32. Physiology - Regulation of Breathing

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Questions and Answers

What type of breathing influence is primarily exerted by the hypothalamic thermoregulatory center?

Changes due to emotional stress

Regulation based on body temperature (correct)

Cognitive control over breathing

Voluntary modulation during speech

What is the primary consequence of powerful emotions on respiratory rhythm?

They increase the rate of oxygen intake.

They have no significant effect on breathing.

They fundamentally alter respiratory rhythm. (correct)

They stabilize the respiratory rate.

Which hormone synthesized in the hypothalamus influences breathing by affecting T3 and T4 levels?

Luteinizing hormone

Prolactin

Gonadotropin releasing hormone

Thyrotropin releasing hormone (correct)

How do voluntary control pathways for breathing operate in the central nervous system?

They synapse on respiratory motoneurons. Signup and view all the answers

What phenomenon may occur in an individual with congenital central hypoventilation syndrome?

Preservation of involuntary control only Signup and view all the answers

Where are the peripheral chemoreceptors primarily located?

In the bifurcation of the common carotid arteries Signup and view all the answers

What effect do thyroid hormones and progesterone have on breathing?

They stimulate breathing. Signup and view all the answers

Which part of the central nervous system is responsible for involuntary control of breathing?

Brainstem respiratory centers Signup and view all the answers

What is the approximate normal resting value for ventilation?

10 L/min Signup and view all the answers

Which physiological role primarily influences ventilation during non-rapid eye movement sleep?

Both central and peripheral chemoreceptors Signup and view all the answers

What determines the stimulation level of the peripheral chemoreflex?

Level of arterial PO2 Signup and view all the answers

What happens to ventilation if carbon dioxide is above the chemoreflex threshold during sleep?

Ventilation remains stable Signup and view all the answers

Which parameter is NOT typically measured to determine stable breathing during sleep?

Heart rate variability Signup and view all the answers

At what partial pressure (mmHg) does the normal level of oxygen in arterial blood typically lie?

100 mmHg Signup and view all the answers

What role do behavioral and arousal influences play in ventilation at low carbon dioxide levels?

They help maintain ventilation Signup and view all the answers

What does a stable oxygen saturation level during sleep indicate?

Stable ventilation Signup and view all the answers

What phenomenon occurs at the intersection of the metabolic hyperbola and the arterial PO2 line at 100 mmHg?

It symbolizes the normal resting equilibrium point for ventilation Signup and view all the answers

What primarily keeps ventilation from dropping to zero below the carbon dioxide threshold?

The influence of behavioral factors Signup and view all the answers

What is the primary function of pulmonary stretch receptors during lung inflation?

To inhibit the firing of neurons in the DRG Signup and view all the answers

Under what condition does the Hering-Breuer reflex typically operate in adult humans?

When tidal volume is three times the normal value Signup and view all the answers

What initiates the cough reflex according to the receptors described?

Mechanical and chemical stimuli detected by airway mucosa receptors Signup and view all the answers

What role do irritant receptors play in the respiratory system?

To initiate protective reflexes in response to irritating stimuli Signup and view all the answers

How do pulmonary stretch receptors contribute to breathing regulation in relation to the vagus nerve?

By prolonging inspiration when the vagus nerve is cut Signup and view all the answers

Which statement is true regarding the carotid bodies?

They have a higher blood flow per unit weight than any other tissue. Signup and view all the answers

What primarily initiates an increase in carotid body activity?

Partial pressure of oxygen falling below 60-70 mmHg. Signup and view all the answers

Which of the following neurotransmitters is implicated in the carotid body's response to partial pressure of oxygen?

Dopamine Signup and view all the answers

How do the carotid bodies primarily detect carbon dioxide levels?

Through hydrogen ions generated by carbonic anhydrase. Signup and view all the answers

Which nerve innervates the carotid bodies?

Glossopharyngeal nerve Signup and view all the answers

What is the role of the aortic bodies in humans?

