BCR 13 - Control of Breathing, Pulmonary Circulation & Hypoxaemia

What is hyperventilation

Breathing in excess of metabolic needs, meaning ventilation exceeds the required oxygen uptake and carbon dioxide removal

How does hyperventilation differ from exercise-related increased breathing

Hyperventilation exceeds metabolic demand, whereas exercise-related increased breathing matches increased metabolic needs

What is hyperpnoea

An increase in breathing that is appropriate and proportional to increased metabolic demand

When is hyperpnoea typically seen

During exercise when oxygen demand and carbon dioxide production increase

What is tachypnoea

An increased respiratory rate above normal

What is the normal resting respiratory rate in adults

Approximately 15 breaths per minute

At what respiratory rate is tachypnoea usually considered present

Around 20 breaths per minute or higher

How is tachypnoea often described in terms of breathing pattern

Rapid and often shallow breathing

What is hypoventilation

Breathing that is insufficient to meet metabolic needs, leading to inadequate oxygen intake or carbon dioxide removal

What are common causes of hypoventilation

Reduced respiratory frequency, drug overdose, neuromuscular disorders, or any condition limiting effective ventilation

What is apnoea

Complete absence of airflow

What are two main causes of apnoea

Absence of respiratory effort or airway obstruction

What is dyspnoea

The subjective sensation of laboured or difficult breathing, often described as shortness of breath

Is dyspnoea a disease or a symptom

It is a symptom associated with many respiratory and cardiac disorders

When does the respiratory centre develop

Early in pregnancy as part of foetal brainstem development

Why is early development of the respiratory centre important

It is essential for establishing automatic rhythmic breathing after birth

How does breathing continue after birth

Through uninterrupted rhythmic activity generated automatically by the brainstem

Is breathing primarily automatic or voluntary

Primarily automatic but can be voluntarily overridden

How can voluntary control override automatic breathing

Through cortical input such as consciously holding breath or altering breathing pattern

What involuntary reflexes can temporarily override breathing

Sneezing, vomiting, hiccupping and coughing

How is breathing controlled at a physiological level

Through closely regulated chemical and physical reflexes

What do airway nerves and circulating hormones regulate in the lungs

Airway diameter, smooth muscle tone, blood flow, mucous secretion, inflammation and host defence

What are neural stimuli in respiratory control

Responses mediated by the autonomic nervous system involving neural activation and neurotransmitter release

What are humoral stimuli in respiratory control

Hormonal responses triggered by changes in extracellular fluid composition, ion levels or circulating blood chemistry

Why are neural and humoral mechanisms clinically important in airway disease

Their dysregulation alters airway tone and inflammation, contributing to conditions such as asthma and COPD

How is the nervous system divided structurally

Into the central nervous system and the peripheral nervous system

What structures make up the central nervous system

The brain and spinal cord

What is the peripheral nervous system

All neural tissue outside the brain and spinal cord

What are the two main divisions of the peripheral nervous system

The somatic nervous system and the autonomic nervous system

What is the function of the somatic nervous system

Controls skeletal muscle and carries sensory and motor signals

What is the function of the autonomic nervous system

Regulates internal organs and glands through involuntary control

What are the two divisions of the autonomic nervous system

Parasympathetic and sympathetic systems

What is the general role of the parasympathetic nervous system

Rest and digest functions that promote energy conservation

What is the general role of the sympathetic nervous system

Fight or flight responses that prepare the body for stress

How do the parasympathetic and sympathetic systems interact

They work together to maintain homeostasis through opposing but coordinated actions

Where is the respiratory control centre located

In the brainstem within the medulla and pons

How are the lungs innervated

By the autonomic nervous system with both sensory and motor fibres

Which respiratory muscles are under somatic motor control

The diaphragm and intercostal muscles

Where does parasympathetic innervation to the lungs originate

From the medulla via cranial nerve X, the vagus nerve

How do parasympathetic fibres reach the lungs

Preganglionic fibres travel in the vagus nerve and synapse in ganglia near airways and vessels

Which lung structures are innervated by parasympathetic postganglionic fibres

Airway smooth muscle, blood vessels, bronchial epithelial cells, goblet cells and submucosal glands

What effect does parasympathetic stimulation have on airway smooth muscle

Causes smooth muscle constriction leading to bronchoconstriction

What effect does parasympathetic stimulation have on airway blood vessels

Causes vasodilation

What effect does parasympathetic stimulation have on airway secretions

Increases secretion from bronchial epithelial cells and glands

Where does sympathetic innervation to the lungs originate

From the thoracic and lumbar regions of the spinal cord

How do sympathetic fibres reach the lungs

Preganglionic fibres exit via ventral roots, synapse in sympathetic chain ganglia and postganglionic fibres project to the lungs

