Week 5 Lecture 2 Flashcards
Inhalation & exhalation
Inhalation
• Just before each inhalation
• Lung air pressure = atmosphere air pressure
• To allow air flow into the lungs
• Pulmonary alveoli pressure < atmospheric pressure
• Increase the size of the lungs
• Active process (muscular contractions)
Inhalation diaphragm
Diaphragm contracts
• Flattens & lowers dome
• Increase vertical diameter of thoracic cavity
• 75% of air entering lungs in quiet breathing
Inhalation external intercostals
External intercostals
• Contract and elevate the ribs
• Increase anteroposterior and lateral diameters of chest cavity
• 25% of air entering lungs in quiet breathing
Inhalation Accessory muscles
Accessory muscles
• Exercise or forced breathing
• Sternocleidomastoid muscles
- Elevate the sternum
• Scalene muscles
-Elevate first two ribs
• Pectoralis minor muscles
-Elevateribs3–5
Exhalation
Passive process (no muscular contractions)
• Lung air pressure > atmosphere air pressure
• Elastic recoil of chest wall and lungs
—Recoil of elastic fibres stretched during inhalation
—Inward pull of surface tension of film of intrapleural fluid
• Begins when inspiratory muscles relax
Exhalation diaphragm
Diaphragm relaxes – moves up
• External intercostals relax – ribs
depress
• Reduce diameter of thoracic cavity
• Lung volume decreases
• Alveolar pressure increases & air flows out of the lungs
Forceful breathing - exhalation
Muscles of exhalation contract
— Abdominal & internal intercostals
• Increases pressure in abdominal region & thorax
• Contraction of abdominal
—Move inferior ribs downward, compresses
the abdominal viscera
— Forces diaphragm up
• Contraction of internal intercostals
— Pulls ribs inferiorly
Factors affecting pulmonary ventilation
Surface tension of alveolar fluid
• Pulmonary alveoli – smallest diameter
• Surfactant (phospholipids and lipoproteins)
• Lung compliance
• Effort required to stretch the lungs and chest wall
• High – expand easily
• Low – resist expansion
•
Things that effect lung compliance
Elasticity and surface tension
• Decreased
• Scar tissue
• Pulmonaryoedema
• Surfactant deficiency
Airway resistance
• Decreased with larger diameter
• Sympathetic stimulation
• Bronchodilation
• Relax bronchiolar smooth muscle
• Parasympathetic
• Bronchoconstriction
• Contract bronchiolar smooth muscle • Increased resistance
• Asthma or COPD
• Increased airway resistance with obstruction or collapse of airways
Summary 1
Inhalation
• Pulmonary alveoli pressure < atmospheric
pressure
• Increase the size of the lungs
• Contraction of the diaphragm and external intercostals
• Forced breathing – accessory muscles
Exhalation
• Passive process
• Pulmonary alveoli pressure > atmospheric pressure
• Elastic recoil and relaxation of inhalation muscles • Forced breathing – exhalation muscles contract
Factors affecting pulmonary ventilation
• Surface tension of alveolar fluid • Lung compliance
• Airway resistance
What controls respiration?
Two main mechanisms
• CENTRAL PATTERN (AUTOMATIC) • Inspiratory and expiratory muscles
• Contract and relax
• Controlled by medulla neurons • Fine tuned by pons
• VOLUNTARY
• Origin in Cerebral cortex
• Additional influences
What controls respiration? Pt2
Respiratory centre
• Medulla respiratory centre in medulla
oblongata
• Pontine respiratory group in the pons
• Medulla
• Co-ordinates quiet and forced
breathing
• Controls frequency of ventilation
• Pons
• Controls volume and depth of ventilation
Medullary respiratory centre
Dorsal respiratory group (DRG) • Controls diaphragm & external
intercostal muscles
• Inspiration and expiration in quiet breathing
•
Ventral respiratory group (VRG)
• Controls accessory inspiratory and
expiratory muscles
• Inspiration and expiration during forced breathing
Quiet breathing
Forced breathing
DRG activates VRG ( accessory muscles )
Pontine respiratory group
Transmits nerve impulses to medulla DRG
• Modifies basic rhythm of breathing generated by VRG
• Exercising, speaking or sleeping
Regulation of respiratory centre
Cortical influences
• Voluntarily alter our breathing pattern
• Protective mechanism
• Increased CO2 & H+ stimulates the DRG neurons • Breathing resumes
Chemoreceptor regulation
Monitor CO2, O2 and H+
• Central chemoreceptors • Medulla oblongata
• CSF-CO2andH+
• Peripheral chemoreceptors
• Aortic bodies & carotid bodies • Blood - CO2, O2 and H+
Maintenance of homeostasis
Controlled condition
• Monitor
• Control Centre
• Effect a change
• Monitor
Stretch receptors – inflation reflex
Baroreceptors in the bronchi & bronchiole walls
• Stretched during overinflation of the lungs – forced breathing
• Nerve impulses – vagus nerves to DRG
• DRG is inhibited – diaphragm & intercostals relax
• Exhalation begins
Other influences
Limbic system
• Excitatory input to DRG increasing rate and depth of breathing • e.g., emotional anxiety
• Temperature
• Pain
• Severe pain – apnea
• Prolonged somatic pain – increases breathing rate • Visceral pain – slow rate
Other influences pt 2
Airway irritation
• Cessation of breathing and then coughing
• Blood pressure
• Increase – decrease in breathing rate • Decrease – increase in breathing rate
Baroreceptors
Increased blood pressure
• Carotid sinuses, aortic arch, atria and ventricles
• Decrease ventilation
• Decreased blood pressure • Increase ventilation
• Very minor influence
Summary pt4
Respiratory control – Central & voluntary
• Medulla respiratory centre
• Frequency of ventilation
• Dorsal Respiratory Group – quiet breathing
• Ventral Respiratory Group – forced breathing
• Pons
• Volume and depth of ventilation
Summary pt5
Other influences
• Cortical
• Chemoreceptors • Baroreceptors
• Limbic system
• Pain
Gaseous exchange external respiration
External respiration
• Diffusion of O2 in the air in the pulmonary alveoli to blood in pulmonary capillaries
• Diffusion of CO2 in the opposite direction
• Pulmonary gas exchange
• Deoxygenated blood from the right side of the heart
• Oxygenated blood returned to left side of the heart
• Gas diffuses from higher partial pressure to lower partial pressure
Gaseous exchange internal respiration
Internal respiration
• Exchange of O2 and CO2 between systemic capillaries and tissue cells
• Systemic gas exchange
• Oxygenated blood is converted to deoxygenated blood
• Occurs in tissues throughout the body
• PO2 is higher in systemic capillaries than tissue cells as cells are using O2 in respiration
Gaseous exchange
Rate of pulmonary and systemic gas exchange depends on:
• Partial pressure difference of the gases
• Surface area available for gas exchange
• Diffusion distance
• Molecular weight and solubility of gases
Summary
Gaseous exchange
• Gas diffuses from higher partial pressure to lower partial pressure
• Rate of exchange depends on:
• Diffusion distance
• Surface area
• Partial pressure
• Gas solubility