They do not have a significant role in the control of breathing. Signup and view all the answers

Which factor does NOT stimulate carotid body activity?

High partial pressure of oxygen Signup and view all the answers

What percentage of the hypercapnic ventilatory response is attributed to the carotid bodies?

15 - 25 % Signup and view all the answers

What physiological change occurs in the glomus cells in response to low oxygen levels?

Increase in intracellular calcium ions. Signup and view all the answers

What happens to the diameter of the upper airway after the ventilator is turned off and carbon dioxide levels decrease?

It gradually decreases. Signup and view all the answers

What physiological effect does a reduction in carbon dioxide have on hypoglossal motoneurons?

It leads to disfacilitation. Signup and view all the answers

What is the likely outcome when carbon dioxide levels drop below the apneic threshold?

Central apnea occurs. Signup and view all the answers

During the arousal following apnea, what muscle activity is restored?

Genioglossus muscle activity. Signup and view all the answers

How does hyperventilation affect carbon dioxide levels during an episode of apnea?

It reduces carbon dioxide below the normal range. Signup and view all the answers

What could potentially perpetuate apneic events throughout the sleep period?

The combination of hyperventilation and transition to sleep. Signup and view all the answers

What type of apnea occurs as a result of both central and obstructive events?

Complex apnea. Signup and view all the answers

What triggers increased ventilatory effort after experiencing an apnea?

Hypoxia and hypercapnia. Signup and view all the answers

What role does the genioglossus muscle play in airway maintenance?

It contributes to maintaining airway patency. Signup and view all the answers

What happens to ventilation after apneic events due to hypoxemia and hypercapnia?

Ventilation increases to restore blood gas values. Signup and view all the answers

Study Notes

Hypothalamic Influence on Breathing

The hypothalamus can influence breathing in three ways: through thermoregulatory center, emotional responses, and releasing hormones.
Changes in body temperature elicit changes in breathing rate via the hypothalamic thermoregulatory center.
Powerful emotions like fear, anxiety, and rage significantly affect respiratory rhythm, stemming largely from the hypothalamus.
Releasing hormones synthesized in the hypothalamus influence breathing.
- Thyrotropin-releasing hormone influences T3 and T4 levels, both of which stimulate breathing.
- Gonadotropin-releasing hormone influences progesterone levels, which also stimulate breathing.

Voluntary vs. Involuntary Breathing Control

While breathing is generally involuntary, conscious control is possible.
We can hold our breath, hyperventilate, and the cerebral cortex influences breathing patterns during speech, singing, and playing musical instruments.
Voluntary pathways originating in the pyramidal tracts travel in the corticospinal tracts, bypassing brainstem respiratory centers and directly synapsing on respiratory motoneurons.
Involuntary pathways from brainstem respiratory centers travel in the bulbospinal tracts within the ventral and ventrolateral columns.
Damage to the central nervous system, such as a stroke, can disrupt this balance, either preserving involuntary control or leaving only voluntary control, as seen in congenital central hypoventilation syndrome (Ondine's Curse).

Locomotory Pattern Generator Influence

The "locomotory pattern generator" relays through the thalamus, influencing breathing patterns and entraining them to locomotory rhythms like running and swimming.

Peripheral Chemoreceptors: Carotid Bodies

Located at the bifurcation of the common carotid arteries, peripheral chemoreceptors are richly supplied with blood.
Innervated by the carotid sinus nerve, a branch of the glossopharyngeal nerve (cranial nerve IX), they consist of two cell types.
Exhibit low activity at normal oxygen levels, becoming silent with increased oxygen intake.
Activity rises significantly when blood perfusing the carotid bodies falls, particularly below a partial pressure of 60-70 mmHg.
Respond to the partial pressure of oxygen, not oxygen content, thus reacting to hypoxemia (high altitude or pulmonary disease) but not anemia or carbon monoxide poisoning.