Which lung structures are innervated by sympathetic fibres

Airway smooth muscle, blood vessels and glandular cells

What effect does sympathetic stimulation have on airway smooth muscle

Causes smooth muscle relaxation resulting in bronchodilation

What effect does sympathetic stimulation have on airway blood vessels

Causes vasoconstriction

What effect does sympathetic stimulation have on airway secretions

Decreases glandular secretion

What are beta2 adrenergic receptors

Receptors on airway smooth muscle that respond to circulating catecholamines

How does activation of beta2 adrenergic receptors affect the airways

It causes bronchodilation by relaxing airway smooth muscle

Why are beta2 adrenergic receptors important clinically

They are targets for bronchodilator therapy in asthma

What are the three main components of the respiratory control system

The central controller, sensors and effectors

What structures form the central controller of breathing

The pons and medulla

What types of sensors regulate breathing

Chemoreceptors, lung receptors and other body receptors

What are the effectors in the respiratory control system

The respiratory muscles including the diaphragm and intercostals

How does feedback regulation of breathing occur

Sensory input is sent to the brainstem which adjusts respiratory rate and depth via motor output to respiratory muscles

How is inspiration initiated at the neuronal level

By a burst of action potentials that gradually increase in a ramp pattern until threshold is reached

What happens when inspiratory neurones reach threshold

Signals are sent via spinal motor nerves to inspiratory muscles

How does expiration occur during quiet breathing

Inspiratory neurones stop firing and passive elastic recoil of the lungs causes expiration

When are expiratory neurones actively involved in breathing

During exercise or forced expiration

Where is neural control of rhythmic breathing located

In the brainstem within the medulla and pons

How many main neuronal groups control minute to minute breathing

Three main groups of neurones

Where is the dorsal respiratory group located

In the dorsal region of the medulla

What is the function of the dorsal respiratory group

It fires during inspiration and sends impulses to the diaphragm and external intercostals

Where is the ventral respiratory group located

In the ventral region of the medulla

What is the main function of the ventral respiratory group

Controls expiration, especially during forced breathing

What is the Pre-Botzinger complex

A cluster of neurones within the ventral respiratory group that generates respiratory rhythm

What is the role of the Pre-Botzinger complex

Acts as a pacemaker network setting the basal respiratory rate

Do the dorsal and ventral respiratory groups communicate

Yes, interneurones coordinate activity between inspiratory and expiratory centres

Where is the apneustic centre located

In the lower pons

What is the function of the apneustic centre

Provides excitatory input to inspiratory neurones and prolongs the inspiratory ramp (promotes inhalation)

Where is the pneumotaxic centre located

In the upper pons

What is the function of the pneumotaxic centre

Inhibits inspiration and helps control inspiratory volume and rate

Is the pneumotaxic centre essential for basic respiratory rhythm

No, basic rhythm can persist without it

What types of sensory inputs influence the respiratory control centre

Chemoreceptors, lung stretch receptors, airway irritant receptors, cardiovascular receptors, J receptors, muscle and joint receptors and skin temperature receptors

How do lung stretch receptors influence breathing

They detect lung inflation and contribute to reflex control of breathing pattern

How do airway irritant receptors affect breathing

They respond to noxious gases and trigger protective reflexes such as coughing

What are J receptors

Juxtacapillary receptors located near pulmonary capillaries that respond to changes such as pulmonary congestion

How do muscle and joint receptors influence breathing during exercise

They detect movement and send early signals to increase respiratory rate

How does increased skin temperature affect breathing

Heat receptors increase respiratory frequency and may promote panting

What is a chemoreceptor

A receptor that responds to changes in chemical composition of blood or surrounding fluid

What are the two main types of chemoreceptors involved in breathing

Central and peripheral chemoreceptors

What do central chemoreceptors primarily detect

Changes in carbon dioxide levels and pH in cerebrospinal fluid (due to hydrogen ion concentration)

What do peripheral chemoreceptors detect

Changes in arterial oxygen, carbon dioxide and pH

What variables do chemoreceptors monitor in general

Partial pressure of oxygen, partial pressure of carbon dioxide and pH changes in blood and extracellular fluid

What is the overall function of the respiratory control centre

To adjust ventilation in response to sensory input to maintain appropriate gas exchange

Where is respiratory rhythm generated

Primarily in the medulla by the dorsal and ventral respiratory groups with modulation from pontine centres

What is a chemoreceptor

A receptor that responds to changes in the chemical composition of blood or surrounding fluid

What are the two main classes of chemoreceptors involved in breathing control

Peripheral chemoreceptors and central chemoreceptors

Where are peripheral chemoreceptors located

In the carotid bodies, aortic bodies and paraganglia along the vagus nerve

Where are the carotid bodies located

At the bifurcation of the common carotid arteries

Where are the aortic bodies located

Above and below the aortic arch

Which peripheral chemoreceptor is the dominant sensor for hypoxia

The carotid body

What is the basic structure of the carotid body

It contains glomus cells and has a very rich capillary blood supply

What are type 1 glomus cells

Chemosensitive cells in the carotid body that contain dopamine and lie close to afferent nerve endings

What is the role of type 2 glomus cells

Supportive cells within the carotid body that assist type 1 cells

Why do carotid bodies have a very high blood flow

To allow rapid detection of changes in arterial blood gases

What stimuli activate peripheral arterial chemoreceptors

Increased arterial carbon dioxide, decreased arterial oxygen, decreased arterial pH and increased potassium