Respiration 4: Its Regulation

Describe the direct and indirect effects of ⬆ body temperature on respiration

Direct - directly acts on respiratory center Indirect - ⬆ energy use throughout body ⬆ chemical signals

What is the Hering-Breuer reflex?

lungs overstretched → in walls of bronchi/bronchioles, stretch receptors activate → signals to vagus → dorsal respiratory group → limits duration of inspiration

When does low O2 start to effect alveolar ventilation?

when PO2 is very low, about 1/2 normal, Eggena says 60 mmHg PO2

Do more H+ ions reach the chemosensitive areas when blood CO2 levels ⬆ or when H+ levels ⬆?

when blood CO2 levels ⬆ (quantitatively, CO2 more important functionally)

What is the most common type of period breathing? Describe it.

Cheyne-Stokes breathing person doesn't breathe for 45 sec-3 min, then overbreathes

feedback excitation of respirator center activity by changes in CO2, H+, and O2 and excitatory signal from other parts of the nervous system (especially in exercise) both ⬆ what?

⬆ levels of breathing

What do some say cutting the vagi or decreasing vagal. tone does to depth of respiration?

Cutting the vagi or decreasing vagal tone→↑ depth of respiration

What happens to the lungs when the apneustic center acts? What happens to expiration?

lungs become greatly inflated, short expiratory bursts occur

Describe 3 cases of respiratory center depression mentioned in the packet.

1. Cerebrovascular disease - most common long term 2. Acute brain edema - ex. from concussion, anything compressing cerebral arteries against the brain case, cutting off blood flow 3. Anesthesia - desirable to use one to depress cortex more than respiration, ex. good = halothane, bad = opiates

Name 3 causes of periodic breathing listed in the packet, and describe them.

1. Heart failure - long transit time of blood b/w lungs to brain, changes in blood not detected for many seconds 2. Damage to respiratory center: central sleep apnea - one form = ⬆ sensitivity → responds hyperactively and then not at all 3. Obstructive sleep apnea - wake up to breathe → exhausted; 6-7x car accident rate; primarily middle aged obese males; associated w/ snoring and ⬇ longevity; CPAP continuous positive airway pressure often used

Describe the functions of the ventral respirator group in inspiration and expiration

1. almost entirely inactive in normal breathing, doesn't participate in basic rhythm 2. If respiratory drive > normal, spillover from dorsal respiratory group - basic oscillation spills over 3. electrical stimulation in some cells causes inspiration in some, expiration in others - this area contributes to both 4. very important in active breathing, when active expiration is needed

What # - # breaths/min from strong stimulation of the pneumotaxic center?

30-40 breaths/min

Changes in CO2 level have a very ______ acute effect and a very ______ chronic effect. A. strong, strong B. weak, weak C. strong, weak D. weak, strong

C. strong acute effect weak chronic effect (w/i few minutes of CO2 rise, ⬆ respiration reaches max, declines over day or two)

How does CO2 indirectly effect chemosensitive areas?

CO2 diffuses easily into brain from blood → combines w/ H2O → H2CO3 formed → dissociates into HCO3- and H+ → H+ ions stimulate central chemoreceptors directly

In chronic respiratory conditions, which mechanism adapts and which mechanism may be the only mechanism driving respiration?

CO2 mechanism adapts low O2 mechanism may be the only mechanism driving respiration

Why do H+ changes have a much less effect in stimulating the chemosensitive neurons than changes in CO2 levels?

H+ doesn't cross the blood brain area easily

If CO2 and H+ are prevented from decreasing at the same time as there is a stimulus to respiration from low O2, all 3 mechanisms will support each other in the same direction. In what types of cases will this occur? Examples?

In cases in which gases are not easily exchanged between air and blood ex. pneumonia, COPD

Why is there little ⬆ in breathing to low PO2?

PC02 and pH regulatory mechanisms oppose it and are more powerful. When low 02 would ⬆ respiration, the beginning of an ⬆ in respiration blows off C02 and ⬇ the H+ concentration. Reducing these has a more powerful effect in stopping respiration and the low 02 mechanism does not get a chance.