Carotid Body Chemoreceptor Mechanism

The exact mechanism for detecting changes in oxygen partial pressure is unclear, but appears to involve an increase in calcium ions in glomus cells.
The signaling mechanism between glomus cells and the carotid sinus nerve is complex, involving several neurotransmitters and neuromodulators.
- Dopamine levels in type I cells are altered in response to oxygen partial pressure changes.
- Acetylcholine stimulates increased activity in the carotid sinus nerve, acting through both nicotinic and muscarinic receptors.
- Neuropeptides, particularly adenosine and substance P, also increase the activity of the carotid sinus nerve.
Carotid bodies also respond to increases in carbon dioxide partial pressure, detected through hydrogen ions generated within the glomus cells via carbonic anhydrase.

Carotid Body vs. Central Chemoreceptor Response

Although carotid bodies contribute only 15-25% of the hypercapnic ventilatory response, they offer a much faster response compared to central chemoreceptors.
The degree of peripheral chemoreflex stimulation depends on the level of arterial PO2.

Role of Central Chemoreceptors

Central chemoreceptors are located in the ventral surface of the medulla oblongata and are exposed to cerebrospinal fluid (CSF).
They respond to increases in hydrogen ion concentration (acidity) in the CSF, which is primarily due to increased carbon dioxide levels.
Central chemoreceptors account for 75-85% of the hypercapnic ventilatory response.

The Hypercapnic Ventilatory Response

Represents the increase in ventilation that occurs in response to an increase in the partial pressure of carbon dioxide in arterial blood.
This response is a critical component of the body's ability to maintain blood gas homeostasis during various physiological conditions.
Described as a metabolic hyperbola, with a threshold below which carbon dioxide increase does not affect ventilation.
Other stimuli, like behavioral and arousal influences, contribute to maintaining ventilation below this threshold.

Stable Breathing during Sleep

Arousal and behavioral influences are absent during sleep, making peripheral and central chemoreceptors the primary regulators of ventilation during non-rapid eye movement sleep.
Ventilation remains stable during non-rapid eye movement sleep if carbon dioxide levels are above the chemoreflex threshold.
Snoring intensity, abdominal and rib cage movements, oro-nasal airflow, and oxygen saturation are measured during sleep to assess breathing stability.

Sleep Apnea and Disfacilitation of Hypoglossal Motoneurons

Apnea, a cessation of breathing, can occur during sleep, leading to hypoxia (low oxygen) and hypercapnia (high carbon dioxide).
Hypoxia and hypercapnia induce increased ventilatory effort and often awaken the individual.
Upon awakening, pharyngeal muscle activity is restored, the airway opens, and ventilation increases to restore blood gas values.
However, hyperventilation in response to hypoxia and hypercapnia can reduce carbon dioxide below the apneic threshold, potentially leading to another apneic event.
These cycles can perpetuate apneic events throughout the sleep period, leading to complex apnea (central and obstructive events combined).

Lung and Airway Receptors

Lung and airway receptors monitor the respiratory system, alerting the respiratory center to changes in various variables.
Pulmonary stretch receptors, located throughout lung connective tissue, respond to stretching caused by lung inflation.
Vagal afferents from pulmonary stretch receptors inhibit neurons in the dorsal respiratory group (DRG), halting inspiration and initiating expiration, contributing to phase switching (the Hering-Breuer reflex).
The Hering-Breuer reflex operates on a breath-by-breath basis in many species, but in humans it only operates when tidal volume exceeds normal (e.g., during intense exercise or chemical stimuli).
It plays a significant role in stabilizing breathing patterns in infants during their first year of life.
Irritant receptors, found throughout the airway, respond to irritating stimuli and initiate protective reflexes, such as coughing.

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Description

Explore the fascinating influence of the hypothalamus on breathing regulation. This quiz covers the effects of thermoregulation, emotional responses, and hormone release on respiratory patterns, as well as the distinction between voluntary and involuntary control of breathing. Test your knowledge on these critical physiological processes.