Download Lecture 6 th week

Department of medical physiology
6th week
Semester: winter
Study program: Dental medicine
Lecture: RNDr. Soňa Grešová, PhD.
Department of medical physiology
Faculty of Medicine PJŠU
Department of medical physiology
6th, week
1. Regulation of the respiratory activity
2. Hypoxia
1. Regulation of the respiratory activity
• 4 control mechanisms play a role in the
regulation of breathing disorders and their
compensation :
1. neural mechanisms of brainstem
2. chemical control
3. reflex mechanisms
4. voluntary respiration
1. Regulation of the respiratory activity
• Respiratory centers located in
the medulla, where there are
two groups of neurons:
• Dorsal respiratory group
- The apneustic center
- Pneumotaxic center
• The ventral respiratory group
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
1. Regulation of the respiratory activity
Dorsal respiratory group
• composed only of inspiratory
neurons (PACEMAKER). Is
the switching station of
many respiratory reflexes.
The activity of this group is
transferred to the main
breathing muscle (C3,C4,C5diaphragm), ex.intercostal
muscles.
• Ondine´s curse
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
1. Regulation of the respiratory activity
Dorsal respiratory group
• Sets the basic respiratory rate.
• Stimulates the inspiratory muscles
to contract (diaphragm).
• The signals it sends for inspiration
start weakly and steadily increase
for ~ 2 sec. This is called a ramp
and produces a gradual inspiration.
• The ramp then stops abruptly for ~
3 sec and the diaphragm relaxes.
The vagus nerve and glossopharyngeal
nerves receive input from:
• Peripheral chemoreceptors
• Baroreceptors
• Several pulmonary receptors
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
1. Regulation of the respiratory activity
The apneustic center
Located in the lower pons.
• Excitatory to DRG which
prevents the SWITCH OFF of
the ramp signal .
• Therefore activity in the
apneustic center stimulates
DRG or Inspiratory Center and
causes Apneusis.
• Apneusis is a prolonged
inspiratory spasm that
resembles breath holding.
• Inhibited by signals from
Pneumotaxic centre & by
Vagus
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
1. Regulation of the respiratory activity
Pneumotaxic center
• Controls stopping point
of the dorsal group
ramp.
• SWITCH OFF centre of
inspiratory neurons
(PACEMAKER)
• Strong pneumotaxic
stimulation shortens the
duration of inspiration
and expiration.
• Weak pneumotaxic
stimulation can increase
and prolong the duration
of inspiration
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
1. Regulation of the respiratory activity
Ventral respiratory group
• Composed of inspiratory and
expiratory neurons. Provide motor
innervation of accessory
respiratory muscles.
• Inactive during normal, quiet
respiration.
• At times of increased ventilation,
signals from the dorsal group
stimulate the ventral group.
• The ventral group then stimulates
both inspiratory and expiratory
muscles. E.g., the abdominal
muscles are stimulated to contract
and help force expiration.
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
1. Regulation of the respiratory activity
2. chemical control
• Chemical control of respiration.
• Importance: It adjusts ventilation so
as to maintain the arterial PO2,PCO2
and H+ concentration in the normal
range.
• The Respiratory Center stimulated by1. Hypoxia - Fall in arterial PO2
2.Acidosis- Fall in pH or increase H+
concentration of arterial blood.
3. Hypercapnia -Rise in arterial PCO2 .
•
Mediated through the
Chemoreceptors.
1. Regulation of the respiratory activity
2. chemical control. Central chemoreceptors
• In the chemosensitive areas of
the respiratory center
(ventrolateral area), increased H+
is the main stimulus.
• The blood-brain barrier is not
very permeable to H+; however,
CO2 easily diffuses across the
BBB.
• Increases in CO2 cause increases
in H+.
• CO2 diffuses into the
chemosensitive regions of the
CNS, H+ is formed and stimulates
the dorsal group and thus
increase the respiration rate.
1. Regulation of the respiratory activity
2. chemical control. Peripheral chemoreceptors
•
Peripheral chemoreceptors are located
in carotid and aortic bodies and sense
the level of O2 (PO2), low sense the
level of H+ (independent of CO2 level)
and PCO2
•
Blood flow to the receptors is very
high; so very little deoxygenated
(venous) blood accumulates.
•
Low PO2 levels stimulates the dorsal
respiratory group
(PO2 < 60mmHg). K dependent-AP,
neurotransmitter – Dopamin.
