Control Of Respiration Flashcards by Emily Mosher

Medullary respiratory center

. Generate basic rhythmic pattern of breathing
. Both inspiratory and expiratory neurons
. Dorsal respiratory group (inspiratory) synapse on motor neurons that supply mm. Of inspiration
. Ventral respiratory group (inspiratory and expiratory) only active during forced inspiration/expiration
. Pre-Botzinger complex: contain network of neurons that is involved in respiratory rhythm-generating process

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Nucleus tractus solitarius

Important autonomic integrative center w/in brainstem
. DRG neurons located w/in ventrolateral portion of NTS
. Cardio-respiratory afferent project to NTS subdivisions
. Peripheral chemoreceptors and pulmonary stretch receptors project onto lat. regions
. Arterial baroreceptors project to dorsolat. And med. portions

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Pontine respiratory center

. Apneustic center: prolongs inspiratory effort by providing excitatory input to inspiratory neurons in pre-botzinger complex
. Pneumatic center: switch off further inspiration
. Influence output from medullary respiratory centers
. Provide fine-tuning of the activity of medullary respiratory centers

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Cortex control of respiration

Modifies activity of brainstem neurons bc breathing can be voluntarily altered
. Alllows speaking, yawning, coughing

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T/F limbic system and hypothalamus are involved in control of emotional responses and can alter breathing pattern

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Neural control of ventilation

. Main inspiratory mm. Are innervated by phrenic n. And intercostal n.
. Cell bodies of nn. In spinal cord
. Neural impulses from inspiratory neurons
. When inspiratory neurons w/in brainstem are activated and motor neurons connected to inspiratory mm. Activate
. Produces contraction of mm. Producing inspiratory effort
. When inspiratory neuron stop firing, the inspiratory mm. Relax producing passive expiration
. Expiratory neurons will fire during forced expiration

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Chemoreceptors

. Responds to change in chemical composition of blood or fluid

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Arterial chemoreceptors

. Located in carotid bodies at bifurcation of common carotids
. Respond to changes in blood, specifically PaO2
. Send afferent impulses to the lat. NTS w/in medulla
. Carotid body chemoreceptor afferents travel via CN IX
. Aortic body chemoreceptor afferents travel via CN X

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What happens when PaO2 falls below 60 mmHg?

Respiratory centers w/in the brainstem are stimulated by signals from peripheral chemoreceptors to inc. ventilation
. Shows that peripheral chemoreceptors only function when PaO2 is dangerously low level

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Carotid body structure

. Contains 2 types globus cells
. Type I cells: large vesicles containing dopamine
. Cells in close opposition to the endings of carotid sinus n. (Branch of CN IX)
. Type II cells: no dopamine vesicles

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Carotid body function

. When PaO2 dec. there is inc. in dopamine release by type I cells inc. in firing rate along carotid sinus n.
. Partial pressure of O2 (not O2 content) of arterial blood is stimulus for inc. discharge rate
. Type I cell is site of chemoreception
. Carotid body excitation may depends upon ratio of ATP to ADP w/in Type I cell mitochondria
. Modulation of neurotransmitter release from these cells by physiological and chemical stimuli may affect discharge rate of carotid soy afferent fibers

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Central chemoreceptors

. Important in minute-by-minute control of ventilation
. Situated along ventrolat. Surface of the medulla
. Located near the VRG
. Applying H or dissolved CO2 to the brain ECF that babes the central chemoreceptors stimulates breathing
.

