Transport of gases. Regulation of respiration

Stages of exchange of gases } ventilation 1. exchange of gases between atmospheric air and intraalveolar air 2. exchange of gases between intraalveolar air and blood 3. transport of gases 4. exchange of gases between blood and tissue 5. internal (tissue) respiration } diffusion } perfusion

Partial pressure is characterized as a partial quantity of a certain gas in a mixture of gases. It is equal to the total pressure times the fraction of the total amount of gas it represents. Tension of a certain gas means its quantity dissolved in a liquid.

Aerohaematic barrier (pulmonary membrane) includes: - a thin layer of liquid on the surface of alveolar cells and surfactant molecules. -alveolar epithelium; - a layer of connective tissue; - a layer of endothelial cells of capillaries; - a layer of plasma;  - membrane of erythrocyte.

Tension of CO2 in venous blood is 46 mm Hg, whereas in alveolar air its 40 mm Hg, that makes CO2 to diffuse from the blood into the alveoli along this gradient. CO2 tension in blood leaving the lungs is 40 mm Hg. CO2 passes through all biologic membranes with ease, and the pulmonary diffusion capacity for CO2 is much greater than the capacity for O2.

Partial pressure and diffusion at the respiratory membrane.

The volume of gas that passes through the aero-hematic barrier in 1 minute at pressure gradient of gas on both sides of the barrier at 1 mm Hg is called diffusive lung capacity. Diffusion capacity in human lungs for oxygen is 25 ml O2/min*mm Hg.

Carbon dioxide is 20 times more soluble in lipids and water than oxygen. Therefore, despite the smaller pressure gradient (for CO2 - 6 mm Hg. and 60 mm Hg for O2), CO2 passes through the pulmonary membrane faster than O2

Reverse Chloride Shift in Lungs Insert fig. 16.39 Figure 16.39

Exchange of gases between blood and tissue

The transfer of CO2 from tissues to blood cells also occurs by diffusion. The average tension of CO2 in blood is 40 mm Hg and in tissues - 50-60 mm Hg. CO2 tension in tissues is largely dependent on the intensity of oxidative processes (CO2 production).

Oxygen hemoglobin dissociation curve, pH 7,40. temperature 380.

RESPIRATORY NEURONS 1. Early inspiratory neurons (impulses grow rapidly and slowly decreases during inspiration). 2. Late inspiratory neurons (activated at the end of inhalation). 3. Total inspiratory neurons (slowly activated during inspiration). 4. Bulbospinal inspiratory neurons (activated during inspiration and activity gradually decreases after inspiration) 5. Postinspiratory neurons (impulsation increases after inhalation). 6. Late expiratory neurons (activated during exhalation).

Respiratory neurons of the brain stem have two types - Inhalation (inspirational, I-neurons) - Exhalation (expiratory, E-neurons).   Exhalation is passive during calm reathing, so E-neurons are at rest. They become active if pulmonary ventilation increases.

Functions of the respiratory center in the respiratory system : - Motor – contraction of respiratory muscles. - Homeostatic - involves changes in breathing when disorders of internal O2 and CO2 content occure.

Mechanisms of periodic activity of the respiratory cycle The breathing rate is caused by : 1) coordinated activity of different parts of the respiratory center; 2) reception of impulses from receptors; 3) reception of signals from other parts of the CNS, including those from the cerebral cortex.

Receptors that are involved in the regulation of breathing 1. Hemoreceptors: a) central;                                b) peripheral. 2. Mechanoreceptors of upper and lower respiratory ways. 3. J-receptors. 4. Irritant receptors. 5. Receptors of pleura. 6. Proprioreceptors of respiratory muscles

Arterial chemoreceptors

Location of the carotid and aortic bodies Location of the carotid and aortic bodies. Note that each carotid body is quite close to a carotid sinus, the major arterial baroreceptor. Both right and left common carotid bifurcations contain a carotid sinus and a carotid body.

Reflexive regulation of breathing - Reflexes from the mucosa of the nasal cavity. Stimulation of irritational receptors of the nasal cavity mucose (tobacco smoke, dust particles and gaseous substances, water) cause: - narrowing of the bronchi, vocal fissure.   - bradycardia, - decrease in cardiac output, - narrowing of the vessels of skin and muscles

Respiratory Structures in the Brainstem

Reflexes from the larynx and trachea. Receptors are stimulated by dust, caustic gases, bronchial secret and alien bodies. It causes a cough reflex, which is expresed in a quick exhalation on a background of narrowing of the larynx and contraction of bronchial smooth muscle, which remains long after the reflex. Cough reflex is the main pulmonary reflex of the vagus nerve

Proprioreceptive control of breathing. Intercostal muscles, and diaphragm in a less extent, contain a large number of muscle fibers. Proprioreceptors become active during passive stretching of muscles, isometric contraction and the isolated contraction of intrafusal muscle bobbins. Receptors send signals to the corresponding segments of the spinal cord. Lack of contraction effort of inspiratory or expiratory muscles increases the impulsation from muscle bobbins, that increases gamma-motoneuron and then alpha- motoneuron activity, in the means of dosing muscular effort. Receptors of the chest joints send impulses to the cerebral cortex. These impulses are the only source of information about the movements of the chest and respiratory volumes.

Summary of factors that stimulate ventilation during exercise