors through vagus and glossopharyngeal nerves.

Effect of stimulation• Electrical stimulation of inspiratory centre in

animals causes contraction of inspiratory muscles and prolonged inspiration.

Expiratory Centre• It is situated in the medulla oblangata anterior

and lateral to inspiratory centre, (is also called the Ventral group of respiratory neurons).

• The neurons form nucleus ambiguus anteriorly and nucleus retroambiguous posteriorly.

Function• This centre is inactive during quiet breathing

and the inspiratory centre is active.• Expiratory centre becomes active during

forced breathing or when the inspiratory centre is inhibited.

• But during quiet breathing expiration ia passive process and is due to the recoiling property of thoracic cage and lungs.

Effect of stimulation• Electrical stimulation in animals causes

contraction of expiratory muscles and expiration.

Pneumotaxic Centre• Is situated in dorsalateral part of reticular

formation in upper pons.Function• To control the medullary respiratory centres

particularly the inspiratory centre through apneustic centre.

• Pneumotaxic centre increases the respiratory rate by reducing the duration of inspiration.

Effect of stimulation• Stimulation does not produce any typical effectApneustic Centre• Is situated in reticular formation of lower pons.Function• Accelerates the depth of inspiration by acting

directly on inspiratory centre

Effect of stimulation• Stimulation increases the duration of

inspiration with short expiratory gasp.• So, respiration is called gasping type of

respiration.

Nervous Connection of Respiratory Centres

Efferent Pathway• Nerve fibre from the respiratory centres leave

trainstem and descend in anterior part of lateral columns of spinal cord.

• They terminate in motor neurons in the anterior horn cells of cervical and thoracic segments of spinal cord.

• From the motor neurons of spinal cord, two sets of nerve fibres arise which:

Phrenic nerve fibres which supply the diaphram Intercostal nerve fibres, which supply the

intercostal muscles.Vagus nerve also contains some afferent fibres

from respiratory centres.Afferent Pathway • Impulses from peripheral chemoreceptors and

baroreceptors are carried to respiratory centres

by fibres of glossopharyngeal and vagus nerves.• Vagal nerve fibres also carry impulses from the

stretch receptors of lungs to the respiratory centres.

• Therefore, respiratory centres receive afferent impulses from different parts of the body and, accordingly modulate the movements of thoracic cage and lungs through afferent nerve fibres

Integration of Respiratory Centres

Role of Medullary Centres• Inspiratory RampInspiratory centre,i.e. dorsal group of

respiratory neurons is responsible for normal rhythm of respiration.

These neurons discharge impulses intermittently at regular intervals and impulses cause inspiration

This type of fire/discharge from inspiratory centre is called inspiratory ramp signals.

The significance of inspiratory ramp signals is that there is a slow and steady inspiration so that, the filling of lungs with air is also steady.

Role of Pontine Centres

• The medullary respiratory centres are under the influence of pontine centres.

• The apneustic centre always accelerates the activity of inspiratory centre, cause prolonged inspiration.

• The pneumotaxic centre inhibits the apneustic centre and restricts the duration of inspiration.

Factors affecting Respiratory Centres

Respiratory centres regulate the respiratory movements by receiving impulses from various sources:

1. Impulses from anterior cingulate gyrus genu of corpus collusum, olfactory tubercle and posterior orbital gyrus of cerebral cortex inhibit respiration.

2. Impulses from stretch receptors of lungs – Hering Breuer reflex.

• Impulses from lungs bring about a respiratory reflex called Hering – Breuer reflex.

• There are some stretch receptors on the wall of bronchi and bronchioles of lungs.

• Stretch receptors give response to stretch of the lung tissues.

• This reflex is a protective reflex because, it restricts inspiration and limits overstretch of lung tissues.

3. Impulses from J receptors of lungs• ‘J’ receptors are juxta capillary receptors.• They are the nerve endings of the vagus.• They are present on the wall of alveoli and

have close contact with pulmonary capillaries.

• They are stimulated during the following: Pulmonary congestion

Pulmonary edemaPneumoniaHyperinflation of lungsMicroembolism in pulmonary capillaries• Some exogenous and endogenous chemical

substances like histamine, halothane,bradykinin, serotonin also stimulate ‘J’ receptors.

4.Impulses from Irritant Receptors of Lungs• Are situated on the wall of bronchi and

bronchioles of lungs.• They also send afferent impulses to respiratory

centres via vagal nerve fibres• Are stimulated by harmful chemical agents like

ammonia and sulfur dioxide.• Stimulation of irritant receptors produce reflex

hyperventilation along with bronchospasm.

• Hyperventilation along with bronchospasm prevent the entry of harmful agents into alveoli.

5. Impulses from Baroreceptors• These are situated in carotid sinus and arch of

aorta.• Are endings of Hering’s nerve (sinus nerve)

which is branch of glossopharyngeal nerve.

• Aortic baroreceptors are supplied by vagal nerve fibres.

• They give response to increase in BP.• Whenever BP is increased, they are activated, in

turn send impulses to medullar oblangata and causes inhibition of respiration.

6. Impulses from Chemoreceptors• Chemoreceptors play important role in the

regulation of respiration (later).

7. Impules from proprioceptors• These receptors give response to change in

position of different parts of the body.• They are situated in joints, tendons and

muscles.• They stimulated during muscular exercises,

send impulses to cerebral cortex in turn cause hyperventilation by sending impulses to medullary respiratory centres.

