Week 5 Lecture 2

Question 1

Inhalation & exhalation

Answer 1

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)

Question 2

Inhalation diaphragm

Answer 2

Diaphragm contracts
• Flattens & lowers dome
• Increase vertical diameter of thoracic cavity
• 75% of air entering lungs in quiet breathing

Question 3

Inhalation external intercostals

Answer 3

External intercostals
• Contract and elevate the ribs
• Increase anteroposterior and lateral diameters of chest cavity
• 25% of air entering lungs in quiet breathing

Question 4

Inhalation Accessory muscles

Answer 4

Accessory muscles
• Exercise or forced breathing
• Sternocleidomastoid muscles
- Elevate the sternum
• Scalene muscles
-Elevate first two ribs
• Pectoralis minor muscles
-Elevateribs3–5

Question 5

Exhalation

Answer 5

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

Question 6

Exhalation diaphragm

Answer 6

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

Question 7

Forceful breathing - exhalation

Answer 7

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

Question 8

Factors affecting pulmonary ventilation

Answer 8

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

Question 9

Summary 1

Answer 9

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

Question 10

What controls respiration?

Answer 10

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

Question 11

What controls respiration? Pt2

Answer 11

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

Question 12

Medullary respiratory centre

Answer 12

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

Question 13

Quiet breathing

Question 14

Forced breathing

Answer 14

DRG activates VRG ( accessory muscles )

Question 15

Pontine respiratory group

Answer 15

Transmits nerve impulses to medulla DRG
• Modifies basic rhythm of breathing generated by VRG
• Exercising, speaking or sleeping

Question 16

Regulation of respiratory centre

Answer 16

Cortical influences
• Voluntarily alter our breathing pattern
• Protective mechanism
• Increased CO2 & H+ stimulates the DRG neurons • Breathing resumes

Question 17

Chemoreceptor regulation

Answer 17

Monitor CO2, O2 and H+
• Central chemoreceptors • Medulla oblongata
• CSF-CO2andH+
• Peripheral chemoreceptors
• Aortic bodies & carotid bodies • Blood - CO2, O2 and H+

Question 18

Maintenance of homeostasis

Answer 18

Controlled condition
• Monitor
• Control Centre
• Effect a change
• Monitor

Question 19

Stretch receptors – inflation reflex

Answer 19

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

Question 20

Other influences

Answer 20

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

Question 21

Other influences pt 2

Answer 21

Airway irritation
• Cessation of breathing and then coughing
• Blood pressure
• Increase – decrease in breathing rate • Decrease – increase in breathing rate

Question 22

Baroreceptors

Answer 22

Increased blood pressure
• Carotid sinuses, aortic arch, atria and ventricles
• Decrease ventilation
• Decreased blood pressure • Increase ventilation
• Very minor influence

Question 23

Summary pt4

Answer 23

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

Question 24

Summary pt5

Answer 24

Other influences
• Cortical
• Chemoreceptors • Baroreceptors
• Limbic system
• Pain

Question 25

Gaseous exchange external respiration

Answer 25

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

Question 26

Gaseous exchange internal respiration

Answer 26

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

Question 27

Gaseous exchange

Answer 27

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

Question 28

Summary

Answer 28

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