Neural Substrates of Breathing

Neural Substrates of Breathing

Neural Substrates of Breathing

A.    Medulla Respiratory Centers

Inspiratory Center (Dorsal Resp Group - rhythmic breathing) → phrenic nerve→ intercostal nerves→ diaphragm + external intercostals

Expiratory Center (Ventral Resp Group - forced expiration) → phrenic nerve → intercostal nerves → internal intercostals + abdominals (expiration)

1.    eupnea - normal resting breath rate (12/minute)
2.    drug overdose - causes suppression of Inspiratory Center

B.    Pons Respiratory Centers

1.    pneumotaxic center - slightly inhibits medulla, causes shorter, shallower, quicker breaths
2.    apneustic center - stimulates the medulla, causes longer, deeper, slower breaths

C.    Control of Breathing Rate & Depth

1.    breathing rate - stimulation/inhibition of medulla
2.    breathing depth - activation of inspiration muscles
3.    Hering-Breuer Reflex - stretch of visceral pleura that lungs have expanded (vagal nerve)

D.    Hypothalamic Control - emotion + pain to the medulla

E.    Cortex Controls (Voluntary Breathing) - can override medulla as during singing and talking


Surface Tension

1.    Maintains stability of alveolus, preventing collapse

2.    Surfactant (Type II pneumocytes) = dipalmityl lecithin

3.    Type II pneumocyte appears at 24 weeks of gestation;
1.    Surfactant production, 28-32 weeks;
    2.    Surfactant in amniotic fluid, 35 weeks.
    3.    Laplace equation for thin walled spheres P = 2T
        a.    P = alveolar internal pressure r
        b.    T = tension in the walls r = radius of alveolus
4.    During normal tidal respiration

    1.    Some alveoli do collapse (Tidal pressure can't open)
    2.    Higher than normal pressure needed (Coughing)
    3.    Deep breaths & sighs promote re-expansion
    4.    After surgery/Other conditions, Coughing, deep breathing, sustained maximal respiration

Asthma = Reversible Bronchioconstruction 4%-5% of population
    Extrinsic / Atopic = Allergic, inherited (familia), chromosome 11
    IgE, Chemical Mediators of inflammation
a.    Intrinsic = Negative for Allergy, Normal IgE, Negative Allergic Tests

    Nucleotide Imbalance cAMP/cGMP: cAMP = Inhibits mediator release, cGMP = Facilitates mediator release
b.    Intolerance to Asprin (Triad Asthma)
c.    Nasal Polyps & Asthma

d.    Treatment cause, Symptoms in Acute Asthma
    1.    Bronchial dilators
    2.    steroids edema from Inflamation
    3.    Bronchiohygene to prevent Secondary Infection, (Remove Excess Mucus)
    4.    Education

Cystic Fibrosis
→ Thick mucus coagulates in ducts, produces obstruction, Too thick for cilia to move
→ Major Systems Affected: Respiratory System, G. I. Tract,Reproductive Tract

→ Inherited, autosomal recessive gene, most common fatal genetic disorder

→    Major characteristic, Altered electrolyte composition (Saliva & sweat Na+, K+, Cl-)

→    Family history of Cystic Fibrosis
→    Respiratory Infections & G.I.Tract malabsorption
→    Predisposes lung to Secondary infection (Staphylococcus, Pseudomonas)
→    Damages Respiratory Bronchioles and Alveolar ducts, Produces Fibrosis of Lungs, Large cystic dilations)

(RDS) Respiratory distress of Newborn
1.    hyaline membrane disease of the new born
2.    decrease in surfactant, Weak, Abnormal complience of chest wall
3.    Small alveoli, difficult to inflate, Alveoli tent to collapse, many of varied sizes
4.    decrease in O2 diffusion area, lung difficult to expand, in compliance

COPD and Cancer

A.    Chronic Obstructive Pulmonary Disease (COPD)

1.    Common features of COPD

a.    almost all have smoking history
b.    dyspnea - chronic "gasping" for air
c.    frequent coughing and infections
d.    often leads to respiratory failure

2.    obstructive emphysema - usually results from smoking

a.    enlargement & deterioration of alveoli
b.    loss of elasticity of the lungs
c.    "barrel chest" from bronchiole opening during inhalation & constriction during exhalation

3.    chronic bronchitis - mucus/inflammation of mucosa

B.    Lung Cancer

1.    squamous cell carcinoma (20-40%) - epithelium of the bronchi and bronchioles
2.    adenocarcinoma (25-35%) - cells of bronchiole glands and cells of the alveoli
3.    small cell carcinoma (10-20%) - special lymphocyte-like cells of the bronchi
4.    90% of all lung cancers are in people who smoke or have smoked