1. Automatic control (sensory) of respiration is in - brainstem (midbrain) 

2. Behavioral/voluntary control is in - the cortex

3. Alveolar ventilation -the amount of atmospheric air that actually reaches the alveolar per breath and that can participate in the exchange of gasses between alveoli and blood

4. Only way to increase gas exchange in alveolar capillaries - perfusion-limited gas exchange 

5. Pulmonary ventiliation not effected by - concentration of bicarbonate ions

6. Central chemoreceptors - medulla -  CO2, O2 and H+ concentrations

7. Peripheral chemoreceptors - carotid and aortic bodies- PO2, PCO2 and pH 

8. Major stimulus for respiratory centers - arterial PCO2 

9. Rhythmic breathing depends on 
1. continuous (tonic) inspiratory drive from DRG (dorsal respiratory group)
2. intermittent (phasic) expiratory input from cerebrum, thalamus, cranial nerves and ascending spinal cord sensory tracts

10. Primary site for gas exchange - type I epithelial cells for alveoli

Abnormalities of Salt, Water or pH

• Examples:
  • Hyperkalemia: caused by kidney disease & medical malpractice
    • High K+ in blood- can stop the heart in contraction (systole)
  • Dehydration: walking in desert- can lose 1-2 liters/hour through sweat
    • Blood becomes too viscous to circulate well -> loss of temperature regulation -> hyperthermia, death
  • Acidosis: many causes including diabetes mellitus and respiratory problems; can cause coma, death

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 
 

Serum Lipids

• Total cholesterol is the sum of
  • HDL cholesterol
  • LDL cholesterol and
  • 20% of the triglyceride value
• Note that
  • high LDL values are bad, but
  • high HDL values are good.
• Using the various values, one can calculate a
  cardiac risk ratio = total cholesterol divided by HDL cholesterol
• A cardiac risk ratio greater than 7 is considered a warning.

Events in gastric function:

1) Signals from vagus nerve begin gastric secretion in cephalic phase.

2) Physical contact by food triggers release of pepsinogen and H⁺ in gastric phase.

3) Muscle contraction churns and liquefies chyme and builds pressure toward pyloric sphincter.

4) Gastrin is released into the blood by cells in the pylorus. Gastrin reinforces the other stimuli and acts as a positive feedback mechanism for secretion and motility.

5) The intestinal phase begins when acid chyme enters the duodenum. First more gastrin secretion causes more acid secretion and motility in the stomach.

6) Low pH inhibits gastrin secretion and causes the release of enterogastrones such as GIP into the blood, and causes the enterogastric reflex. These events stop stomach emptying and allow time for digestion in the duodenum before gastrin release again stimulates the stomach.

Oxygen Uptake in the Lungs is Increased About 70X by Hemoglobin in the Red Cells

• In the lungs oxygen must enter the blood
• A small amount of oxygen dissolves directly in the serum, but 98.5% of the oxygen is carried by hemoglobin
• All of the hemoglobin is found within the red blood cells (RBCs or erythrocytes)
• The hemoglobin content of the blood is about 15 gm/deciliter (deciliter = 100 mL)
• Red cell count is about 5 million per microliter

Each Hemoglobin Can Bind Four O₂ Molecules (100% Saturation)

• Hemoglobin is a protein molecule with 4 protein sub-units (2 alphas and 2 betas)
  • Each of the 4 sub-units contains a heme group which gives the protein a red color
  • Each heme has an iron atom in the center which can bind an oxygen molecule (O2)
  • The 4 hemes in a hemoglobin can carry a maximum of 4 oxygen molecules
• When hemoglobin is saturated with oxygen it has a bright red color; as it loses oxygen it becomes bluish (cyanosis)

The Normal Blood Hematocrit is Just Below 50%

• Blood consists of cells suspended in serum
• More than 99% of the cells in the blood are red blood cells designed to carry oxygen
  • 25% of all the cells in the body are RBCs
• The volume percentage of cells in the blood is called the hematocrit
• Normal hematocrits are about 40% for women and 45% for men

At Sea Level the Partial Pressure of O₂ is High Enough to Give Nearly 100% Saturation of Hemoglobin

• As the partial pressure of oxygen in the alveoli increases the hemoglobin in the red cells passing through the lungs rises until the hemoglobin is 100% saturated with oxygen
  • At 100% saturation each hemoglobin carries 4 O₂ molecules
  • This is equal to 1.33 mL O₂ per gram of hemoglobin
• A person with 15 gm Hb/deciliter can carry:
  • Max O₂ carriage = 1.33 mL O₂/gm X 15 gm/deciliter = 20 mL O₂/deciliter
• A plot of % saturation vs pO2 gives an S-shaped "hemoglobin dissociation curve"
• At 100% saturation each hemoglobin binds 4 oxygen molecules

At High Altitudes Hemoglobin Saturation May be Well Below 100%

• At the alveolar pO₂ of 105 mm Hg at sea level the hemoglobin will be about 97% saturated, but the saturation will fall at high altitudes
• At 12,000 feet altitude alveolar pO₂ will be about 60 mm Hg and the hemoglobin will be 90% saturated
• At 29,000 feet (Mt. Everest) alveolar pO₂ is about 24 mm Hg and the hemoglobin will be only 42% saturated
• At very high altitudes most climbers must breath pure oxygen from tanks
• During acclimatization to high altitude the hematocrit can rise to about 60%- this increases the amount of oxygen that can be carried
• Hematocrits above 60% are not useful because the blood viscosity will increase to the point where it impairs circulation