Control of respiration.
Prof. Omer Abdel Aziz Musa
Faculty of medicine,
National Ribat University.
Objectives
Respiratory center
 Chemical control
 Neural control
 Exercise & altitude

Review
Mention three factors affecting gas
exchange at the alveoli?
 What are the factors leading to increased
P50 for oxygen?
 Mention three factors leading to increased
bronchial tone?
 What is the effect of the following on
surfactant: cortisol, smoking.

Neural & Chemical Control:
 Rythmic
breathing is generated
in the brain stem (Respiratory
centre).
 Chemoreceptors,
mechanoreceptors and higher
centers regulate breathing.
 Basically
the control is neural
through the resp. centre .
Respiratory centre:

Pre-BÖttzinger complex in the
medulla.
Respiratory Centre:
Medullary centers:
1. Dorsal respiratory group (DRG):
close to nucleus of tractus
solitarius from which it receives
and integrates afferent information
from resp. mechano- and
chemoreceptors.
Composed of inspiratory neurons (I neurons) and supply contralateral
phrenic nerve.
Medullary cont.
2. Ventral respiratory group (VRG):
 Receives afferents from DRG and
has both inspiratory and expiratory
neurons (E-neurons)
Pontine influences:
1. Pneumotaxic centre: in upper
pons and contains both inspiratory
and expiratory cells. Normal
function is unknown but it may
tune fine breathing pattern
switching insp. to exp.
2. Apneustic centre: in caudal pons.
If damaged it will lead to arrest of
breathing in inspiration. It receives
afferents from pneumotaxic centre
and vagus.
Quiz
Rythmicity center is most likely in :
 1. Pre-Bottzinger complex
 2. DRG
 3. VRG
 4. Apneostic center
 5. Pneumotaxic center

Regulation of the respiratory
centre
1.Chemical control:
 Chemoreceptors in carotid and aortic bodies
and medulla are stimulated by:
 a-Increased PaCO2 ( via CSF & brain
interstitial H).
 b- decreased pH ( carotid & aortic)
 C- decreased PaO2 ( carotid &
aortic).
Regulation cont.
2.Non-chemical (neural):
 a-vagal afferents.
 b- afferents from pons,
hypothalamus & limbic system.
 c-afferents from proprioceptors.
 d-
afferents from pharynx, trachea
& bronchi.
 e- afferents from barroreceptors.
Chemical control :

Chemoreceptors are stimulated by an
increased PaCO2 or [H] or a decline in
PaO2.
1.Peripheral chemoreceptors
Carotid chemoreceptors:
 Near carotid bifurcation. It has two
types of cells 1&11. Impulses carried by
the glossopharyngeal nerve & carotid
sinus to the medulla.

More sensitive to drop of O2 by type 1
cells.
 Type 1 cells contain dopamine which is
released in response to low O2.

They are stimulated by a drop in
dissolved oxygen, so they are not
stimulated in anemia and CO poisoning.
 They can be stimulated by cyanide,
nicotine & increased K.


Aortic bodies: are in the arch of the
aorta and more responsive to increased
PaCO2.Impulses carried by the vagus.
Q






Carotid bodies chemoreceptors:
1. Contain type 11 cells which secrete
surfactant.
2. Are found at the beginning of the common
carotid a.
3.Has type 1 cells which are sensitive to low
PaO2.
4. Has type 11 cells which contains dopamine.
5. are stimulated by barroreceptors.
2.Chemo receptors in the brain
stem:

Located in the medulla oblongata near
the resp. centre and responds mainly
to an increased PCO2 and a drop in
PO2.

CO2 easily penetrate the blood brain
barrier combining with water to form
H2CO3 which dissociate to give (H) and
HCO3. Hydrogen ion stimulate
receptors sensitive to it, stimulating
respiration, leading to loss of CO2 and
consequently a drop in PaCO2.

Sever drop in PaO2 (<60) stimulate
these receptors.
Q
Mention the components of the resp.
center?
 How do carotids chemoreceptors work?
 How are the medullary chemoreceptors
stimulated by PCO2?

