Anatomy & Physiology of Respiratory System

Question 1

Type I pneumocytes

Answer 1

Squamous epithelial cells
Covers 90-95% of alveolar surface area
Not capable of multiplying (mitosis)

Question 2

Type II pneumonocytes

Answer 2

Cuboidal epithelial cells
Covers about 3% of alveolar surface area (but makes up for most cells in the alveolar unit, more than type I pneumonocytes)

“Defender of the alveolus”

Produce surfactant –> reduces surface tension

Replicate and replace damaged type I pneumocytes under physiologic and pathologic conditions (takes 2-5 days)

Question 3

Capillary endothelium

Answer 3

Loose junctions --> leaky
Converts angiotensin I --> angiotensin II 
Produces adenosine, prostaglandins 
Inactivates bradykinin
Clears serotonin, norepinephrine

Question 4

Doral Respiratory Group [Medullary Respiratory Center]

Answer 4

Location (nucleus)- Medulla-> Tractus Solitarius

Function- inspiratory neurons

Afferents-CN IX, X

Efferents- Contralateral spinal cord –> main input to phrenic nerves

Question 5

Ventral Respiratory Group [Medullary Respiratory Center]

Answer 5

Location (nucleus)- Medulla –> Nucleus ambiguus
Retrofacial: Botzinge, Pre-Botzinger
Para-ambigualis
Retro-ambigualis

Function- inspiratory & expiratory neurons

Afferents-collateral fibers from DRG

Efferents- pharyngeal, laryngeal, intercostal muscles. Pre-Botzinger complex is the “pacemaker” of respiratory system

Question 6

Apneustic Center

[Medullary Respiratory Center]

Answer 6

Location (nucleus)- Lower Pons

Function- Terminates inspiration

Afferents-CN X

Efferents- Medullary inspiratory neurons

Question 7

Pontine Respiratory Group [Medullary Respiratory Center]

Answer 7

Location (nucleus)- Upper pons –> parabrachialis medialis
Kolliker-Fuse

Function- “Fine-tune” breathing pattern

Afferents-Pulmonary inflation stretch receptors –> inhibit PRG

Efferents- Modulate medullary neurons

Question 8

Herin-Breuer inflation reflex

Answer 8

Receptor: slowly adapting pulmonary stretch receptors in airways

Pathway: inflation –> CN X –> cessation/reduced inspiration effort

Question 9

Herin-Breuer deflation reflex

Answer 9

Receptor: stretch, irritant, and J receptors

Pathway: Deflation –> CN X –> hyperpnea

Question 10

Paradoxic reflex of head

Answer 10

Receptor: Stretch receptors

Pathway: inflation –> C X –> deep inspiration (sighs)

Question 11

Cough reflex

Answer 11

Receptor: Irritant receptors in upper airway

Pathway: Stimulus –> CN X –> cough, bronchoconstriction

Question 12

Sneeze reflex

Answer 12

Receptor: Irritant receptors in nasal mucosa

Pathway: Stimulus –> trigeminal/olfactory nerves –> sneeze, bronchoconstriction

Question 13

Chemoreceptor reflex

Answer 13

Receptor: carotid and aortic bodies

Pathway: low PaO2, high PaCO2, low pH –> hypercapnia –> CN IX, X –> DRG –> hyperpnea, bronchoconstriction, bradycardia

Question 14

Baroreceptor reflex

Answer 14

Receptor: carotid sinus and aortic arch stretch receptors

Pathway: high blood pressure –> CN IX, X –> Apnea, bronchodilation, bradycardia

Question 15

Pulmonary embolism or vascular congestion

Answer 15

Receptor: J receptors in pulmonary vessels

Pathway: Vascular stimulus –> CN X –> tachypnea