8.Impulses from Thermoreceptors• These respond to change in body

temperature.• Are cutanervous receptors.• When body is exposed to cold or when cold

water is applied over the body, the cold receptors are stimulated and , send impulses to cerebral cortex via somatic afferent nerves.

• Cerebral cortex in turn stimulates the respiratory centres and cause hyperventilation

9. Impulses from Pain Receptors• These give response to pain stimulus.• When stimulated, impulses are send from hem

to cerebral cortex via somatic afferent nerves• Somatic cortex in turn stimulates the respiratory

centres and causes hyperventilation.

10. Cough Reflex• Is a protective reflex caused by irritation of

parts of respiratory tract beyond nose, i.e. larynx, trachea and bronchi

• Irritation in any of these parts causes stimulation of vagal nerve endings and cough occurs.

• This temporary arrest of respiration is called apnea.

11. Sneezing Reflex• Is also a protective reflex• This occurs due to the irritation of the nasal

mucus membrane• During the irritation of nasal mucous

membrane, the olfactory receptors and trigeminal nerve endings in nasal mucosa are stimulated leading to sneezing.

• Sneezing starts with deep inspiration, followed by forceful expiratory effort with opened glottis and the irritants are expelled out of respiratory tract.

12. Deglutition Reflex• During swallowing of food, respiration is

arrested for a while.• The temporary arrest is called apnea.

• Apnea during swallowing is called swallowing apnea or deglutition apnea.

• It occurs during pharyngeal stage, i.e. 2 stage of deglutition.

• It prevents entry food particles into respiratory tract.

• The nerve involved in this reflex is glossopharyngneal.

3. CHEMICAL MECHANISM

• The chemical mechanism of regulation of respiration is opperated through chemoreceptors.Chemoreceptors

• These are receptor which give response to change in chemical constituents of blood.

• The chemoreceptors give response to the following changes in the chemical constituents of blood:

Hypoxia Hyperoapnea and Increased hydrogen ion concentration• Chemoreceptors are classified into two groups:Central chemoreceptorsPeripheral chemoreceptorsCentral Chemoreceptors • These are present in the brain

• They are situiated in deep part of medullar oblangata, close to dorsal group of neurons.

• These chemoreceptors are in close contact with blood and ceretrospinal fluid.

Mechanism of action• Main stimulant for central chemoreceptors is the

increased hydrogen ion concentration• If hydrogen ion concentration increases in blood, it cannot

stimulate the central chemoreceptors because, the hydrogen ions from blood cannot cross the blood brain barrier and blood cerebrospinal fluid barrier.

• On the other hand, if carbon dioxide increases in the blood, it can easily cross the blood brain barrier and blood cerebrospinal barrier and entre the interstitial fluid of brain or cerebrospinal fluid.

• There, the carbon dioxide molecules combine with water to form carbonic acid.

• Since carbonic acid is unstable, it immediately dissociates into hydrogen ion and bicarbonate ion.

• The hydrogen ions now stimulate the central chemoreceptors

• The chemoreceptors send inhibitory impulses to inspiratory centre causing increased rate and force of breathing.

• Because of this excess carbon dioxide is washed out and the respiration is brought back to normal.

• Lack of oxygen does not have any significant effect on the central chemoreceptors except that

it generally depresses the overall function of the brain

Peripheral Chemoreceptors• They are situated in the carotid body and aortic

body.• Carotid body is present over the internal

carotid artery near the bifurcation of common carotid artery into internal and external carotid arteries.

Nerve Supply• Chemoreceptors in the carotid body are

supplied by sinus nerve, which is a branch of glossopharyngeal nerve.

• The sinus nerve is also called Hering ‘s nerve.• The chemoreceptors in aortic body are supplied

by the aortic nerve, which is branch of the vagus nerve.

•

Mechanism of Action• Reduction in partial pressure of oxygen is the

most potent stimulant for peripheral chemoreceptors.

• Whenever, the partial pressure of oxygen decreases, these chemoreceptors are activated and send impulses through the aortic and sinus nerves.

• These impulse reach the respiratory centres

particularly the inspiratory centre and stimulate them.

• So, rate and force of respiration is increased.• This provides enough oxygen and rectifies the

lack of oxygen.

Disturbances of Respiration

IntroductionEupnea refers to normal respiration. Following are the forms used for some of the altered patterns of respiration:

• Tachypnea: The increase in rate of respiration is called tachypnea.

• Bradypnea: The decrease in rate of respiration is called bradypnea.

• Polypnea: Polypnea means rapid, shallow breathing resembling panting dogs. In this, only the rate of inspiration is increased but the force does not increase significantly.

• Hyperpnea: hyperpnea refers to a highly significant in pulmonary ventilation due to increase in rate or force of respiration or sometimes due to both with more change in rate.

• Apnea: Apnea means temporary arrest of breathing.

• Hyperventilation: increase in rate and force of respiration is called hyperventilation.

• Dyspnea: Dyspnea means difficult breathing.• Periodic breathing: The abnormal breathing is

called periodic breathing.• Tachypnea: Increased ventilation frequency,

usually with a decrease in ventilatory volume.

• Hypoxia: Reduced availability of oxygen to cells. The word anoxia refers to absence of oxygen. Since, there is no possibility for total absence of oxygen in living conditions, the use of this term has been abandoned.