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Function of central chemoreceptors

. Inc. in PaCO2 causes rise in PCO2 of cerebrospinal fluid
. BBB is impermeable to to HCO3 and H but is permeable to CO2
. When CO2 diffuses into brain, it dissociates and causes corresponding inc. in H conc. In CSF
. The H ions diffuse from CSF into the ECF
. Dec. ECF pH stimulates central chemoreceptors which stimulates medullary respiratory centers to inc. ventilation to blow off excess CO2
. Opposite occurs for higher pH from dec. PaCO2

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Dec. in PaCO2 effect of peripheral and central chemoreceptors

. P: stimulates when PaO2 falls under 60 mmHg

. C: no direct effect, severe hypoxia depresses neuronal activity of all brain tissue, including respiratory centers

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Effect of inc. arterial PCO2 on peripheral and central chemoreceptors

. P: weakly stimulates

. C: strongly stimulates (primary respiratory signal)

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Inc. arterial H effect on peripheral and central chemoreceptor

. P: stimulates

. C: does not effect (can’t penetrate BBB)

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Types of pulmonary receptors

. Pulmonary stretch receptors
. Irritant receptors
. J receptors

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Pulmonary stretch receptors

. Located w/in smooth m. Layer of lung airways
. Stretching of the lungs during inspiration activates receptors
. Towards end of inspiration APs from these travel to medullary respiratory centers to inhibit further activity from inspiratory neurons
. Neg. feedback called Breuer-Hering reflex
. Most important when tidal volume is over 1000 ml (during exercise)

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Irritant receptors

. Lie btw airway epithelial cells
. Noxious stimulus stimulates these which reflexively produce bronchoconstriction and rapid shallowing breathing
. Can limit penetration of dangerous agents
.. May play role in asthma attacks
. Can also initiate cough or sneeze

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Pulmonary C fibers/J receptors

. Located in interstitium near alveolar capillaries
. Stimulated by interstitial edema
. Activates J reflex causing laryngeal closure and apnea followed by rapid and shallow breathing
. Responsible for rapid breathing seen in patients w/ pulmonary embolus, edema, or pneumonia
. May be responsible for feeling of dyspnea encountered during pulmonary vascular congestion from LV failure

Joint and muscle receptors

. Found in skeletal joints and muscles
. Innervated by spinal nn.
. Limb movement stimulates it
. Causes inc. ventilation during exercise

Nasal receptors

. W/in mucosa of nose and nasal passages
. Innervated by CN V
. Mechanical and chemical irritants stimulate it
. Causes sneeze or apnea

Laryngeal receptors

. W/in laryngeal mucosa
. Innervated by CN X
. Stimulated by mechanical and chemical irritants
. Causes sniff, aspiration, or swallowing movement

Most important factor in control of ventilation

PCO2 of arterial blood
. Usually varies less than 3 mmHg
. Inc. produces inc. ventilation

What occurs at any level of PO2 when PCO2 inc.?

Inc. ventilation

What occurs when PCO2 is constant and PO2 dec.?

Inc. ventilation . If PCO2 is normal at 40 mmHg, the PO2 can be reduced to 60 mmHg before you really see the inc. in ventilation . Overall role of hypoxia in minute-by-minute ventilation is small . At low PO2 there is a greater inc. in ventilation for every mmHg inc. in PCO2

Hypocapnia

CO2 below 40 mmHg | . Hypercapnia is over normal level

Alveolar PO2 and PCO2 when breathing air w/ low PO2

. PO2 dec. | . PCO2 no change

Alveolar PO2 and PCO2 when there is inc. ventilation and unchanged metabolism

. PO2 inc. | . PCO2 dec.

Alveolar PO2 and PCO2 when there is dec. in alveolar ventilation and unchanged metabolism

. PO2 dec. | . PCO2 in.

alveolar PO2 and PCO2 when there is inc. in metabolism and unchanged alveolar ventilation

. PO2 dec. | . PCO2 inc.

