Transport of gases. Regulation of respiration

Stages of exchange of gases 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 } ventilation } 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.

Partial pressure of oxygen in alveoli = 105 mmHg, but in venous blood it equals 40mmHg, which makes a gradient of 65mm Hg, that causes diffusion of oxygen into the blood. Blood leaving the alveolar capillaries returns to the left atrium and is pumped by the left ventricle into the systemic circulation. This blood travels through arteries & arterioles and into the systemic, or body, capillaries. As blood travels through arteries & arterioles, no gas exchange occurs.

Tension of CO 2 in venous blood is 46 mm Hg, whereas in alveolar air its 40 mm Hg, that makes CO 2 to diffuse from the blood into the alveoli along this gradient. CO 2 tension in blood leaving the lungs is 40 mm Hg. CO 2 passes through all biologic membranes with ease, and the pulmonary diffusion capacity for CO 2 is much greater than the capacity for O 2.

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 O 2 /min*mm Hg.

Features of diffusion of oxygen and carbon dioxide through the pulmonary membrane Gas exchange through this membrane depends on: 1) the surface area through which diffusion occurs (50-90 m2); 2) membrane thickness (0,4-1,5 m); 3) gradient of gas pressures in the alveoli and blood; 4) diffusion coefficient; 5) state of the membrane.

Carbon dioxide is 20 times more soluble in lipids and water than oxygen. Therefore, despite the smaller pressure gradient (for CO mm Hg. and 60 mm Hg for O 2 ), CO 2 passes through the pulmonary membrane faster than O 2

C0 2 transported in the blood: HC0 3 - (70%). Dissolved C0 2 (10%). Carbaminohemoglobin (20%). C0 2 Transport H C0 2 H 2 C0 3 ca High P C0 2

Carbon Dioxide Transport and Chloride Shift Insert fig Figure 16.38

Reverse Chloride Shift in Lungs Insert fig Figure 16.39

Features of oxygen transport in the blood - Oxygen entering the bloodstream is initially dissolved in plasma. - The compound of oxygen with hemoglobin - oxyhemoglobin (HbO 2 ). One molecule can conjunct four molecules of O 2 ; in terms of 1 g of heamoglobin ml O 2. Oxygen capacity of blood equals 1,34ml. 100 ml of blood contain only 0.3 ml of dissolved O 2. Solubility of gas in a liquid depends on temperature, liquid composition, gas pressure and its nature.

Exchange of gases between blood and tissue

The transfer of CO 2 from tissues to blood cells also occurs by diffusion. The average tension of CO 2 in blood is 40 mm Hg and in tissues mm Hg. CO 2 tension in tissues is largely dependent on the intensity of oxidative processes (CO 2 production).

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

Factors that affect the oxyhemoglobin dissociation curve - temperature, - PH, - concentration of 2,3-DPG in erythrocyte. - reducing the pH shifts the curve to the right, due to reduce of the affinity of Hb to O 2. Increasing the pH increases the affinity of Hb to O 2 and the curve shifts to the left. - formation of large quantities of CO 2 in the tissues increases oxygen release in tissues by lowering its affinity with Hb. - with the decrease of temperature O 2 release by oxyhemoglobin slows down, and with the increase its accelerating. - displacement of the curve to the right also contributes to increased content of 2,3-DPG in erythrocytes.

Transport of carbon dioxide 1) Bicarbanate ion (HCO3-) - 70% CO 2 ; 2) Carbohemoglobin (HHbCO2) - 23% CO 2. 3) Carbonic acid (H2CO3) - 7% CO 2 ;

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 O 2 and CO 2 content occure.

Motor function of the respiratory center - generation of respiratory rhythm and its pattern (generation of inspiration effort in the respiratory center and its termination). - Breathing pattern - duration of inhalation and exhalation, tidal volume, minute volume of respiration. - Motor function of the respiratory center adapts breathing to the metabolic needs of an organism and provides integration of breathing with other functions of CNS.

Homeostatic function - Supports normal values ​ of respiratory gases (O 2, CO 2 ) and pH of blood and brain extracellular fluid. - Regulates breathing due to change of body temperature. adapts respiration to the conditions of a modified atmosphere (at low and high barometric pressure).

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 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. 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

Reflexes from bronchiole receptors - Irritation causes hyperpnoe, bronchoconstriction, laryngeal spasm, mucus hypersecretion, but never accompanied by cough. Receptors are most sensitive to three types of stimuli: 1) tobacco smoke, numerous passive and irritational chemicals; 2) damage and mechanical stretching of airways during deep breathing, and pneumothorax 3) pulmonary embolism, pulmonary capillary hypertension and pulmonary anaphylactic phenomena.

Reflexes of the J-receptors J-receptors are situated in alveolar walls in contact with capillaries. These receptors are very sensitive to interstitial edema, pulmonary venous hypertension, microembolism, irritant gases and inhalational narcotic substances. Stimulation of J-receptors causes apnea, then superficial tachypnea, hypotension and bradycardia.

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

Effects of suprapontinal structures on activity of respiratory center Hypothalamus and limbic system - change breathing with a change of emotional state. Cortex - voluntary control over breathing movements (axon collaterals of pyramidal tract conduct signal from the cortex directly to the medulla oblongata.)

The value of an arbitrary change of breathing 1. Speech forming 2. Diagnostic. 3. Preventive and healing. 4. Professional.