Pulmonary and myocardial
chemoreceptor:
 Non
physiologic.
 Injection of nicotine leads to
apnea?
Hormonal effects
 During
the luteal phase of the
menstrual cycle and in
pregnancy ventilation
increases. This could be due to
activation of estrogendependent progesterone
receptors in the hypothalamus.
Neural control


Afferents from higher centers:
1. Cerebral cortex: voluntary control of
respiration.( Ondine curse)

2.Cerebellum: coordination with swallowing
and talking

3.Hypothalamus: increased resp, with high
temp.

4. Limbic system: pain and emotional stimuli
affect resp.
Reflex control:
1. Pulmonary receptors:

Inflation of the lungs will stimulate stretch
receptors on smooth muscles & through the
vagus inhibits insp. Deflation of the lungs in
expiration will stimulate pulmonary deflation
receptors, triggering inflation ( HeringBreuer reflex).
Reflex cont.
2. Lung irritant receptors:
Mechanical and chemical irritants can
stimulate lung irritant receptors, vagal
nerve endings in epithelia of trachea
and large airways.
 Stimulation of trachea & extrapulm.
bronchi leads to cough ( deep insp.
followed by forced exp. against a
closed glottis).

Stimulation of irritant receptors inside
the lung can lead to
bronchoconstriction ( histamine ).
 Stimulation of nerve ending of the
olfactory and trigeminal nerves in the
nose leads to sneezing.

Reflex cont.
3. J-receptors( juxtacapillary):

Stimulated by hyperinflation and chemicals
(pulmonary chemoreflex) producing
apnea followed by rapid breathing,
bradycardia and hypotention . They are
stimulated during pulmonary congestion,
microembolism in pulmonary capillaries &
pneumonia.
4 Afferents from proprioceptors. :

Exercise, passive or active movements of
joints, stimulate resp.
Respiratory components of
visceral reflexes
Inhibition of respiration and closure of
glottis occur during vomiting and
swallowing.
 Hiccup is a spasmodic contraction of
the diaphragm that produces insp.
during which the glottis suddenly
closes. It can be stopped by?
 Yawning? Sighing?

Baroreceptors stimulation inhibits resp.
slightly.
 Thermo-receptors: cold stimulates cold
receptors, which send impulses to the
brain which stimulates the resp. center
to increase ventilation.

Reflex cont.
Heart & lung transplant:
 Lungs and heart nerves are cut up to carina.
 1. Cough reflex due to trachea stimulation is
normal but to bronchi is abscent.
 2. Bronchi dilated.
 3.Normal number of sighs and yawning.
 4. Lack of Hering-Breuer reflex.
 5. Pattern of breathing at rest is normal.
Q
Respiration can increase in:
 1. Luteal phase of menses.
 2. Hering Breuer reflex.
 3. Swallowing.
 4. Baroreceptors stimulation.
 5. Proprioreceptors stimulation.

High altitude:
‫بسم هللا الرحمن الرحيم‬
‫إل ْسالَ ِم َو َمن يُ ِر ْد أَن‬
‫‪{ ‬فَ َمن يُ ِر ِد ه‬
‫اّللُ أَن يَ ْه ِديَهُ يَ ْش َر ْح َ‬
‫ص ْد َرهُ ِل ِ‬
‫س َماء َكذَ ِل َك‬
‫صعَّدُ ِفي ال َّ‬
‫ض ِيهقا ً َح َرجا ً َكأَنَّ َما يَ َّ‬
‫ص ْد َرهُ َ‬
‫يُ ِ‬
‫ضلَّهُ يَ ْجعَ ْل َ‬
‫ون }األنعام‪125‬‬
‫ين لَ يُمْ ِمنُ َ‬
‫علَى الَّ ِذ َ‬
‫يَ ْجعَ ُل ه‬
‫اّللُ ِ ه‬
‫س َ‬
‫الر ْج َ‬
‫‪‬‬
‫بسم هللا الرحمن الرحيم‬
‫‪‬‬
‫‪ ‬سبحان الذى أسرى بعبده ليالً من المسجد الحرام إلى المسجد‬
‫القصى الذى باركنا حوله لنريه من آياتنا انه هو السميع‬
‫البصير‬
‫‪( ‬السراء ‪) 1‬‬
Exercise.
Hypoxia:
Decreased O2 supply to the tissues
produces hypoxia. Types:
 1. : decreased PaO2 as in pulmonary and
cardiac diseases, high altitude.