What causes SIDS (sudden infant death syndrome)?

Probably a # of causes Majority of babies suffocate from sleeping on belly in blankets and pillows

Packet II pg. 15, figure 41-1 organization of the respiratory center What does respiratory group and pre-botzinger complex do? Pneumotaxic center? Vagus and glossopharyngeal? Ventral respiratory group? Apneustic center?

Respiratory group and pre-botzinger complex - causes inspiration Pneumotaxic center - shuts off inspiration Vagus and glossopharyngeal - carries sensory info about status of breathing Ventral respiratory group - can cause either expiration or inspiration depending on which cells are stimulated, important in active breathing Apneustic center - prevents switching off of inspiration, may provide additional inspiratory drive

Why is oxygen regulation of respiration not normally needed?

The respiratory system normally maintains a P02 in the alveoli that is higher than necessary to almost completely saturate the Hb. It would not matter if P02 were 10x normal. If it were ½ normal, the degree of saturation would still be quite high, so it is not important for the body to monitor the levels that closely.

When do chemical signals come into play in exercise?

They fine tune respiratory level as exercise proceeds

If CO2 and H+ are prevented from decreasing at the same time as there is a stimulus to respiration from low O2, what will happen?

all 3 mechanisms will support each other in the same direction

Other factors that affect respiration include: A. voluntary control B. vasomotor center activity C. ⬆body temperature D. the diving reflex

all of the above

Packet II pg. 15, figure 41-1 organization of the respiratory center Which factor may not be that important normally, other than ventral respiratory group?

apneustic center

Why is it better that CO2 is the regulator of respiration, as opposed to oxygen?

blood and tissue CO2 changes a lot w/ ventilation, and CO2 affects H+

If all sensory inputs were cut and if the brainstem was cut above and below the medulla, what would happen to the cells in the dorsal respiratory group?

cells would have repetitive burst corresponding to what would have been inspiration

The control areas of the respiratory center aren't directly responsive to CO2 or H+ concentration. What do we have instead to excite other areas of the respiratory center, particularly the inspiratory center?

chemosensitive area of respiratory center beneath the surface of the ventral medulla is sensitive to changes in blood CO2 or H+, excites other areas

Where is the sensory termination of the vagus and glossopharyngeal nerves from peripheral chemoreceptors, baroreceptors, and lung receptors?

dorsal respiratory group

What happens with the oxygen lack mechanism at high altitude?

first, low O2 stimulation of respiration is opposed by blowing off CO2 → CO2 mechanism adapt → alveolar ventilation ⬆over several days b/c low O2 mechanism is unopposed

Where are the peripheral chemoreceptors located?

in the carotid and aortic bodies (don't get confused -not carotid sinus and aortic arch baroreceptors!!)

Does CO2 have a direct or indirect effect on chemosensitive areas?

indirect

The peripheral chemoreceptors respond to H+ and CO2. Are the effects of H+ and CO2 more powerful on the peripheral chemoreceptor system or on the respiratory center?

more powerful on the respiratory center

What causes ventilation to ⬆so much at the beginning of exercise? (Hint: not chemicals)

not known exactly; probably because of the following: 1. when the motor cortex sends signals to the muscles to move, it probably sends them to the respiratory center to ⬆respiration 2. body movements probably excite join proprioceptors, which send signals to excite the respiratory center (even passive limb movements stimulate respiration)

what is the only O2 mechanism in respiratory control?

peripheral chemoreceptor system

Packet II pg. 15, figure 41-1 organization of the respiratory center What limits the duration of inspiration and ⬆respiratory rate? Explain

pneumotaxic center limits duration of inspiration, which shortens respiration as a whole, thus causing an ⬆ in respiration rate

When does Guyton say the Hering-Breuer reflex will be activated?

probably not until lungs become very overinflated - 1.5 L Vt (meaning its protective against excess inflation vs normal inspiration)