•
The signal is sent to the respiratory
center DRG via the vagus (X.) or
glossopharyngeal nerve (IX) increase
ventilation.
Copyright: https://quizlet.com/19158008/respiratory-physiology-flash-cards/
1. Regulation of the respiratory activity
3. reflex mechanisms. Pulmonary Stretch Receptors:
• Over inflation of lung will
stimulate stretch receptors
located in the smooth
muscle of the airways via
vagi (X.) inhibit DRG (Expiration occur) HeringBreuer Inflation Reflex
• Protective mechanism for
preventing excess lung
inflation
• Threshold for this reflex is
1-1.5 L of Tidal volume
1. Regulation of the respiratory activity
3. reflex mechanisms. J Receptors
• Present between alveolar
wall and the pulmonary
capillary.(Juxta-capillary)
• Stimulated by pulmonary
edema fluid alveolus),
exercise, between
capillary an inhalation of
irritant gases etc.
• Stimulation of J receptors
causes tachypnoea that is
rapid shallow respiration.
Copyright: http://www.emsworld.com/article/10263561/regulation-of-ventilation
1. Regulation of the respiratory activity
3. reflex mechanisms. Irritant receptors
• Irritant receptors are
myelinated vagal afferent
nerve endings which are
located in the large airways
like trachea up to respiratory
bronchiole.
• Stimulation: The irritant
receptors are stimulated by
smoke, chemicals, or
mechanical irritants.
• They produce reflex coughing,
rapid shallow breathing,
bronchial constriction and
breath holding.
1. Regulation of the respiratory activity
3. reflex mechanisms. Other receptors cooperating with the respiratory center
Role of afferents from higher centers.
•
Painful stimuli, emotional stimuli affect respiration.
The afferents are from the limbic system and the
hypothalamus to the respiratory neurons.
Role of afferents from proprioceptors.
•
During muscular exercise proprioceptors presents in
muscles tendons and joints send afferent impulses
to the DRG and stimulate respiration. Respiratory
rate increase in muscular exercise.
Role of arterial baroreceptor stimulation on respiration
•
Afferent stimulation from carotid sinus
baroreceptors (caused by increase blood pressure)
inhibits DRG and causes Apnea. Other effects of
baroreceptor stimulation are hypotension and
bradycardia.
1. Regulation of the respiratory activity
4. voluntary respiration
• It originates in the cerebral
cortex and sends impulses to the
nerves of the respiratory
muscles via the corticospinal
tracts. In addition, ingoing
impulses from many parts of the
body modify the activity of the
respiratory centers and
consequently alter the outgoing
impulses to the respiratory
muscles to coordinate rhythm,
rate or depth of breathing with
other activities of the body.
• Emotional stimuly acting
through the limbic system and
hypothalamus.
Copyright:
http://intranet.tdmu.edu.ua/data/kafedra/internal/normal_phiz/classes_stud/en/med/lik/2%20course/4
%20Cycle%20Physiology%20of%20breathing/02%20%20Regulation%20of%20breathing.htm
Neural mechanisms of brain stem
•
A:Complete transection above the
pons-regular breathing continuesshows that centres controlling
respiration are in the Pons & Medulla
normal breathing
•
B: A midpontine section with vagi
intact - cutting the influence of
pneumotaxic center on apneustic
center. Depth of respiration increases
and slowing of respiration. Both the
vagus and pneumotaxic center
inhibit the inspiratory center (DRG)
•
•
C: Section between lower pons &
Medulla with or without intact vagi
results in continuation of respiration.
Though irregular, it is rhythmic
showing that medullary neurons
posses spontaneous rhythmic
discharge. gasps – gasping
D: Complete transection of the
brainstem below the medulla (WITH
or WITHOUT VAGI) stops respiration.
Apnea occurs. completely remove
the breathing
A
B
C
D
Copyright: http://www.zuniv.net/physiology/book/images/16-1.jpg
3.
2. Hypoxia
1.
2.
4.
1. Hypoxic hypoxia
-
-
decrease in atmospheric
pressure (1.)
obstruction COPD (Asthma)(2.)
respiratory pump failure (3.)
Shunting (edema)
2. Anemic hypoxia
3. Stagnant or
ischemic hypoxia
4. Histotoxic or
cytotoxic hypoxia
-
Cyanide poisoning
5.
7.
6.
8.