Department of medical physiology6th week

Semester: winterStudy program: Dental medicineLecture: RNDr. Soňa Grešová, PhD.Department of medical physiologyFaculty of Medicine PJŠU

Department of medical physiology6th, 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 theircompensation :

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.

• 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,C5-diaphragm), ex.intercostalmuscles.

• Ondine´s curse

1. Regulation of the respiratory activityDorsal 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 activityDorsal 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 rampand produces a gradual inspiration.

• The ramp then stops abruptly for ~ 3 sec and the diaphragm relaxes.

The vagus nerve and glossopharyngealnerves 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 activityThe 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 activityPneumotaxic center

• Controls stopping point of the dorsal group ramp.

• SWITCH OFF centre of inspiratory neurons(PACEMAKER)

• Strong pneumotaxicstimulation shortens the duration of inspiration and expiration.

• Weak pneumotaxicstimulation can increaseand 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 activityVentral 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 activity2. chemical control

• Chemical control of respiration.

• Importance: It adjusts ventilation so as to maintain the arterial PO2,PCO2and H+ concentration in the normal range.

• The Respiratory Center stimulated by-1. Hypoxia - Fall in arterial PO22.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 activity2. 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 activity2. 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 activity3. 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) Hering-Breuer 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 activity3. 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 activity3. 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 activity3. 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 activity4. voluntary respiration

• It originates in the cerebral cortex and sends impulses to the nerves of the respiratory muscles via the corticospinaltracts. 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 actingthrough 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 continues-shows that centres controlling respiration are in the Pons & Medullanormal breathing

• B: A midpontine section with vagiintact - cutting the influence of pneumotaxic center on apneusticcenter. 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 vagiresults 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

2. Hypoxia

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

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