1. Hypoxic hypoxia

Decreased oxygen supply to the blood
leading to decreased PaO2
Causes of hypoxic hypoxia
1.Low PO2 in inspired air: high altitude,
breathing air from a closed space.
 2. Respiratory disorders: obstructive lung
diseases ( asthma, chronic bronchitis),
poliomyelitis affecting respiratory muscles,
brain tumors affecting the respiratory
center, pneumothorax, pleural effusion,
haemothorax..


3. Cardiac disorders: congestive heart
failure, arterio-venous shunts
High altitude:
‫بسم هللا الرحمن الرحيم‬
‫إل ْسالَ ِم َو َمن يُ ِر ْد أَن‬
‫‪{ ‬فَ َمن يُ ِر ِد ه‬
‫اّللُ أَن يَ ْه ِديَهُ يَ ْش َر ْح َ‬
‫ص ْد َرهُ ِل ِ‬
‫س َماء َكذَ ِل َك‬
‫صعَّدُ ِفي ال َّ‬
‫ض ِيهقا ً َح َرجا ً َكأَنَّ َما يَ َّ‬
‫ص ْد َرهُ َ‬
‫يُ ِ‬
‫ضلَّهُ يَ ْجعَ ْل َ‬
‫ون }األنعام‪125‬‬
‫ين لَ يُمْ ِمنُ َ‬
‫علَى الَّ ِذ َ‬
‫يَ ْجعَ ُل ه‬
‫اّللُ ِ ه‬
‫س َ‬
‫الر ْج َ‬
‫‪‬‬
‫بسم هللا الرحمن الرحيم‬
‫‪‬‬
‫‪ ‬سبحان الذى أسرى بعبده ليالً من المسجد الحرام إلى المسجد‬
‫القصى الذى باركنا حوله لنريه من آياتنا انه هو السميع‬
‫البصير‬
‫‪( ‬السراء ‪) 1‬‬
Exercise.
2. Anaemic Hypoxia

Causes:
- Anaemia
- CO poisoning
- Methaemoglobin formation: poisoning
with chlorates, nitrates, ferricyanide
3. Stagnant hypoxia
Due to decreased flow of blood
 Causes
- CHF
- Hemorrhage
- Shock
- Thrombosis & embolism
- Vasospasm

4. Histotoxic hypoxia

Prevention of oxygen utilization at tissues
level eg cyanide poisoning.
Effects of hypoxia
1. Increased erythropoietin release which
increase RBC.
 2. Initially increase HR, force of
contraction, COP & BP, later they
decrease.
 3. Increase resp. rate but if continued will
lead to resp. centers failure.

4. Associated with loss of appetit, nausea
& vomitting with feeling of thirst.
 5. Depression, apathy, ill tempered, lack of
coordination, loss of consciousness and
coma leading to death.
 6.Mountain sickness (delayed effect):
nausea, vomiting, depression, weakness
and fatigue.

Oxygen therapy in hypoxia

Oxygen therapy can help in hypoxic
hypoxia & slightly in anemic and stagnant
hypoxia but not in histotoxic hypoxia.
Asphyxia: Decreased PaO2, increased
PCO2.
 Hypercapnia: increased PCO2.
 Hypocapnia: decreased PCO2.

Cyanosis




Definition: it is diffused bluish coloration of skin
and mucus membranes due to presence of large
amount of reduced Hb (5 g or more).
Types:
1.Central: in heart failure, right to left shunts;
cyanosis is general( tongue & extremities)
2. Peripheral: flow of blood is slowed in
capillaries as in cold, venous obstruction & heart
failure.
Summary
Respiratory center.
 Chemical control
 Neural control.
 Hypoxia
 Cyanosis.

Thanks
It has a rostral group in nucleus 
ambiguus which supplies the
ipsilateral accessory muscles; and
a caudal group in nucleus
retroambigualis.
‫ل تنسونا من صالح الدعاء‬