Questions and Answers
What reaction occurs when CO2 combines with H2O in the blood?
The blood-brain barrier (BBB) is permeable to H+ and HCO3- ions.
False
What happens to CO2 in the cerebrospinal fluid (CSF)?
It is converted to H+ and HCO3-.
Increased arterial PaCO2 results in a decrease in _____ due to an increased concentration of H+.
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What initiates hyperventilation?
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Match the following chemoreceptors with their locations:
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Peripheral chemoreceptors are sensitive to increases in PO2.
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How do peripheral chemoreceptors relay information to the DRG?
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Peripheral chemoreceptors can only sense _____ oxygen molecules, not those bound to hemoglobin.
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What happens to hemoglobin when dissolved oxygen levels drop to zero?
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What is the primary function of peripheral chemoreceptors?
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The Hering-Breuer reflex increases the breathing rate.
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What neurotransmitters are released by glomus cells in response to decreased PaO2?
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High altitude can lead to __________ due to increased breathing rate and respiratory alkalosis.
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Match the following receptors with their respective functions:
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What occurs when the pO2 decreases below 60 mmHg?
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Hyperventilation can lead to respiratory acidosis.
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Name one long-term adjustment the body makes in response to high altitude.
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The __________ centers in the brain are activated to increase breathing rate during exercise.
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What is the result of hypoxic vasoconstriction when there is generalized hypoxia?
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What is the primary role of the dorsal respiratory group (DRG)?
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The ventral respiratory group (VRG) is active during normal quiet respiration.
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What is the function of the pneumotaxic center?
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The ________ is responsible for detecting changes in blood levels of CO2 and pH.
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Match the respiratory control components with their functions:
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What primarily drives the increase in breathing rate during heavy exercise?
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Chemoreceptors are insensitive to changes in PaCO2 levels.
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Explain how the ramp signal affects respiration.
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The basic rhythm of respiration is generated mainly in the ________.
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Which sensory information is most important for the brain stem's control of breathing?
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Study Notes
Control of Ventilation
- The nervous system adjusts alveolar ventilation to meet body demands without significantly altering arterial Po2 and Pco2, even during exercise.
- Ventilation equation: VE = VT x f, where VE is minute ventilation, VT is tidal volume, and f is respiratory rate.
- Increased oxygen supply requires an increase in tidal volume (VT), respiratory rate (f), or both.
Brain Stem Control
- Ventilation is managed by centers in the medulla oblongata and pons, containing various groups of neurons.
- Major centers include the Dorsal Respiratory Group (DRG), Ventral Respiratory Group (VRG), and Pneumotaxic Center.
- Breathing can be voluntarily controlled through inputs from the cerebral cortex.
Dorsal Respiratory Group (DRG)
- DRG is crucial for initiating inspiration, primarily located in the nucleus of the tractus solitarius (NTS).
- Receives sensory signals from various peripheral receptors and baroreceptors.
- Generates a ramp signal for respiration, which gradually increases for about 2 seconds, followed by about 3 seconds of silence for passive expiration.
- Characteristics controlled: ramp signal rate and cessation point, affecting depth and frequency of respiration.
Pneumotaxic Center
- Located in the pons, it signals the inspiratory area to control the duration of inspiration.
- Strong signals can increase breathing rates to 30–40 breaths per minute, while weak signals can decrease it to 3–5 breaths per minute.
Ventral Respiratory Group (VRG)
- Operates during high pulmonary ventilation demands, such as during heavy exercise.
- Inactive during normal respiration, becomes active for inspiratory and expiratory muscles when needed.
Sensory Information Processing
- Breathing is regulated by processing sensory information related to arterial gases (PaO2, PaCO2, pH).
- Signals from peripheral and central chemoreceptors are essential for this process.
Central Chemoreceptors
- Located in the brain stem, crucial for minute-to-minute control of breathing.
- Sensitive to increases in PaCO2 and local decreases in pH, signaling the inspiratory center.
- CO2 crosses the blood-brain barrier, affecting CSF pH, prompting an increase in breathing rate and depth.
Peripheral Chemoreceptors
- Found in carotid and aortic bodies with high blood flow, relaying information to the DRG.
- Sensitive to declines in PaO2, increases in PCO2, and decreases in pH.
- Respond primarily to dissolved oxygen, not oxygen bound to hemoglobin.
Summary of Functionality
- The respiratory centers and chemoreceptors work together to maintain homeostasis in the respiratory system, adjusting to changes in metabolic demands efficiently.### Oxygen Sensing and Chemoreceptors
- Arterial blood oxygen concentration below normal stimulates chemoreceptors.
- Mechanism of low PaO2 excitation in carotid and aortic bodies is not fully understood.
- Glomus cells in these bodies function as chemoreceptors, synapsing with nerve endings.
Peripheral Chemoreceptors
- pO2 decrease below 60 mmHg closes potassium channels, leading to cell depolarization.
- Opening of voltage-gated calcium channels increases cytosolic calcium, stimulating neurotransmitter release (ATP and acetylcholine).
- Afferent fibers activate the central nervous system, increasing respiration.
- Sensory neuron firing rate increases significantly with low PaO2, particularly between 60 and 30 mmHg.
Other Receptors in Breathing Control
- Lung Stretch Receptors: Mechanoreceptors in airway smooth muscle prevent over-inflation via the Hering-Breuer reflex, reducing breathing rate.
- Joint and Muscle Receptors: Mechanoreceptors sense limb movement, signaling the inspiratory center to enhance ventilation during exercise.
- Irritant Receptors: Located in airway epithelium, respond to noxious chemicals, triggering bronchial smooth muscle constriction and increased breathing rate.
Respiratory System Response to Exercise
- Increased exercise demand raises O2 supply via ventilation increase, maintaining balance between O2 consumption, CO2 production, and ventilation.
- Arterial PO2, PCO2, and pH remain stable during moderate exercise; venous PCO2 often rises.
Response to High Altitude
- High altitude causes hypoxemia, stimulating hyperventilation in response to decreased PO2.
- Barometric pressure and PO2 significantly decrease at high altitudes, affecting gas exchange.
- Hyperventilation can induce respiratory alkalosis, temporarily inhibiting chemoreceptor activity until bicarbonate excretion increases.
Long-term Adaptations to High Altitude
- Increased erythrocyte production under erythropoietin influence contributes to enhanced oxygen transport.
- Decreased hemoglobin affinity for oxygen caused by elevated 2,3-DPG levels.
- Angiogenesis increases capillary density in muscles to improve oxygen delivery.
Hypoxic Vasoconstriction
- Beneficial for localized alveolar hypoxia but can lead to serious complications in generalized hypoxia.
- In high-altitude cattle, generalized hypoxic vasoconstriction raises pulmonary arterial pressure, potentially leading to right-sided heart failure ("brisket disease").
Neural Control of Breathing
- Medulla oblongata and pons regulate respiratory rate and depth, responding to systemic stimuli influenced mainly by CO2 levels.
- Peripheral and central chemoreceptors monitor chemical concentrations, triggering adjustments in breathing mechanics.
- Increased hydrogen ion levels in the brain initiate respiratory center stimulation, enhancing contraction of diaphragm and intercostal muscles.
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Description
Explore the mechanisms behind the control of ventilation, focusing on how the nervous system adjusts alveolar ventilation during various activities, including exercise. Understand the roles of various centers in the brain stem, particularly the Dorsal and Ventral Respiratory Groups, in managing respiratory processes.