Alveolar PO2 and PCO2 when there is proportional inc. in metabolism and alveolar ventilation

No change in either

Cheyne-stokes breathing

. Periodic breathing patterncharacterized by period of apnea 10-20s in duration . Separated by periods of hyperventilation when tidal volume gradually and cyclically inc. and dec. . Alternating periods of apnea and hyperventilation caused by time delay in ECF pH changes . Manifestation of instability in central respiratory control system . Often seen at high altitude and at night during sleep . Also seen in patients w/ severe hypoxemia from CHF

Regulation of breathing during sleep

. During slow wave sleep, there is withdrawal of cerebral influences and dec. ventilation which inc. PaCO2 and CO2 response curve is shifted right . Tonic REM: sleep breathing maintains regularity but tidal volume may inc. . Phasic REM: irregular breathing due to intrinsic activity of higher brain centers dominates respiratory neuron activity . Activity of upper airway muscles is reduced causing dec. of caliber of upper airways that inc.r existence to flow . Brief periods of obstruction can be normal during sleep (snoring)

Sleep apnea

. Apneic periods that can last for over 10s and assoc. w/ drop in PaO2 as low as 75% . Occur at all sleep stages but more common during REM and lighter stages of slow wave

Central sleep apnea

. Cessation of respiratory effort (absence of changes in pleural pressure

Obstructive sleep apnea

. Air flow ceases bc of total obstruction of upper airways despite persistent respiratory efforts . Common sites: larynx, pharynx, and oropharynx . Arousal from apnea results from chemoreceptors activation due to developing hypoxia and hypercapnia . May lead to right-sided heart failure and pulmonary hypertension

Respiration in fetus

. Gas exchange through placenta . Maternal blood enters placenta from uterine aa. . Gas exchange occurs across barrier that separates mother and fetal blood w/in intervillous sinusoids . PO2 of fetal blood is about 30 mmHg bc placental blood mixes w/ mixed venous blood . PO2 in fetal descending aorta is only 22 mmmHg . After 24 weeks the respiratory epithelium begins to thin out and become closer to pulmonary capillaries and surfactant synthesis and storage begins

first breath in newborn

. High distending forces needed in first few breaths to move liquid out of lung and to overcome surface forces that oppose movement or air . Intrapleural pressure can fall to -40 cmH2O before air enters lungs . Pulmonary surfactant stabilizes open alveoli

Respiratory distress syndrome (RDS)

. Surfactant deficiency in newborns | . Affects 10-15% of premature infants

Transitions from fetal and newborn respiration systems

. Fetus has high pulmonary vascular resistance, low blood flow, and high arterial pressure . At birth: dec. in vascular resistance that occurs during 1st breaths from abrupt inc. in PO2 that abolishes hypoxic pulmonary vasoconstriction . Pulmonary circulation now receives entire CO not just 7% . Placental circulation closes . All open valves only foe fetus close

Apnea in newborns

. Predominantly central because central respiratory control is still immature . Occurs mostly in preemies

Sudden infant death syndrome (SIDS)

. Pure obstructive apnea | . Lack of chemoreceptors responsiveness esp. to CO2 bc it is less well-developed

Diffusing capacity as infants transition to children

. Diffusing capacity inc. as alveolar surface area enlarges . By 6 y/o the capacity is about the same as adult . New alveoli are added until child is about 8 y/o

Respiration in. Older adults

. Elastic recoil dec. and compliance inc. causes inc. FRC . Inc. RV and closing capacity . FEV1 and FEF are dec. . Chest wall stiffens and becomes less compliant from structural changes . Respiratory mm. Strength dec. which dec. vital capacity and forced expiration flow rate . Total lung capacity stays constant w/ age if adjusted for dec. in height seen . Internal lung SA dec., alveoli become wider and shallower causing dec. diffusing capacity and dec. exchange rate . Inc. in difference of PaO2 and PAO2 . Ventilator responses reduced but PCO2 unchanged

Asphyxia

. O2 starvation of tissues | . Caused by lack of O2 in air, Respiratory impairment , or Inability of tissues to utilize O2

Eupnea

Normal breathing

Respiratory arrest

. Permanent cessation of breathing unless clinically corrected

Suffocation

. O2 deprivation as result of inability to breath oxygenated air