Notes: Respiratory System
- Conducting Zone: brings oxygen to alveoli; includes nose, pharynx, larynx, bronchi, and bronchioles.
- Respiratory zone: alveoli; may include alveolar sacs (clusters); air in the alveolar
spaces separated from blood by just two cell diameters.
- Boyle’s Law: behavior of gasses when volume and pressure change.
P= 1/v. As the volume increases, pressure decreases; as volume decreases, the pressure increases.
- diaphragm contracts (drops) increasing volume of thoracic cavity
- contraction of external intercostals muscle helps increase volume of
- pressure in thoracic cavity↓.
- Lower pressure in thoracic cavity pulls on lungs causing inflation
- Inflation of lungs increases internal volume, decreasing their
- air flows into lungs due to lower pressure inside
- Diaphragm relaxes and rises up; volume in thoracic cavity↓
- Contraction of internal intercostals muscles helps decrease volume of
- ↓ volume in thoracic cavity increases pressure
- ↑ thoracic pressure pushes lungs deflating them somewhat
- Deflated lungs have a lower internal volume and thus a higher internal
pressure forces air out of lungs.
- Compliance: lungs being stretchable; can expand during inspiration
- Elasticity: return of lungs back to original shape; this allows lungs to expel air during expiration.
- Surface tension: water in the alveoli will stick to itself causing surface tension; lungs must overcome this force or lungs will collapse.
- Surfactant: produced by the alveolar cells; reduces surface tension of water in the alveoli making it easier to overcome surface tension; not made until 8th month of fetal life.
- a. Tidal volume: amount of air inspired under normal quiet breathing
b. Inspiratory reserve: volume of air above tidal volume that can be inhaled during a maximal forceful inspiration
c. Expiratory reserve volume: volume of air above tidal volume that can beexhaled during a maximal forceful expiration.
d. vital capacity: total amount of exchangeable air (TV + IRV + ERV)
e. Anatomical dead space: trapped air that does not reach the alveolar spaces
(150 ml) within the conducting system; does not participate in gas exchange;
If tidal volume is not above the volume of anatomical dead space, no air will reach the alveoli and no gas exchange will occur.
f. Residual volume: air remaining in alveoli after forced exhalation
- Medulla: contains a rhythmicity center with two types of interacting neurons that will regulate breathing patterns.
- I neurons: cause inspiration by sending impulses to motor neurons that cause contraction of the diaphragm.
E neurons: cause expiration by inhibiting the I neurons, causing the relaxation of the diaphragm.
- Pons: influences breathing by interfacing with the medulla oblongata.
- Pneumotaxic center: area of the pons that inhibits inspiration; antagonizes the apneustic center that causes inspiration by stimulating I neurons
- Cerebral cortex: exerts voluntary control over internal and external intercostal muscles .
- Chemoreceptors: detect chemicals in blood; sites are in the medulla oblongata and peripheral areas
- Aortic bodies: chemoreceptors in the aortic arch
Carotid bodies: chemoreceptors in carotid sinus
- Carbon dioxide effect: CO2 combines with water→ carbonic acid; the chemoreceptors detect H+; high levels of CO2 cause more rapid deeper breathing; ↓ levels of CO2 cause breathing to become slower and more shallow
- Oxygen: concentration changes very little because most oxygen is attached to hemoglobin (Hb); at low O2 pressure, chemoreceptors become more sensitive to CO2; at high oxygen pressure chemoreceptors become less sensitive to CO2.
- Pulmonary stretch reflex: found in lungs; inhibit inspiration when lungs are stretched; helps to prevent damage to lungs due to excessive expansion during ventilation.
- Oxygen exchange in tissues: partial pressure of oxygen in blood is 100mmHg;
In tissues, it is 40mmHg; blood diffuses out of blood into tissues.
- Hemoglobin: Hb structure consists of globin with 4 polypeptide chains, each polypeptide holding one heme.
Heme: organic molecule with an iron atom at its center; iron atom can bind with one oxygen molecule
- Oxyhemoglobin dissociation curve: at high PO2 large pressure changes are needed to unload oxygen, but at low PO2, little change in pressure is needed to unload oxygen .
- Effect of pH on oxyhemoglobin: low pH causes Hb to give up Oxygen at lower PO2; curve shifts to the left; muscles that are being exercised→ lactic acid and CO2 which lower the pH; exercising muscle need extra O2 and the lower pH causes Hb to release O2 more easily.
- Effect of temperature on oxyhemoblogin: ↑ temperature causes release of O2 at a lower PO2; exercising muscles generate heat causing Hb to release O2 more easily.
- Myoglobin: red pigment in muscle similar to globin in Hb; it can hold one O2 molecule; used as a storage mechanism for O2 reserve.
- Carbon dioxide
- CO2 dissolved in the blood (plasma) 10% of blood CO2.
- Carbaminohemoglobin: CO2 attaches to an amino acid of Hb; 20%;
CO2 does not bind to the iron atom and thus does not block O2 binding.
- bicarbonate: 70% of the CO2 in the blood combines with water to form
carbonic acid; this breaks down into HCO3- + H+.
- Removal of CO2: reversal of the bicarbonate formation to form carbonic acid, then CO2 and H2O; carbon dioxide diffuses out of the blood into the alveolar sacs for removal during expiration.