Control of Ventilation

Flashcards covering key terms, physiological thresholds, neural structures, and chemoreceptor mechanisms involved in the control of ventilation.

Volatile Acids

Acids that can be converted from a liquid state to a gaseous state to facilitate being excreted by the lungs.

Fixed Acids

Acids that cannot be converted into a gas and must be excreted in a liquid state in the urine via the kidneys.

Carbonic Acid ($H_2CO_3$)

A volatile acid formed when $CO_2$ builds up at the tissue level, leading to an increase in hydrogen ions ($H^+$).

Plasma Bicarbonate ($HCO_3^-$)

The major blood base of clinical significance, whose level in the body is carefully controlled by the kidneys.

Normal Blood pH

The standard physiological pH level of blood is $7.40$, with an acceptable clinical range of $7.35\text{--}7.45$.

Acidosis

A condition defined as a blood pH level of less than $7.35$.

Alkalosis

A condition defined as a blood pH level of greater than $7.45$.

Normal $PaCO_2$ Range

The normal range for the partial pressure of carbon dioxide in arterial blood, which is $35\text{--}45\text{ mmHg}$.

Normal Plasma $HCO_3^-$ Range

The normal clinical range for plasma bicarbonate levels, which is $22\text{--}26\text{ mEq/L}$.

Brainstem Respiratory Control Centers

Structures located in the pons (Pneumotaxic center, Apneustic center) and medulla (Pre-Bötzinger complex, Dorsal respiratory group, Ventral respiratory group) that generate and regulate rhythmic ventilatory impulses.

Dorsal Respiratory Group (DRG)

A group consisting primarily of inspiratory neurons in the medulla oblongata responsible for generating basic ventilatory rhythm and providing primary inspiratory stimulus to the diaphragm; inhibited by the Hering-Breuer reflex.

Ventral Respiratory Group (VRG)

A group consisting of inspiratory and expiratory neurons in the medulla; inspiratory neurons send signals to laryngeal, pharyngeal, diaphragm, and external intercostal muscles, while expiratory neurons send signals to internal intercostal muscles.

Central Chemoreceptors

Receptors located in the medulla in direct contact with cerebrospinal fluid (CSF) rather than arterial blood, which stimulate ventilation in response to increased $H^+$ concentration.

Peripheral Chemoreceptors

Small, highly vascular structures called the carotid and aortic bodies that increase firing rates in response to increased arterial $H^+$ concentrations or when arterial $PaO_2$ falls below $60\text{ mmHg}$.

Arterial Hypoxemic Ventilatory Threshold

The arterial partial pressure threshold ($PaO_2 < 60\text{ mmHg}$) below which arterial hypoxemia significantly stimulates ventilation via peripheral chemoreceptors in a healthy patient at sea level.

Ventilatory Drive in Chronic Hypercapnia

An adaptation where sustained high $PaCO_2$ leads the kidneys to retain $HCO_3^-$, buffering CSF $H^+$ levels and causing hypoxemia to become the main driver of ventilation (e.g., in severe COPD).

Bicarbonate Buffer Reaction

The reversible chemical reaction $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$ that balances carbon dioxide, water, carbonic acid, hydrogen ions, and bicarbonate ions in the body.